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Document And Entity Information - USD ($)	12 Months Ended
Document And Entity Information - USD ($)	Apr. 30, 2013	Jun. 30, 2013	Oct. 31, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	Ocean Power Technologies, Inc.
Document Type	10-K
Current Fiscal Year End Date	--04-30
Entity Common Stock, Shares Outstanding		10,355,140
Entity Public Float			$ 23,800,000
Amendment Flag	false
Entity Central Index Key	0001378140
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Smaller Reporting Company
Entity Well-known Seasoned Issuer	No
Document Period End Date	Apr. 30, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	FY

Consolidated Balance Sheets - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Current assets:
Cash and cash equivalents	$ 6,372,788	$ 9,353,460
Marketable securities	13,996,705	22,369,484
Accounts receivable, net	796,332	1,064,796
Unbilled receivables	127,598	223,050
Other current assets	152,962	842,820
Total current assets	21,446,385	33,853,610
Property and equipment, net	700,968	682,933
Patents, net	1,044,902	1,269,457
Restricted cash	1,366,256	1,453,712
Other noncurrent assets	272,548	181,925
Total assets	24,831,059	37,441,637
Current liabilities:
Accounts payable	510,031	440,773
Accrued expenses	3,900,623	2,770,094
Deferred credits payable		600,000
Unearned revenues	1,117,115	1,073,389
Current portion of long-term debt	100,000	100,000
Total current liabilities	5,627,769	4,984,256
Long-term unearned revenues	232,033
Long-term debt	250,000	350,000
Deferred credits payable-noncurrent	600,000
Total liabilities	6,709,802	5,334,256
Commitments and contingencies (note 13)
Ocean Power Technologies, Inc. Stockholders’ equity:
Preferred stock, $0.001 par value; authorized 5,000,000 shares, none issued or outstanding	0	0
Common stock, $0.001 par value; authorized 105,000,000 shares, issued 10,403,215 and 10,407,389 shares, respectively	10,403	10,407
Treasury stock, at cost; 33,771 and 23,544 shares, respectively	(123,893)	(102,388)
Additional paid-in capital	159,155,365	158,296,458
Accumulated deficit	(140,671,311)	(125,989,474)
Accumulated other comprehensive loss	(79,786)	(78,990)
Total Ocean Power Technologies, Inc. stockholders’ equity	18,290,778	32,136,013
Noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd…	(169,521)	(28,632)
Total equity	18,121,257	32,107,381
Total liabilities and stockholders’ equity	$ 24,831,059	$ 37,441,637

Consolidated Balance Sheets (Parentheticals) - $ / shares	Apr. 30, 2013	Apr. 30, 2012
Preferred stock par value (in Dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock par value (in Dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	105,000,000	105,000,000
Common stock, shares issued	10,403,215	10,407,389
Treasury stock, shares	33,771	23,544

Consolidated Statements of Operations - USD ($)	12 Months Ended
Consolidated Statements of Operations - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Revenues	$ 3,616,129	$ 5,738,506
Cost of revenues	3,480,821	5,683,731
Gross profit	135,308	54,775
Operating expenses:
Product development costs	7,327,766	8,337,424
Selling, general and administrative costs	9,126,757	8,274,096
Total operating expenses	16,454,523	16,611,520
Operating loss	(16,319,215)	(16,556,745)
Interest income, net	126,377	418,052
Foreign exchange loss	(83,416)	(104,739)
Loss before income taxes	(16,276,254)	(16,243,432)
Income tax benefit	1,453,243	1,053,427
Net loss	(14,823,011)	(15,190,005)
Less: Net loss attributable to the noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd.	141,174	49,503
Net loss attributable to Ocean Power Technologies, Inc	$ (14,681,837)	$ (15,140,502)
Basic and diluted net loss per share (in Dollars per share)	$ (1.42)	$ (1.47)
Weighted average shares used to compute basic and diluted net loss per share (in Shares)	10,304,044	10,277,661

Consolidated Statements of Comprehensive Loss - USD ($)	12 Months Ended
Consolidated Statements of Comprehensive Loss - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Net Loss	$ (14,823,011)	$ (15,190,005)
Foreign currency translation adjustment	(511)	(255,974)
Total comprehensive loss	(14,823,522)	(15,445,979)
Comprehensive loss attributable to the noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd.	140,889	50,580
Comprehensive loss attributable to Ocean Power Technologies, Inc.	$ (14,682,633)	$ (15,395,399)

Consolidated Statements of Stockholders' Equity - USD ($)	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Parent [Member]	Noncontrolling Interest [Member]	Total
Balance, April 30 at Apr. 30, 2011	$ 10,419	$ (42,734)	$ 157,174,930	$ (110,848,972)	$ 175,907	$ 46,469,550	$ 21,948	$ 46,491,498
Balance, April 30 (in Shares) at Apr. 30, 2011	10,419,183	(7,685)
Net loss				(15,140,502)		(15,140,502)	(49,503)	(15,190,005)
Foreign currency translation adjustment					(254,897)	(254,897)	(1,077)	(255,974)
Total comprehensive loss						(15,395,399)	(50,580)	(15,445,979)
Stock based compensation			1,008,473			1,008,473		1,008,473
Issuance (forfeiture) of restricted stock, net	$ (12)		113,055			113,043		113,043
Issuance (forfeiture) of restricted stock, net (in Shares)	(11,794)
Acquisition of treasury stock		$ (59,654)				(59,654)		$ (59,654)
Acquisition of treasury stock (in Shares)		(15,859)						(15,859)
Balance, April 30 at Apr. 30, 2012	$ 10,407	$ (102,388)	158,296,458	(125,989,474)	(78,990)	32,136,013	(28,632)	$ 32,107,381
Balance, April 30 (in Shares) at Apr. 30, 2012	10,407,389	(23,544)
Net loss				(14,681,837)		(14,681,837)	(141,174)	(14,823,011)
Foreign currency translation adjustment					(796)	(796)	285	(511)
Total comprehensive loss						(14,682,633)	(140,889)	(14,823,522)
Stock based compensation			814,407			814,407		814,407
Issuance (forfeiture) of restricted stock, net	$ (4)		44,500			44,496		44,496
Issuance (forfeiture) of restricted stock, net (in Shares)	(4,174)
Acquisition of treasury stock		$ (21,505)				(21,505)		$ (21,505)
Acquisition of treasury stock (in Shares)		(10,227)						(10,227)
Balance, April 30 at Apr. 30, 2013	$ 10,403	$ (123,893)	$ 159,155,365	$ (140,671,311)	$ (79,786)	$ 18,290,778	$ (169,521)	$ 18,121,257
Balance, April 30 (in Shares) at Apr. 30, 2013	10,403,215	(33,771)

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Short-Term [Member]
Changes in operating assets and liabilities:
Unearned revenues	$ 46,451	$ 729,367
Long-Term [Member]
Changes in operating assets and liabilities:
Unearned revenues	232,033
Net loss	(14,823,011)	(15,190,005)
Foreign exchange loss	83,416	104,739
Depreciation and amortization	502,099	436,062
Loss on disposals of property, plant and equipment	44,067	52,128
Impairment of long-lived assets	7,718	358,447
Provision for doubtful accounts		298,534
Treasury note discount amortization	(12,191)	(33,353)
Compensation expense related to stock option grants and restricted stock	858,902	1,121,528
Accounts receivable	264,077	(126,722)
Unbilled receivables	95,451	226,840
Other current assets	685,523	(17,291)
Other noncurrent assets	(93,700)	43,504
Accounts payable	105,036	(546,709)
Accrued expenses	1,158,481	(1,371,912)
Net cash used in operating activities	(10,845,648)	(13,914,843)
Cash flows from investing activities:
Purchases of marketable securities	(16,678,329)	(18,574,454)
Maturities of marketable securities	25,055,534	38,559,110
Restricted cash	75,000	53,936
Purchases of equipment	(394,632)	(547,252)
Payments of patent costs		(180,011)
Net cash provided by investing activities	8,057,573	19,311,329
Cash flows from financing activities:
Repayment of debt	(100,000)	(139,378)
Acquisition of treasury stock	(21,505)	(59,654)
Net cash used in financing activities	(121,505)	(199,032)
Effect of exchange rate changes on cash and cash equivalents	(71,092)	(220,130)
Net (decrease) increase in cash and cash equivalents	(2,980,672)	4,977,324
Cash and cash equivalents, beginning of period	9,353,460	4,376,136
Cash and cash equivalents, end of period	$ 6,372,788	9,353,460
Supplemental disclosure of noncash investing and financing activities:
Capitalized purchases of equipment financed through accounts payable and accrued expenses		$ 42,344

Note 1 - Background and Liquidity

12 Months Ended

Apr. 30, 2013

Disclosure Text Block [Abstract]

Business Description and Basis of Presentation [Text Block]

(1) Background and Liquidity

(a) Background

Ocean Power Technologies, Inc. (the “Company”) was incorporated in April 1984 in New Jersey, commenced business operations in 1994 and re-incorporated in Delaware in April 2007. The Company develops and is seeking to commercialize proprietary systems that generate electricity by harnessing the renewable energy of ocean waves. The Company markets its products in the United States and internationally. Since fiscal 2002, the US Navy and other government agencies have accounted for a significant portion of the Company’s revenues. These revenues were largely for the support of product development efforts. The Company’s goal is that an increased portion of its revenues be from the sale of products and maintenance services, as compared to revenue to support its product development efforts. As the Company continues to advance its proprietary technologies, it expects to continue to have a net decrease in cash from operating activities unless and until it achieves positive cash flow from the planned commercialization of its products and services.

(b) Liquidity

The Company has incurred net losses and negative operating cash flows since inception. As of April 30, 2013, the Company had accumulated deficit of $140.7 million. As of April 30, 2013, the Company’s cash and cash equivalents, marketable securities and restricted cash balance was approximately $21.7 million. Based upon the Company’s cash and cash equivalents and marketable securities balance as of April 30, 2013, the Company believes that it will be able to finance its capital requirements and operations through, at least, July 31, 2014.

During 2013 and 2012, the Company has continued to make investments in ongoing product development efforts in anticipation of future growth. The Company’s future results of operations involve significant risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited, to risks from competition, new products, technological change, recent economic activity and dependence on key personnel. In order to complete its future growth strategy, the Company will require additional equity and/or debt financing. There is no assurance that additional equity and/or debt financing will be available to the Company as needed. If financing is not achieved, the Company may be required to further curtail or limit certain product development costs, and/or selling, general and administrative, activities in order to reduce its cash expenditures. On June 6, 2013, the Company entered into an At the Market Offering Agreement. See Subsequent Event - Note 15.

Note 2 - Summary of Significant Accounting Policies

12 Months Ended

Apr. 30, 2013

Significant Accounting Policies [Text Block]

Significant Accounting Policies [Text Block]

(2) Summary of Significant Accounting Policies

(a) Consolidation and Cost Method Investment

The accompanying consolidated financial statements include the accounts of the Company and its majority-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. Participation of stockholders other than the Company in the net assets and in the earnings or losses of a consolidated subsidiary is reflected as a noncontrolling interest in the Company's Consolidated Balance Sheets and Statements of Operations, which adjusts the Company's consolidated results of operations to reflect only the Company's share of the earnings or losses of the consolidated subsidiary. As of April 30, 2013, there was one noncontrolling interest, consisting of 11.8% of the Company's Australian subsidiary, Ocean Power Technologies (Australasia) Pty. Ltd.

In addition, the Company evaluates its relationships with other entities to identify whether they are variable interest entities, and to assess whether it is the primary beneficiary of such entities. If the determination is made that the Company is the primary beneficiary, then that entity is included in the consolidated financial statements. As of April 30, 2013, there were no such entities.

The Company has a 10% investment in Iberdrola Energias Marinas de Cantabria, S.A. (Iberdrola Cantabria). During the fourth quarter of fiscal 2012, the Company evaluated the realizability of this investment and concluded that it was impaired. Accordingly, the Company recorded an impairment expense of $0.3 million representing 100% of the investment amount. In addition, outstanding receivables from Iberdrola Cantabria in the amount of $0.3 million as of April 2012 were fully reserved during the fourth quarter of fiscal 2012. The investment in Iberdrola Cantabria and net accounts receivable and unbilled receivables from Iberdrola Cantabria were $0 as of April 30, 2013 and April 30, 2012.

(b) Use of Estimates

The preparation of the consolidated financial statements requires management of the Company to make a number of estimates and assumptions relating to the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the period. Significant items subject to such estimates and assumptions include the recoverability of the carrying amount of property and equipment and patents; valuation allowances for receivables and deferred income tax assets; and percentage of completion of customer contracts for purposes of revenue recognition. Actual results could differ from those estimates. The current economic environment has increased the degree of uncertainty inherent in those estimates and assumptions.

(c) Revenue Recognition

The Company’s contracts are either cost plus or fixed price contracts. Under cost plus contracts, customers are billed for actual expenses incurred plus an agreed-upon fee. Currently, the Company has two types of fixed price contracts, firm fixed price and cost-sharing. Under firm fixed price contracts, the Company receives an agreed-upon amount for providing products and services specified in the contract. Under cost-sharing contracts, the fixed amount agreed upon with the customer is only intended to fund a portion of the costs on a specific project.

Generally, the Company recognizes revenue using the percentage-of-completion method based on the ratio of costs incurred to total estimated costs at completion. In certain circumstances, revenue under contracts that have specified milestones or other performance criteria may be recognized only when the customer acknowledges that such criteria have been satisfied. In addition, recognition of revenue (and the related costs) may be deferred for fixed-price contracts until contract completion if the Company is unable to reasonably estimate the total costs of the project prior to completion. Because the Company has a small number of contracts, revisions to the percentage-of-completion determination or delays in meeting performance criteria or in completing projects may have a significant effect on revenue for the periods involved. Upon anticipating a loss on a contract, the Company recognizes the full amount of the anticipated loss in the current period.

Under cost plus and firm fixed price contracts there is a profit or loss on the project depending on whether actual costs are more or less than the agreed upon amount. Under cost sharing contracts, an amount corresponding to the revenue is recorded in cost of revenues, resulting in gross profit on these contracts of zero. The Company’s share of the costs is recorded as product development expense.

Unbilled receivables represent expenditures on contracts, plus applicable profit margin, not yet billed. Unbilled receivables are normally billed and collected within one year. Billings made on contracts are recorded as a reduction of unbilled receivables, and to the extent that such billings and cash collections exceed costs incurred plus applicable profit margin, they are recorded as unearned revenues.

(d) Cash and Cash Equivalents

Cash equivalents consist of investments in short-term financial instruments with initial maturities of three months or less from the date of purchase. Cash and cash equivalents include the following:

	April 30,
	2013		2012

Checking and savings accounts	$	2,184,322		2,051,918
Certificates of deposits and US Treasury obligations	―			5,998,925
Money market funds		4,188,466		1,302,617
	$	6,372,788		9,353,460

(e) Marketable Securities

Marketable securities with original maturities longer than three months but mature in less than one year from the balance sheet date are classified as current assets. Marketable securities that mature more than one year from the balance sheet date are classified as noncurrent assets. Marketable securities that the Company has the intent and ability to hold to maturity are classified as investments held-to-maturity and are reported at amortized cost. The difference between the acquisition cost and face values of held-to-maturity investments is amortized over the remaining term of the investments and added to or subtracted from the acquisition cost and interest income. As of April 30, 2013 and 2012, all of the Company's investments were classified as held-to-maturity.

(f) Restricted Cash and Credit Facility

A portion of the Company’s cash is restricted under the terms of two security agreements.

One agreement is between Ocean Power Technologies, Inc. and Barclays Bank. Under this agreement, the cash is on deposit at Barclays Bank and serves as security for letters of credit that are expected to be issued by Barclays Bank on behalf of Ocean Power Technologies Ltd., one of the Company's subsidiaries, under a €800,000 ($1,046,000 at April 30, 2013) credit facility established by Barclays Bank for Ocean Power Technologies Ltd. The credit facility is for the issuance of letters of credit and bank guarantees and carries a fee of 1% per annum of the amount of any such obligations issued by Barclays Bank. As of April 30, 2013, there were €266,000 ($348,000) in letters of credit outstanding under this agreement. Subsequent to the year ended April 30, 2013, the Company issued two additional letters of credit for €278,828 ($364,512) under this agreement. The credit facility does not have an expiration date, but is cancelable at the discretion of the bank.

The other agreement is between Ocean Power Technologies, Inc. and the New Jersey Board of Public Utilities (NJBPU). The Company received a $500,000 recoverable grant award from the NJBPU. Under this agreement, the Company is required to assign to the NJBPU a certificate of deposit in an amount equal to the outstanding grant balance. See Note 7.

Cash restricted under security agreements is as follows:

	April 30,
	2013		2012

Barclays Bank agreement	$	941,256		953,712
NJBPU agreement		425,000		500,000
	$	1,366,256		1,453,712

(g) Property and Equipment

Property and equipment is stated at cost, less accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives (three to seven years) of the assets. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the remaining lease term. Expenses for maintenance and repairs are charged to operations as incurred.

(h) Foreign Exchange Gains and Losses

The Company has invested in certain certificates of deposit and has maintained cash accounts that are denominated in British pounds sterling, Euros and Australian dollars. These amounts are included in cash, cash equivalents, restricted cash and marketable securities on the accompanying consolidated balance sheets. Such positions may result in realized and unrealized foreign exchange gains or losses from exchange rate fluctuations, which gains and losses are included in foreign exchange loss in the accompanying consolidated statements of operations.

	Year Ended April 30,
	2013			2012

Foreign exchange loss	$	(83,416	)		(104,739	)

	April 30,
	2013		2012
Foreign currency denominated certificates of deposit and cash accounts	$	2,491,714		2,826,000

(i) Patents

Prior to February 1, 2012, external patent costs were amortized on a straight-line basis over a 17-year period commencing with the issuance date of each patent. The Company operates in the renewable energy industry. Wave energy technology is still at an early stage of development, and as a result, it continues to evolve and change as such technology is developed. Costs are expensed when it is no longer probable that such technology will be utilized. Additionally, the Company continually re-assesses the remaining useful lives of its long-lived assets. Patents are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the patent may not be recoverable. Based on the Company’s prior year assessment, the Company evaluated the remaining useful lives of its existing patents as of February 1, 2012 and concluded that the remaining amortization should be recorded over periods ranging from three to seven years. In the fourth quarter of fiscal 2013, the Company performed its recurring assessment of the realizability of its patents and recorded impairment expenses of approximately $8,000. Amortization expense was approximately $217,000 and $110,000 for the years ended April 30, 2013 and 2012, respectively. This increase in amortization expense was largely as a result of this change in estimated useful life. Amortization expense for the next five fiscal years related to amounts capitalized for patents as of April 30, 2013 is estimated to be approximately $191,000 per year.

(j) Long-Lived Assets

Long-lived assets, such as property and equipment, and patents subject to amortization and cost-basis investments, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of the asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of the asset exceeds its estimated future cash flows, then an impairment charge is recognized by the amount by which the carrying amount of the asset exceeds the fair value of the asset. The Company reviewed its long-lived assets for impairment for the years ended April 30, 2013 and 2012. The Company recorded impairment charges of approximately $8,000 related to patents in the year ended April 30, 2013 and approximately $358,000 related to patents and an investment in a joint venture in the year ended April 30, 2012.

(k) Concentration of Credit Risk

Financial instruments that potentially subject the Company to concentration of credit risk consist principally of cash balances, bank certificates of deposit and trade receivables. The Company invests its excess cash in highly liquid investments (principally short-term bank deposits, Treasury bills, Treasury notes and money market funds) and does not believe that it is exposed to any significant risks related to its cash accounts, money market funds or certificates of deposit.

The table below shows the percentage of the Company's revenues derived from customers whose revenues accounted for at least 10% of the Company's consolidated revenues for at least one of the periods indicated:

	Years Ended April 30,
	2013			2012

US Department of Energy		51	%		32	%
Mitsui Shipbuilding & Engineering		20	%		3	%
European Union (WavePort project)		17	%		13	%
US Navy		3	%		29	%
UK Government's Technology Strategy Board		3	%		20	%

The loss of, or a significant reduction in revenues from, any of the current customers could significantly impact the Company's financial position or results of operations. The Company does not require its customers to post collateral.

(l) Net Loss per Common Share

Basic and diluted net loss per share for all periods presented is computed by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Due to the Company's net losses, potentially dilutive securities, consisting of outstanding stock options and non-vested performance-based shares, were excluded from the diluted loss per share calculation due to their anti-dilutive effect.

In computing diluted net loss per share, options to purchase shares of common stock and non-vested restricted stock issued to employees and non-employee directors, totaling 1,360,790 and 1,447,313 for the years ended April 30, 2013 and 2012, respectively, were excluded from the computations as the effect would be anti-dilutive due to the Company's losses.

(m) Stock-Based Compensation

Costs resulting from all share-based payment transactions are recognized in the consolidated financial statements at their fair values. Compensation cost for the portion of the awards for which the requisite service had not been rendered that were outstanding as of May 1, 2006 is being recognized in the consolidated statements of operations over the remaining service period after such date based on the award's original estimated fair value. The aggregate share-based compensation expense recorded in the consolidated statements of operations for the years ended April 30, 2013 and 2012 was approximately $859,000 and $1,121,000 respectively.

Valuation Assumptions for Options Granted During the Years Ended April 30, 2013 and 2012

The fair value of each stock option granted during the years ended April 30, 2013 and 2012 was estimated at the date of grant using the Black-Scholes option pricing model, assuming no dividends and using the weighted average valuation assumptions noted in the following table. The risk-free rate is based on the US Treasury yield curve in effect at the time of grant. The expected life (estimated period of time outstanding) of the stock options granted was estimated using the "simplified" method as permitted by the Securities and Exchange Commission's Staff Accounting Bulletin No. 107, Share-Based Payment. Expected volatility was based on historical volatility for a peer group of companies for a period equal to the stock option's expected life, calculated on a daily basis.

	Years Ended April 30,
	2013			2012

Risk-free interest rate		0.88	%		1.83	%
Expected dividend yield		0.0	%		0.0	%
Expected life (in years)		6.06			5.83
Expected volatility		86.15	%		94.5	%

The above assumptions were used to determine the weighted average per share fair value of $1.58 and $2.98 for stock options granted during the years ended April 30, 2013 and 2012 respectively.

(n) Income Taxes

Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences and operating loss and tax credit carryforwards are expected to be recovered, settled or utilized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date.

The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained upon examination. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest related to unrecognized tax benefits in interest expense and penalties in selling, general, and administrative expenses, to the extent incurred.

(o) Accumulated Other Comprehensive Loss

The functional currency for the Company's foreign operations is the applicable local currency. The translation from the applicable foreign currencies to US dollars is performed for balance sheet accounts using the exchange rates in effect at the balance sheet date and for revenue and expense accounts using an average exchange rate during the period. The unrealized gains or losses resulting from such translation are included in accumulated other comprehensive loss within stockholders' equity.

(p) Recent Accounting Pronouncements

In May 2011, the Financial Accounting Standards Board (FASB) issued additional authoritative guidance related to fair value measurements and disclosures. The new guidance results in a consistent definition of fair value and common requirements for measurement of and disclosure about fair value between accounting principles generally accepted in the United States (US GAAP) and International Financial Reporting Standards (IFRS). The guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2011.

In June 2011, the FASB issued amended guidance on the presentation of comprehensive income in financial statements. This amendment provides companies the option to present the components of net income and other comprehensive income either as one continuous statement of comprehensive income or as two separate but consecutive statements. It eliminates the option to present components of other comprehensive income as part of the statement of changes in stockholders' equity. The guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2011. The Company adopted both of these pronouncements during fiscal year ended April 30, 2013. The adoption of these two pronouncements did not impact the Company’s financial position, results in operation or cash flow.

In December 2011, the FASB issued ASU No. 2011-11, Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities. ASU 2011-11 requires an entity to disclose information about offsetting and related arrangements to enable users of financial statements to understand the effect of those arrangements on its financial position, and to allow investors to better compare financial statements prepared under U.S. GAAP with financial statements prepared under International Financial Reporting Standards (IFRS). The new standards are effective for annual periods beginning January 1, 2013, and interim periods within those annual periods. Retrospective application is required. We are currently assessing the impact of this guidance.

Note 3 - Marketable Securities

12 Months Ended

Apr. 30, 2013

Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]

Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]

(3) Marketable Securities

Marketable securities are classified as current assets and are summarized as follows:

	April 30,
	2013		2012

Certificates of deposit denominated in Australian Dollars	$	—		556,437
Certificates of deposit denominated in US Dollars		—		3,806,808
US Treasury obligations		13,996,705		18,006,239
	$	13,996,705		22,369,484

The Company had no marketable securities classified as noncurrent assets as of April 30, 2013 and April 30, 2012.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Note 4 - Property and Equipment

12 Months Ended

Apr. 30, 2013

Property, Plant and Equipment Disclosure [Text Block]

Property, Plant and Equipment Disclosure [Text Block]

(4) Property and Equipment

The components of property and equipment are as follows:

				April 30,
	Life (in years)			2013			2012

Computers and software		3		$	566,353			696,784
Equipment	3	to	7		1,170,473			1,080,039
Office furniture and equipment	3	to	7		293,880			287,492
Leasehold improvements		2			182,285			149,505
					2,212,991			2,213,820
Less accumulated depreciation and amortization					(1,512,023	)		(1,530,887	)
				$	700,968			682,933

Depreciation expense was $285,263 and $326,205 for the years ended April 30, 2013 and 2012, respectively.

Note 5 - Balance Sheet Detail

12 Months Ended

Apr. 30, 2013

Supplemental Balance Sheet Disclosures [Text Block]

Supplemental Balance Sheet Disclosures [Text Block]

(5) Balance Sheet Detail

	April 30,
	2013			2012

Accounts receivable, net
Accounts receivable	$	1,086,847			1,369,400
Allowance for doubtful accounts		(290,515	)		(304,604	)
	$	796,332			1,064,796

Patents
Patents	$	1,558,630			1,574,044
Accumulated amortization		(513,728	)		(304,587	)
	$	1,044,902			1,269,457


Accrued expenses
Project costs	$	1,698,959			244,892
Contract loss reserves		785,000			785,000
Employee incentive payments		249,469			661,328
Accrued salary and benefits		547,404			521,058
Investment in joint venture		173,842			176,110
Legal and accounting fees		214,891			193,720
Other		231,058			187,986
	$	3,900,623			2,770,094

Note 6 - Related Party Transactions

12 Months Ended

Apr. 30, 2013

(6) Related Party Transactions

In August 1999, the Company entered into a consulting agreement with an individual for the provision of marketing services. Currently, this agreement provides for fees at a rate of $950 per day of services provided. The individual became a member of the board of directors in June 2006. In addition, this individual is also the chief executive officer of a company that provides engineering and technical services to the Company. The Company also provides services to the company where this individual is the chief executive officer. This individual did not stand for re-election to the board of directors at the Company’s Annual Meeting on October 4, 2012, and is no longer considered a related party. Accordingly, transactions after such date are not included in the amounts below.

	Year Ended April 30,
	2013		2012
Related party consulting expense	$	42,000		86,000
Expenses for services provided by related party company		-		29,000
Revenue for services provided to related party company		32,000		126,000

	April 30,
	2013		2012

Consulting fees payable to related party	$	-		7,000
Payable to related party company		-		-
Receivable from related party company		-		-

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

Note 7 - Debt

12 Months Ended

Apr. 30, 2013

Debt Disclosure [Text Block]

Debt Disclosure [Text Block]

(7) Debt

The Company was awarded a recoverable grant totaling $500,000 from the NJBPU under the Renewable Energy Business Venture Assistance Program. Under the terms of this agreement, the amount to be repaid is a fixed monthly amount of principal only, repayable over a five-year period beginning in November 2011. The terms also required the Company to assign to the NJBPU a certificate of deposit in an amount equal to the outstanding grant balance. See Note 2(f).

	April 30, 2013			April 30, 2012

Total debt	$	350,000			450,000
Current portion of long-term debt		(100,000	)		(100,000	)
Long-term debt	$	250,000			350,000

Note 8 - Deferred Credits Payable

12 Months Ended

Apr. 30, 2013

Customer Advances And Deposits Disclosure [Text Block]

Customer Advances And Deposits Disclosure [Text Block]

(8) Deferred Credits Payable

During the year ended April 30, 2001, in connection with the sale of common stock to an investor, the Company received $600,000 from the investor in exchange for an option to purchase up to 500,000 metric tons of carbon emissions credits generated by the Company during the years 2008 through 2012, at a 30% discount from the then-prevailing market rate. If the Company received emission credits under applicable laws and failed to sell to the investor the credits up to the full amount of emission credits covered by the option, the investor was entitled to liquidated damages equal to 30% of the aggregate market value of the shortfall in emission credits (subject to a limit on the market price of emission credits). Under the terms of the agreement, if the Company did not become entitled under applicable laws to the full amount of emission credits covered by the option by December 31, 2012, the Company was obligated to return the option fee of $600,000, less the aggregate discount on any emission credits sold to the investor prior to such date. In December 2012, the Company and the investor agreed to extend the period for the sale of emission credits until December 31, 2017. As of April 30, 2013, the Company has not generated any emissions credits eligible for purchase under the agreement and the Company does not believe it is probable that it will generate any eligible emissions credits before December 31, 2017. Accordingly, the $600,000 has been classified as a noncurrent liability as of April 30, 2013 and as a current liability as of April 30, 2012.

Note 9 - Common Stock

12 Months Ended

Apr. 30, 2013

Stockholders' Equity Note Disclosure [Text Block]

Stockholders' Equity Note Disclosure [Text Block]

(9) Common Stock

On April 30, 2007, the Company completed an initial public offering in the United States on the NASDAQ Global Market by issuing 5,000,000 shares of its common stock for a purchase price of $20.00 per share, resulting in net proceeds to the Company of approximately $89,900,000. See Subsequent Event – Note 15.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph d
-Article 4

Reference 15: http://www.xbrl.org/2003/role/presentationRef
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-Name Regulation S-X (SX)
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Reference 16: http://www.xbrl.org/2003/role/presentationRef
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Reference 17: http://www.xbrl.org/2003/role/presentationRef
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-Number 210
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Reference 18: http://www.xbrl.org/2003/role/presentationRef
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Reference 19: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

+ Details

Note 10 - Preferred Stock

12 Months Ended

Apr. 30, 2013

Preferred Stock [Text Block]

Preferred Stock [Text Block]

(10) Preferred Stock

The Company has authorized 5,000,000 shares of undesignated preferred stock with a par value of $0.001 per share. As of April 30, 2013, and 2012, no shares of preferred stock had been issued.

Note 11 - Share-Based Compensation

12 Months Ended

Apr. 30, 2013

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

(11) Share-Based Compensation

In August 2001, the Company approved the 2001 Stock Plan, which provides for the grant of incentive stock options and nonqualified stock options. A total of 1,000,000 shares were authorized for issuance under the 2001 Stock Plan. As of April 30, 2013, the Company had issued or reserved 196,675 shares for issuance under the 2001 Stock Plan. After the effectiveness of the 2006 Stock Incentive Plan, no further options or other awards have been or will be granted under the 2001 Stock Plan.

On April 24, 2007, the Company's 2006 Stock Incentive Plan became effective. A total of 803,215 shares were authorized for issuance under the 2006 Stock Incentive Plan. On October 2, 2009, an amendment to the 2006 Stock Incentive Plan was approved, increasing the aggregate number of shares authorized for issuance by 850,000 shares to 1,653,215. As of April 30, 2013, the Company had issued share-based awards for 1,302,174 shares of common stock and had reserved an additional 351,041 shares of common stock for future issuance under the 2006 Stock Incentive Plan. The Company's employees, officers, directors, consultants and advisors are eligible to receive awards under the 2006 Stock Incentive Plan; however, incentive stock options may only be granted to employees. The maximum number of shares of common stock with respect to which awards may be granted to any participant under the 2006 Stock Incentive Plan is 200,000 per calendar year. Vesting provisions of stock options are determined by the board of directors. The contractual term of these stock options is up to ten years. The 2006 Stock Incentive Plan is administered by the Company's board of directors, who may delegate authority to one or more committees or subcommittees of the board of directors or to the Company's officers. If the board of directors delegates authority to an officer, the officer has the power to make awards to any of the Company's employees, other than executive officers. The board of directors will fix the terms of the awards to be granted by such officer. No award may be granted under the 2006 Stock Incentive Plan after December 7, 2016, but the vesting and effectiveness of awards granted before that date may extend beyond that date.

(a) Stock Options

A summary of stock options under the plans described above is as follows:

	Shares Under Option			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
						(In Years)

Outstanding April 30, 2011		1,353,935			10.30		5.7
Forfeited		(268,784	)		10.94
Granted		268,322			3.97
Outstanding April 30, 2012		1,353,473			8.92		6.1
Forfeited		(429,244	)		7.29
Granted		381,759			1.98
Outstanding April 30, 2013		1,305,988			7.43		5.9
Exercisable April 30, 2013		836,026			9.64		4.5

As of April 30, 2013, the total intrinsic value of outstanding options was approximately $0 and the total intrinsic value of exercisable options was $0. As of April 30, 2013, approximately 470,000 additional options were expected to vest, which have approximately $0 of intrinsic value and a weighted-average remaining contractual term of 8.3 years. There was approximately $713,000 and $932,000 of total recognized compensation cost related to employees for stock options during the years ended April 30, 2013 and 2012, respectively. As of April 30, 2013, there was approximately $670,000 of total unrecognized compensation cost related to non-vested stock options granted under the plans. This cost is expected to be recognized over a weighted-average period of 2.6 years. The Company normally issues new shares to satisfy option exercises under these plans.

Certain options were granted to non-employee directors and consultants during the years ended April 30, 2013 and 2012. The Company has charged compensation expense of approximately $101,000 and $77,000 related to these option grants for which the majority relates to non-employee directors. These expenses have been included in selling, general and administrative costs in the accompanying consolidated statements of operations for the years ended April 30, 2013 and 2012, respectively.

(b) Restricted Stock

Compensation expense for restricted stock is generally recorded based on its market value on the date of grant and recognized ratably over the associated service and performance period. There were 31,744 and 14,634 shares of restricted stock granted to employees and non-employee board members with service and/or performance-based vesting requirements during the years ended April 30, 2013 and 2012, respectively.

A summary of non-vested restricted stock under the plans is as follows:

	Number of Shares			Weighted Average Price per Share

Issued and unvested at April 30, 2011		150,953			6.16
Granted		14,634			3.86
Forfeited		(26,428	)		5.93
Vested		(45,319	)		6.18
Issued and unvested at April 30, 2012		93,840			5.86
Granted		31,744			2.39
Forfeited		(35,918	)		4.70
Vested		(34,864	)		6.02
Issued and unvested at April 30, 2013		54,802			4.52

There was approximately $28,000 and $100,000 of total recognized compensation cost relating to restricted stock granted to employees during the years ended April 30, 2013 and 2012 respectively. Certain shares of restricted stock were granted to non-employee directors during the years ended April 30, 2013 and 2012. The Company recorded compensation expenses of approximately $16,000 and $13,000 in 2013 and 2012, respectively. As of April 30, 2013, there was approximately $47,000 of total unrecognized compensation cost related to non-vested restricted stock granted under the plans. This cost is expected to be recognized over a weighted-average period of 2.4 years.

(c) Treasury Stock

During the years ended April 30, 2013 and 2012, 10,227 and 15,859 shares of common stock, respectively, were purchased by the Company from employees to pay taxes related to the vesting of restricted stock.

Note 12 - Income Taxes

12 Months Ended

Apr. 30, 2013

Income Tax Disclosure [Text Block]

Income Tax Disclosure [Text Block]

(12) Income Taxes

Loss before income taxes for the year ended April 30, 2013 and 2012 consist of the following components:

	April 30,
	2013			2012

Domestic	$	(13,630,946	)		(13,700,366	)
Foreign		(2,645,308	)		(2,543,066	)
Total loss before income taxes	$	(16,276,254	)		(16,243,432	)

The components of income taxes (benefit) for the year ended April 30, 2013 and 2012 are as follows:

	April 30,
	2013			2012

Curent:
Federal	−			−
State		(1,453,243	)		(1,053,427	)
Foreign	−			−
Total current		(1,453,243	)		(1,053,427	)

Deferred:
Federal	−			−
State	−			−
Foreign	−			−
Total deferred		-			-
Total provision (benefit) for income taxes	$	(1,453,243	)		(1,053,427	)

Tax Rate Reconciliation

The effective income tax rate differed from the percentages computed by applying the US federal income tax rate of 34% to loss before income taxes as a result of the following:

	Years Ended April 30,
	2013			2012

Computed "expected" tax benefit		(34	)%		(34	)%
Increase (reduction) in income taxes resulting from:
State income taxes, net of federal benefit		(5	)		(5	)
Stock-based compensation expense		1			2
Federal research and development tax credits		(1	)		(2	)
Foreign rate differential		2			2
Other non-deductible expenses		―			2
Expiration of net operating losses and tax credit carryforwards		23			―
Expiration in compensatory options		9			―
Proceeds of sale of New Jersey tax benefits		(9	)		―
Other		5			6
Increase in valuation allowance		―			23
Income tax benefit		(9	)%		(6	)%

Significant Components of Deferred Taxes

The tax effects of temporary differences and carryforwards that give rise to the Company's deferred tax assets and deferred tax liabilities are presented below.

	April 30,
	2013			2012

Deferred tax assets:
Federal net operating loss carryforwards	$	25,396,000			27,788,000
Foreign net operating loss carryforwards		5,340,000			4,875,000
New Jersey state operating loss carryforwards		1,741,000			3,567,000
Federal research and development tax credits		2,630,000			2,149,000
Foreign research and development tax credits		659,000			715,000
Stock compensation		721,000			2,548,000
Capitalized research and development costs, net of amortization		5,692,000			676,000
Unrealized foreign exchange loss		289,000			291,000
Accrued expenses		610,000			726,000
Other		647,000			342,000
Gross deferred tax assets		43,725,000			43,677,000
Valuation allowance		(43,725,000	)		(43,677,000	)
Net deferred tax assets	$	-			-

In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences and carryforwards become deductible or are utilized. As of April 30, 2013 and 2012, based upon the level of historical taxable losses, valuation allowances of $43,725,000 and $43,677,000, respectively, were recorded to fully offset deferred tax assets. The valuation allowance increased $48,000 and $3,771,000 during the years ended April 30, 2013 and 2012, respectively.

As of April 30, 2013, the Company had net operating loss carryforwards for federal income tax purposes of approximately $74,693,000, which begin to expire in 2013. The Company also had federal research and experimental tax credit carryforwards of approximately $2,094,000 as of April 30, 2013, which begin to expire in 2013. The Tax Reform Act of 1986 contains provisions that limit the utilization of net operating loss and tax credit carryforwards if there has been an ownership change, as defined. The Company has determined that such an ownership change, as described in Section 382 of the Internal Revenue Code, occurred in conjunction with the Company's US initial public offering in April 2007. The Company's annual Section 382 limitation is approximately $3,300,000. The Section 382 limitation is cumulative from year to year, and thus, to the extent net operating loss or other credit carryforwards are not utilized up to the amount of the available annual limitation, the limitation is carried forward and added to the following year's available limitation. The Company has not performed additional analysis on ownership changes that may have occurred subsequently to further limit the ability to utilize net tax attributes. As of April 30, 2013, the Company had state net operating loss carryforwards of approximately $28,586,000, which begin to expire in 2026, which also may be limited to utilization limitations. As of April 30, 2013, the Company had foreign net operating loss carryforwards of approximately $20,946,000, which begin to expire in 2024. The ability to utilize these carryforwards may also be limited in the event of a significant change in ownership.

During the years ended April 30, 2013 and 2012, the Company sold New Jersey State net operating losses in the amount of $18,673,000 and $12,862,000, respectively, resulting in the recognition of income tax benefits of $1,453,000 and $1,053,000, respectively, recorded in the Company’s Statement of Operations.

The Company applies the guidance issued by the FASB for the accounting and reporting of uncertain tax positions. The guidance requires the Company to recognize in its consolidated financial statements the impact of a tax position if that position is more likely than not to be sustained upon examination, based on the technical merits of the position. At April 30, 2013 and 2012, the Company had no unrecognized tax positions. The Company does not expect any material increase or decrease in its income tax expense in the next twelve months, related to examinations or uncertain tax positions. US federal and state income tax returns were audited through fiscal 2007 and fiscal 2010, respectively. Net operating loss and credit carryforwards since inception remain open to examination by taxing authorities, and will continue to remain open for a period of time after utilization.

The Company does not have any interest or penalties accrued related to uncertain tax positions as it does not have any unrecognized tax benefits.

Note 13 - Commitments and Contingencies

12 Months Ended

Apr. 30, 2013

Commitments and Contingencies Disclosure [Text Block]

Commitments and Contingencies Disclosure [Text Block]

(13) Commitments and Contingencies

(a) Operating Lease Commitments

The Company leases office, laboratory, manufacturing and other space in Pennington, New Jersey and Warwick, United Kingdom under operating leases that expire on various dates through April 30, 2015. Rent expense under operating leases was approximately $383,000 and $507,000 for the years ended April 30, 2013 and 2012, respectively. Future minimum lease payments under this operating lease as of April 30, 2013 are as follows:

Year ending April 30:
2014	$	257,000
2015		257,000
	$	514,000

(b) Litigation

The Company is involved from time to time in certain legal actions arising in the ordinary course of business. Management believes that the outcome of such actions will not have a material adverse effect on the Company's financial position or results of operations.

(c) 2006 Spain Construction Agreement

The Company is currently engaged in discussions with Iberdrola Cantabria (see Note 2(a)) regarding modifications to its agreement for the first phase of the construction of a wave power station off the coast of Spain. This phase was due to be completed by December 31, 2009. If no modification is agreed to by the parties, the customer may, subject to certain conditions in the agreement, terminate the agreement and would not be obligated to make any more milestone payments. The agreement also provides that the customer may seek reimbursement for direct damages only, limited to amounts specified in the agreement, if the Company is in default of its obligations under the agreement. As of April 30, 2013, the Company does not believe that the outcome of this matter will have a material adverse effect on the Company's financial position or results of operations.

(d) Spain IVA (sales tax)

The Company received notice that the Spanish Tax Authorities are inquiring into its 2010 IVA (value-added tax) filing for which the Company benefitted from the offset of approximately $250,000 of input tax. The Company believes that the inquiry will find that the tax credit was properly claimed and, therefore, no liability has been recorded. Subsequent to the year ended April 30, 2013, the Company issued two letters of credit in the amount of €278,828 ($364,512) at the request of the Spanish tax authorities. This is a customary request during the inquiry period.

(e) Commercial Dispute

The Company is subject to certain claims filed by a contractor and subcontractor in connection with a dispute over a contract to perform certain work for the Company related to the deployment of an anchor/mooring system off the Oregon coast. The Company has claimed that the contractor and subcontractor were responsible for damage to the system during the deployment process. The parties are currently involved in ongoing settlement discussions. As of April 30, 2013, the Company has accounted for the outcome of this matter in its financial statements.

Note 14 - Operating Segments and Geographic Information

12 Months Ended

Apr. 30, 2013

Segment Reporting Disclosure [Text Block]

Segment Reporting Disclosure [Text Block]

(14) Operating Segments and Geographic Information

The Company's business consists of one segment as this represents management's view of the Company's operations. The Company operates on a worldwide basis with one operating company in the US and operating subsidiaries in the UK and in Australia. Revenues and expenses are generally attributed to the operating unit that bills the customers.

Geographic information is as follows:

	Year Ended April 30, 2013
	North America			Europe			Asia and Australia			Total
Revenues from external customers	$	3,497,338			118,791			—			3,616,129
Operating loss		(14,048,062	)		(1,091,473	)		(1,179,680	)		(16,319,215	)
Long-lived assets		675,354			24,128			1,486			700,968
Total assets		23,097,183			1,518,496			215,380			24,831,059

	Year Ended April 30, 2012
	North America			Europe			Asia and Australia			Total
Revenues from external customers	$	4,603,652			1,134,854			—			5,738,506
Operating loss		(14,432,825	)		(1,672,636	)		(451,284	)		(16,556,745	)
Long-lived assets		585,818			97,115			—			682,933
Total assets		35,181,637			1,619,973			640,027			37,441,637

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Note 15 - Subsequent Event

12 Months Ended

Apr. 30, 2013

Subsequent Events [Text Block]

Subsequent Events [Text Block]

(15) Subsequent Event

In January 2013, the Company filed a shelf registration statement on Form S-3 with the SEC registering the sale of up to $40,000,000 of debt, equity and other securities (the “S-3 Shelf”). The S-3 Shelf was declared effective in February 2013. On June 6, 2013, the Company entered into an At the Market Offering Agreement (the “Offering Agreement”) with Ascendiant Capital Markets, LLC (the “Manager”). Pursuant to the Offering Agreement, the Company may offer and sell shares of its common stock having an aggregate offering price of up to $10,000,000 from time to time over the three-year term of the Offering Agreement, through or to the Manager, acting as sales agent and/or principal. Subject to certain limited exceptions, these sales will be made in ordinary brokerage transactions at prevailing market prices. The sale of shares under the Offering Agreement will be made pursuant to the Company’s instructions (including any price, time or size limits or other customary conditions or parameters that it may impose) and in reliance on, and subject to the limitations of, General Instruction I.B.6 of Form S-3 and other applicable law and regulation. The sale of shares pursuant to the Offering Agreement has been registered on the S-3 Shelf.

The Company has not sold any shares pursuant to the Offering Agreement as of the date of filing of this Annual Report on Form 10-K.

Accounting Policies, by Policy (Policies)	12 Months Ended
Accounting Policies, by Policy (Policies)	Apr. 30, 2013
Accounting Policies [Abstract]
Consolidation, Policy [Policy Text Block]	*Consolidation and Cost Method Investment* The accompanying consolidated financial statements include the accounts of the Company and its majority-owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation. Participation of stockholders other than the Company in the net assets and in the earnings or losses of a consolidated subsidiary is reflected as a noncontrolling interest in the Company's Consolidated Balance Sheets and Statements of Operations, which adjusts the Company's consolidated results of operations to reflect only the Company's share of the earnings or losses of the consolidated subsidiary. As of April 30, 2013, there was one noncontrolling interest, consisting of 11.8% of the Company's Australian subsidiary, Ocean Power Technologies (Australasia) Pty. Ltd. In addition, the Company evaluates its relationships with other entities to identify whether they are variable interest entities, and to assess whether it is the primary beneficiary of such entities. If the determination is made that the Company is the primary beneficiary, then that entity is included in the consolidated financial statements. As of April 30, 2013, there were no such entities. The Company has a 10% investment in Iberdrola Energias Marinas de Cantabria, S.A. (Iberdrola Cantabria). During the fourth quarter of fiscal 2012, the Company evaluated the realizability of this investment and concluded that it was impaired. Accordingly, the Company recorded an impairment expense of $0.3 million representing 100% of the investment amount. In addition, outstanding receivables from Iberdrola Cantabria in the amount of $0.3 million as of April 2012 were fully reserved during the fourth quarter of fiscal 2012. The investment in Iberdrola Cantabria and net accounts receivable and unbilled receivables from Iberdrola Cantabria were $0 as of April 30, 2013 and April 30, 2012.
Use of Estimates, Policy [Policy Text Block]	*Use of Estimates* The preparation of the consolidated financial statements requires management of the Company to make a number of estimates and assumptions relating to the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the period. Significant items subject to such estimates and assumptions include the recoverability of the carrying amount of property and equipment and patents; valuation allowances for receivables and deferred income tax assets; and percentage of completion of customer contracts for purposes of revenue recognition. Actual results could differ from those estimates. The current economic environment has increased the degree of uncertainty inherent in those estimates and assumptions.
Revenue Recognition, Policy [Policy Text Block]	*Revenue Recognition* The Company’s contracts are either cost plus or fixed price contracts. Under cost plus contracts, customers are billed for actual expenses incurred plus an agreed-upon fee. Currently, the Company has two types of fixed price contracts, firm fixed price and cost-sharing. Under firm fixed price contracts, the Company receives an agreed-upon amount for providing products and services specified in the contract. Under cost-sharing contracts, the fixed amount agreed upon with the customer is only intended to fund a portion of the costs on a specific project. Generally, the Company recognizes revenue using the percentage-of-completion method based on the ratio of costs incurred to total estimated costs at completion. In certain circumstances, revenue under contracts that have specified milestones or other performance criteria may be recognized only when the customer acknowledges that such criteria have been satisfied. In addition, recognition of revenue (and the related costs) may be deferred for fixed-price contracts until contract completion if the Company is unable to reasonably estimate the total costs of the project prior to completion. Because the Company has a small number of contracts, revisions to the percentage-of-completion determination or delays in meeting performance criteria or in completing projects may have a significant effect on revenue for the periods involved. Upon anticipating a loss on a contract, the Company recognizes the full amount of the anticipated loss in the current period. Under cost plus and firm fixed price contracts there is a profit or loss on the project depending on whether actual costs are more or less than the agreed upon amount. Under cost sharing contracts, an amount corresponding to the revenue is recorded in cost of revenues, resulting in gross profit on these contracts of zero. The Company’s share of the costs is recorded as product development expense. Unbilled receivables represent expenditures on contracts, plus applicable profit margin, not yet billed. Unbilled receivables are normally billed and collected within one year. Billings made on contracts are recorded as a reduction of unbilled receivables, and to the extent that such billings and cash collections exceed costs incurred plus applicable profit margin, they are recorded as unearned revenues.
Cash and Cash Equivalents, Policy [Policy Text Block]	*Cash and Cash Equivalents* Cash equivalents consist of investments in short-term financial instruments with initial maturities of three months or less from the date of purchase.
Marketable Securities, Policy [Policy Text Block]	*Marketable Securities* Marketable securities with original maturities longer than three months but mature in less than one year from the balance sheet date are classified as current assets. Marketable securities that mature more than one year from the balance sheet date are classified as noncurrent assets. Marketable securities that the Company has the intent and ability to hold to maturity are classified as investments held-to-maturity and are reported at amortized cost. The difference between the acquisition cost and face values of held-to-maturity investments is amortized over the remaining term of the investments and added to or subtracted from the acquisition cost and interest income. As of April 30, 2013 and 2012, all of the Company's investments were classified as held-to-maturity.
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	*Restricted Cash and Credit Facility* A portion of the Company’s cash is restricted under the terms of two security agreements. One agreement is between Ocean Power Technologies, Inc. and Barclays Bank. Under this agreement, the cash is on deposit at Barclays Bank and serves as security for letters of credit that are expected to be issued by Barclays Bank on behalf of Ocean Power Technologies Ltd., one of the Company's subsidiaries, under a €800,000 ($1,046,000 at April 30, 2013) credit facility established by Barclays Bank for Ocean Power Technologies Ltd. The credit facility is for the issuance of letters of credit and bank guarantees and carries a fee of 1% per annum of the amount of any such obligations issued by Barclays Bank. As of April 30, 2013, there were €266,000 ($348,000) in letters of credit outstanding under this agreement. Subsequent to the year ended April 30, 2013, the Company issued two additional letters of credit for €278,828 ($364,512) under this agreement. The credit facility does not have an expiration date, but is cancelable at the discretion of the bank. The other agreement is between Ocean Power Technologies, Inc. and the New Jersey Board of Public Utilities (NJBPU). The Company received a $500,000 recoverable grant award from the NJBPU. Under this agreement, the Company is required to assign to the NJBPU a certificate of deposit in an amount equal to the outstanding grant balance. See Note 7.
Property, Plant and Equipment, Policy [Policy Text Block]	*Property and Equipment* Property and equipment is stated at cost, less accumulated depreciation and amortization. Depreciation and amortization is calculated using the straight-line method over the estimated useful lives (three to seven years) of the assets. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the remaining lease term. Expenses for maintenance and repairs are charged to operations as incurred.
Foreign Currency Transactions and Translations Policy [Policy Text Block]	*Foreign Exchange Gains and Losses* The Company has invested in certain certificates of deposit and has maintained cash accounts that are denominated in British pounds sterling, Euros and Australian dollars. These amounts are included in cash, cash equivalents, restricted cash and marketable securities on the accompanying consolidated balance sheets. Such positions may result in realized and unrealized foreign exchange gains or losses from exchange rate fluctuations, which gains and losses are included in foreign exchange loss in the accompanying consolidated statements of operations.
Intangible Assets, Finite-Lived, Policy [Policy Text Block]	*Patents* Prior to February 1, 2012, external patent costs were amortized on a straight-line basis over a 17-year period commencing with the issuance date of each patent. The Company operates in the renewable energy industry. Wave energy technology is still at an early stage of development, and as a result, it continues to evolve and change as such technology is developed. Costs are expensed when it is no longer probable that such technology will be utilized. Additionally, the Company continually re-assesses the remaining useful lives of its long-lived assets. Patents are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the patent may not be recoverable. Based on the Company’s prior year assessment, the Company evaluated the remaining useful lives of its existing patents as of February 1, 2012 and concluded that the remaining amortization should be recorded over periods ranging from three to seven years. In the fourth quarter of fiscal 2013, the Company performed its recurring assessment of the realizability of its patents and recorded impairment expenses of approximately $8,000. Amortization expense was approximately $217,000 and $110,000 for the years ended April 30, 2013 and 2012, respectively. This increase in amortization expense was largely as a result of this change in estimated useful life. Amortization expense for the next five fiscal years related to amounts capitalized for patents as of April 30, 2013 is estimated to be approximately $191,000 per year.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	*Long-Lived Assets* Long-lived assets, such as property and equipment, and patents subject to amortization and cost-basis investments, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of the asset to estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of the asset exceeds its estimated future cash flows, then an impairment charge is recognized by the amount by which the carrying amount of the asset exceeds the fair value of the asset. The Company reviewed its long-lived assets for impairment for the years ended April 30, 2013 and 2012. The Company recorded impairment charges of approximately $8,000 related to patents in the year ended April 30, 2013 and approximately $358,000 related to patents and an investment in a joint venture in the year ended April 30, 2012.
Concentration Risk, Credit Risk, Policy [Policy Text Block]	*Concentration of Credit Risk* Financial instruments that potentially subject the Company to concentration of credit risk consist principally of cash balances, bank certificates of deposit and trade receivables. The Company invests its excess cash in highly liquid investments (principally short-term bank deposits, Treasury bills, Treasury notes and money market funds) and does not believe that it is exposed to any significant risks related to its cash accounts, money market funds or certificates of deposit.
Earnings Per Share, Policy [Policy Text Block]	*Net Loss per Common Share* Basic and diluted net loss per share for all periods presented is computed by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Due to the Company's net losses, potentially dilutive securities, consisting of outstanding stock options and non-vested performance-based shares, were excluded from the diluted loss per share calculation due to their anti-dilutive effect. In computing diluted net loss per share, options to purchase shares of common stock and non-vested restricted stock issued to employees and non-employee directors, totaling 1,360,790 and 1,447,313 for the years ended April 30, 2013 and 2012, respectively, were excluded from the computations as the effect would be anti-dilutive due to the Company's losses.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	*Stock-Based Compensation* Costs resulting from all share-based payment transactions are recognized in the consolidated financial statements at their fair values. Compensation cost for the portion of the awards for which the requisite service had not been rendered that were outstanding as of May 1, 2006 is being recognized in the consolidated statements of operations over the remaining service period after such date based on the award's original estimated fair value. The aggregate share-based compensation expense recorded in the consolidated statements of operations for the years ended April 30, 2013 and 2012 was approximately $859,000 and $1,121,000 respectively. Valuation Assumptions for Options Granted During the Years Ended April 30, 2013 and 2012 The fair value of each stock option granted during the years ended April 30, 2013 and 2012 was estimated at the date of grant using the Black-Scholes option pricing model, assuming no dividends and using the weighted average valuation assumptions noted in the following table. The risk-free rate is based on the US Treasury yield curve in effect at the time of grant. The expected life (estimated period of time outstanding) of the stock options granted was estimated using the "simplified" method as permitted by the Securities and Exchange Commission's Staff Accounting Bulletin No. 107, Share-Based Payment. Expected volatility was based on historical volatility for a peer group of companies for a period equal to the stock option's expected life, calculated on a daily basis.
Income Tax, Policy [Policy Text Block]	*Income Taxes* Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences and operating loss and tax credit carryforwards are expected to be recovered, settled or utilized. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained upon examination. Recognized income tax positions are measured at the largest amount that is greater than 50% likely of being realized. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. The Company records interest related to unrecognized tax benefits in interest expense and penalties in selling, general, and administrative expenses, to the extent incurred.
Comprehensive Income, Policy [Policy Text Block]	*Accumulated Other Comprehensive Loss* The functional currency for the Company's foreign operations is the applicable local currency. The translation from the applicable foreign currencies to US dollars is performed for balance sheet accounts using the exchange rates in effect at the balance sheet date and for revenue and expense accounts using an average exchange rate during the period. The unrealized gains or losses resulting from such translation are included in accumulated other comprehensive loss within stockholders' equity.
New Accounting Pronouncements, Policy [Policy Text Block]	*Recent Accounting Pronouncements* In May 2011, the Financial Accounting Standards Board (FASB) issued additional authoritative guidance related to fair value measurements and disclosures. The new guidance results in a consistent definition of fair value and common requirements for measurement of and disclosure about fair value between accounting principles generally accepted in the United States (US GAAP) and International Financial Reporting Standards (IFRS). The guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2011. In June 2011, the FASB issued amended guidance on the presentation of comprehensive income in financial statements. This amendment provides companies the option to present the components of net income and other comprehensive income either as one continuous statement of comprehensive income or as two separate but consecutive statements. It eliminates the option to present components of other comprehensive income as part of the statement of changes in stockholders' equity. The guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2011. The Company adopted both of these pronouncements during fiscal year ended April 30, 2013. The adoption of these two pronouncements did not impact the Company’s financial position, results in operation or cash flow. In December 2011, the FASB issued ASU No. 2011-11, Balance Sheet (Topic 210): Disclosures about Offsetting Assets and Liabilities. ASU 2011-11 requires an entity to disclose information about offsetting and related arrangements to enable users of financial statements to understand the effect of those arrangements on its financial position, and to allow investors to better compare financial statements prepared under U.S. GAAP with financial statements prepared under International Financial Reporting Standards (IFRS). The new standards are effective for annual periods beginning January 1, 2013, and interim periods within those annual periods. Retrospective application is required. We are currently assessing the impact of this guidance.

Note 2 - Summary of Significant Accounting Policies (Tables)

12 Months Ended

Apr. 30, 2013

Significant Accounting Policies [Text Block]

Schedule of Cash and Cash Equivalents [Table Text Block]

	April 30,
	2013		2012

Checking and savings accounts	$	2,184,322		2,051,918
Certificates of deposits and US Treasury obligations	―			5,998,925
Money market funds		4,188,466		1,302,617
	$	6,372,788		9,353,460

Schedule of Restricted Cash and Cash Equivalents [Table Text Block]

	April 30,
	2013		2012

Barclays Bank agreement	$	941,256		953,712
NJBPU agreement		425,000		500,000
	$	1,366,256		1,453,712

Schedule of Foreign Exchange Gain (Loss) [Table Text Block]

	Year Ended April 30,
	2013			2012

Foreign exchange loss	$	(83,416	)		(104,739	)

	April 30,
	2013		2012
Foreign currency denominated certificates of deposit and cash accounts	$	2,491,714		2,826,000

Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block]

	Years Ended April 30,
	2013			2012

US Department of Energy		51	%		32	%
Mitsui Shipbuilding & Engineering		20	%		3	%
European Union (WavePort project)		17	%		13	%
US Navy		3	%		29	%
UK Government's Technology Strategy Board		3	%		20	%

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Years Ended April 30,
	2013			2012

Risk-free interest rate		0.88	%		1.83	%
Expected dividend yield		0.0	%		0.0	%
Expected life (in years)		6.06			5.83
Expected volatility		86.15	%		94.5	%

Note 3 - Marketable Securities (Tables)

12 Months Ended

Apr. 30, 2013

Current [Member]

Note 3 - Marketable Securities (Tables) [Line Items]

Marketable Securities [Table Text Block]

	April 30,
	2013		2012

Certificates of deposit denominated in Australian Dollars	$	—		556,437
Certificates of deposit denominated in US Dollars		—		3,806,808
US Treasury obligations		13,996,705		18,006,239
	$	13,996,705		22,369,484

Note 4 - Property and Equipment (Tables)

12 Months Ended

Apr. 30, 2013

Property, Plant and Equipment Disclosure [Text Block]

Property, Plant and Equipment [Table Text Block]

				April 30,
	Life (in years)			2013			2012

Computers and software		3		$	566,353			696,784
Equipment	3	to	7		1,170,473			1,080,039
Office furniture and equipment	3	to	7		293,880			287,492
Leasehold improvements		2			182,285			149,505
					2,212,991			2,213,820
Less accumulated depreciation and amortization					(1,512,023	)		(1,530,887	)
				$	700,968			682,933

Note 5 - Balance Sheet Detail (Tables)

12 Months Ended

Apr. 30, 2013

Supplemental Balance Sheet Disclosures [Text Block]

Schedule of Other Assets and Other Liabilities [Table Text Block]

	April 30,
	2013			2012

Accounts receivable, net
Accounts receivable	$	1,086,847			1,369,400
Allowance for doubtful accounts		(290,515	)		(304,604	)
	$	796,332			1,064,796

Patents
Patents	$	1,558,630			1,574,044
Accumulated amortization		(513,728	)		(304,587	)
	$	1,044,902			1,269,457


Accrued expenses
Project costs	$	1,698,959			244,892
Contract loss reserves		785,000			785,000
Employee incentive payments		249,469			661,328
Accrued salary and benefits		547,404			521,058
Investment in joint venture		173,842			176,110
Legal and accounting fees		214,891			193,720
Other		231,058			187,986
	$	3,900,623			2,770,094

Note 6 - Related Party Transactions (Tables)

12 Months Ended

Apr. 30, 2013

	Year Ended April 30,
	2013		2012
Related party consulting expense	$	42,000		86,000
Expenses for services provided by related party company		-		29,000
Revenue for services provided to related party company		32,000		126,000

	April 30,
	2013		2012

Consulting fees payable to related party	$	-		7,000
Payable to related party company		-		-
Receivable from related party company		-		-

Note 7 - Debt (Tables)

12 Months Ended

Apr. 30, 2013

Debt Disclosure [Text Block]

Schedule of Debt [Table Text Block]

	April 30, 2013			April 30, 2012

Total debt	$	350,000			450,000
Current portion of long-term debt		(100,000	)		(100,000	)
Long-term debt	$	250,000			350,000

Note 11 - Share-Based Compensation (Tables)

12 Months Ended

Apr. 30, 2013

Disclosure of Compensation Related Costs, Share-based Payments [Text Block]

Schedule of Share-based Compensation, Activity [Table Text Block]

	Shares Under Option			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term
						(In Years)

Outstanding April 30, 2011		1,353,935			10.30		5.7
Forfeited		(268,784	)		10.94
Granted		268,322			3.97
Outstanding April 30, 2012		1,353,473			8.92		6.1
Forfeited		(429,244	)		7.29
Granted		381,759			1.98
Outstanding April 30, 2013		1,305,988			7.43		5.9
Exercisable April 30, 2013		836,026			9.64		4.5

Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]

	Number of Shares			Weighted Average Price per Share

Issued and unvested at April 30, 2011		150,953			6.16
Granted		14,634			3.86
Forfeited		(26,428	)		5.93
Vested		(45,319	)		6.18
Issued and unvested at April 30, 2012		93,840			5.86
Granted		31,744			2.39
Forfeited		(35,918	)		4.70
Vested		(34,864	)		6.02
Issued and unvested at April 30, 2013		54,802			4.52

Note 12 - Income Taxes (Tables)

12 Months Ended

Apr. 30, 2013

Income Tax Disclosure [Text Block]

Schedule of Components of Loss Before Income Taxes [Table Text Block]

	April 30,
	2013			2012

Domestic	$	(13,630,946	)		(13,700,366	)
Foreign		(2,645,308	)		(2,543,066	)
Total loss before income taxes	$	(16,276,254	)		(16,243,432	)

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

	April 30,
	2013			2012

Curent:
Federal	−			−
State		(1,453,243	)		(1,053,427	)
Foreign	−			−
Total current		(1,453,243	)		(1,053,427	)

Deferred:
Federal	−			−
State	−			−
Foreign	−			−
Total deferred		-			-
Total provision (benefit) for income taxes	$	(1,453,243	)		(1,053,427	)

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	Years Ended April 30,
	2013			2012

Computed "expected" tax benefit		(34	)%		(34	)%
Increase (reduction) in income taxes resulting from:
State income taxes, net of federal benefit		(5	)		(5	)
Stock-based compensation expense		1			2
Federal research and development tax credits		(1	)		(2	)
Foreign rate differential		2			2
Other non-deductible expenses		―			2
Expiration of net operating losses and tax credit carryforwards		23			―
Expiration in compensatory options		9			―
Proceeds of sale of New Jersey tax benefits		(9	)		―
Other		5			6
Increase in valuation allowance		―			23
Income tax benefit		(9	)%		(6	)%

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	April 30,
	2013			2012

Deferred tax assets:
Federal net operating loss carryforwards	$	25,396,000			27,788,000
Foreign net operating loss carryforwards		5,340,000			4,875,000
New Jersey state operating loss carryforwards		1,741,000			3,567,000
Federal research and development tax credits		2,630,000			2,149,000
Foreign research and development tax credits		659,000			715,000
Stock compensation		721,000			2,548,000
Capitalized research and development costs, net of amortization		5,692,000			676,000
Unrealized foreign exchange loss		289,000			291,000
Accrued expenses		610,000			726,000
Other		647,000			342,000
Gross deferred tax assets		43,725,000			43,677,000
Valuation allowance		(43,725,000	)		(43,677,000	)
Net deferred tax assets	$	-			-

Note 13 - Commitments and Contingencies (Tables)

12 Months Ended

Apr. 30, 2013

Commitments and Contingencies Disclosure [Text Block]

Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]

Year ending April 30:
2014	$	257,000
2015		257,000
	$	514,000

Note 14 - Operating Segments and Geographic Information (Tables)

12 Months Ended

Apr. 30, 2013

Segment Reporting Disclosure [Text Block]

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

	Year Ended April 30, 2013
	North America			Europe			Asia and Australia			Total
Revenues from external customers	$	3,497,338			118,791			—			3,616,129
Operating loss		(14,048,062	)		(1,091,473	)		(1,179,680	)		(16,319,215	)
Long-lived assets		675,354			24,128			1,486			700,968
Total assets		23,097,183			1,518,496			215,380			24,831,059

	Year Ended April 30, 2012
	North America			Europe			Asia and Australia			Total
Revenues from external customers	$	4,603,652			1,134,854			—			5,738,506
Operating loss		(14,432,825	)		(1,672,636	)		(451,284	)		(16,556,745	)
Long-lived assets		585,818			97,115			—			682,933
Total assets		35,181,637			1,619,973			640,027			37,441,637

Note 1 - Background and Liquidity (Details) - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Disclosure Text Block [Abstract]
Retained Earnings (Accumulated Deficit)	$ (140,671,311)	$ (125,989,474)
Cash and Cash Equivalents, Marketable Securities and Restricted Cash	$ 21,700,000

Note 2 - Summary of Significant Accounting Policies (Details)	12 Months Ended
	Apr. 30, 2013
Minimum [Member]
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Maximum [Member]
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	7 years

Note 2 - Summary of Significant Accounting Policies (Details) - Cash and Cash Equivalents - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Checking and savings accounts [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 2,184,322	$ 2,051,918
Certificates of deposits and US Treasury obligations [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	0	5,998,925
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 4,188,466	$ 1,302,617

Note 2 - Summary of Significant Accounting Policies (Details) - Cash Restricted Under Security Agreements - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Barclays Bank Agreement [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	$ 941,256	$ 953,712
NJBPU Agreement [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	$ 425,000	$ 500,000

Note 2 - Summary of Significant Accounting Policies (Details) - Foreign Exchange Gain (Loss) - USD ($)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Foreign Exchange Gain (Loss) [Abstract]
Foreign exchange loss	$ (83,416)	$ (104,739)
Foreign currency denominated certificates of deposit and cash accounts	$ 2,491,714	$ 2,826,000

Note 2 - Summary of Significant Accounting Policies (Details) - Percentage of the Company’s Revenues Derived From Major Customers - Sales [Member]	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
US Department of Energy [Member]
Revenue, Major Customer [Line Items]
Customer	51.00%	32.00%
Mitsui Shipbuilding & Engineering [Member]
Revenue, Major Customer [Line Items]
Customer	20.00%	3.00%
European Union (WaverPort Project) [Member]
Revenue, Major Customer [Line Items]
Customer	17.00%	13.00%
US Navy [Member]
Revenue, Major Customer [Line Items]
Customer	3.00%	29.00%
UK Government's Technology Strategy Board [Member]
Revenue, Major Customer [Line Items]
Customer	3.00%	20.00%

Note 2 - Summary of Significant Accounting Policies (Details) - Valuation Assumptions for Options Granted	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Valuation Assumptions for Options Granted [Abstract]
Risk-free interest rate	0.88%	1.83%
Expected dividend yield	0.00%	0.00%
Expected life (in years)	6 years 21 days	5 years 302 days
Expected volatility	86.15%	94.50%

Note 3 - Marketable Securities (Details) - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]
Marketable Securities, Noncurrent	$ 0	$ 0

Note 3 - Marketable Securities (Details) - Marketable Securities That Mature Within One Year - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Certificates of deposit denominated in Australian dollars [Member]
Note 3 - Marketable Securities (Details) - Marketable Securities That Mature Within One Year [Line Items]
Marketable Securities		$ 556,437
Certificate of deposit denominated in US dollars [Member]
Note 3 - Marketable Securities (Details) - Marketable Securities That Mature Within One Year [Line Items]
Marketable Securities		3,806,808
US Treasury obligations [Member]
Note 3 - Marketable Securities (Details) - Marketable Securities That Mature Within One Year [Line Items]
Marketable Securities	$ 13,996,705	18,006,239
Marketable Securities	$ 13,996,705	$ 22,369,484

Note 4 - Property and Equipment (Details) - USD ($)	12 Months Ended
Note 4 - Property and Equipment (Details) - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Property, Plant and Equipment Disclosure [Text Block]
Depreciation	$ 285,263	$ 326,205

Note 4 - Property and Equipment (Details) - Components of property and equipment	12 Months Ended
	Apr. 30, 2013
Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Lfe	3 years
Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Lfe	7 years
Office Furniture and Equipment (Member) \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Lfe	3 years
Office Furniture and Equipment (Member) \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Lfe	7 years
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Lfe	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Lfe	7 years

Note 5 - Balance Sheet Detail (Details) - Balance Sheet Detail - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Accounts receivable, net
Accounts receivable	$ 1,086,847	$ 1,369,400
Allowance for doubtful accounts	(290,515)	(304,604)
	796,332	1,064,796
Patents
Patents	1,558,630	1,574,044
Accumulated amortization	(513,728)	(304,587)
	1,044,902	1,269,457
Accrued expenses
Project costs	1,698,959	244,892
Contract loss reserves	785,000	785,000
Employee incentive payments	249,469	661,328
Accrued salary and benefits	547,404	521,058
Investment in joint venture	173,842	176,110
Legal and accounting fees	214,891	193,720
Other	231,058	187,986
	$ 3,900,623	$ 2,770,094

Note 6 - Related Party Transactions (Details)	1 Months Ended
Note 6 - Related Party Transactions (Details)	Aug. 31, 1999 USD ($)
Director [Member]
Note 6 - Related Party Transactions (Details) [Line Items]
Related Party Transaction, Amounts of Transaction	$ 950

Note 6 - Related Party Transactions (Details) - Related Party Transactions - USD ($)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Related Party Transactions [Abstract]
Related party consulting expense	$ 42,000	$ 86,000
Expenses for services provided by related party company	0	29,000
Revenue for services provided to related party company	32,000	126,000
Consulting fees payable to related party	0	7,000
Payable to related party company	0	0
Receivable from related party company	$ 0	$ 0

Note 7 - Debt (Details) - USD ($)	Apr. 30, 2013	Apr. 30, 2012	Nov. 30, 2011
New Jersey Board of Public Utilities [Member]
Note 7 - Debt (Details) [Line Items]
Long-term Debt (in Dollars)			$ 500,000
Long Term Debt Payment Terms			5 years
Long-term Debt (in Dollars)	$ 350,000	$ 450,000

Note 7 - Debt (Details) - Long-term Debt - USD ($)	Apr. 30, 2013	Apr. 30, 2012
Long-term Debt [Abstract]
Total debt	$ 350,000	$ 450,000
Current portion of long-term debt	(100,000)	(100,000)
Long-term debt	$ 250,000	$ 350,000

Note 8 - Deferred Credits Payable (Details)	Apr. 30, 2013 USD ($)	Apr. 30, 2012 USD ($)	Apr. 30, 2001 USD ($) T
Customer Advances And Deposits Disclosure [Text Block]
Customer Advances and Deposits			$ 600,000
Deferred Credits Payable Option Details (in US Ton) \| T			500,000
Deferred Credits Payable Market Discount Rate			30.00%
Deferred Credits Payable Market Liquidated Damages Rate	30.00%
Customer Advances or Deposits, Noncurrent	$ 600,000
Customer Advances and Deposits, Current		$ 600,000

Note 9 - Common Stock (Details)	Apr. 30, 2007 USD ($) $ / shares shares
Stockholders' Equity Note Disclosure [Text Block]
Stock Issued During Period, Shares, New Issues \| shares	5,000,000
Share Price (in Dollars per share) \| $ / shares	$ 20.00
Proceeds from Issuance of Common Stock (in Dollars) \| $	$ 89,900,000

Note 10 - Preferred Stock (Details) - $ / shares	Apr. 30, 2013	Apr. 30, 2012
Preferred Stock [Text Block]
Preferred Stock, Shares Authorized	5,000,000	5,000,000
Preferred Stock, Par or Stated Value Per Share (in Dollars per share)	$ 0.001	$ 0.001
Preferred Stock, Shares Issued	0	0

Note 11 - Share-Based Compensation (Details)	12 Months Ended
Note 11 - Share-Based Compensation (Details)	Apr. 30, 2013
Stock Incentive Plan 2006 (Member) \| Maximum [Member]
Note 11 - Share-Based Compensation (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options Outstanding, Contractual Term	10 years

Note 11 - Share-Based Compensation (Details) - Stock Options Under the Plans - $ / shares	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Stock Options Under the Plans [Abstract]
Shares Under Options, Outstanding	1,305,988	1,353,473	1,353,935
Weighted Average Exercise Price, Outstanding (in Dollars per share)	$ 7.43	$ 8.92	$ 10.30
Weighted Average Remaining Contractual Term, Outstanding	5 years 328 days	6 years 36 days	5 years 255 days
Exercisable April 30, 2013	836,026
Exercisable April 30, 2013 (in Dollars per share)	$ 9.64
Exercisable April 30, 2013	4 years 6 months
Shares Underlying Options, Forfeited	(429,244)	(268,784)
Weighted Average Exercise Price,Forfeited (in Dollars per share)	$ 7.29	$ 10.94
Shares Underlying Options, Granted	381,759	268,322
Weighted Average Exercise Price, Granted (in Dollars per share)	$ 1.98	$ 3.97

Note 11 - Share-Based Compensation (Details) - Non-Vested Restricted Stock Under the Plans - Non-vested Restricted Stock [Member] - $ / shares	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Note 11 - Share-Based Compensation (Details) - Non-Vested Restricted Stock Under the Plans [Line Items]
Number of Shares, Issued and Unvested	93,840	150,953
Weighted Average Price Per Share, Issued and Unvested (in Dollars per share)	$ 5.86	$ 6.16
Number of Shares, Granted	31,744	14,634
Weighted Average Price Per Share, Granted (in Dollars per share)	$ 2.39	$ 3.86
Number of Shares, Forfeited	(35,918)	(26,428)
Weighted Average Price Per Share, Forfeited (in Dollars per share)	$ 4.70	$ 5.93
Number of Shares, Vested	(34,864)	(45,319)
Weighted Average Price Per Share, Vested (in Dollars per share)	$ 6.02	$ 6.18
Number of Shares, Issued and Unvested	54,802	93,840
Weighted Average Price Per Share, Issued and Unvested (in Dollars per share)	$ 4.52	$ 5.86

Note 12 - Income Taxes (Details) - USD ($)	12 Months Ended
Note 12 - Income Taxes (Details) - USD ($)	Apr. 30, 2013	Apr. 30, 2012
New Jersey State Operating Loss Sold (Member)
Note 12 - Income Taxes (Details) [Line Items]
Operating Loss Carryforwards	$ 18,673,000	$ 12,862,000
Federal [Member]
Note 12 - Income Taxes (Details) [Line Items]
Operating Loss Carryforwards	74,693,000
Deferred Tax Assets, Tax Credit Carryforwards, Research	2,094,000
State and Local Jurisdiction [Member]
Note 12 - Income Taxes (Details) [Line Items]
Operating Loss Carryforwards	28,586,000
Foreign Tax Authority [Member]
Note 12 - Income Taxes (Details) [Line Items]
Operating Loss Carryforwards	20,946,000
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 659,000	$ 715,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	34.00%	34.00%
Deferred Tax Assets, Valuation Allowance	$ 43,725,000	$ 43,677,000
Valuation Allowance, Deferred Tax Asset, Change in Amount	$ 48,000	3,771,000
Operating Loss Carryforwards, Limitations on Use	$3,300,000
Income Tax Expense (Benefit)	$ (1,453,243)	(1,053,427)
Unrecognized Tax Benefits	0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 0

Note 12 - Income Taxes (Details) - Components of Loss Before Income Taxes - USD ($)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Components of Loss Before Income Taxes [Abstract]
Domestic	$ (13,630,946)	$ (13,700,366)
Foreign	(2,645,308)	(2,543,066)
Total loss before income taxes	$ (16,276,254)	$ (16,243,432)

Note 12 - Income Taxes (Details) - Components of Income Taxes (Benefit) - USD ($)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Curent:
Federal	$ 0	$ 0
State	(1,453,243)	(1,053,427)
Foreign	0	0
Total current	(1,453,243)	(1,053,427)
Deferred:
Federal	0	0
State	0	0
Foreign	0	0
Total deferred	0	0
Total provision (benefit) for income taxes	$ (1,453,243)	$ (1,053,427)

Note 12 - Income Taxes (Details) - Effective Income Tax Rate Reconciliation	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
Effective Income Tax Rate Reconciliation [Abstract]
Computed "expected" tax benefit	(34.00%)	(34.00%)
Increase (reduction) in income taxes resulting from:
State income taxes, net of federal benefit	(5.00%)	(5.00%)
Stock-based compensation expense	1.00%	2.00%
Federal research and development tax credits	(1.00%)	(2.00%)
Foreign rate differential	2.00%	2.00%
Other non-deductible expenses		2.00%
Expiration of net operating losses and tax credit carryforwards	23.00%
Expiration in compensatory options	9.00%
Proceeds of sale of New Jersey tax benefits	(9.00%)
Other	5.00%	6.00%
Increase in valuation allowance		23.00%
Income tax benefit	(9.00%)	(6.00%)

Note 12 - Income Taxes (Details) - Deferred Tax Assets and Deferred Tax Liabilities - USD ($)	Apr. 30, 2013	Apr. 30, 2012
New Jersey State (Member)
Deferred tax assets:
New Jersey state operating loss carryforwards	$ 1,741,000	$ 3,567,000
Domestic Tax Authority [Member]
Deferred tax assets:
Research and Development Tax Credits	2,630,000	2,149,000
Foreign Tax Authority [Member]
Deferred tax assets:
Research and Development Tax Credits	659,000	715,000
Federal net operating loss carryforwards	25,396,000	27,788,000
Foreign net operating loss carryforwards	5,340,000	4,875,000
Stock compensation	721,000	2,548,000
Capitalized research and development costs, net of amortization	5,692,000	676,000
Unrealized foreign exchange loss	289,000	291,000
Accrued expenses	610,000	726,000
Other	647,000	342,000
Gross deferred tax assets	43,725,000	43,677,000
Valuation allowance	(43,725,000)	(43,677,000)
Net deferred tax assets	$ 0	$ 0

Note 13 - Commitments and Contingencies (Details)	12 Months Ended
Note 13 - Commitments and Contingencies (Details)	Apr. 30, 2013 USD ($)	Apr. 30, 2012 USD ($)	Jun. 30, 2013 USD ($)	Jun. 30, 2013 EUR (€)
Subsequent Event [Member]
Note 13 - Commitments and Contingencies (Details) [Line Items]
Letters of Credit Outstanding, Amount (in Euro)			$ 364,512	€ 278,828
Letters of Credit Outstanding, Amount			$ 364,512	€ 278,828
Spanish Tax Authorities [Member]
Note 13 - Commitments and Contingencies (Details) [Line Items]
Input Tax	$ 250,000
Operating Leases, Rent Expense	$ 383,000	$ 507,000

Note 13 - Commitments and Contingencies (Details) - Future Minimum Lease Payments under Operating Lease	Apr. 30, 2013 USD ($)
Future Minimum Lease Payments under Operating Lease [Abstract]
2014	$ 257,000
2015	257,000
	$ 514,000

Note 14 - Operating Segments and Geographic Information (Details)	12 Months Ended
	Apr. 30, 2013
United States [Member]
Note 14 - Operating Segments and Geographic Information (Details) [Line Items]
Number of Operating Segments	1
Number of Reportable Segments	1

Note 14 - Operating Segments and Geographic Information (Details) - Geographic Segment Information - USD ($)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 3,497,338	$ 4,603,652
Operating loss	(14,048,062)	(14,432,825)
Long-lived assets	675,354	585,818
Total assets	23,097,183	35,181,637
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	118,791	1,134,854
Operating loss	(1,091,473)	(1,672,636)
Long-lived assets	24,128	97,115
Total assets	1,518,496	1,619,973
Asia and Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	0	0
Operating loss	(1,179,680)	(451,284)
Long-lived assets	1,486	0
Total assets	215,380	640,027
Revenues from external customers	3,616,129	5,738,506
Operating loss	(16,319,215)	(16,556,745)
Long-lived assets	700,968	682,933
Total assets	$ 24,831,059	$ 37,441,637

Note 15 - Subsequent Event (Details) - USD ($)	Jun. 06, 2013	Jan. 31, 2013
Subsequent Event [Member]
Note 15 - Subsequent Event (Details) [Line Items]
Offering Agreement, Maximum Offering Amount	$ 10,000,000
Offering Agreement, Offering Term	3 years
Shelf Registration, Debt, Equity and other Securities Registered		$ 40,000,000

Label	Element	Value
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	$ 1.58
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue	$ 2.98
Cost-method Investments, Other than Temporary Impairment	us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment	$ 300,000
Less accumulated depreciation and amortization	us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	(1,512,023)
Less accumulated depreciation and amortization	us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	(1,530,887)
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	$ 191,000
Line of Credit Facility, Commitment Fee Percentage	us-gaap_LineOfCreditFacilityCommitmentFeePercentage	1.00%
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	$ 859,000
Allocated Share-based Compensation Expense	us-gaap_AllocatedShareBasedCompensationExpense	1,121,000
Impairment of Intangible Assets, Finite-lived	us-gaap_ImpairmentOfIntangibleAssetsFinitelived	8,000
Amortization of Intangible Assets	us-gaap_AmortizationOfIntangibleAssets	217,000
Amortization of Intangible Assets	us-gaap_AmortizationOfIntangibleAssets	110,000
Restricted Cash	us-gaap_RestrictedCashAndCashEquivalents	1,366,256
Restricted Cash	us-gaap_RestrictedCashAndCashEquivalents	$ 1,453,712
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners	11.80%
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 2,212,991
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 2,213,820
Finite-Lived Intangible Asset, Useful Life	us-gaap_FiniteLivedIntangibleAssetUsefulLife	17 years
Line of Credit Facility, Maximum Borrowing Capacity	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity	$ 800,000
Line of Credit Facility, Maximum Borrowing Capacity	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity	$ 1,046,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue	$ 0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1,360,790
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1,447,313
Line of Credit Facility, Amount Outstanding	us-gaap_LineOfCreditFacilityAmountOutstanding	$ 266,000
Line of Credit Facility, Amount Outstanding	us-gaap_LineOfCreditFacilityAmountOutstanding	$ 348,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	$ 0
Subsequent Event [Member]
Line of Credit Facility, Amount Outstanding	us-gaap_LineOfCreditFacilityAmountOutstanding	$ 278,828
Line of Credit Facility, Amount Outstanding	us-gaap_LineOfCreditFacilityAmountOutstanding	$ 364,512
Expected To Vest [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	8 years 109 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber	470,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue	$ 0
Including Non-employee Compensation [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions	$ 670,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1	2 years 219 days
Leasehold Improvements [Member]
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 182,285
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 149,505
Property, Plant and Equipment, Useful Lfe	us-gaap_PropertyPlantAndEquipmentUsefulLife	2 years
Computersand Software [Member]
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 566,353
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 696,784
Property, Plant and Equipment, Useful Lfe	us-gaap_PropertyPlantAndEquipmentUsefulLife	3 years
Equipment [Member]
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 1,170,473
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	1,080,039
Office Furnitureand Equipment [Member]
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	293,880
Property, Plant and Equipment	us-gaap_PropertyPlantAndEquipmentGross	$ 287,492
Stock Incentive Plan 2006 [Member]
Common Stock, Capital Shares Reserved for Future Issuance	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance	351,041
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized	850,000
ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInceptionToDate	optt_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInceptionToDate	1,302,174
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	803,215
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	1,653,215
ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesGrantsPerParticipant	optt_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesGrantsPerParticipant	200,000
Stock Plan 2001 [Member]
ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInceptionToDate	optt_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInceptionToDate	196,675
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized	1,000,000
New Jersey Boardof Public Utilities [Member]
Restricted Cash	us-gaap_RestrictedCashAndCashEquivalents	$ 500,000
Iberdrola Cantabria [Member]
OwnershipPercentage	optt_OwnershipPercentage	10.00%
Accounts Receivable, Net	us-gaap_AccountsReceivableNet	$ 0
Provision for doubtful accounts	us-gaap_ProvisionForDoubtfulAccounts	300,000
Options Granted To Consultants [Member]
Issuance of Stock and Warrants for Services or Claims	us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims	101,000
Issuance of Stock and Warrants for Services or Claims	us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims	$ 77,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	31,744
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	14,634
Compensation expense related to stock option grants and restricted stock	us-gaap_ShareBasedCompensation	$ 28,000
Compensation expense related to stock option grants and restricted stock	us-gaap_ShareBasedCompensation	100,000
Restricted Stock [Member] \| Including Non-employee Compensation [Member]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	$ 47,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1	2 years 146 days
Employee Stock Option [Member]
Compensation expense related to stock option grants and restricted stock	us-gaap_ShareBasedCompensation	$ 713,000
Compensation expense related to stock option grants and restricted stock	us-gaap_ShareBasedCompensation	932,000
Non Employee Directors [Member]
Issuance of Stock and Warrants for Services or Claims	us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims	16,000
Issuance of Stock and Warrants for Services or Claims	us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims	$ 13,000