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Document And Entity Information - shares	3 Months Ended
Document And Entity Information - shares	Jul. 31, 2013	Aug. 31, 2013
Document and Entity Information [Abstract]
Entity Registrant Name	Ocean Power Technologies, Inc.
Document Type	10-Q
Current Fiscal Year End Date	--04-30
Entity Common Stock, Shares Outstanding		10,356,946
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	Jul. 31, 2013
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q1

Consolidated Balance Sheets (Current Period Unaudited) - USD ($)	Jul. 31, 2013	Apr. 30, 2013
Current assets:
Cash and cash equivalents	$ 7,337,651	$ 6,372,788
Marketable securities	9,996,250	13,996,705
Accounts receivable, net	323,852	796,332
Unbilled receivables	89,722	127,598
Other current assets	373,905	152,962
Total current assets	18,121,380	21,446,385
Property and equipment, net	662,713	700,968
Patents, net	992,124	1,044,902
Restricted cash	1,279,864	1,366,256
Other noncurrent assets	305,693	272,548
Total assets	21,361,774	24,831,059
Current liabilities:
Accounts payable	1,068,379	510,031
Accrued expenses	3,766,394	3,900,623
Unearned revenues	533,825	1,117,115
Current portion of long-term debt	100,000	100,000
Total current liabilities	5,468,598	5,627,769
Long-term debt	225,000	250,000
Long-term unearned revenues	516,782	232,033
Deferred credits	600,000	600,000
Total liabilities	6,810,380	6,709,802
Commitments and contingencies (note 8)
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 10,394,798 and 10,403,215 shares, respectively	10,395	10,403
Treasury stock, at cost; 37,852 and 33,771 shares, respectively	(130,707)	(123,893)
Additional paid-in capital	159,385,020	159,155,365
Accumulated deficit	(144,421,281)	(140,671,311)
Accumulated other comprehensive loss	(98,576)	(79,786)
Total Ocean Power Technologies, Inc. stockholders’ equity	14,744,851	18,290,778
Noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd.	(193,457)	(169,521)
Total equity	14,551,394	18,121,257
Total liabilities and stockholders’ equity	$ 21,361,774	$ 24,831,059

Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - $ / shares	Jul. 31, 2013	Apr. 30, 2013
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	10,394,798	10,403,215
Treasury stock, shares	37,852	33,771

Consolidated Statements of Operations (Unaudited) - USD ($)	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Revenues	$ 460,927	$ 982,396
Cost of revenues	460,376	979,860
Gross profit	551	2,536
Operating expenses:
Product development costs	1,270,945	1,927,427
Selling, general and administrative costs	2,547,759	2,384,338
Total operating expenses	3,818,704	4,311,765
Operating loss	(3,818,153)	(4,309,229)
Interest income, net	358	55,424
Foreign exchange gain (loss	21,770	(108,323)
Net loss	(3,796,025)	(4,362,128)
Less: Net loss attributable to the noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd.	46,055	26,075
Net loss attributable to Ocean Power Technologies, Inc.	$ (3,749,970)	$ (4,336,053)
Basic and diluted net loss per share (in Dollars per share)	$ (0.36)	$ (0.42)
Weighted average shares used to compute basic and diluted net loss per share (in Shares)	10,321,457	10,295,999

Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($)	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Net loss	$ (3,796,025)	$ (4,362,128)
Foreign currency translation adjustment	3,329	(10,484)
Total comprehensive loss	(3,792,696)	(4,372,612)
Comprehensive loss attributable to the noncontrolling interest in Ocean Power Technologies (Australasia) Pty Ltd.	23,936	27,136
Comprehensive loss attributable to Ocean Power Technologies, Inc.	$ (3,768,760)	$ (4,345,476)

Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Short-Term [Member]
Changes in operating assets and liabilities:
Unearned revenues	$ (581,096)	$ (226,967)
Long-Term [Member]
Changes in operating assets and liabilities:
Unearned revenues	284,749
Net cash used in operating activities	(3,077,530)	(3,374,213)
Net loss	(3,796,025)	(4,362,128)
Foreign exchange (gain) loss	(21,770)	108,323
Depreciation and amortization	107,237	116,492
Treasury note premium amortization	5,392	7,734
Compensation expense related to stock option grants and restricted stock	229,655	386,550
Accounts receivable	472,480	(99,302)
Unbilled receivables	37,877	(12,443)
Other current assets	(224,240)	120,649
Other noncurrent assets	(35,344)	(13,252)
Accounts payable	562,092	230,884
Accrued expenses	(118,537)	369,247
Cash flows from investing activities:
Purchases of marketable securities	(6,998,108)	(9,833,736)
Maturities of marketable securities	10,993,172	9,171,233
Restricted cash	100,000	75,000
Purchases of equipment	(14,522)	(224,891)
Net cash provided by (used in) investing activities	4,080,542	(812,394)
Cash flows from financing activities:
Repayment of debt	(25,000)	(25,000)
Acquisition of treasury stock	(6,814)	(9,122)
Net cash used in financing activities	(31,814)	(34,122)
Effect of exchange rate changes on cash and cash equivalents	(6,335)	(43,074)
Net increase (decrease) in cash and cash equivalents	964,863	(4,263,803)
Cash and cash equivalents, beginning of period	6,372,788	9,353,460
Cash and cash equivalents, end of period	7,337,651	5,089,657
Supplemental disclosure of noncash investing and financing activities:
Capitalized purchases of equipment financed through accounts payable and accrued expenses	$ 1,590	$ 80,125

Consolidated Statements of Stockholders' Equity - 3 months ended Jul. 31, 2013 - 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, 2013	$ 10,403	$ (123,893)	$ 159,155,365	$ (140,671,311)	$ (79,786)	$ (169,521)	$ 18,121,257	$ 18,121,257
Balance, April 30 (in Shares) at Apr. 30, 2013	10,403,215	(33,771)
Net loss				(3,749,970)		(46,055)	(3,796,025)	$ (3,796,025)
Stock based compensation			220,109				220,109
Issuance (forfeiture) of restricted stock, net	$ (8)		9,546				9,538
Issuance (forfeiture) of restricted stock, net (in Shares)	(8,417)
Acquisition of treasury stock		$ (6,814)					(6,814)
Acquisition of treasury stock (in Shares)		(4,081)						(3)
Total comprehensive loss					(18,790)	22,119	3,329	$ (3,792,696)
Balance, April 30 at Jul. 31, 2013	$ 10,395	$ (130,707)	$ 159,385,020	$ (144,421,281)	$ (98,576)	$ (193,457)	$ 14,551,394	$ 14,551,394
Balance, April 30 (in Shares) at Jul. 31, 2013	10,394,798	(37,852)

Note 1 - Background and Liquidity

3 Months Ended

Jul. 31, 2013

Disclosure Text Block [Abstract]

Business Description and Basis of Presentation [Text Block]

(1) Background, Basis of Presentation and Liquidity

a) Background

Ocean Power Technologies, Inc. (the “Company”) was incorporated in 1984 in New Jersey, commenced business operations in 1994 and re-incorporated in Delaware in 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) Basis of Presentation

The accompanying unaudited consolidated financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, all adjustments (consisting of normal recurring adjustments) considered necessary for a fair presentation have been included. The interim operating results are not necessarily indicative of the results for a full year or for any other interim period. Further information on potential factors that could affect the Company's financial results can be found in the Company's Annual Report on Form 10-K for the year ended April 30, 2013 filed with the Securities and Exchange Commission (“SEC”) and elsewhere in this Form 10-Q.

c) Liquidity

The Company has incurred net losses and negative operating cash flows since inception. As of July 31, 2013, the Company had an accumulated deficit of $144.4 million. As of July 31, 2013, the Company’s cash and cash equivalents, marketable securities and restricted cash balance was approximately $18.6 million. Based upon the Company’s cash and cash equivalents and marketable securities balance as of July 31, 2013, the Company believes that it will be able to finance its capital requirements and operations into the fourth calendar quarter of 2014.

During fiscal 2014 and 2013, 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.

In January 2013, the Company filed with the SEC a shelf registration statement on Form S-3 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 Company did not sell any shares pursuant to the Offering Agreement in the quarter ended July 31, 2013. Sales commenced during the second quarter, and an immaterial amount has been sold as of the date of the filing of this Quarterly Report on Form 10-Q. Any 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 will be registered on the S-3 Shelf in reliance on, and subject to the limitations of, General Instruction I.B.6 of Form S-3 and other applicable law and regulation. In particular, Form S-3, limits the aggregate market value of securities that the Company is permitted to offer in any 12-month period under Form S-3, whether under the Offering Agreement or otherwise, to one third the Company’s public float. The Company is under no obligation to sell, and the Manager is under no obligation to purchase or place, securities under the Offering Agreement, and there can be no assurance that we will do so or will be able to do so on favorable terms or at all.

Note 2 - Summary of Significant Accounting Policies

3 Months Ended

Jul. 31, 2013

Accounting Policies [Abstract]

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 July 31, 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 July 31, 2013, there were no such entities.

The Company has a 10% investment in Iberdrola Energias Marinas de Cantabria, S.A. (“Iberdrola Cantabria”) and certain outstanding receivables from Iberdrola Cantabria. The investment in Iberdrola Cantabria and net accounts receivable and unbilled receivables from Iberdrola Cantabria were $0 as of April 30, 2012. See Note 8.

(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, particularly the macroeconomic pressures in certain European countries, 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, a profit or loss on a project is recognized 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:

	July 31, 2013		April 30, 2013

Checking and savings accounts	$	2,148,700		2,184,322
Money market funds		5,188,951		4,188,466
	$	7,337,651		6,372,788

(e) Marketable Securities

Marketable securities with original maturities longer than three months but that 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 July 31, 2013 and April 30, 2013, 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 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 July 31, 2013, there were €544,828 ($722,551) in letters of credit outstanding 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 5.

Cash restricted under security agreements is as follows:

	July 31, 2013		April 30, 2013

Barclays Bank agreement	$	954,864		941,256
NJBPU agreement		325,000		425,000
	$	1,279,864		1,366,256

(g) 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.

		July 31, 2013				April 30, 2013
Foreign currency denominated certificates of deposit and cash accounts		$	2,686,916				2,491,714

(h) Long-Lived Assets

Long-lived assets, such as property and equipment and patents subject to amortization, 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 in 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 and determined there was no impairment for the three months ended July 31, 2013.

(i) 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:

	Three months ended July 31,
Customer	2013			2012

UK Government's Technology Strategy Board		38	%		5	%
European Union (WavePort project)		35	%		17	%
US Department of Energy		26	%		63	%
US Navy		---			6	%

		99	%		91	%

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 maintain collateral.

(j) 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 1,290,274 for the three months ended July 31, 2013, and 1,625,397 for the three months ended July 31, 2012, were excluded from the computations as the effect would be anti-dilutive due to the Company's losses.

(k) Recently Issued Accounting Standards

There were no Accounting Standards issued during the quarter ended July 31, 2013 for the Company’s consideration.

Note 3 - Marketable Securities

3 Months Ended

Jul. 31, 2013

Investments, Debt and Equity Securities [Abstract]

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

(3) Marketable Securities

Marketable securities with initial maturities longer than three months but that mature within one year from the balance sheet date are classified as current assets and are summarized as follows:

		July 31, 2013				April 30, 2013
US Treasury obligations		$	9,996,250				13,996,705

- Definition

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

+ References + Details

Note 4 - Balance Sheet Detail

3 Months Ended

Jul. 31, 2013

Disclosure Text Block Supplement [Abstract]

Supplemental Balance Sheet Disclosures [Text Block]

(4) Balance Sheet Detail

	July 31, 2013			April 30, 2013

Accounts Receivable, net
Accounts receivable	$	628,901			1,086,847
Allowance for doubtful accounts		(305,049	)		(290,515	)
	$	323,852			796,332

Property and Equipment
Property and Equipment	$	2,225,575			2,212,991
Accumulated depreciation and amortization		(1,562,862	)		(1,512,023	)
	$	662,713			700,968

Patents
Patents	$	1,560,250			1,558,630
Accumulated amortization		(568,126	)		(513,728	)
	$	992,124			1,044,902


Accrued Expenses
Project costs	$	1,735,098			1,698,959
Contract loss reserves		785,000			785,000
Employee incentive payments		56,212			249,469
Accrued salary and benefits		524,267			547,404
Investment in joint venture		176,367			173,842
Legal and accounting fees		247,682			214,891
Other		241,768			231,058

	$	3,766,394			3,900,623

Note 5 - Debt

3 Months Ended

Jul. 31, 2013

Debt Disclosure [Abstract]

Debt Disclosure [Text Block]

(5) 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).

	July 31, 2013			April 30, 2013

Total debt	$	325,000			350,000
Current portion of long-term debt		(100,000	)		(100,000	)
Long-term debt	$	225,000			250,000

Note 6 - Deferred Credits Payable

3 Months Ended

Jul. 31, 2013

Customer Advances And Deposits Disclosure [Abstract]

Customer Advances And Deposits Disclosure [Text Block]

(6) 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 July 31, 2013, the Company has not generated any emissions credits eligible for purchase under the agreement. The $600,000 has been classified as a noncurrent liability as of July 31, 2013.

Note 7 - Stock-Based Compensation

3 Months Ended

Jul. 31, 2013

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

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

(7) Stock-Based Compensation

Costs resulting from all stock-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 stock-based compensation expense related to all stock-based transactions recorded in the consolidated statements of operations was approximately $230,000 and $387,000 for the three months ended July 31, 2013 and 2012, respectively.

(a) Stock Options

Valuation Assumptions for Options Granted During the Three Months Ended July 31, 2013 and 2012

The fair value of each stock option granted, for both service-based and performance-based vesting requirements, during the three months ended July 31, 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 SEC's Staff Accounting Bulletin No. 107, Share-Based Payment. Expected volatility was based on the Company’s historical volatility for the three months ended July 31, 2013 and historical volatility for a peer group of companies for the three months ended July 31, 2012 for a period equal to the stock option's expected life, calculated on a daily basis.

	Three Months Ended July 31,
	2013			2012
Risk-free interest rate		1.6	%		0.9	%
Expected dividend yield		0.0	%		0.0	%
Expected life (years)		6.3			6.3
Expected volatility		74.61	%		86.15	%

The above assumptions were used to determine the weighted average per share fair value of $1.12 and $1.46 for stock options granted during the three months ended July 31, 2013 and 2012, respectively.

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

	Shares Underlying Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (In Years)
Outstanding as of April 30, 2013		1,305,988		$	7.43
Forfeited		(86,792	)		6.57
Exercised		—			—
Granted		234,787			1.67
Outstanding as of July 31, 2013		1,453,983			6.53		6.6
Exercisable as of July 31, 2013		902,337			8.95		5.2

As of July 31, 2013, the total intrinsic value of outstanding and exercisable options was $0. As of July 31, 2013, approximately 552,000 additional options are expected to vest in the future, which options had no intrinsic value and a weighted average remaining contractual term of 8.9 years. There was approximately $220,000 and $372,000 of total recognized compensation cost related to stock options for the three months ended July 31, 2013 and 2012, respectively. As of July 31, 2013, there was approximately $735,000 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 2.9 years. The Company normally issues new shares to satisfy option exercises under these plans. During the three months ended July 31, 2013, stock options granted included 30,520 stock options which are subject to performance-based vesting requirements. Stock options outstanding as of July 31, 2013 included 60,821 stock options subject to performance-based vesting requirements.

(b) Restricted Stock

Compensation expense for non-vested restricted stock was historically recorded based on its market value on the date of grant and recognized over the associated service and performance period. During the three months ended July 31, 2013, there were 7,000 shares of non-vested restricted stock granted to employees with performance-based vesting requirements. During the three months ended July 31, 2013, 15,417 shares of non-vested restricted stock subject to performance-based vesting requirements were forfeited in accordance with performance objectives. Restricted stock issued and unvested at July 31, 2013 included 13,331 shares of non-vested restricted stock subject to performance-based vesting requirements.

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

	Number of Shares			Weighted Average Price perShare

Issued and unvested at April 30, 2013		54,802		$	4.52
Granted		7,000			1.68
Forfeited		(15,417	)		5.84
Vested		(14,919	)		5.70
Issued and unvested at July 31, 2013		31,466			2.56

There was approximately $10,000 and $15,000 of total recognized compensation cost related to restricted stock for the three months ended July 31, 2013 and 2012, respectively. As of July 31, 2013, there was approximately $42,000 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 2.2 years.

(c)Treasury Stock

During the three months ended July 31, 2013 and 2012, 4,081 and 4,274 shares, respectively, of common stock were purchased by the Company from employees to pay taxes related to the vesting of restricted stock.

Note 8 - Commitments and Contingencies

3 Months Ended

Jul. 31, 2013

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies Disclosure [Text Block]

(8) Commitments and Contingencies

(a) 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.

(b) Spain Construction Agreement

The Company is currently engaged with Iberdrola Cantabria in discussions regarding modifications to its agreement for the first phase of the construction of a wave power project off the coast of Spain. This first 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 July 31, 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.

(c) 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. The Company issued two letters of credit in the amount of €278,828 ($369,782) at the request of the Spanish tax authorities. This is a customary request during the inquiry period.

(d) 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 July 31, 2013 and April 30, 2013, the Company has accounted for the outcome of this matter in its financial statements.

Note 9 - Income Taxes

3 Months Ended

Jul. 31, 2013

Income Tax Disclosure [Abstract]

Income Tax Disclosure [Text Block]

(9) Income Taxes

The Company did not recognize any consolidated income tax benefit (expense) for the three month periods ended July 31, 2013 and 2012. The Company has recorded a valuation allowance to reduce its net deferred tax asset to an amount that is more likely than not to be realized in future years. Accordingly, the benefit of the net operating loss that would have been recognized was offset by changes in the valuation allowance.

During the three months ended July 31, 2013, the Company had no material changes in uncertain tax positions.

Note 10 - Operating Segments and Geographic Information

3 Months Ended

Jul. 31, 2013

Segment Reporting [Abstract]

Segment Reporting Disclosure [Text Block]

(10) Operating Segments and Geographic Information

The Company views its business as one segment, which is the development and sale of its PowerBuoy product for wave energy applications. The Company operates on a worldwide basis with one operating company in the US, one operating subsidiary in the UK and one operating subsidiary in Australia, which are categorized below as North America, Europe, and Asia and Australia, respectively. Revenues are generally attributed to the operating unit that bills the customers.

Geographic information is as follows:

	North America			Europe			Asia and Australia			Total
Three months ended July 31, 2013
Revenues from external customers	$	287,752			173,175			—			460,927
Operating loss		(3,122,599	)		(315,402	)		(380,152	)		(3,818,153	)

Three months ended July 31, 2012
Revenues from external customers		930,903			51,493			—			982,396
Operating loss		(3,851,720	)		(234,974	)		(222,535	)		(4,309,229	)


July 31, 2013
Long-lived assets		640,910			20,778			1,025			662,713
Total assets		19,373,116			1,858,080			130,578			21,361,774

April 30, 2013
Long-lived assets		675,354			24,128			1,486			700,968
Total assets	$	23,097,183			1,518,496			215,380			24,831,059

- 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
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-Name Accounting Standards Codification
-Topic 280
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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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
-Publisher FASB
-Name Accounting Standards Codification
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Name Accounting Standards Codification
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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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Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8906-108599

+ Details

Note 11 - Subsequent Event

3 Months Ended

Jul. 31, 2013

Subsequent Events [Abstract]

Subsequent Events [Text Block]

(11) Subsequent Event

On August 30, 2013, the Company issued a letter of credit for $375,000 in favor of the Oregon Department of State Lands. This letter of credit relates to the expected removal of certain of the Company’s anchoring and mooring equipment from the seabed off the coast of Oregon. This letter of credit is secured by a Certificate of Deposit with PNC Bank for a term through August 30, 2014.

Accounting Policies, by Policy (Policies)	3 Months Ended	12 Months Ended
Accounting Policies, by Policy (Policies)	Jul. 31, 2013	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 July 31, 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 July 31, 2013, there were no such entities. The Company has a 10% investment in Iberdrola Energias Marinas de Cantabria, S.A. (“Iberdrola Cantabria”) and certain outstanding receivables from Iberdrola Cantabria. The investment in Iberdrola Cantabria and net accounts receivable and unbilled receivables from Iberdrola Cantabria were $0 as of 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, particularly the macroeconomic pressures in certain European countries, 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, a profit or loss on a project is recognized 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 that 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 July 31, 2013 and April 30, 2013, 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 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 July 31, 2013, there were €544,828 ($722,551) in letters of credit outstanding 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 5.
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.
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, 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 in 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 and determined there was no impairment for the three months ended July 31, 2013.
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.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]		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:
Income Tax, Policy [Policy Text Block]		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.
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 1,290,274 for the three months ended July 31, 2013, and 1,625,397 for the three months ended July 31, 2012, were excluded from the computations as the effect would be anti-dilutive due to the Company's losses.
New Accounting Pronouncements, Policy [Policy Text Block]	*Recently Issued Accounting Standards* There were no Accounting Standards issued during the quarter ended July 31, 2013 for the Company’s consideration.

Note 2 - Summary of Significant Accounting Policies (Tables)

3 Months Ended

Jul. 31, 2013

Accounting Policies [Abstract]

Schedule of Cash and Cash Equivalents [Table Text Block]

	July 31, 2013		April 30, 2013

Checking and savings accounts	$	2,148,700		2,184,322
Money market funds		5,188,951		4,188,466
	$	7,337,651		6,372,788

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

	July 31, 2013		April 30, 2013

Barclays Bank agreement	$	954,864		941,256
NJBPU agreement		325,000		425,000
	$	1,279,864		1,366,256

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

		July 31, 2013				April 30, 2013
Foreign currency denominated certificates of deposit and cash accounts		$	2,686,916				2,491,714

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

	Three months ended July 31,
Customer	2013			2012

UK Government's Technology Strategy Board		38	%		5	%
European Union (WavePort project)		35	%		17	%
US Department of Energy		26	%		63	%
US Navy		---			6	%

		99	%		91	%

Note 3 - Marketable Securities (Tables)

3 Months Ended

Jul. 31, 2013

Current [Member]

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

Marketable Securities [Table Text Block]

		July 31, 2013				April 30, 2013
US Treasury obligations		$	9,996,250				13,996,705

Note 4 - Balance Sheet Detail (Tables)

3 Months Ended

Jul. 31, 2013

Disclosure Text Block Supplement [Abstract]

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

	July 31, 2013			April 30, 2013

Accounts Receivable, net
Accounts receivable	$	628,901			1,086,847
Allowance for doubtful accounts		(305,049	)		(290,515	)
	$	323,852			796,332

Property and Equipment
Property and Equipment	$	2,225,575			2,212,991
Accumulated depreciation and amortization		(1,562,862	)		(1,512,023	)
	$	662,713			700,968

Patents
Patents	$	1,560,250			1,558,630
Accumulated amortization		(568,126	)		(513,728	)
	$	992,124			1,044,902


Accrued Expenses
Project costs	$	1,735,098			1,698,959
Contract loss reserves		785,000			785,000
Employee incentive payments		56,212			249,469
Accrued salary and benefits		524,267			547,404
Investment in joint venture		176,367			173,842
Legal and accounting fees		247,682			214,891
Other		241,768			231,058

	$	3,766,394			3,900,623

Note 5 - Debt (Tables)

3 Months Ended

Jul. 31, 2013

Debt Disclosure [Abstract]

Schedule of Debt [Table Text Block]

	July 31, 2013			April 30, 2013

Total debt	$	325,000			350,000
Current portion of long-term debt		(100,000	)		(100,000	)
Long-term debt	$	225,000			250,000

Note 7 - Stock-Based Compensation (Tables)

3 Months Ended

Jul. 31, 2013

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

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

	Three Months Ended July 31,
	2013			2012
Risk-free interest rate		1.6	%		0.9	%
Expected dividend yield		0.0	%		0.0	%
Expected life (years)		6.3			6.3
Expected volatility		74.61	%		86.15	%

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

	Shares Underlying Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (In Years)
Outstanding as of April 30, 2013		1,305,988		$	7.43
Forfeited		(86,792	)		6.57
Exercised		—			—
Granted		234,787			1.67
Outstanding as of July 31, 2013		1,453,983			6.53		6.6
Exercisable as of July 31, 2013		902,337			8.95		5.2

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

	Number of Shares			Weighted Average Price perShare

Issued and unvested at April 30, 2013		54,802		$	4.52
Granted		7,000			1.68
Forfeited		(15,417	)		5.84
Vested		(14,919	)		5.70
Issued and unvested at July 31, 2013		31,466			2.56

Note 10 - Operating Segments and Geographic Information (Tables)

3 Months Ended

Jul. 31, 2013

Segment Reporting [Abstract]

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

	North America			Europe			Asia and Australia			Total
Three months ended July 31, 2013
Revenues from external customers	$	287,752			173,175			—			460,927
Operating loss		(3,122,599	)		(315,402	)		(380,152	)		(3,818,153	)

Three months ended July 31, 2012
Revenues from external customers		930,903			51,493			—			982,396
Operating loss		(3,851,720	)		(234,974	)		(222,535	)		(4,309,229	)


July 31, 2013
Long-lived assets		640,910			20,778			1,025			662,713
Total assets		19,373,116			1,858,080			130,578			21,361,774

April 30, 2013
Long-lived assets		675,354			24,128			1,486			700,968
Total assets	$	23,097,183			1,518,496			215,380			24,831,059

Note 1 - Background and Liquidity (Details) - USD ($)	1 Months Ended	3 Months Ended
Note 1 - Background and Liquidity (Details) - USD ($)	Jan. 31, 2013	Jul. 31, 2013	Jun. 06, 2013	Apr. 30, 2013
Disclosure Text Block [Abstract]
Retained Earnings (Accumulated Deficit)		$ (144,421,281)		$ (140,671,311)
Cash and Cash Equivalents, Marketable Securities and Restricted Cash		$ 18,600,000
Debt, equity and other securities under shelf registration	$ 40,000,000
Maximum amount of common stock offered available for sale			$ 10,000,000
Sale of Stock, Number of Shares Issued in Transaction (in Shares)		0

Note 2 - Summary of Significant Accounting Policies (Details)	3 Months Ended
	Jul. 31, 2013 USD ($) shares	Jul. 31, 2012 shares	Jul. 31, 2013 EUR (€)	Apr. 30, 2013 USD ($)	Apr. 30, 2012 USD ($)
New Jersey Board of Public Utilities [Member]
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]
Restricted Cash and Cash Equivalents (in Dollars)	$ 500,000
Iberdrola Cantabria [Member]
Note 2 - Summary of Significant Accounting Policies (Details) [Line Items]
Ownership Percentage	10.00%		10.00%
Accounts Receivable, Net (in Dollars)					$ 0
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners	11.80%		11.80%
Line of Credit Facility, Maximum Borrowing Capacity (in Euro) \| €			€ 800,000
Line of Credit Facility, Commitment Fee Percentage	1.00%
Line of Credit Facility, Amount Outstanding (in Euro)	$ 722,551		544,828
Line of Credit Facility, Amount Outstanding (in Dollars)	722,551		€ 544,828
Restricted Cash and Cash Equivalents (in Dollars)	1,279,864			$ 1,366,256
Impairment of Long-Lived Assets Held-for-use (in Dollars)	$ 0
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in Shares) \| shares	1,290,274	1,625,397

Note 2 - Summary of Significant Accounting Policies (Details) - Cash and Cash Equivalents - USD ($)	Jul. 31, 2013	Apr. 30, 2013
Checking and savings accounts [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 2,148,700	$ 2,184,322
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 5,188,951	$ 4,188,466

Note 2 - Summary of Significant Accounting Policies (Details) - Cash Restricted Under Security Agreements - USD ($)	Jul. 31, 2013	Apr. 30, 2013
Barclays Bank Agreement [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	$ 954,864	$ 941,256
NJBPU Agreement [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted Cash	$ 325,000	$ 425,000

Note 2 - Summary of Significant Accounting Policies (Details) - Foreign Exchange Gain (Loss) - USD ($)	Jul. 31, 2013	Jul. 31, 2012
Foreign Exchange Gain (Loss) [Abstract]
Foreign currency denominated certificates of deposit and cash accounts	$ 2,686,916	$ 2,491,714

Note 2 - Summary of Significant Accounting Policies (Details) - Percentage of the Company’s Revenues Derived From Major Customers - Sales [Member]	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
UK Government's Technology Strategy Board [Member]
Revenue, Major Customer [Line Items]
Customer	38.00%	5.00%
European Union (WaverPort Project) [Member]
Revenue, Major Customer [Line Items]
Customer	35.00%	17.00%
US Department of Energy [Member]
Revenue, Major Customer [Line Items]
Customer	26.00%	63.00%
US Navy [Member]
Revenue, Major Customer [Line Items]
Customer		6.00%
Customer	99.00%	91.00%

Note 3 - Marketable Securities (Details) - Marketable Securities That Mature Within One Year - USD ($)	Jul. 31, 2013	Apr. 30, 2013
US Treasury obligations [Member]
Note 3 - Marketable Securities (Details) - Marketable Securities That Mature Within One Year [Line Items]
US Treasury obligations	$ 9,996,250	$ 13,996,705
US Treasury obligations	$ 9,996,250	$ 13,996,705

Note 4 - Balance Sheet Detail (Details) - Balance Sheet Detail - USD ($)	Jul. 31, 2013	Apr. 30, 2013
Accounts Receivable, net
Accounts receivable	$ 628,901	$ 1,086,847
Allowance for doubtful accounts	(305,049)	(290,515)
	323,852	796,332
Property and Equipment
Property and Equipment	2,225,575	2,212,991
Accumulated depreciation and amortization	(1,562,862)	(1,512,023)
	662,713	700,968
Patents
Patents	1,560,250	1,558,630
Accumulated amortization	(568,126)	(513,728)
	992,124	1,044,902
Accrued Expenses
Project costs	1,735,098	1,698,959
Contract loss reserves	785,000	785,000
Employee incentive payments	56,212	249,469
Accrued salary and benefits	524,267	547,404
Investment in joint venture	176,367	173,842
Legal and accounting fees	247,682	214,891
Other	241,768	231,058
	$ 3,766,394	$ 3,900,623

Note 5 - Debt (Details) - USD ($)	Jul. 31, 2013	Apr. 30, 2013	Nov. 30, 2011
New Jersey Board of Public Utilities [Member]
Note 5 - Debt (Details) [Line Items]
Long-term Debt (in Dollars)			$ 500,000
Long Term Debt Payment Terms			5 years
Long-term Debt (in Dollars)	$ 325,000	$ 350,000

Note 5 - Debt (Details) - Long-term Debt - USD ($)	Jul. 31, 2013	Apr. 30, 2013
Long-term Debt [Abstract]
Total debt	$ 325,000	$ 350,000
Current portion of long-term debt	(100,000)	(100,000)
Long-term debt	$ 225,000	$ 250,000

Note 6 - Deferred Credits Payable (Details)	Jul. 31, 2013 USD ($)	Apr. 30, 2013 USD ($)	Apr. 30, 2001 USD ($) T
Customer Advances And Deposits Disclosure [Abstract]
Customer Advances and Deposits (in Dollars)			$ 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 (in Dollars)	$ 600,000	$ 600,000

Note 7 - Stock-Based Compensation (Details) - USD ($)	3 Months Ended		12 Months Ended	15 Months Ended
Note 7 - Stock-Based Compensation (Details) - USD ($)	Jul. 31, 2013	Jul. 31, 2012	Apr. 30, 2013	Jul. 31, 2013
Expected to Vest [Member]
Note 7 - Stock-Based Compensation (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number (in Shares)	552,000			552,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	8 years 328 days
Employee Stock Option [Member]
Note 7 - Stock-Based Compensation (Details) [Line Items]
Share-based Compensation	$ 220,000	$ 372,000
Performance-based vesting [Member]
Note 7 - Stock-Based Compensation (Details) [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in Shares)	30,520
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures (in Shares)	60,821
Restricted Stock [Member]
Note 7 - Stock-Based Compensation (Details) [Line Items]
Allocated Share-based Compensation Expense	$ 10,000	15,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 73 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in Shares)	7,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures (in Shares)	15,417
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 42,000			$ 42,000
Stock Incentive Plan 2006 (Member)
Note 7 - Stock-Based Compensation (Details) [Line Items]
Allocated Share-based Compensation Expense	$ 230,000	$ 387,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in Dollars per share)	$ 1.12	$ 1.46
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 0			$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term				5 years 73 days
Share-based Compensation	$ 229,655	$ 386,550
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options			$ 735,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			2 years 328 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in Shares)				234,787
Stock Issued During Period, Shares, Restricted Stock Award, Gross (in Shares)	13,331
Treasury Stock, Shares, Acquired (in Shares)	3	4,274

Note 7 - Stock-Based Compensation (Details) - Weighted Average Fair Value Assumptions for Stock-Based Compensation	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012
Weighted Average Fair Value Assumptions for Stock-Based Compensation [Abstract]
Risk-free interest rate	1.60%	0.90%
Expected dividend yield	0.00%	0.00%
Expected life (years)	6 years 109 days	6 years 109 days
Expected volatility	74.61%	86.15%

Note 7 - Stock-Based Compensation (Details) - Stock Options Under the Plans - $ / shares	15 Months Ended
	Jul. 31, 2013	Apr. 30, 2013
Stock Options Under the Plans [Abstract]
Shares Under Options, Outstanding	1,453,983	1,305,988
Weighted Average Exercise Price, Outstanding (in Dollars per share)	$ 6.53	$ 7.43
Weighted Average Remaining Contractual Term, Outstanding	6 years 219 days
Exercisable as of July 31, 2013	902,337
Exercisable as of July 31, 2013 (in Dollars per share)	$ 8.95
Exercisable as of July 31, 2013	5 years 73 days
Forfeited	(86,792)
Forfeited (in Dollars per share)	$ 6.57
Granted	234,787
Granted (in Dollars per share)	$ 1.67

Note 7 - Stock-Based Compensation (Details) - Non-Vested Restricted Stock Under the Plans - Non-vested Restricted Stock [Member]	3 Months Ended
	Jul. 31, 2013 $ / shares shares
Note 7 - Stock-Based Compensation (Details) - Non-Vested Restricted Stock Under the Plans [Line Items]
Granted \| shares	7,000
Granted (in Dollars per share) \| $ / shares	$ 1.68
Forfeited \| shares	(15,417)
Forfeited (in Dollars per share) \| $ / shares	$ 5.84
Vested \| shares	(14,919)
Vested (in Dollars per share) \| $ / shares	$ 5.70
Number of Shares, Issued and Unvested \| shares	31,466
Weighted Average Price Per Share, Issued and Unvested (in Dollars per share) \| $ / shares	$ 2.56

Note 8 - Commitments and Contingencies (Details)	3 Months Ended
Note 8 - Commitments and Contingencies (Details)	Jul. 31, 2013 USD ($)	Sep. 01, 2013 USD ($)	Jun. 30, 2013 USD ($)	Jun. 30, 2013 EUR (€)
Subsequent Event [Member]
Note 8 - Commitments and Contingencies (Details) [Line Items]
Letters of Credit Outstanding, Amount (in Euro)		$ 375,000	$ 369,782	€ 278,828
Letters of Credit Outstanding, Amount		$ 375,000	$ 369,782	€ 278,828
Spanish Tax Authorities [Member]
Note 8 - Commitments and Contingencies (Details) [Line Items]
Input Tax	$ 250,000

Note 9 - Income Taxes (Details) - USD ($)	3 Months Ended
Note 9 - Income Taxes (Details) - USD ($)	Jul. 31, 2013	Jul. 31, 2012
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit)	$ 0	$ 0
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 0

Note 10 - Operating Segments and Geographic Information (Details)	3 Months Ended
	Jul. 31, 2013
United States [Member]
Note 10 - Operating Segments and Geographic Information (Details) [Line Items]
Number of Reportable Segments	1
United Kingdom [Member]
Note 10 - Operating Segments and Geographic Information (Details) [Line Items]
Number of Reportable Segments	1
Australia [Member]
Note 10 - Operating Segments and Geographic Information (Details) [Line Items]
Number of Reportable Segments	1
Number of Operating Segments	1

Note 10 - Operating Segments and Geographic Information (Details) - Geographic Segment Information - USD ($)	3 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Apr. 30, 2013
North America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 287,752	$ 930,903
Operating loss	(3,122,599)	(3,851,720)
July 31, 2013
Long-lived assets	640,910		$ 675,354
Total assets	19,373,116		23,097,183
Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	173,175	51,493
Operating loss	(315,402)	(234,974)
July 31, 2013
Long-lived assets	20,778		24,128
Total assets	1,858,080		1,518,496
Asia and Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	0	0
Operating loss	(380,152)	(222,535)
July 31, 2013
Long-lived assets	1,025		1,486
Total assets	130,578		215,380
Revenues from external customers	460,927	982,396
Operating loss	(3,818,153)	$ (4,309,229)
Long-lived assets	662,713		700,968
Total assets	$ 21,361,774		$ 24,831,059

Note 11 - Subsequent Event (Details)	Sep. 01, 2013 USD ($)	Jun. 30, 2013 USD ($)	Jun. 30, 2013 EUR (€)
Subsequent Event [Member]
Note 11 - Subsequent Event (Details) [Line Items]
Letters of Credit Outstanding, Amount	$ 375,000	$ 369,782	€ 278,828

Label	Element	Value
Accumulated Other Comprehensive Income (Loss) [Member]
Total comprehensive loss	us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	$ (9,423)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(78,990)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(88,413)
Treasury Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(102,388)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(111,510)
Treasury Stock, Value, Acquired, Cost Method	us-gaap_TreasuryStockValueAcquiredCostMethod	$ 9,122
Treasury Stock, Shares, Acquired	us-gaap_TreasuryStockSharesAcquired	4,274
Shares, Outstanding	us-gaap_SharesOutstanding	(23,544)
Shares, Outstanding	us-gaap_SharesOutstanding	(27,818)
Common Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	$ 10,407
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	10,405
Issuance (forfeiture) of restricted stock, net	us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	$ (2)
Issuance (forfeiture) of restricted stock, net (in Shares)	us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures	(1,950)
Shares, Outstanding	us-gaap_SharesOutstanding	10,407,389
Shares, Outstanding	us-gaap_SharesOutstanding	10,405,439
Noncontrolling Interest [Member]
Total comprehensive loss	us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	$ (10,484)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	32,107,381
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	28,112,197
Treasury Stock, Value, Acquired, Cost Method	us-gaap_TreasuryStockValueAcquiredCostMethod	9,122
Stock based compensation	us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	371,784
Issuance (forfeiture) of restricted stock, net	us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	14,766
Net loss	us-gaap_ProfitLoss	(4,362,128)
Parent [Member]
Total comprehensive loss	us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	(1,061)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(28,632)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(55,768)
Net loss	us-gaap_ProfitLoss	(26,075)
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(125,989,474)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	(130,325,527)
Net loss	us-gaap_ProfitLoss	(4,336,053)
Additional Paid-in Capital [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	158,296,458
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	158,683,010
Stock based compensation	us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	371,784
Issuance (forfeiture) of restricted stock, net	us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures	$ 14,768
Nonvested Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	54,802
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue	$ 4.52