| Significant Accounting Policies (Policies) | 9 Months Ended |
| Jan. 31, 2016 |
| Accounting Policies [Abstract] | |
| Basis of Accounting, Policy [Policy Text Block] | 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, 2015 filed with the Securities and Exchange Commission (“SEC”) and elsewhere in this Form 10-Q. |
| Liquidity Disclosure [Policy Text Block] | c) Liquidity The Company has incurred net losses and negative operating cash flows since inception. As of January 31, 2016, the Company had an accumulated deficit of $173.9 million. As of January 31, 2016, the Company’s cash and cash equivalents and marketable securities balance was approximately $9.5 million. Based upon the Company’s cash and cash equivalents and marketable securities balance as of January 31, 2016, the Company believes that it will be able to finance its capital requirements and operations into the quarter ending October 31, 2016. In addition, as of January 31, 2016, the Company’s restricted cash balance was approximately $0.4 million. The Company will require additional equity and/or debt financing to continue its operations as a going concern. If the Company is unable to raise additional funds when needed, its ability to operate and grow its business could be impaired. The Company cannot assure that it will be able to secure additional funding when needed or at all, or, if secured, that such funding on favorable terms. The Company continues 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 lack of available financing and insufficient capital, performance of PowerBuoys, its inability to market and commercialize its PowerBuoys, technology development, scalability of technology and production, dependence on skills of key personnel, concentration of customers and suppliers, deployment risks and laws, regulations and permitting. In order to continue to implement its business strategy, the Company requires additional equity and/or debt financing. The Company does not currently have any committed sources of debt or equity financing, and the Company cannot assure you that additional equity and/or debt financing will be available to the Company as needed on acceptable terms, or at all. Historically, the Company has raised capital through securities sales in the public capital markets. If sufficient additional financing is not obtained when needed, the Company may be required to further curtail or limit operations, product development costs, and/or selling, general and administrative activities in order to reduce its cash expenditures to a sustainable level. This could cause the Company to be unable to execute its business plan, take advantage of future opportunities and may cause it to scale back, delay or eliminate some or all of its product development activities and/or reduce the scope of its operations. In January 2013, the Company filed a shelf registration statement on Form S-3 (the “2013 Form S-3” or the “2013 Form S-3 Shelf”). The 2013 Form S-3 Shelf was declared effective by the SEC in February 2013. Under the 2013 Form S-3 Shelf in June 2013, the Company established an At the Market Offering Facility (the “ATM Facility”) with Ascendiant Capital Markets, LLC (“Ascendiant”) via an At the Market Offering Agreement (the “ATM Agreement”). Under the ATM Agreement, the Company offered and sold shares of its common stock, par value $0.001 per share (the “Common Stock”) from time to time through Ascendiant, acting as sales agent, in ordinary brokerage transactions at prevailing market prices. Under the ATM Facility, during fiscal 2014, the Company issued 330,633 shares of its Common Stock at an average price to the public of $30.20 per share, receiving net proceeds from the ATM Facility of approximately $9,698,000. Also in fiscal 2014, the Company entered into an Underwriting Agreement with Roth Capital Partners, LLC on April 4, 2014, (the “Underwriting Agreement”) with respect to the issuance and sale in an underwritten public offering of an aggregate of 380,000 shares of its Common Stock at a price of $31.00 per share (the “Public Offering”) under the 2013 Form S-3. The Underwriting Agreement contained customary representations, warranties and agreements by the Company, customary conditions to closing, indemnification obligations, and a 90-day lock-up period that limited transactions in its Common Stock by the Company. Net proceeds from the Public Offering, which was completed in early April 2014, were approximately $10,828,000. During fiscal 2015, we did not sell any securities under or receive any proceeds from the sale of securities under the 2013 Form S-3 Shelf. In October 2015, the Company entered into an At the Market Offering Agreement (the “Offering Agreement”) with Rodman & Renshaw, a unit of H. C. Wainwright & Co., LLC (the “Manager”) under which the Company may offer and sell shares of its Common Stock, having an aggregate offering price of up to $2,906,836 from time to time through or to the Manager, acting as sales agent and/or principal, in reliance on and subject to the limitations of General Instruction I.B.6 of Form S-3 and other applicable laws and regulations (the “2015 ATM Offering”). Under the Offering Agreement, during the quarter ended January 31, 2016, we sold 95,024 shares of Common Stock under the Offering Agreement at an average price of $2.13 per share, for net proceeds to the Company of approximately $199,000 and we paid the Manager a sales commission of approximately $3,000 related to those shares. The Company has no obligation to sell shares of Common Stock under the Offering Agreement and may at any time upon notice terminate the Offering Agreement. Form S-3 limits the aggregate market value of securities that the Company is permitted to offer in any 12-month period under its 2013 Form S-3 Shelf, whether under the ATM Agreement, the Underwriting Agreement or otherwise, to one-third of its public float. In 2014, the Company fully utilized its available transaction capacity to sell securities using the 2013 Form S-3 Shelf in the ATM offering. However, the Company regained the ability to utilize the 2013 Form S-3 Shelf as we entered fiscal 2016. Under the SEC’s regulations, the securities registered under its 2013 Form S-3 Shelf may only be offered and sold if not more than three years have elapsed from the initial effective date of the Form S-3, except that if a new shelf registration statement is filed then the Company is permitted to continue to offer and sell securities under the Form S-3 until the earlier of the effective date of the new shelf registration statement or 180 days after the third anniversary of the initial effective date. On February 12, 2016, the Company filed a new Form S-3 shelf registration statement (the “2016 Form S-3” or the “2016 Form S-3 Shelf”) to register the offering and sale of up to $15 million in securities. The 2016 Form S-3 registration statement has not yet been declared effective by the SEC. Subject to compliance with applicable laws and regulations, the Company may continue to offer and sell shares of its Common Stock in the 2015 ATM offering with the Manager under the Offering Agreement until the earlier of August 10, 2016 or the date on which the SEC declares effective the 2016 Form S-3. Under the terms of the Offering Agreement with the Manager, the Company may offer and sell up to $2,906,836 of its Common Stock in the 2015 ATM Offering. However, pursuant to General Instruction I.B.6 of Form S-3, at the time of filing the 2016 Form S-3, the Company was able to offer and sell only $1,597,102 of its common stock under the 2016 Form S-3, and, as of the date of that filing, the Company had already offered and sold $251,603 in value of its common stock under the Offering Agreement. Thus, under the 2016 Form S-3, the Company is seeking to register the offering and sale of up to $1,345,499 in value of its Common Stock for sale in the 2015 ATM Offering pursuant to the Offering Agreement, which securities are included in the $15 million of securities the Company is seeking to register for offer and sale on the 2016 Form S-3. The sale of additional equity or convertible securities could result in dilution to the Company’s stockholders. If additional funds are raised through the issuance of debt securities or preferred stock, these securities could have rights senior to those associated with the Company’s Common Stock and could contain covenants that would restrict its operations. Financing may not be available in amounts or on terms acceptable to it, or at all. If the Company is unable to obtain financing when required, it may be required to reduce the scope of its operations, current projects, planned product development and marketing efforts, and/or selling, general and administrative activities which could materially and adversely affect the Company’s future opportunities, financial condition and operating results. |
| Common Stock Disclosure [Policy Text Block] | (d) Reverse Stock Split At the annual meeting of stockholders on October 22, 2015, the Company’s stockholders approved a proposal to amend the Certificate of Incorporation of the Company to effect a reverse split of its Common Stock, at a ratio to be determined by the Company’s Board of Directors within a specific range and a reduction in the authorized number of shares of its Common Stock. On October 27, 2015, the Company filed a Certificate of Amendment to its Certificate of Incorporation to effect a one-for-10 reverse stock split of its Common Stock and to decrease the number of authorized shares of its Common Stock to 50,000,000 shares (the “Reverse Stock Split”). As a result of the Reverse Stock Split, as of the effective date of the Reverse Stock Split, every 10 shares of issued and outstanding Common Stock were combined into one issued and outstanding share of Common Stock, without any change in the par value per share. No fractional shares were issued in connection with the All share and per share data included in this report has been retroactively restated to reflect the Reverse Stock Split. |
| Consolidation, Policy [Policy Text Block] | (a) Consolidation 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 non-controlling 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 January 31, 2016, there were no non-controlling interests. In September 2015, the Company re-purchased the non-controlling interest (consisting of 11.8%) of the Company's Australian subsidiary, Ocean Power Technologies (Australasia) Pty. Ltd. (“OPTA”) for nominal consideration and now has 100% ownership of OPTA. OPTA owns 100% of Victorian Wave Partners Pty. Ltd. (“VWP”), which is also organized under the laws of Australia. The Company also periodically 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 January 31, 2016, there were no such entities. |
| Use of Estimates, Policy [Policy Text Block] | (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 legal costs associated with shareholder litigation and SEC subpoena; recoverability of the carrying amount of property and equipment; valuation allowances for receivables and deferred income tax assets; estimated costs to complete projects; and percentage of completion of customer contracts for purposes of revenue recognition. Actual results may differ from those estimates. |
| Revenue Recognition, Policy [Policy Text Block] | (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. These contracts are subject to interpretation, and management may make a judgment as to the amount of revenue earned and recorded. Because the Company has a small number of contracts, revisions to the percentage-of-completion determination, management interpretation or delays in meeting performance and contractual 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 Some of the Company’s projects are under cost-sharing contracts. |
| Cash and Cash Equivalents, Policy [Policy Text Block] | (d) Cash and Cash Equivalents The Company considers all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. The Company invests excess cash in an overnight U.S. government securities repurchase bank account and a money market account. In accordance with the terms of the repurchase agreement, the Company does not take possession of the related securities. The agreement contains provisions to ensure that the market value of the underlying assets remains sufficient to protect the Company in the event of default by the bank by requiring that the underlying securities have a total market value of at least 100% of the bank’s total obligations under the agreement. January 31, 2016 April 30, 2015 Checking and money market accounts $ 4,697,646 $ 4,614,400 Overnight repurchase account 4,715,612 12,721,334 $ 9,413,258 $ 17,335,734 |
| Marketable Securities, Policy [Policy Text Block] | (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 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 January 31, 2016 and April 30, 2015, 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] | (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 and bank guarantees that are expected to be issued by Barclays Bank on behalf of OPT LTD, one of the Company's subsidiaries, under a credit facility established by Barclays Bank for OPT LTD. The credit facility carries a fee of 1% per annum of the amount of any such obligations issued by Barclays Bank. The credit facility does not have an expiration date, but is cancelable at the discretion of the bank. As of January 31, 2016, there was €278,828 ($301,915) in letters of credit outstanding under this agreement. The second 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 of which $75,000 is outstanding at January 31, 2016. Under this arrangement, the Company annually assigns to the NJBPU a certificate of deposit in an amount equal to the outstanding grant balance. See Note 6. In addition, the Company previously had a letter of credit outstanding for the benefit of the Oregon Department of State Lands for the removal of certain of the Company’s anchoring and mooring equipment from the seabed off the coast of Oregon. During fiscal 2015, the Company completed the removal activity and reduced the letters of credit from $1,200,000 to $0. Restricted cash includes the following: January 31, 2016 April 30, 2015 Current: NJBPU agreement $ 75,000 $ 100,000 Barclay's Bank Agreement 302,101 338,561 $ 377,101 $ 438,561 January 31, 2016 April 30, 2015 Long Term: NJBPU agreement $ ? $ 50,000 $ ? $ 50,000 |
| Foreign Currency Transactions and Translations Policy [Policy Text Block] | (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. Three Months Ended January 31, Nine Months Ended January 31, 2016 2015 2016 2015 Foreign exchange loss $ (188,424 ) $ (246,002 ) $ (194,266 ) $ (467,909 ) Foreign currency denominated certificates of deposit and cash accounts: January 31, 2016 April 30, 2015 Restricted $ 302,101 $ 338,561 Unrestricted 1,037,590 1,100,371 $ 1,339,691 $ 1,438,932 |
| Property, Plant and Equipment, Policy [Policy Text Block] | (h) 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. Property and equipment is also 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. |
| Concentration Risk, Credit Risk, Policy [Policy Text Block] | (i) Concentration of Credit Risk Financial instruments that potentially subject the Company to concentration of credit risk consist principally of cash balances, overnight repurchase accounts, bank certificates of deposit and trade receivables. The Company invests its excess cash in highly liquid investments (typically, 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 January 31, Nine months ended January 31, Customer 2016 2015 2016 2015 US Department of Energy 100 % 25 % 33 % 37 % European Union (WavePort project) ? ? 67 % 26 % Mitsui Engineering & Shipbuilding ? 75 % ? 37 % 100 % 100 % 100 % 100 % 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. |
| Earnings Per Share, Policy [Policy Text Block] | (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 restricted stock, 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 154,537 for the three and nine months ended January 31, 2016, and 193,701 for the three and nine months ended January 31, 2015, 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] | (k) Recently Issued Accounting Standards In May 2014, the Financial Accounting Standards Board (FASB) issued a new revenue recognition standard entitled “Revenue from Contracts with Customers.” In August 2014, the FASB issued ASU 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In April 2015, the FASB issued ASU 2015-03, Simplifying the Presentation of Debt Issuance Costs, In November 2015, the FASB issued ASU 2015-17, Income Taxes (ASC 740): Balance Sheet Classification of Deferred Taxes In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU No. 2016-02, Leases |
