| Significant Accounting Policies (Policies) | 3 Months Ended |
| Jul. 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, 2016 filed with the Securities and Exchange Commission (“SEC”) and elsewhere in this Form 10-Q. |
| Liquidity, Policy [Policy Text Block] | c) Liquidity/Going Concern The consolidated financial statements have been prepared assuming the Company will continue as a going concern. The Company has experienced substantial and recurring losses from operations, which losses have caused an accumulated deficit of $181.7 million at July 31, 2016. At July 31, 2016, the Company had approximately $9.0 million in cash on hand. The Company generated revenues of $0.2 million and $0.1 million in the three months ended July 31, 2016 and 2015, respectively. Based on the Company’s cash and cash equivalents and marketable securities as of July 31, 2016, the Company believes that it will be able to finance its capital requirements and operations into at least the quarter ending April 30, 2017. The Company will require additional equity and/or debt financing to continue its operations. The Company cannot assure you that it will be able to secure additional funding when needed or at all, or, if secured, that such funding would be on favorable terms. These factors raise substantial doubt about the Company’s ability to continue as a going concern. The consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded assets amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty. Management is evaluating different strategies to obtain the required additional funding for future operations. These strategies may include, but are not limited to, additional funding from current or new investors, officers and directors; borrowings of debt; a public offering of the Company’s equity or debt securities; partnerships and/or collaborations. There can be no assurance that any of these future-funding efforts will be successful. In fiscal 2017 and 2016, 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 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 our business strategy, the Company requires additional equity and/or debt financing. The Company closed two equity financing arrangements during the three months ended July 31, 2016. The Company does not currently have any committed sources of debt or equity financing, and the Company cannot assure 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 our cash expenditures. 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 or cease its operations. In October 2015, the Company entered into an At the Market Offering Agreement (“2015 ATM Agreement”) with H.C. Wainwright & Co., LLC (“Wainwright”), under which the Company offered from time to time in an at the market offering (the “2015 ATM Facility”) shares of our Common Stock under a shelf registration statement filed in 2013 on Form S-3 (the “2013 Form S-3”) and under a subsequent shelf registration statement on Form S-3 (the “2016 Form S-3”) filed with the SEC in February 2016 and declared effective by the SEC in April 2016. The 2016 Form S-3 registers for sale up to $15 million in securities by the Company in a public offering, although the Company is limited by Instruction I.B.6 in the amount that we may sell under Form S-3 in any 12 calendar month period to one third of our public float. 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 the Company entered fiscal 2016. Under the 2015 ATM Facility, between October 2015 and April 2016, the Company issued and sold 144,571 shares of its Common Stock with an aggregate market value of $293,343 under the 2015 ATM Agreement at an average price of $2.03 per share and paid Wainwright of the 2015 ATM Facility a sales commission of approximately $4,400 related to those shares. The 2015 ATM Agreement was terminated on June 2, 2016, effective immediately, and the 2015 ATM Facility is no longer available for use by the Company. 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”) to register the offering and sale of up to $15 million in securities. The 2016 Form S-3 registration was declared effective by the SEC on April 26, 2016. On June 2, 2016, the Company entered into a securities purchase agreement, which was amended on June 7, 2016 (as amended, the “Purchase Agreement”) with certain institutional purchasers (the “June Purchasers”). Pursuant to the terms of the June Purchase Agreement, the Company sold an aggregate of 417,000 shares of Common Stock together with warrants to purchase up to an aggregate of 145,952 shares of Common Stock. Each share of Common Stock was sold together with a warrant to purchase 0.35 of a share of Common Stock at a combined purchase price of $4.60. The net proceeds to the Company from the offering were approximately $1.7 million, after deducting placement agent fees and estimated offering expenses payable by the Company, but excluding the proceeds, if any, from the exercise of the warrants issued in the offering. The warrants have an exercise price of $6.08 per share, will be exercisable on the date that is six months and one day from the date of issuance (“Initial Exercise Date”), and will expire five years following the Initial Exercise Date. On July 22, 2016, the Company entered into the Second Amendment to the Purchase Agreement (the “Second Amended Purchase Agreement”) with certain purchasers (the “July Purchasers”). Pursuant to the terms of the Second Amended Purchase Agreement, the Company sold an aggregate of 595,000 shares of Common Stock together with warrants to purchase up to an aggregate of 178,500 shares of Common Stock. Each share of Common Stock was sold together with a warrant to purchase 0.30 of a share of Common Stock at a combined purchase price of $6.75. The net proceeds to the Company from the offering were approximately $3.6 million, after deducting placement agent fees and estimated offering expenses payable by the Company, but excluding the proceeds, if any, from the exercise of the warrants issued in the offering. The Warrants were exercisable immediately at an exercise price of $9.36 per share. The Warrants will expire on the fifth (5th) anniversary of the initial date of issuance. The sale of additional equity or convertible securities could result in dilution to stockholders. If additional funds are raised through the issuance of debt securities, these securities could have rights senior to those associated with the Company’s Common Stock and could contain covenants that would restrict our operations. Financing may not be available in amounts or on terms acceptable to the Company, or at all. If the Company is unable to obtain required financing, it may be required to reduce the scope of its operations, including its planned product development and marketing efforts, which could materially and adversely harm its financial condition and operating results. If the Company is unable to secure additional financing, it may be forced to cease operations. |
| 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 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, 2016, there were no non-controlling interests. As of July 31, 2015, there was one noncontrolling interest, consisting of 11.8% of the Company's Australian subsidiary, Ocean Power Technologies (Australasia) Pty. Ltd. (“OPTA”). OPTA owns 100% of Victorian Wave Partners Pty. Ltd. (“VWP”), which is also organized under the laws of Australia. In September 2015, the Company re-purchased the non-controlling interest (consisting of 11.8%) of OPTA for nominal consideration and now has 100% ownership of OPTA. 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 July 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 recoverability of the carrying amount of property and equipment; fair value of warrant liabilities, 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 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] | (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 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. 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 remain 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. July 31, 2016 April 30, 2016 Checking and savings accounts $ 6,505,514 $ 4,534,671 Overnight repurchase account 2,518,998 2,195,143 $ 9,024,512 $ 6,729,814 |
| 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 July 31, 2016 and April 30, 2016, 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 the Company 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 July 31, 2016, there was €278,828 ($241,125) in letters of credit outstanding under this agreement. The second agreement is between the Company. and the New Jersey Board of Public Utilities (“NJBPU”). The Company received a $500,000 recoverable grant award from the NJBPU of which $25,000 is outstanding at July 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. Restricted cash includes the following: July 31, 2016 April 30, 2016 NJBPU agreement $ 25,000 $ 50,000 Barclay's Bank Agreement 241,125 249,543 $ 266,125 $ 299,543 |
| 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 gain in the accompanying consolidated statements of operations. |
| 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, 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 2016 2015 US Department of Energy ― 100 % Mitsui Engineering & Shipbuilding 100 % ― 100 % 100 % The loss of, or a significant reduction in revenues from a current customer could significantly impact the Company's financial position or results of operations. The Company does not require its customers to maintain collateral. |
| Warrant Liability, Policy [Policy Text Block] | (j) Warrant Liability The Company's warrants to purchase shares of its common stock are classified as warrant liability and recorded at fair value. This warrant liability is subject to remeasurement at each balance sheet date and the Company recognizes any change in fair value in its statements of operations as a change in fair value of the warrant liability. The Company will continue to adjust the carrying value of the warrants for changes in the estimated fair value until such time as these instruments are exercised or expire. At that time, the liabilities will be reclassified to additional paid-in capital, a component of stockholders' equity. |
| Earnings Per Share, Policy [Policy Text Block] | (k) 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, warrants on common stock and non-vested restricted stock issued to employees and non-employee directors, totaling 711,453 for the three months ended July 31, 2016, and 188,561 for the three months ended July 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] | (l) Recently Issued Accounting Standards In May 2014, the FASB issued ASU No. 2014-09, “Revenue from Contracts with Customers”. This guidance requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires an entity to disclose sufficient information to enable users of financial statements to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. Qualitative and quantitative information is required about: ● Contracts with customers—including revenue and impairments recognized, disaggregation of revenue and information about contract balances and performance obligations (including the transaction price allocated to the remaining performance obligations). ● Significant judgments and changes in judgments—determining the timing of satisfaction of performance obligations (over time or at a point in time), and determining the transaction price and amounts allocated to performance obligations. ● Certain assets—assets recognized from the costs to obtain or fulfill a contract. In August 2015, the FASB issued updated guidance deferring the effective date of the revenue recognition standard. In March and April 2016, the FASB issued additional updated guidance, which clarifies certain aspects of the ASU and the related implementation guidance issued by the FASB-IASB Joint Transition Resource Group for Revenue Recognition. This guidance is effective for the Company for annual reporting periods beginning after December 15, 2017. The Company is currently evaluating the impact that this guidance will have on its results of operations, financial position and cash flows. In August 2014, the FASB issued ASU 2014-15, “Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern”, which describes how an entity should assess its ability to meet obligations and sets rules for how this information should be disclosed in the financial statements. The standard provides accounting guidance that will be used along with existing auditing standards. The new standard applies to all entities for the first annual period ending after December 15, 2016, and interim periods thereafter. Early application is permitted. The Company is evaluating the effect ASU 2014-15 will have on its consolidated financial statements and disclosures and have not yet determined the effect of the standard on our ongoing financial reporting at this time. In January 2016, the FASB issued ASU No. 2016-01, “Recognition and Measurement of Financial Assets and Financial Liabilities”, which makes limited amendments to the guidance in U.S. GAAP on the classification and measurement of financial instruments. The update significantly revises an entity's accounting related to the classification and measurement of investments in equity securities and the presentation of certain fair value changes for financial liabilities measured at fair value. It also amends certain disclosure requirements associated with the fair value of financial instruments. The update will take effect for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company will evaluate the effect of ASU 2016-01 for future periods as applicable. In February 2016, the FASB issued ASU No. 2016-02, “Leases (Topic 842)”. The new standard establishes a right-of-use (ROU) model that requires a lessee to record a ROU asset and a lease liability on the balance sheet for all leases with terms longer than 12 months. Leases will be classified as either finance or operating, with classification affecting the pattern of expense recognition in the income statement. ASU 2016-02 is effective for annual periods beginning after December 15, 2018, including interim periods within those annual periods, with early adoption permitted. A modified retrospective transition approach is required for lessees for capital and operating leases existing at, or entered into after, the beginning of the earliest comparative period presented in the financial statements, with certain practical expedients available. The Company is evaluating the effect ASU 2016-02 will have on its consolidated financial statements and disclosures and have not yet determined the effect of the standard on our ongoing financial reporting at this time. In March 2016, the FASB issued ASU No. 2016-09, “Compensation - Stock Compensation (Topic 718)”, or ASU No. 2016-09. The amendments of ASU No. 2016-09 were issues as part of the FASB's Simplification initiative focused on improving areas of GAAP for which cost and complexity may be reduced while maintaining or improving the usefulness of information disclosed within the financial statements. The amendments focused on simplification specifically with regard to share-based payment transactions, including income tax consequences, classification of awards as equity or liabilities and classification on the statement of cash flows. The guidance in ASU No. 2016-09 is effective for fiscal years beginning after December 15, 2016, and interim periods within those annual periods. Early adoption is permitted. The Company will evaluate the effect of ASU 2016-09 for future periods as applicable. In June 2016, the FASB issued ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments”. The standard provides for a new impairment model which requires measurement and recognition of expected credit losses for most financial assets held. The ASU is effective for public companies for annual periods, and interim periods within those annual periods, beginning after December 15, 2019. The Company is evaluating the effect ASU 2016-13 will have on its consolidated financial statements and disclosures and have not yet determined the effect of the standard on our ongoing financial reporting at this time. |
