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As filed with the Securities and Exchange Commission on October 22, 2010

Registration No. 333-152671

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

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Amendment No. 10
to
FORM S-1
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

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First Wind Holdings Inc.
(Exact Name of Registrant as Specified in Its Charter)

179 Lincoln Street, Suite 500
Boston, MA 02111
617-960-2888
(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant's Principal Executive Offices)

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Paul Gaynor
Chief Executive Officer
First Wind Holdings Inc.
179 Lincoln Street, Suite 500
Boston, MA 02111
617-960-2888
(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent For Service)

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Copies to:

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Approximate date of commencement of proposed sale to the public:
As soon as practicable after this Registration Statement is declared effective.

          If any securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, as amended (the "Securities Act"), check the following box.    o

          If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

          If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

          If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

          Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definitions of "large accelerated filer," "accelerated filer," and "smaller reporting company" in Rule 12b 2 of the Exchange Act. (Check one):

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          The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act or until this registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

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Explanatory Note

        This Amendment No. 10 is being filed solely for the purpose of filing the exhibits indicated in Item 16 of Part II of the Registration Statement. No change is made to the prospectus constituting Part I of the Registration Statement or Items 13, 14, 15 and 17 or Part II of the Registration Statement.

PART II

INFORMATION NOT REQUIRED IN THE PROSPECTUS

Item 13.    Other Expenses of Issuance and Distribution

        Set forth below are the expenses (other than underwriting discounts and commissions) expected to be incurred in connection with the issuance and distribution of the securities registered hereby. With the exception of the SEC registration fee and the FINRA filing fee, the amounts set forth below are estimates.

Item 14.    Indemnification of Officers and Directors

        Our certificate of incorporation provides that a director will not be liable to the corporation or its stockholders for monetary damages for breach of fiduciary duty as a director, except for liability (1) for any breach of the director's duty of loyalty to the corporation or its stockholders, (2) for acts or omissions not in good faith or which involved intentional misconduct or a knowing violation of the law, (3) under section 174 of the DGCL for unlawful payment of dividends or improper redemption of stock or (4) for any transaction from which the director derived an improper personal benefit. In addition, if the DGCL is amended to authorize the further elimination or limitation of the liability of directors, then the liability of a director of the corporation, in addition to the limitation on personal liability provided for in our certificate of incorporation, will be limited to the fullest extent permitted by the amended DGCL. Our bylaws provide that the corporation will indemnify, and advance expenses to, any officer or director to the fullest extent authorized by the DGCL.

        Section 145 of the DGCL provides that a corporation may indemnify directors and officers as well as other employees and individuals against expenses, including attorneys' fees, judgments, fines and amounts paid in settlement in connection with specified actions, suits and proceedings whether civil, criminal, administrative, or investigative, other than a derivative action by or in the right of the corporation, if they acted in good faith and in a manner they reasonably believed to be in or not opposed to the best interests of the corporation and, with respect to any criminal action or proceeding, had no reasonable cause to believe their conduct was unlawful. A similar standard is applicable in the case of derivative actions, except that indemnification extends only to expenses, including attorneys' fees, incurred in connection with the defense or settlement of such action and the statute requires court approval before there can be any indemnification where the person seeking indemnification has been found liable to the corporation. The statute provides that it is not exclusive of other indemnification

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that may be granted by a corporation's certificate of incorporation, bylaws, disinterested director vote, stockholder vote, agreement or otherwise.

        Our certificate of incorporation also contains indemnification rights for our directors and our officers. Specifically, our certificate of incorporation provides that we shall indemnify our officers and directors to the fullest extent authorized by the DGCL. Further, we may maintain insurance on behalf of our officers and directors against expense, liability or loss asserted incurred by them in their capacities as officers and directors.

        We have obtained directors' and officers' insurance to cover our directors, officers and some of our employees for certain liabilities.

        We will enter into written indemnification agreements with our directors. Under these proposed agreements, if a director makes a claim of indemnification to us, at the director's election, either a majority of the independent directors or independent legal counsel selected by the director, must review the relevant facts and make a determination whether the director has met the standards of conduct under Delaware law that would permit (under Delaware law) and require (under the indemnification agreement) us to indemnify the director.

        The limited liability company agreement of First Wind Holdings, LLC contains provisions limiting the liability of First Wind Holdings, LLC's managing member, members, officers and their respective affiliates, including our Sponsors, to First Wind Holdings, LLC or any of its members. Moreover, the limited liability company agreement contains broad indemnification provisions for First Wind Holdings, LLC's managing member, members, officers and their respective affiliates, including our Sponsors. Because First Wind Holdings, LLC is a limited liability company, these provisions are not subject to the limitations on exculpation and indemnification contained in the Delaware General Corporation Law with respect to the indemnification that may be provided by a Delaware corporation to its directors and officers.

Item 15.    Recent Sales of Unregistered Securities

        In connection with its formation in May 2008, First Wind Holdings Inc. issued one share of its common stock to First Wind Holdings, LLC. The share was issued in reliance upon an exemption from registration afforded by Section 4(2) of the Securities Act. No underwriters, brokers or finders were involved in this issuance. The single share was issued by First Wind Holdings Inc. to First Wind Holdings, LLC in order to form First Wind Holdings Inc. and did not involve a public offering, which would require registration under the Securities Act of 1933.

        Since January 1, 2007, First Wind Holdings, LLC has granted to directors, officers and employees an aggregate of 113,045,903 Series B Units (consisting of Series B-2, B-3, B-4 and B-5 Units), of which 26,308,667 such Series B Units have been forfeited or cancelled. The issuances of the Series B Units to directors, officers and employees were deemed to be exempt from registration under the Securities Act in reliance on Rule 701 as promulgated under the Securities Act.

        In addition, during the past three years, First Wind Holdings, LLC issued unregistered securities to the entities and persons described below. None of these transactions involved any underwriters or any public offerings, and we believe that each of these transactions was exempt from registration requirements pursuant to Section 3(a)(9) or Section 4(2) of the Securities Act of 1933, as amended. The recipients of the securities in these transactions represented their intention to acquire the securities for investment only and not with a view to or for sale in connection with any distribution thereof. The share numbers presented below do not give effect to the reorganization transactions described in the prospectus.

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        During the fiscal year ended December 31, 2007, First Wind Holdings, LLC issued the following unregistered securities for the consideration listed:

        During the fiscal year ended December 31, 2008, First Wind Holdings, LLC issued the following unregistered securities for the consideration listed:

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        Since December 31, 2008, First Wind Holdings, LLC issued the following unregistered securities for the consideration listed:

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Item 16.    Exhibits and Financial Statement Schedule

(a)

Exhibits.

        The following exhibits are filed herewith pursuant to the requirements of Item 601 of Regulation S-K:

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(b)

Financial Statements Schedule

        The following schedule is filed herewith pursuant to the requirements of Regulation S-X:

        All other schedules have been omitted because they are not required, are not applicable, or the information is included in the Consolidated Financial Statements or Notes thereto.

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SCHEDULE I

First Wind Holdings, LLC

Condensed Parent Company Balance Sheets

(in thousands)

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SCHEDULE I

First Wind Holdings, LLC

Condensed Parent Company Statements of Operations

(in thousands)

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SCHEDULE I

First Wind Holdings, LLC

Condensed Parent Company Statements of Cash Flows

(in thousands)

Basis of Presentation

        First Wind Holdings, LLC is a holding company that conducts substantially all of its business operations through its subsidiaries. First Wind Holdings, LLC was formed in Delaware on January 2, 2002. Pursuant to tax equity financing transactions entered into by certain subsidiaries of First Wind Holdings, LLC, there are significant restrictions on the transfer of assets from these subsidiaries to First Wind Holdings, LLC. The restricted net assets represented more than 25% of First Wind Holdings, LLC's consolidated net assets as of December 31, 2009. Accordingly, the condensed financial statements of First Wind Holdings, LLC have been presented on an unconsolidated "parent-only" basis.

        Certain note disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles have been omitted pursuant to the rules and regulations of the Securities and Exchange Commission. Because the unconsolidated condensed financial statements do not include all of the notes required by U.S. generally accepted accounting principles, they should be read in conjunction with the consolidated financial statements of First Wind Holdings, LLC included elsewhere in this registration statement on Form S-1.

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Item 17.    Undertakings

        Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the provisions, or otherwise, the registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

        The undersigned registrant hereby undertakes to provide to the underwriters at the closing specified in the underwriting agreement certificates in such denominations and registered in such names as required by the underwriter to permit prompt delivery to each purchaser.

        The undersigned registrant hereby undertakes that:

        (1)   For purposes of determining any liability under the Securities Act of 1933, the information omitted from the form of prospectus filed as part of this registration statement in reliance upon Rule 430A and contained in a form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of this registration statement as of the time it was declared effective.

        (2)   For the purpose of determining any liability under the Securities Act of 1933, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

        (3)   For the purpose of determining liability under the Securities Act of 1933 to any purchaser, if the registrant is subject to Rule 430C under the Securities Act, each prospectus filed pursuant to Rule 424(b) as part of a registration statement relating to an offering, other than registration statements relying on Rule 430B or other than prospectuses filed in reliance on Rule 430A, shall be deemed to be part of and included in the registration statement as of the date it is first used after effectiveness. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such first use, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such date of first use.

        (4)   For the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities: The undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

          (i)  Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

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         (ii)  Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

        (iii)  The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

        (iv)  Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

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SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Amendment No. 10 to Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Boston, Massachusetts, on October 22, 2010.

        Pursuant to the requirements of the Securities Act of 1933, the Amendment No. 10 to Registration Statement has been signed by the following persons in the capacities indicated below on October 22, 2010.

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INDEX TO EXHIBITS

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QuickLinks

Explanatory Note
PART II INFORMATION NOT REQUIRED IN THE PROSPECTUS

Item 13. Other Expenses of Issuance and Distribution
Item 14. Indemnification of Officers and Directors
Item 15. Recent Sales of Unregistered Securities

Item 16. Exhibits and Financial Statement Schedule

SCHEDULE I First Wind Holdings, LLC Condensed Parent Company Balance Sheets (in thousands)
SCHEDULE I First Wind Holdings, LLC Condensed Parent Company Statements of Operations (in thousands)
SCHEDULE I First Wind Holdings, LLC Condensed Parent Company Statements of Cash Flows (in thousands)

Item 17. Undertakings

SIGNATURES
INDEX TO EXHIBITS