Exhibit 5.1

      ATTORNEYS AT LAW
111 HUNTINGTON AVENUE
BOSTON, MASSACHUSETTS 02199
617.342.4000 TEL
617.342.4001 FAX
www.foley.com

September 29, 2020

FuelCell Energy, Inc.

3 Great Pasture Road

Danbury, Connecticut 06810

Ladies and Gentlemen:

We have acted as counsel to FuelCell Energy, Inc., a Delaware corporation (the “Company”), in connection with the Registration Statement on Form S-3 (the “Registration Statement”) filed by the Company pursuant to Rule 462(b) promulgated under the Securities Act of 1933, as amended (the “Act”), relating to an aggregate of $17,535,048 of shares of common stock, par value $0.0001 per share (the “Common Stock”), of the Company (the “Shares”). The Registration Statement incorporates by reference the registration statement on Form S-3 (File No.333-226792), which was declared effective on August 21, 2018 (the “Prior Registration Statement”), including the prospectus which forms a part of the Prior Registration Statement (the “Base Prospectus”), which provides that it will be supplemented in the future by one or more prospectus supplements (each a “Prospectus Supplement”).

The Shares are being registered for offer and sale from time to time pursuant to Rule 415 under the Securities Act. In connection with this opinion, we have examined and relied upon originals, or copies certified to our satisfaction, of such records, documents, certificates, opinions, memoranda and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not independently verified such matters. In rendering this opinion, we have assumed the genuineness of all signatures, the legal capacity and competency of all natural persons, the authenticity of all documents submitted to us as originals, the conformity to originals of all documents submitted to us as copies; the accuracy, completeness and authenticity of certificates of public officials, and the due authorization, execution and delivery of all documents by all persons other than the Company where authorization, execution and delivery are prerequisites to the effectiveness of such documents.

We have also assumed that (i) all Shares will be issued and sold in compliance with applicable securities laws and in the manner stated in the Registration Statement and any applicable Prospectus Supplement; (ii) a definitive purchase, underwriting or similar agreement with respect to any Shares offered will have been duly authorized and validly executed and delivered by the Company and the other parties thereto; (iii) at the time of issuance and sale, a sufficient number of shares of Common Stock is authorized and reserved or available for issuance and that the consideration for the issuance and sale of the Shares is in an amount that is not less than the par value of the Common Stock; and (iv) the certificates, if any, for the Shares are in the form required under the Delaware General Corporation Law, have been duly executed by the Company, and countersigned by the transfer agent therefor and duly delivered to the purchasers thereof against payment therefor.

AUSTIN Boston CHICAGO dallas DENVER DETROIT houston JACKSONVILLE LOS ANGELES MADISON MEXICO CITY MIAMI MILWAUKEE NEW YORK ORLANDO SACRAMENTO SAN DIEGO SAN FRANCISCO SILICON VALLEY TALLAHASSEE TAMPA WASHINGTON, D.C. BRUSSELS TOKYO

September 29, 2020

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 It is understood that this opinion is to be used only in connection with the offer and sale of the Shares while the Registration Statement is effective.

 Based upon and subject to the foregoing and the other matters set forth herein, and having regard for such legal considerations as we deem relevant, we are of the opinion that with respect to the Shares offered under the Registration Statement, provided the issuance of the Shares has been duly authorized by all necessary corporate action on the part of the Company, then the Shares, when issued and sold as contemplated in the Registration Statement, the Base Prospectus and the related Prospectus Supplement(s), and in accordance with a duly authorized, executed and delivered purchase, underwriting or similar agreement, will be validly issued, fully paid and non-assessable.

 We express no opinion herein as to the laws of any state or jurisdiction other than the General Corporation Law of the State of Delaware and the federal laws of the United States of America.

This opinion is issued as of the date hereof, and we assume no obligation to supplement this opinion if any applicable law changes after the date hereof or if we become aware of any fact that might change the opinion expressed herein after the date hereof. This opinion is limited to the matters set forth herein, and no other opinion should be inferred beyond the matters expressly stated.

We consent to the use of this opinion as an exhibit to the Registration Statement. In giving our consent, we do not admit that we are “experts” within the meaning of Section 11 of the Securities Act or within the category of persons whose consent is required by Section 7 of the Securities Act.

Very truly yours,

/s/ Foley & Lardner LLP

Foley & Lardner LLP