FTC太阳能公司美国存托凭证招股说明书（2025年5月22日版）

FTC SOLAR, INC. Up to $13,755,287Common Stock We have entered into an At the Market Offering Agreement dated as of May 1, 2025 (the “Sales Agreement”) with H.C. Wainwright& Co., LLC (the “Manager”or “Wainwright”), relating to the sale of shares of our common stock, $0.0001 par value per share (the “common stock”). In accordance with the terms of the SalesAgreement, from time to time we may offer and sell shares of our common stock through the Manager acting as sales agent and/or principal. Pursuant to this prospectus Sales of our common stock, if any, under this prospectus supplement and the accompanying base prospectus may be made in sales deemed to be an “at the marketoffering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended (the “Securities Act”), including sales made directly on or through theNasdaq Capital Market (“Nasdaq”), the existing trading market for our common stock, or any other existing trading market in the United States for our common stock,sales made to or through a market maker other than on an exchange or otherwise, directly to the Manager as principal, in negotiated transactions at market pricesprevailing at the time of sale or at prices related to such prevailing market prices, and/or in any other method permitted by law. Subject to terms of the Sales Agreement, The Manager will be entitled to compensation under the terms of the Sales Agreement at a commission rate of up to 3.0% of the gross sales price per share sold. Inconnection with the sale of our shares of common stock on our behalf, the Manager will be deemed to be an “underwriter” within the meaning of the Securities Act and We will pay all of the expenses incident to the registration, offering and sale of the shares of common stock under this prospectus supplement and theaccompanying base prospectus. Our common stock is listed and trades on the Nasdaq Capital Market under the symbol “FTCI.” The last sale price of our shares of common stock on May 14,2025 was $4.10 per share. As of the date of this prospectus supplement, the aggregate market value of our outstanding common stock held bynon-affiliates,computed by reference to theprice at which our common stock was last sold on the Nasdaq Capital Market on May14, 2025, which was $4.10 per share, was $41,265,860, based on 13,083,998shares of our outstanding common stock as of the date of this prospectus supplement, of which 10,064,844 shares were held bynon-affiliates.Pursuant to GeneralInstruction I.B.6 of FormS-3,in no event will we sell securities in a public primary offering with a value exceedingone-thirdof our public float in any12-monthperiod Investing in our shares of common stock involves a high degree of risk. Before making any investment decision, you should carefully review and considerall the information in this prospectus supplement, the accompanying base prospectus and the documents incorporated by reference herein and therein,including the risks and uncertainties described under “Risk Factors” beginning on pageS-10of this prospectus supplement and the risk factors incorporated Neither the U.S. Securities and Exchange Commission (the “SEC”) nor any state securities commission has approved or disapproved of these shares ordetermined if this prospectus supplement or the accompanying base prospectus is truthful or complete. Any representation to the contrary is a criminal offense. The date of this prospectus supplement is May22, 2025. Table of Contents ABOUT THIS PROSPECTUS SUPPLEMENT A registration statement on FormS-3(File No.333-286887) utilizing a shelf registration process relating to the securities described in thisprospectus supplement was filed with the SEC on May 1, 2025 and was declared effective on May 22, 2025. This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of common stock.The second part is the accompanying base prospectus, which provides more general information, some of which may not apply to this offering. Theinformation included or incorporated by reference in this prospectus supplement also adds to, updates and changes information contained orincorporated by reference in the accompanying base prospectus. It is also important for you to read and consider all information contained in thisprospectus supplement and the accompanying base prospectus, including the documents we have referred you to in the section entitled “Where You Can You should rely only on the information incorporated by reference or provided in this prospectus supplement and the accompanying baseprospectus. We have not, and the Manager has not, authorized any person to provide you with any information or to make any representation other thanas contained in this prospectus supplement or in the accompanying base prospectus and the information incorporated by reference herein and therein. Weand the Manager do not take any responsibility for, and can provide