Promissory Note Issued to TortoiseEcofin Sponsor III LLC, dated October 20, 2023

Exhibit 10.1

THIS PROMISSORY NOTE (“NOTE”) HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”). THIS NOTE HAS BEEN ACQUIRED FOR INVESTMENT ONLY AND MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF REGISTRATION OF THE RESALE THEREOF UNDER THE SECURITIES ACT OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY IN FORM, SCOPE AND SUBSTANCE TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

PROMISSORY NOTE

TortoiseEcofin Acquisition Corp. III, a Cayman Islands exempted company and blank check company (the “Maker”), promises to pay to the order of TortoiseEcofin Sponsor III LLC, a Cayman Islands limited liability company, or its registered assigns or successors in interest (the “Payee”), or order, the principal sum of up to One Million Five Hundred Fifty-Three Thousand Eight Hundred Twenty-Three Dollars And Eighteen Cents ($1,553,823.18) in lawful money of the United States of America, on the terms and conditions described below. All payments on this Note shall be made by check or wire transfer of immediately available funds or as otherwise determined by the Maker to such account as the Payee may from time to time designate by written notice in accordance with the provisions of this Note. This Note is being made in connection with Maker extending its termination date of October 22, 2023 for up to an additional six (6) months to April 22, 2024 (the “Extension”).

1. Principal. The principal balance of this Note shall be due and payable by the Maker on the earlier of (such date, the “Maturity Date”), (a) the date that Maker consummates its initial business combination and (b) the date of the liquidation of the Maker. Under no circumstances shall any individual, including, but not limited to, any officer, director, employee or shareholder of the Maker, be obligated personally for any obligations or liabilities of the Maker hereunder.

2. Interest. No interest shall accrue or be charged by Payee on the unpaid principal balance of this Note.

3. Drawdown Requests. The Payee will fund up to One Million Five Hundred Fifty-Three Thousand Eight Hundred Twenty-Three U.S. Dollars And Eighteen Cents ($1,553,823.18) into the trust account (the “Trust Account”) of the Maker established in connection with its initial public offering (the “IPO”), such amounts to be for the benefit of eligible holders of the Maker’s unredeemed Class A ordinary shares upon redemption or liquidation of the Maker, all in accordance with the Maker’s amended and restated memorandum and articles of association, as amended. The principal of this Note may be drawn down in up to 6 monthly installments of approximately $258,970.53 per withdrawal until the earlier of (i) April 22, 2024 and (ii) the date on which the Maker consummates the Business Combination, upon written request from the Maker to the Payee (each, a “Drawdown Request”). Each Drawdown Request must be made on or before the 23rd day of each applicable month, and state the amount to be drawn down. The precise amount of each Drawdown Request may vary as needed, in Maker’s discretion, to satisfy the monthly portion of funds to be deposited in the Trust Account. The Payee, in its sole discretion, shall fund each Drawdown Request via a wire transfer directly to the Trust Account no later than seven (7) calendar days from the beginning of each applicable month (23rd of each month); provided, however, that the maximum amount of drawdowns collectively under this Note shall not exceed One Million Five Hundred Fifty-Three Thousand Eight Hundred Twenty-Three U.S. Dollars And Eighteen Cents ($1,553,823.18). Once an amount is drawn down under this Note, it shall not be available for future Drawdown Requests. Except as set forth herein, no fees, payments or other amounts shall be due to the Payee in connection with, or as a result of, any Drawdown Request by the Maker.

4. Application of Payments. All payments shall be applied first to payment in full of any costs incurred in the collection of any sum due under this Note, including, without limitation, reasonable attorneys’ fees, and then to the payment in full of any late charges and finally to the reduction of the unpaid principal balance of this Note.

5. Use of Proceeds. On or prior to the date of this Note, the Payee shall remit the full principal amount to the Maker. The Maker hereby represents, warrants and covenants to the Payee, that the entire principal amount will be used by the Maker solely for purposes of making a payment for the Extension.

6. Events of Default. The following shall constitute an event of default (“Event of Default”):

(a) Failure to Make Required Payments. Failure by the Maker to pay the principal amount due pursuant to this Note within five (5) business days of the Maturity Date.

(b) Breach of Use of Proceeds. Failure by Maker to comply with the provisions of Section 5 of this Note.

(c) Voluntary Bankruptcy, Etc. The commencement by the Maker of a voluntary case under any applicable bankruptcy, insolvency, reorganization, rehabilitation or other similar law, or the consent by it to the appointment of or taking possession by a receiver, liquidator, assignee, trustee, custodian, sequestrator (or other similar official) of the Maker or for any substantial part of its property, or the making by it of any assignment for the benefit of creditors, or the failure of the Maker generally to pay its debts as such debts become due, or the taking of corporate action by the Maker in furtherance of any of the foregoing.

(d) Involuntary Bankruptcy, Etc. The entry of a decree or order for relief by a court having jurisdiction in the premises in respect of the Maker in an involuntary case under any applicable bankruptcy, insolvency or other similar law, or appointing a receiver, liquidator, assignee, custodian, trustee, sequestrator (or similar official) of the Maker or for any substantial part of its property, or ordering the winding-up or liquidation of its affairs, and the continuance of any such decree or order unstayed and in effect for a period of 60 consecutive days.

7. Remedies.

(a) Upon the occurrence of an Event of Default specified in Section 6(a) or Section 6(b) hereof, the Payee may, by written notice to the Maker, declare this Note to be due immediately and payable, whereupon the unpaid principal amount of this Note, and all other amounts payable hereunder, shall become immediately due and payable without presentment, demand, protest or other notice of any kind, all of which are hereby expressly waived, anything contained herein or in the documents evidencing the same to the contrary notwithstanding.

(b) Upon the occurrence of an Event of Default specified in Section 6(c) and 6(d), the unpaid principal balance of this Note, and all other sums payable with regard to this Note, shall automatically and immediately become due and payable, in all cases without any action on the part of the Payee.

8. Waivers. The Maker and all endorsers and guarantors of, and sureties for, this Note waive presentment for payment, demand, notice of dishonor, protest, and notice of protest with regard to this Note, all errors, defects and imperfections in any proceedings instituted by the Payee under the terms of this Note, and all benefits that might accrue to the Maker by virtue of any present or future laws exempting any property, real or personal, or any part of the proceeds arising from any sale of any such property, from attachment, levy or sale under execution, or providing for any stay of execution, exemption from civil process, or extension of time for payment, and the Maker agrees that any real estate that may be levied upon pursuant to a judgment obtained by virtue hereof or any writ of execution issued hereon, may be sold upon any such writ in whole or in part in any order desired by the Payee.

9. Unconditional Liability. The Maker hereby waives all notices in connection with the delivery, acceptance, performance, default, or enforcement of the payment of this Note, and agrees that its liability shall be unconditional, without regard to the liability of any other party, and shall not be affected in any manner by any indulgence, extension of time, renewal, waiver or modification granted or consented to by the Payee, and consents to any and all extensions of time, renewals, waivers, or modifications that may be granted by the Payee with respect to the payment or other provisions of this Note, and agrees that additional makers, endorsers, guarantors, or sureties may become parties hereto without notice to the Maker or affecting the Maker’s liability hereunder.

10. Notices. All notices, statements or other documents which are required or contemplated by this Note shall be made in writing and delivered: (a) personally or sent by first class registered or certified mail, overnight courier service or facsimile or electronic transmission to the address designated in writing, (b) by facsimile to the number most recently provided to such party or such other address or fax number as may be designated in writing by such party or (c) by electronic mail, to the electronic mail address most recently provided to such party or such other electronic mail address as may be designated in writing by such party. Any notice or other communication so transmitted shall be deemed to have been given on the day of delivery, if delivered personally, on the business day following receipt of written confirmation, if sent by facsimile or electronic transmission, one (1) business day after delivery to an overnight courier service or five (5) days after mailing if sent by mail.

11. Construction; Governing Law; Venue; Waiver Of Jury Trial. THIS NOTE SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO CONFLICT OF LAW PROVISIONS THEREOF. MAKER HEREBY IRREVOCABLY AND UNCONDITIONALLY SUBMITS, FOR ITSELF AND ITS PROPERTY, TO THE NONEXCLUSIVE JURISDICTION OF THE SUPREME COURT OF THE STATE OF NEW YORK SITTING IN NEW YORK COUNTY AND OF THE UNITED STATES DISTRICT COURT OF THE SOUTHERN DISTRICT OF NEW YORK, AND ANY APPELLATE COURT FROM ANY THEREOF, IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS NOTE, OR FOR RECOGNITION OR ENFORCEMENT OF ANY JUDGMENT. EACH PARTY HERETO HEREBY IRREVOCABLY AND UNCONDITIONALLY AGREES THAT ALL CLAIMS IN RESPECT OF ANY SUCH ACTION OR PROCEEDING MAY BE HEARD AND DETERMINED IN SUCH NEW YORK STATE COURT OR, TO THE EXTENT PERMITTED BY APPLICABLE LAW, IN SUCH FEDERAL COURT. EACH PARTY HERETO ALSO HEREBY AGREES THAT A FINAL JUDGMENT IN ANY SUCH ACTION OR PROCEEDING SHALL BE CONCLUSIVE AND MAY BE ENFORCED IN OTHER JURISDICTIONS BY SUIT ON THE JUDGMENT OR IN ANY OTHER MANNER PROVIDED BY APPLICABLE LAW. NOTHING IN THIS NOTE SHALL AFFECT ANY RIGHT THAT THE PAYEE OR ANY OTHER HOLDER MAY OTHERWISE HAVE TO BRING ANY ACTION OR PROCEEDING RELATING TO THIS NOTE AGAINST THE MAKER OR ITS PROPERTIES IN THE COURTS OF ANY OTHER JURISDICTION. IN ANY ACTION, SUIT OR PROCEEDING IN RESPECT OF OR ARISING OUT OF THIS NOTE, THE PAYEE AND THE MAKER WAIVE TRIAL BY JURY, AND EACH OF MAKER AND PAYEE WAIVES (I) THE RIGHT TO INTERPOSE ANY SET-OFF OF ANY NATURE OR DESCRIPTION, (II) ANY OBJECTION BASED ON FORUM NON CONVENIENS OR VENUE, AND (III) ANY CLAIM FOR CONSEQUENTIAL, PUNITIVE, INCIDENTAL, EXEMPLARY OR SPECIAL DAMAGES.

12. Severability. Any provision contained in this Note which is prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof, and any such prohibition or unenforceability in any jurisdiction shall not invalidate or render unenforceable such provision in any other jurisdiction.

13. Trust Waiver. Notwithstanding anything herein to the contrary, but subject to the following sentence of this Section 13, the Payee hereby waives any and all right, title, interest or claim of any kind (“Claim”) in or to any distribution of or from the trust account (the “Trust Account”) established in which the proceeds of the initial public offering (the “IPO”) conducted by the Maker (including the deferred underwriters’ discounts and commissions) and the proceeds of the sale of the warrants issued in a private placement that occurred prior to the closing of the IPO were deposited, as described in greater detail in Maker’s Registration Statement on Form S-1 (No. 333-253586) filed with the Securities and Exchange Commission in connection with the IPO (the “Registration Statement”), and hereby agrees not to seek recourse, reimbursement, payment or satisfaction for any Claim against the Trust Account for any reason whatsoever.

14. Amendment; Waiver. Any amendment hereto or waiver of any provision hereof may be made with, and only with, the written consent of the Maker and the Payee.

15. Assignment. No assignment or transfer of this Note or any rights or obligations hereunder may be made by the Maker (by operation of law or otherwise) without the prior written consent of the Payee and any attempted assignment without the required consent shall be void.

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IN WITNESS WHEREOF, the Maker, intending to be legally bound hereby, has caused this Note to be duly executed by the undersigned as of the day and year first above written.

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