UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D/A

(Amendment No. 14)

Under the Securities Exchange Act of 1934

Atlantica Sustainable Infrastructure plc

(Name of Issuer)

Ordinary Shares, nominal value $0.10 per share

(Title of Class of Securities)

G0751N103

(CUSIP Number)

Jennifer Tindale

Algonquin Power & Utilities Corp.

354 Davis Road, Suite 100

Oakville, ON L6J 2X1

Michael J. Aiello

Matthew Gilroy

Weil, Gotshal & Manges LLP

767 5th Avenue

New York, New York 10153

(212) 310-8000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

December 12, 2024

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box. ☐

The information required on this cover page shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Act”), or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

Item 1. Security and Issuer.

This Amendment No. 14 (this “Amendment No. 14”) to the Schedule 13D initially filed on March 9, 2018 (the “Original Schedule 13D”), as amended by Amendment No. 1 filed on April 27, 2018, as amended by Amendment No. 2 filed on November 21, 2018, as amended by Amendment No. 3 filed on November 27, 2018, as amended by Amendment No. 4 filed on February 15, 2019, as amended by Amendment No. 5 filed on May 13, 2019, as amended by Amendment No. 6 filed on May 24, 2019, as amended by Amendment No. 7 filed on June 3, 2019, as amended by Amendment No. 8 filed on April 6, 2020, as amended by Amendment No. 9 filed on December 10, 2020, as amended by Amendment No. 10 filed on January 7, 2021, as amended by Amendment No. 11 filed on August 4, 2021, as amended by Amendment No. 12 filed on May 10, 2022, as amended by Amendment No. 13 filed on May 28, 2024 (“Amendment No. 13”) with the Securities and Exchange Commission on behalf of Algonquin Power & Utilities, Corp. (“Algonquin”), Algonquin (AY Holdco) B.V. (“AY Holdco”), and Liberty (AY Holdings) B.V. (“AY Holdings”) (collectively, the “Reporting Persons”), relates to the ordinary shares, nominal value of $0.10 per share (“Ordinary Shares”), of Atlantica Sustainable Infrastructure plc (the “Issuer”), a public limited company incorporated under the laws of England and Wales, as described herein in more detail. The Issuer’s principal executive offices are located at Great West House, GW1, 17th Floor, Great West Road, Brentford, United Kingdom TW8 9DF. Unless otherwise indicated, each capitalized term used but not otherwise defined herein shall have the meaning ascribed to such term in the Original Schedule 13D.

Item 2. Identity and Background.

Item 2 is hereby amended as follows:

Schedule A to the Original Schedule 13D is hereby amended and restated as set forth on Schedule A to this Amendment No. 14 and incorporated by reference herein are the names, business addresses, present principal occupations or employments, and citizenship of each director and executive officer of the Reporting Persons.

(d), (e) During the last five years, none of the Reporting Persons and none of the persons set forth on Schedule A (i) has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or (ii) was a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violations with respect to such laws.

Item 4. Purpose of Transaction.

Item 4 is hereby amended as follows:

The information set forth in amended Item 6 below is incorporated by reference herein.

Item 5. Interest in Securities of the Issuer.

Item 5 is hereby amended as follows:

(a), (b) The responses of the Reporting Persons to Rows (7) through (13) of the cover pages of this Amendment No. 14 are incorporated herein by reference. As of December 12, 2024, the Reporting Persons own no Ordinary Shares of the Issuer.

(c) The information set forth in amended Item 6 below is incorporated by reference herein.

(d) Not applicable

(e) December 12, 2024

Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to the Securities of the Issuer.

Item 6 is hereby amended as follows:

On December 12, 2024, the Issuer and California Buyer Limited, a private limited company incorporated in England and Wales (“Bidco”), a vehicle controlled by funds managed or advised by Energy Capital Partners (“ECP”) and which includes a large group of institutional co-investors, consummated the Transaction Agreement (the “Transaction Agreement”). Pursuant to the terms of the Transaction Agreement, Bidco acquired the entire issued and to be issued share capital of the Issuer pursuant to a scheme of arrangement under Part 26 of the U.K. Companies Act 2006 (the “Scheme” and such acquisition, the “Transaction”). Upon completion of the Transaction, the Issuer became a wholly owned subsidiary of ECP and each holder of the Ordinary Shares of the Issuer became entitled to $22.00 per share in cash, without interest. Consequently, the Reporting Persons are no longer beneficial owners of any Ordinary Shares of the Issuer.

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: December 12, 2024

Schedule A

Directors and Executive Officers of the Reporting Persons

The following tables set forth the name, business address, present principal occupation or employment and citizenship of each director and executive officer of the Reporting Persons:

ALGONQUIN POWER & UTILITIES CORP. DIRECTORS

ALGONQUIN POWER & UTILITIES CORP. EXECUTIVE OFFICERS

ALGONQUIN (AY HOLDCO) B.V. DIRECTORS

LIBERTY (AY HOLDINGS) B.V. DIRECTORS