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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G/A

Under the Securities Exchange Act of 1934
(Amendment No. 2)*

Active Power, Inc.
(Name of Issuer)

Common Stock, par value $0.001 per share
(Title of Class of Securities)

00504W308
(CUSIP Number)

December 31, 2013
(Date of Event Which Requires Filing of This Statement)


Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨	Rule 13d-1(b)
x	Rule 13d-1(c)
¨	Rule 13d-1(d)

(Page 1 of 12 Pages)

______________________________

*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("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).

CUSIP No. 00504W308

13G/A

Page 2 of 10 Pages

1	NAME OF REPORTING PERSON Ardsley Partners Fund II, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) x (b) ¨
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES			¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0%
12	TYPE OF REPORTING PERSON PN

CUSIP No. 00504W308

13G/A

Page 3 of 10 Pages

1	NAME OF REPORTING PERSON Ardsley Partners Institutional Fund, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) x (b) ¨
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES			¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0%
12	TYPE OF REPORTING PERSON PN

CUSIP No. 00504W308

13G/A

Page 4 of 10 Pages

1	NAME OF REPORTING PERSON Ardsley Partners Renewable Energy Fund, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) x (b) ¨
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES			¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0%
12	TYPE OF REPORTING PERSON PN

CUSIP No. 00504W308

13G/A

Page 5 of 10 Pages

1	NAME OF REPORTING PERSON Ardsley Advisory Partners
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) x (b) ¨
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION New York
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES			¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0%
12	TYPE OF REPORTING PERSON PN; IA

CUSIP No. 00504W308

13G/A

Page 6 of 10 Pages

1	NAME OF REPORTING PERSON Ardsley Partners I
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) x (b) ¨
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION New York
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES			¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0%
12	TYPE OF REPORTING PERSON PN

CUSIP No. 00504W308

13G/A

Page 7 of 10 Pages

1	NAME OF REPORTING PERSON Philip J. Hempleman
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP		(a) x (b) ¨
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION United States
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER 0
	6	SHARED VOTING POWER 0
	7	SOLE DISPOSITIVE POWER 0
	8	SHARED DISPOSITIVE POWER 0
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 0
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES			¨
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 0.0%
12	TYPE OF REPORTING PERSON IN

CUSIP No. 00504W308

13G/A

Page 8 of 10 Pages

Item 1(a).	NAME OF ISSUER

	The name of the issuer is Active Power, Inc. (the "Company").

Item 1(b).	ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES

	The Company's principal executive offices are located 2128 W. Braker Lane, BK12, Austin, Texas 78758.

Item 2(a).	NAME OF PERSON FILING
	This statement is filed by:

	(i)	Ardsley Partners Fund II, L.P., a Delaware limited partnership ("AP II"), with respect to the shares of common stock, par value $0.001 per share ("Common Stock") directly owned by it;

	(ii)	Ardsley Partners Institutional Fund, L.P., a Delaware limited partnership ("Ardsley Institutional"), with respect to the shares of Common Stock directly owned by it;

	(iii)	Ardsley Partners Renewable Energy Fund, L.P., a Delaware limited partnership ("Ardsley Energy"), with respect to the shares of Common Stock directly owned by it;

	(iv)	Ardsley Advisory Partners, a New York general partnership ("Ardsley") which serves as Investment Adviser of AP II, Ardsley Institutional, Ardsley Energy and a certain managed account, with respect to the shares of Common Stock directly owned by AP II, Ardsley Institutional, Ardsley Energy and the managed account;

	(v)	Ardsley Partners I, a New York general partnership ("Ardsley Partners") which serves as General Partner of AP II, Ardsley Institutional and Ardsley Energy, with respect to the shares of Common Stock owned by AP II, Ardsley Institutional and Ardsley Energy; and

	(viii)	Philip J. Hempleman ("Mr. Hempleman"), the Managing Partner of Ardsley and Ardsley Partners, with respect to the shares of Common Stock owned by AP II, Ardsley Institutional, Ardsley Energy and the managed account.

	The foregoing persons are hereinafter sometimes collectively referred to as the "Reporting Persons." Any disclosures herein with respect to persons other than the Reporting Persons are made on information and belief after making inquiry to the appropriate party. The filing of this statement should not be construed as an admission that any of the Reporting Persons is, for the purposes of Section 13G of the Act, the beneficial owner of the shares of Common Stock reported herein.

Item 2(b).	ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE

	The address of the business office of each of the Reporting Persons is 262 Harbor Drive, Stamford, Connecticut 06902.

Item 2(c).	CITIZENSHIP

	AP II, Ardsley Institutional and Ardsley Energy are Delaware limited partnerships. Ardsley and Ardsley Partners are New York general partnerships. Mr. Hempleman is a United States citizen.

CUSIP No. 00504W308

13G/A

Page 9 of 10 Pages

Item 2(d).	TITLE OF CLASS OF SECURITIES

	Common Stock, par value $0.001 per share.

Item 2(e).	CUSIP NUMBER

	00504W308
Item 3.	IF THIS STATEMENT IS FILED PURSUANT TO Rules 13d-1(b), OR 13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A:

(a)	¨	Broker or dealer registered under Section 15 of the Act;
(b)	¨	Bank as defined in Section 3(a)(6) of the Act;
(c)	¨	Insurance company as defined in Section 3(a)(19) of the Act;
(d)	¨	Investment company registered under Section 8 of the Investment Company Act of 1940;
(e)	¨	An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);
(f)	¨	An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);
(g)	¨	A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);
(h)	¨	A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act;
(i)	¨	A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act;
(j)	¨	A non-U.S. institution in accordance with Rule 13d-1(b)(1)(ii)(J);
(k)	¨	Group, in accordance with Rule 13d-1(b)(1)(ii)(K).

If filing as a non-U.S. institution in accordance with Rule 13d-1(b)(1)(ii)(J), please

specify the type of institution: ________________________________________

Item 4.	OWNERSHIP
	The information required by Items 4(a) - (c) is set forth in Rows 5 - 11 of the cover page for each Reporting Person hereto and is incorporated herein by reference for each Reporting Person.

Item 5.	OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

CUSIP No. 00504W308

13G/A

Page 10 of 10 Pages

	If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than 5 percent of the class of securities, check the following [X]
Item 6.	OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

	Not applicable.

Item 7.	IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY OR CONTROL PERSON

	Not applicable.

Item 8.	IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

	Not applicable.

Item 9.	NOTICE OF DISSOLUTION OF GROUP

	Not applicable.

Item 10.

CERTIFICATION

	Each of the Reporting Persons hereby makes the following certification:

	By signing below each Reporting Person certifies that, to the best of his or its knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

CUSIP No. 00504W308

13G/A

Page 11 of Pages

SIGNATURES

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

DATE: February 14, 2014

	ARDSLEY PARTNERS FUND II, L.P.
	BY: ARDSLEY PARTNERS I,
	GENERAL PARTNER

	BY: /s/ Steve Napoli
	Steve Napoli
	General Partner


	ARDSLEY PARTNERS INSTITUTIONAL FUND, L.P.
	BY: ARDSLEY PARTNERS I,
	GENERAL PARTNER

	BY: /s/ Steve Napoli
	Steve Napoli
	General Partner


	ARDSLEY PARTNERS RENEWABLE ENERGY FUND, L.P.
	BY: ARDSLEY PARTNERS I,
	GENERAL PARTNER

	BY: /s/ Steve Napoli
	Steve Napoli
	General Partner


	ARDSLEY OFFSHORE FUND, LTD.

	BY: /s/ Steve Napoli
	Steve Napoli
	Director


	ARDSLEY RENEWABLE ENERGY OFFSHORE FUND, LTD.

	BY: /s/ Steve Napoli
	Steve Napoli
	Director

CUSIP No. 00504W308

13G/A

Page 12 of Pages

	ARDSLEY ADVISORY PARTNERS

	BY: /s/ Steve Napoli
	Steve Napoli
	Partner


	ARDSLEY PARTNERS I

	BY: /s/ Steve Napoli
	Steve Napoli
	General Partner


	PHILIP J. HEMPLEMAN, INDIVIDUALLY

	BY: /s/ Steve Napoli*
	Steve Napoli
	As attorney in fact for
	Philip J. Hempleman

* Evidence of Power of Attorney was filed with the Schedule 13G/A filed on February 15, 2006 (Acc-no: 0000902664-06-000895) and is incorporated by reference into this filing.