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.