SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  Schedule 13G
                                 (Rule 13d-102)

     INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULES 13d-1
       (b), (c) AND (d) AND AMENDMENTS THERETO FILED PURSUANT TO 13d-2 (b)
                             (Amendment No._______)*


                               Active Power, Inc.
- --------------------------------------------------------------------------------
                                (Name of Issuer)


                                  Common Stock
- --------------------------------------------------------------------------------
                         (Title of Class of Securities)


                                    00504W100
- --------------------------------------------------------------------------------
                                 (CUSIP Number)


                                December 31, 2000
- --------------------------------------------------------------------------------
             (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)

     [ ] Rule 13d-1(c)

     [X] Rule 13d-1(d)

*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
disclosures provided in a prior cover page.

The information required on 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).


                         (Continued on following pages)


                                  Page 1 of 15
                            Exhibit Index on Page 13





- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 2 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Austin Ventures IV-A, L.P. ("AV IV-A")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                883,644 shares, except that AV Partners IV,
      OWNED BY EACH                L.P. ("AVP IV"), the general partner of AV
        REPORTING                  IV-A, may be deemed to have sole power to
          PERSON                   vote these shares, and Joseph C. Aragona
           WITH                    ("Arogona"), Kenneth P. DeAngelis
                                   ("DeAngelis"), Jeffery C. Garvey ("Garvey)
                                   and William P. Wood ("Wood"), the general
                                   partners of AVP IV, may be deemed to have
                                   shared power to vote these shares.
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   See response to row 5.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   883,644 shares, except that AVP IV, the
                                   general partner of AV IV-A, may be deemed to
                                   have sole power to dispose of these shares,
                                   and Aragona, DeAngelis, Garvey and Wood, the
                                   general partners of AVP IV, may be deemed to
                                   have shared power to dispose of these shares.
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   See response to row 7.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                               883,644
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 2.28%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    PN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 3 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Austin Ventures IV-B, L.P. ("AV IV-B")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                1,853,881 shares, except that AVP IV, the
      OWNED BY EACH                general partner of AV IV-B, may be deemed to
        REPORTING                  have sole power to vote these shares, and
          PERSON                   Aragona, DeAngelis, Garvey and Wood, the
           WITH                    general partners of AVP IV, may be deemed to
                                   have shared power to vote these shares.
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   See response to row 5.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   1,853,881 shares, except that AVP IV, the
                                   general partner of AV IV-B, may be deemed to
                                   have sole power to dispose of these shares,
                                   and Aragona, DeAngelis, Garvey and Wood, the
                                   general partners of AVP IV, may be deemed to
                                   have shared power to dispose of these shares.
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   See response to row 7.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                             1,853,881
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 4.78%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    PN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 4 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           AV Partners IV, L.P. ("AVP IV")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                2,737,525 shares, of which 883,644 are
      OWNED BY EACH                directly owned by AV IV-A and 1,853,881 are
        REPORTING                  directly owned by AV IV-B. AVP IV, the
          PERSON                   general partner of AV IV-A and AV IV-B, may
           WITH                    be deemed to have sole power to vote these
                                   shares, and Aragona, DeAngelis, Garvey and
                                   Wood, the general partners of AVP IV, may be
                                   deemed to have shared power to vote these
                                   shares.
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   See response to row 5.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. AVP IV, the
                                   general partner of AV IV-A and AV IV-B, may
                                   be deemed to have sole power to dispose of
                                   these shares, and Aragona, DeAngelis, Garvey
                                   and Wood, the general partners of AVP IV, may
                                   be deemed to have shared power to dispose of
                                   these shares.
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   See response to row 7.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                             2,737,525
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 7.05%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    PN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 5 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Joseph C. Aragona ("Aragona")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     U.S. Citizen
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                0 shares
      OWNED BY EACH
        REPORTING
          PERSON
           WITH
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. Aragona is a
                                   general partner of AVP IV, the general
                                   partner of AV IV-A and AV IV-B, and may be
                                   deemed to have shared power to vote these
                                   shares.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   0 shares
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. Aragona is a
                                   general partner of AVP IV, the general
                                   partner of AV IV-A and AV IV-B, and may be
                                   deemed to have shared power to dispose of
                                   these shares.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                             2,737,525
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 7.05%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    IN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 6 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Kenneth P. DeAngelis ("DeAngelis")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     U.S. Citizen
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                0 shares
      OWNED BY EACH
        REPORTING
          PERSON
           WITH
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. DeAngelis is a
                                   general partner of AVP IV, the general
                                   partner of AV IV-A and AV IV-B, and may be
                                   deemed to have shared power to vote these
                                   shares.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   0 shares
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. DeAngelis is a
                                   general partner of AVP IV, the general
                                   partner of AV IV-A and AV IV-B, and may be
                                   deemed to have shared power to dispose of
                                   these shares.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                             2,737,525
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 7.05%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    IN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 7 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           Jeffery C. Garvey ("Garvey")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     U.S. Citizen
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                0 shares
      OWNED BY EACH
        REPORTING
          PERSON
           WITH
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. Garvey is a
                                   general partner of AVP IV, the general
                                   partner of AV IV-A and AV IV-B, and may be
                                   deemed to have shared power to vote these
                                   shares.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   0 shares
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. Garvey is a
                                   general partner of AVP IV, the general
                                   partner of AV IV-A and AV IV-B, and may be
                                   deemed to have shared power to dispose of
                                   these shares.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                             2,737,525
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 7.05%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    IN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




- -------------------------                              -------------------------
CUSIP NO. 00504W100                    13G                   Page 8 of 15
- -------------------------                              -------------------------


- --------------------------------------------------------------------------------
1    NAME OF REPORTING
     SS OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
           William P. Wood ("Wood")
           Tax ID Number:
- --------------------------------------------------------------------------------
2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                     (a) [ ]   (b) [X]
- --------------------------------------------------------------------------------
3    SEC USE ONLY


- --------------------------------------------------------------------------------
4    CITIZENSHIP OR PLACE OF ORGANIZATION

     U.S. Citizen
- --------------------------------------------------------------------------------
        NUMBER OF             5    SOLE VOTING POWER
          SHARES
       BENEFICIALLY                27,581 shares, of which 1,577 are directly
      OWNED BY EACH                owned by Wood and 26,004 shares are directly
        REPORTING                  owned by Silverton Partners, L.P.
          PERSON                   ("Silverton"), a Texas limited partnership,
           WITH                    and Wood, the sole general partner of
                                   Silverton, may be deemed to have sole power
                                   to vote these shares.
                              --------------------------------------------------
                              6    SHARED VOTING POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. Wood is a general
                                   partner of AVP IV, the general partner of AV
                                   IV-A and AV IV-B, and may be deemed to have
                                   shared power to vote these shares.
                              --------------------------------------------------
                              7    SOLE DISPOSITIVE POWER

                                   27,581 shares, of which 1,577 are directly
                                   owned by Wood and 26,004 shares are directly
                                   owned by Silverton, and Wood, the sole
                                   general partner of Silverton, may be deemed
                                   to have sole power to dispose of these
                                   shares.
                              --------------------------------------------------
                              8    SHARED DISPOSITIVE POWER

                                   2,737,525 shares, of which 883,644 are
                                   directly owned by AV IV-A and 1,853,881 are
                                   directly owned by AV IV-B. Wood is a general
                                   partner of AVP IV, the general partner of AV
                                   IV-A and AV IV-B, and may be deemed to have
                                   shared power to dispose of these shares.
- --------------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                                                             2,765,106
- --------------------------------------------------------------------------------
10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                   [ ]
- --------------------------------------------------------------------------------
11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

                                                                 7.12%
- --------------------------------------------------------------------------------
12   TYPE OF REPORTING PERSON*

                                                                    IN
- --------------------------------------------------------------------------------

                     * SEE INSTRUCTIONS BEFORE FILLING OUT!




                                                                    Page 9 of 15


ITEM 1(A). NAME OF ISSUER

           Active Power, Inc.


ITEM 1(B). ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES

           11525 Stonehollow Drive
           Suite 110
           Austin, TX 78758


ITEM 2(A). NAME OF PERSONS FILING

           This  Statement is filed by Austin  Ventures  IV-A,  L.P., a Delaware
           limited  partnership  ("AV  IV-A"),  Austin  Ventures  IV-B,  L.P., a
           Delaware  limited  partnership  ("AV IV-B"),  AV Partners IV, L.P., a
           Delaware   limited   partnership   ("AVP  IV"),   Joseph  C.  Aragona
           ("Arogona"),  Kenneth P. DeAngelis  ("DeAngelis"),  Jeffery C. Garvey
           ("Garvey) and William P. Wood ("Wood"),  the general  partners of AVP
           IV. The foregoing entities and individuals are collectively  referred
           to as the "Reporting Persons."

           AVP IV, the general  partner of AV IV-A and AV IV-B, may be deemed to
           have sole  power to vote and sole  power to  dispose of shares of the
           issuer  directly  owned by AV IV-A and AV IV-B.  Aragona,  DeAngelis,
           Garvey and Wood are  general  partners of AVP IV and may be deemed to
           have  shared  power to vote and shared  power to dispose of shares of
           the issuer directly owned by AV IV-A and AV IV-B.


ITEM 2(B). ADDRESS OF PRINCIPAL OFFICE

           The address for each of the Reporting Persons is:

           Austin Ventures
           701 N. Brazos St., Suite 1400
           Austin, Texas 78701


ITEM 2(C) CITIZENSHIP

           AV  IV-A,  AV IV-B  and AVP IV,  are  Delaware  limited  partnerships
           Aragona, DeAngelis, Garvey and Wood are United States citizens.


ITEM 2(D) AND (E). TITLE OF CLASS OF SECURITIES AND CUSIP NUMBER

           Common Stock
           CUSIP # 00504W100


ITEM 3.    Not Applicable

ITEM 4.    OWNERSHIP

           The following information with respect to the ownership of the Common
           Stock of the issuer by the persons  filing this Statement is provided
           as of December 31, 2000:

               (a) Amount beneficially owned:

                   See Row 9 of cover page for each Reporting Person.

               (b) Percent of Class:






                                                                   Page 10 of 15


                   See Row 11 of cover page for each Reporting Person.

               (c) Number of shares as to which such person has:

                       (i)     Sole power to vote or to direct the vote:

                               See  Row  5 of  cover  page  for  each  Reporting
                               Person.

                       (ii)    Shared power to vote or to direct the vote:

                               See  Row  6 of  cover  page  for  each  Reporting
                               Person.

                       (iii)   Sole   power  to   dispose   or  to  direct   the
                               disposition of:

                               See  Row  7 of  cover  page  for  each  Reporting
                               Person.

                       (iv)    Shared   power  to   dispose  or  to  direct  the
                               disposition of:

                               See  Row  8 of  cover  page  for  each  Reporting
                               Person.


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

           Not applicable.


ITEM 6.    OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON.

           Under  certain  circumstances  set forth in the  limited  partnership
           agreements  of AV IV-A,  AV IV-B and AVP IV, the  general and limited
           partners of each of such  entities may be deemed to have the right to
           receive  dividends  from, or the proceeds from, the sale of shares of
           the issuer owned by each such entity of which they are a partner.


ITEM 7.    IDENTIFICATION  AND  CLASSIFICATION  OF THE SUBSIDIARY WHICH ACQUIRED
           THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY

           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.

           Not applicable





                                                                   Page 11 of 15


                                   SIGNATURES

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

Date:  February 14, 2001


                                  AUSTIN VENTURES IV-A, L.P., a Delaware Limited
                                  Partnership

                                  By: AV Partners IV, L.P., a Delaware Limited
                                      Partnership
                                      Its General Partner


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis
                                      General Partner



                                  AUSTIN VENTURES IV-B, L.P., a Delaware Limited
                                  Partnership

                                  By: AV Partners IV, L.P., a Delaware Limited
                                      Partnership
                                      Its General Partner


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis
                                      General Partner



                                  AV PARTNERS IV, L.P.., a Delaware Limited
                                  Partnership


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis
                                      General Partner






                                                                   Page 12 of 15


                                  JOSEPH C. ARAGONA


                                  By: /s/ Joseph C. Aragona
                                      ------------------------------------------
                                      Joseph C. Aragona



                                  KENNETH P. DeANGELIS


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis



                                  JEFFERY C. GARVEY


                                  By: /s/ Jeffery C. Garvey
                                      ------------------------------------------
                                     Jeffery C. Garvey



                                  WILLIAM P. WOOD


                                  By: /s/ William P. Wood
                                      ------------------------------------------
                                      William P. Wood






                                                                   Page 13 of 15


                                  EXHIBIT INDEX


                                                                   Found on
                                                                 Sequentially
Exhibit                                                          Numbered Page
- -------                                                          -------------
Exhibit A:  Agreement of Joint Filing                                 14






                                                                   Page 14 of 15


                                    EXHIBIT A

                            Agreement of Joint Filing

         The  undersigned  hereby  agree  that a  single  Schedule  13G  (or any
amendment  thereto)  relating to the Common Stock of Active Power, Inc. shall be
filed on behalf of each of the  undersigned  and that  this  Agreement  shall be
filed as an exhibit to such Schedule 13G.

Date:  February 14, 2001


                                  AV PARTNERS IV, L.P.,
                                  a Delaware Limited Partnership


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis, General Partner



                                  AUSTIN VENTURES IV-A, L.P.,
                                  a Delaware Limited Partnership

                                  By: AV Partners IV, L.P.,
                                      a Delaware Limited Partnership
                                      Its General Partner


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis, General Partner



                                  AUSTIN VENTURES IV-B, L.P.,
                                   a Delaware Limited Partnership

                                  By: AV Partners IV, L.P.,
                                      a Delaware Limited Partnership
                                      Its General Partner

p
                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis, General Partner


                                  By: /s/ Joseph C. Aragona
                                      ------------------------------------------
                                      Joseph C. Aragona





                                                                   Page 15 of 15


                                  By: /s/ Kenneth P. DeAngelis
                                      ------------------------------------------
                                      Kenneth P. DeAngelis


                                  By: /s/ Jeffery C. Garvey
                                      ------------------------------------------
                                     Jeffery C. Garvey


                                  By: /s/ William P. Wood
                                      ------------------------------------------
                                      William P. Wood