[LOGO]                          45 FIRST AVENUE, WALTHAM, MA 02454


                           NOTICE OF SPECIAL MEETING

                                                                          , 1999

TO THE HOLDERS OF THE COMMON STOCK OF
THERMO POWER CORPORATION

    I am pleased to give you notice of and cordially invite you to attend in
person or by proxy the Special Meeting of the stockholders of Thermo Power
Corporation, a Massachusetts corporation (the "Company" or "Thermo Power"),
which will be held on       , at 10:00 a.m., at the executive offices of Thermo
Electron Corporation ("Thermo Electron"), 81 Wyman Street, Waltham,
Massachusetts 02454, and at any adjournment or adjournments thereof (the
"Special Meeting"). At the Special Meeting, stockholders will:

    1.  Consider and vote on a proposal to approve an Agreement and Plan of
       Merger dated as of May 5, 1999 (the "Merger Agreement") pursuant to which
       TP Acquisition Corporation, a newly-formed subsidiary of Thermo Electron
       (the "Merger Sub"), would be merged with and into Thermo Power (the
       "Merger"). Upon the Merger, each stockholder of the Company (other than
       stockholders who perfect their dissenters' rights and Thermo Electron)
       would become entitled to receive $12.00 in cash, without interest, for
       each outstanding share of common stock, $.10 par value, of the Company
       (the "Common Stock") owned by such stockholder immediately prior to the
       effective time of the Merger. A copy of the Merger Agreement is attached
       as Appendix A to, and is described in, the accompanying Proxy Statement.

    2.  Transact such other business as may properly come before the Special
       Meeting.

    Only stockholders of record at the close of business on             , 1999
will receive notice of and be able to vote at the Special Meeting.

    The accompanying Proxy Statement describes the Merger Agreement, the
proposed Merger and the actions to be taken in connection with the Merger. The
Company's by-laws require that the holders of a majority of the outstanding
shares of Common Stock entitled to vote be present or represented by proxy at
the Special Meeting in order to constitute a quorum for the transaction of
business. It is important that your shares be represented at the Special Meeting
regardless of the number of shares you hold. Whether or not you are able to be
present in person, please sign and return promptly the enclosed Proxy Card in
the accompanying envelope, which requires no postage if mailed in the United
States. You may revoke your proxy in the manner described in the accompanying
Proxy Statement at any time before it is voted at the Special Meeting.


    Stockholders who properly demand appraisal prior to the stockholder vote at
the Special Meeting, who do not vote in favor of approval of the Merger
Agreement and who otherwise comply with the provisions of Sections 85 through
98, inclusive, of the Massachusetts Business Corporation Law (the "MBCL") will
be entitled, if the Merger is completed, to statutory appraisal of the fair
value of their shares of Common Stock. See "RIGHTS OF DISSENTING STOCKHOLDERS"
in the accompanying Proxy Statement and the full text of Sections 85 through 98,
inclusive, of the MBCL, which is attached as Appendix C to, and is described in,
the accompanying Proxy Statement, for a description of the procedures that you
must follow in order to exercise your appraisal rights.


    This Notice, the Proxy Card and Proxy Statement enclosed herewith are sent
to you by order of the Board of Directors.

                                          SANDRA L. LAMBERT
                                          CLERK


    WHETHER OR NOT YOU PLAN TO ATTEND, IT IS IMPORTANT THAT YOUR SHARES ARE
REPRESENTED AT THE SPECIAL MEETING. TO APPROVE THE MERGER AGREEMENT, THE
AFFIRMATIVE VOTE OF THE HOLDERS OF TWO-THIRDS OF THE OUTSTANDING SHARES OF
COMMON STOCK ENTITLED TO VOTE THEREON IS REQUIRED. YOU ARE REQUESTED TO PROMPTLY
COMPLETE, SIGN AND DATE THE ENCLOSED PROXY CARD AND RETURN IT IN THE ENVELOPE
PROVIDED. YOU MAY REVOKE YOUR PROXY AT ANY TIME PRIOR TO ITS EXERCISE IN THE
MANNER DESCRIBED IN THE ATTACHED PROXY STATEMENT. ANY STOCKHOLDER PRESENT AT THE
SPECIAL MEETING MAY REVOKE SUCH HOLDER'S PROXY AND VOTE PERSONALLY ON THE MERGER
AGREEMENT AT THE SPECIAL MEETING.


    THE BOARD OF DIRECTORS RECOMMENDS THAT STOCKHOLDERS VOTE "FOR" APPROVAL OF
THE MERGER AGREEMENT. IN CONSIDERING THE RECOMMENDATION OF THE BOARD OF
DIRECTORS WITH RESPECT TO THE MERGER AGREEMENT, THE STOCKHOLDERS OF THE COMPANY
OTHER THAN THERMO ELECTRON AND THE DIRECTORS AND OFFICERS OF EACH OF THE COMPANY
AND THERMO ELECTRON (THE "PUBLIC STOCKHOLDERS") SHOULD BE AWARE THAT CERTAIN
OFFICERS AND DIRECTORS OF THE COMPANY HAVE CERTAIN INTERESTS THAT ARE IN
ADDITION TO, OR DIFFERENT FROM, THE INTERESTS OF THE PUBLIC STOCKHOLDERS. SEE
"SPECIAL FACTORS--CONFLICTS OF INTEREST."

    IF A PROPERLY EXECUTED PROXY CARD IS SUBMITTED AND NO INSTRUCTIONS ARE
GIVEN, THE SHARES OF COMMON STOCK REPRESENTED BY THAT PROXY WILL BE VOTED "FOR"
APPROVAL OF THE MERGER AGREEMENT.

    PLEASE DO NOT SEND YOUR STOCK CERTIFICATES TO THE COMPANY AT THIS TIME.