[LOGO]                          45 FIRST AVENUE, WALTHAM, MA 02454


                                                                          , 1999

Dear Stockholder:

    I am pleased to invite you to a Special Meeting of the stockholders of
Thermo Power Corporation ("Thermo Power") at which you will be asked to approve
an Agreement and Plan of Merger (the "Merger Agreement") dated as of May 5, 1999
among Thermo Power, Thermo Electron Corporation, the parent company of Thermo
Power ("Thermo Electron"), and TP Acquisition Corporation, a newly-formed
subsidiary of Thermo Electron (the "Merger Sub"). The Special Meeting will take
place at 10:00 a.m. on                 , 1999 at the executive offices of Thermo
Electron, 81 Wyman Street, Waltham, Massachusetts 02454.


    Under the terms of the Merger Agreement, the Merger Sub would merge with and
into Thermo Power, with Thermo Power being the surviving corporation (the
"Merger"). Each issued and outstanding share of Thermo Power common stock (other
than shares held by Thermo Electron and stockholders who properly dissent under
Massachusetts law) would be converted into the right to receive $12.00 in cash.
Thermo Power would become a private company and a wholly owned subsidiary of
Thermo Electron. The Merger is more fully described in the Merger Agreement,
which is attached as Appendix A to the enclosed Proxy Statement. If you choose
to dissent from the Merger and wish to seek appraisal of the fair value of your
stock, please refer to the sections of the Proxy Statement regarding the rights
of dissenting stockholders under Massachusetts law.


    A special committee of Thermo Power's Board of Directors (the "Special
Committee"), acting in the interests of the stockholders of Thermo Power other
than Thermo Electron and the officers and directors of each of Thermo Power and
Thermo Electron (the "Public Stockholders"), evaluated the merits of, and
negotiated the terms of, the Merger. The Special Committee received an opinion
from its financial advisor, Invemed Associates LLC, as to the fairness of the
Merger from a financial point of view to the Public Stockholders. The Special
Committee recommended that Thermo Power's Board of Directors approve the Merger
Agreement. Please read carefully the written opinion of Invemed Associates LLC,
dated May 4, 1999, which is attached as Appendix B to the enclosed Proxy
Statement.


    Thermo Power's Board of Directors believes the Merger is fair to the Public
Stockholders and unanimously 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, stockholders should be aware
that six of the eight members of Thermo Power's Board of Directors are either
directors of Thermo Electron or employees of Thermo Electron or its subsidiaries
and thus have interests that are in addition to, or different from, your
interests as stockholders of Thermo Power.


    Massachusetts law requires the affirmative vote of the holders of two-thirds
of the outstanding shares of Thermo Power common stock entitled to vote at the
Special Meeting in order for the Merger Agreement to be approved. Thermo
Electron, which owns approximately 78% of Thermo Power's outstanding common
stock, intends to vote its shares in favor of approving the Merger Agreement,
thus assuring that the Merger Agreement will be approved. Only stockholders of
record at the close of business on                 , 1999 will receive notice of
and be able to vote at the Special Meeting or any adjournment or adjournments
thereof.

    The accompanying Proxy Statement provides you with a summary of the Merger
and additional information about the parties involved and their interests.
Please give all this information your careful attention. You can also obtain
other information about Thermo Power and Thermo Electron from documents filed
with the Securities and Exchange Commission.

    WHETHER OR NOT YOU PLAN TO ATTEND THE SPECIAL MEETING, PLEASE TAKE THE TIME
TO VOTE BY COMPLETING AND MAILING THE ENCLOSED PROXY CARD TO US TODAY. IF YOU
DATE, SIGN AND MAIL YOUR PROXY CARD WITHOUT INDICATING

HOW YOU WISH TO VOTE, YOUR PROXY WILL BE COUNTED AS A VOTE IN FAVOR OF THE
MERGER AGREEMENT. YOUR VOTE IS VERY IMPORTANT, REGARDLESS OF THE NUMBER OF
SHARES THAT YOU OWN.

    Your Board of Directors believes that the transaction with Thermo Electron
is in the best interests of Thermo Power and its Public Stockholders and has
unanimously approved it. Your Board of Directors unanimously recommends that
stockholders vote for approval of the Merger Agreement. On behalf of the Board
of Directors, I urge you to sign, date and return the enclosed proxy today.

    Please do not send any stock certificates to us now. Assuming the Merger
Agreement is approved, we will send you instructions concerning the surrender of
your shares.

    Thank you for your interest and participation.


                             
                                Yours very truly,

                                /s/ J. TIMOTHY CORCORAN
                                ------------------------------------------
                                J. Timothy Corcoran
                                PRESIDENT AND CHIEF EXECUTIVE OFFICER