EXHIBIT 10.104

                                 PROMISSORY NOTE

Amount:     $48,575.00                                  Date: September 9, 1997

         For value received, I, Robert I. Weisberg (the "Maker"), a Director of
Environmental Power Corporation, a Delaware corporation (the "Company"), hereby
promise to pay the Company ON DEMAND the principal amount of Forty-Eight
Thousand Five Hundred Seventy-Five Dollars & 00/100 ($48,575.00) with interest
(computed on the basis of a 360 day year of twelve 30-day months) payable from
the date hereof on the unpaid balance of such principal amount, such interest to
be payable monthly.

         The interest payable on this Note shall track the Applicable Federal
"short-term monthly" Rate as defined in Section 1274(d) of the Internal Revenue
Code of 1954, as amended.

         As security for payments to be made by the Maker pursuant to this Note,
the Company shall retain custody of, and a security interest in, the certificate
or certificates representing 80,000 Shares of the Company's Common Stock, such
security interest to lapse at such time as all of the obligations of the Maker
under this Note have been satisfied in full or the Note has been canceled.

         The Company shall have full recourse against the Maker for collection
and payment of the debt evidenced by this Note and may seek personal judgment
against the Maker for payment of this Note.

         All or any part of the principal and accrued interest may be prepaid at
anytime without the payment of any penalty or premium.

         In case any payment herein provided shall not be paid when due, the
Maker further promises to pay all costs at collection, including all attorney's
fees.

         This Note shall be governed by and construed in accordance with the
laws of the State of New Hampshire and shall have the effect of a sealed
instrument.

         The Maker and all endorsers and guarantors of this Note hereby waive
presentment, demand, notice of nonpayment, protest and all other demands and
notices in connection with the delivery, acceptance, performance or enforcement
of the Note.

                                      Maker

                                      /s/Robert I. Weisberg
                                      ---------------------
                                      Robert I. Weisberg