Fourth Amendment to Additional Investment Senior Secured Convertible Promissory



 Exhibit 10.1 
 EXECUTION COPY 
 FOURTH AMENDMENT TO ADDITIONAL INVESTMENT SENIOR SECURED 
 CONVERTIBLE PROMISSORY NOTES 
 FOURTH AMENDMENT TO ADDITIONAL INVESTMENT SENIOR SECURED CONVERTIBLE PROMISSORY NOTES (this “Fourth Amendment”), dated as of May 30, 2008, by and between Distributed Energy Systems Corp., a Delaware
corporation (the “Company”) and Perseus Partners VII, L.P., a Delaware limited partnership (the “Holder”). Unless otherwise indicated, all capitalized terms used herein and not otherwise defined have the
respective meanings provided such terms in the Purchase Agreement and the Notes referred to below. 
 W I T N E S S E T H:

 WHEREAS, the Company and the Holder are parties to a Securities Purchase Agreement, dated as of May 10, 2007 and amended
on March 13, 2008 (as further amended, modified and/or restated from time to time, the “Purchase Agreement”); 
 WHEREAS, under the terms of the Purchase Agreement, on March 13, 2008 the Company issued to the Holder a senior secured convertible promissory note in the principal amount of $1,500,000.00 (the “Additional Investment
Note”); 
 WHEREAS, on April 1, 2008, the Company issued to the Holder an additional senior secured convertible
promissory note in the principal amount of $9,246.58 as payment for interest due and payable on the Additional Investment Note (the “PIK Note”, and together with the Additional Investment Note, the “Notes”, and each
individually, a “Note”); 
 WHEREAS, the Company and the Holder amended certain provisions of the Notes effective
May 8, 2008 (the “First Amendment”), May 16, 2008 and May 22, 2008; and 
 WHEREAS, the Company has
requested an amendment of certain provisions of the Notes as herein provided; 
 NOW, THEREFORE, it is agreed: 
 1. Amendment of Each Note. The Holder and the Company hereby agree that as of the Fourth Amendment Effective Date (as defined below) and through
6:00 p.m. EDT on June 3, 2008, Section 4(i) of each Note is amended by: 
 (a) setting the Net Working Capital
benchmark at $1,000,000; and 
 (b) setting the unrestricted cash and cash equivalents benchmark at $2,000,000. 
 After 6:00 p.m. EDT on June 3, 2008, each benchmark will revert to the benchmark in place prior to the effective date of the First Amendment. 







 2. Representations and Warranties. The representations and warranties of the Company contained in
the Purchase Agreement or in any other Transaction Document that are qualified as to materiality are true and correct, and all other representations and warranties of the Company contained in the Purchase Agreement or in any other Transaction
Document that are not so qualified are true and correct in all material respects, in each case with the same effect as though made as of the date of this Fourth Amendment, except that the accuracy of representations and warranties that by their
terms speak as of a specified date are determined as of such date and except for matters arising after the Effective Date of the Purchase Agreement that, (A) when viewed in the aggregate, have not had and are not reasonably likely to have a
Material Adverse Effect or (B) have been disclosed in writing or electronically to the Holder or its representatives. 
 3.
GOVERNING LAW. THIS FOURTH AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE LAW OF THE STATE OF NEW YORK. 
 4. Effectiveness. This Fourth Amendment is effective upon execution of this Fourth Amendment by both Parties (the “Fourth Amendment
Effective Date”). 
 5. Waiver and Release. The Company by signing below hereby waives and releases the Holder, its
respective affiliates and its and its affiliates’ respective directors, officers, employees and attorneys from any and all claims, offsets, defenses and counterclaims of the Company arising on or prior to the date hereof in connection with any
action or inaction taken by any such Person pursuant to this Fourth Amendment, such waiver and release being with full knowledge and understanding of the circumstances and effect thereof and after having consulted legal counsel with respect thereto.

 6. Expenses. The Company hereby reconfirms its obligations under Section 8.6(a)(ii) of the Purchase Agreement to pay and
reimburse the Holder for all reasonable out-of-pocket expenses and fees and disbursements, including attorneys’ and accountants’ fees, incurred by the Holder and its representatives in connection with this Fourth Amendment. 
 7. Transaction Documents. From and after the Fourth Amendment Effective Date, all references in the Purchase Agreement and each of the other
Transaction Documents to each Note shall be deemed to be references to such Note as amended, modified and/or restated hereby. 
 8.
Counterparts. Signatures on this Fourth Amendment may be communicated by facsimile or electronic transmission and shall be binding upon the Parties so transmitting their signatures. Counterparts with original signatures shall be provided to
the other Party following the applicable facsimile or electronic transmission, provided that the failure to provide the original counterpart shall have no effect on the validity or the binding nature of this Fourth Amendment. No Party shall raise
facsimile or electronic delivery of a signature or the fact that any signature or agreement or instrument was transmitted or communicated by a facsimile or e-mail as a defense to the formation nor enforceability of a contract and each such Party
forever waives any such defense. 







 IN WITNESS WHEREOF, the Parties hereto have caused their duly authorized officers to execute and
deliver this Fourth Amendment as of the date first above written. 
  

			
	DISTRIBUTED ENERGY SYSTEMS CORP.
		
	By:	 	 /s/ Peter J. Tallian

	Name:	 	Peter J. Tallian
	Title:	 	CFO
	
	PERSEUS PARTNERS VII, L.P.
		
	By:	 	 Perseus Partners VII GP, L.P. 
 its general
partner

		
	By:	 	 Perseus Partners VII GP, L.L.C. 
 its general
partner

		
	By:	 	 /s/ Teresa Y. Bernstein

		 	Teresa Y. Bernstein
		 	Secretary