PURCHASE MONEY
                         PROMISSORY NOTE


June 25, 1997
Minneapolis, Minnesota                                 $2,700,000


    FOR VALUE RECEIVED, NRG San Diego, Inc., a Delaware corporation (the 
"Debtor"), hereby promises to pay to the order of Ridgewood Electric Power 
Trust II, a Delaware business trust, or its assigns (the "Holder"), the 
principal sum of Two Million Seven Hundred Thousand and no/100s Dollars 
($2,700,000.00), together with interest, in the manner provided herein.  
All principal and interest amounts due under this Note are referred to 
herein as the "Obligations" and are subject to the provisions of this Note. 

Payment of Principal and Interest

    1.   Debtor shall pay the principal, together with interest thereon at 
an interest rate of eight percent (8%) in 72 consecutive equal monthly 
installments of Forty-Seven Thousand Three Hundred Thirty Nine and 75/100 
Dollars ($47,339.75) commencing on July 25, 1997 and on the 25th day of 
each month thereafter through and including June 25, 2003.

Acceleration

    2.   Upon the occurrence of any Event of Default,  Holder may, at its 
election, by written notice to Debtor declare all Obligations that are past 
due or are to become due to become immediately due and payable, whereupon 
the same shall become due and payable without further notice or demand.

Event of Default

    3.   For purposes of this Note, an Event of Default shall mean: 

         (a)  the failure by Debtor to make any payment of principal or 
interest required hereunder and such default is not cured within thirty 
(30) days after notice of such default has been delivered to Debtor in 
accordance with the provisions hereof; 

         (b)  Debtor's failure to generally pay its debts as such debts 
become due, or its admission in writing of its insolvency or its inability 
to pay its debts generally, or the making of a general assignment for the 
benefit of creditors; 

         (c)  the initiation of any proceeding by or against the Debtor 
seeking to adjudicate the Debtor a bankrupt or insolvent, or seeking 
liquidation, winding up, reorganization, arrangement, adjustment, 
custodianship, protection, relief, or composition of the Debtor or the 
Debtor's debts under any now existing or future applicable law relating to 
bankruptcy, insolvency or reorganization or relief of debtors, or seeking 
the entry of an order for relief, or the appointment of a receiver, 
custodian, trustee, sequestrator, assignee, or other similar official for 
such party or for any substantial part of such party's property, except 
that if such proceeding is instituted involuntarily against the Debtor, an 
Event of Default will occur only if the proceeding has not been dismissed 
within sixty (60) days of the commencement of such     proceeding; 

         (d)  the Debtor's action to authorize any of the actions set forth 
in (b) or (c) above; 

         (e)  the occurrence and continuance of a Default under the 
Security and Pledge Agreement of even date herewith between Debtor, NRG del 
Coronado, Inc., a Delaware corporation ("NRGdC") and Holder (the "Security 
and Pledge Agreement"); or

         (f)  sale, transfer or other disposition of the majority of the 
stock or assets of Debtor or assets of San Diego Power & Cooling Company to 
any person or entity which is not, directly or indirectly through one or 
more intermediaries, controlled by or under common control with NRG Energy, 
Inc., a Delaware corporation. 
    
Prepayment

    4.   This Note shall be subject to prepayment at any time, without 
premium or penalty.

General

    5.   The indebtedness evidenced by this Note is secured by the Security 
and Pledge Agreement.

    6.   Debtor hereby:

         (a)  waives diligence, presentment, demand for payment, notice of 
dishonor, notice of non-payment, protest, notice of protest, and any and 
all other demands in connection with the delivery, acceptance, performance, 
default or enforcement of this Note;

         (b)  agrees that Holder shall have the right, without notice, to 
grant any extension of time for payment of any indebtedness evidenced by 
this Note or any other indulgence or forbearance whatsoever;

         (c)  agrees that no failure on the part of Holder to exercise any 
power, right or privilege hereunder, or to insist upon prompt compliance 
with the terms of this Note shall constitute a waiver of that power, right 
or privilege; and

         (d)  agrees that the acceptance at any time by Holder of any past 
due amounts shall not be deemed to be a waiver of the requirement to make 
prompt payment when due of any other amounts then or hereafter due and 
payable.

    7.   The payment obligations of Debtor hereunder are subject to the 
set-off rights described in the Partnership Interest Purchase Agreement, 
dated the date hereof, by and among Debtor, NRGdC, Holder and RSD Power 
Corp., a Delaware corporation.

    8.   This Note shall be governed in all respects by the laws of the 
State of Minnesota without giving effect to the principles of conflicts of 
law. 

    9.   In the event that Debtor defaults in the payment of any Obligation 
due hereunder, Debtor shall pay Holder's out-of-pocket collection costs, 
including without limitation reasonable attorneys' fees and legal costs, 
whether or not any suit or enforcement proceeding is commenced. 

                             NRG SAN DIEGO, INC.

                             By:_____________________________
                              Its:_____________________________