<PAGE>   1

                                                                   Exhibit 10.23

                        POWER SALES AND AGENCY AGREEMENT

      THIS POWER SALES AND AGENCY AGREEMENT (this "Agreement") is entered into
as of this 15th day of December, 1999 between NRG Power Marketing, Inc. ("Power
Marketing"), a Delaware corporation, and Middletown Power LLC, a Delaware
limited liability company (the "Owner Entity") (each individually a "Party", or
collectively the "Parties").

                                    RECITALS

      1. The Owner Entity has acquired the Middletown Generating Station located
in Middletown, Connecticut.

      2. Power Marketing has entered into a Standard Offer Service Wholesale
Sales Agreement with The Connecticut Light and Power Company (CL&P), pursuant to
which Power Marketing will supply to CL&P a specified share of a portion of
CL&P's aggregate retail load (the "Standard Offer Service Agreement").

      3. The Owner Entity wishes to retain the services of Power Marketing, as
its agent, to (i) manage, market and sell its Power (including any Power
necessary to meet the obligations of Power Marketing under the Standard Offer
Service Agreement), (ii) to manage, procure and provide, as the case may be, the
requirements of the Owner Entity for Fuel (as defined below) and to (iii)
market, sell and purchase, as the case may be, the Emission Credits (as defined
below) generated in or necessary for the conduct of the business of the Owner
Entity.

      4. Power Marketing desires to (i) manage, market and sell all of the Owner
Entity's Power (including any Power necessary to meet the obligations of Power
Marketing under the Standard Offer Service Agreement), (ii) to manage, purchase
and provide the Owner Entity's requirements for Fuel and (iii) to market, sell
and purchase, as the case may be, the Emission Credits generated in or necessary
for the conduct of the business of the Owner Entity.

                                    AGREEMENT

      In consideration of the premises and the covenants, conditions, and
agreements contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledge, the parties hereto
agree as follows:

                                    ARTICLE 1
                                   DEFINITIONS

      Whenever used in this Agreement with initial capitalization, the following
terms shall have the meanings specified or referred to in this Article 1.

      "Affiliate" means with respect to any person or entity, (i) each entity
that such person or entity Controls, (ii) each person or entity that Controls
such person or entity, and (iii) each entity that is under common Control with
such person or entity.

      "Agreement" shall have the meaning provided in the introductory paragraph
hereof.

      "All-in Fuel Cost' means, for any period, the actual cost incurred, on a
FIFO basis, by Power Marketing for any natural gas supplied by Power Marketing
to the Owner Entity during such period, including the spot or contract price
paid therefor by Power Marketing, all costs of transportation and delivery of
such gas, and all taxes paid or payable by Power Marketing in association
therewith.

      "Ancillary Services" means reserves and other ancillary services provided
for in the rules of the Power Pool.

      "Business Day" means any day other than a Saturday, a Sunday, or a holiday
on which national banking associations in Minnesota or New York are not open for
business. A Business Day shall begin at 8:00 am. and end at 5:00 p.m. Eastern
Standard (or Daylight) time.
<PAGE>   2

      "Capacity" means the aggregate installed generating capability of all of
the Units located at the Station, measured in megawatts ("MW") or kilowatts
("KW").

      "Control" means the possession, directly or indirectly, through one or
more intermediaries, of (i) in the case of a corporation, a majority of the
outstanding voting securities thereof; (ii) in the case of a limited liability
company, partnership, limited partnership or venture, the right to more than 50%
of the distributions therefrom (including liquidating distributions); (iii) in
the case of a trust or estate, including a business trust, a majority of the
beneficial interest therein; and (iv) in the case of any other entity, a
majority of the economic or beneficial interest therein.

      "Delivery Point" means the point at which the Station is connected to The
Connecticut Light and Power Company's transmission system as indicated in
Schedule A to the Interconnection Agreement or such other delivery point as
Power Marketing and the Owner Entity shall Mutually agree.

      "Dispatch" means the direction of the Power output of the Station,
including direction in accordance with instructions from the ISO.

      "Fuel" means coal, natural gas, fuel oil, petroleum and petroleum
distillates required to operate the Units.

      "Emissions Credits" means credits, in units established by applicable
regulatory authorities, resulting from the reduction of air pollutants
(including NOx and SOx) from an emitting source or facility, that have been
certified by the applicable regulatory authority.

      "Energy" means electric energy, measured in megawatt hours ("MWh") or
kilowatt hours ("KWh"), generated and deliverable by the Owner Entity.

      "Force Majeure" means an event which (i) is not within the reasonable
control of the Party claiming Force Majeure (the "Claiming Party"), (ii) was not
caused by the acts, omissions or delays of the Claiming Party or any person over
whom the Claiming Party has control, (iii) is not an act event or condition the
risks or consequences of which the Claiming Party has expressly agreed to assume
pursuant to this Agreement, and (iv) by the prompt exercise of due diligence,
the Claiming Party is unable to overcome or avoid or cause to be avoided.
Subject to the foregoing, Force Majeure includes, but is not restricted to acts
of God, fire, civil disturbance, labor dispute, labor or material shortage,
sabotage, or action or restraint by court order of any public or governmental
authority (so long as the Claiming Party has not applied for or assisted in the
application for, and has opposed where and to the extent reasonable, such
government action).

      "Good Utility Practice" means any of the practices, methods and acts
engaged in or approved by a significant portion of the electric utility industry
during the relevant time period, or any of the practices, methods and acts
which, in the exercise of reasonable judgment in light of the facts known at the
time the decision was made, could have been expected to accomplish the desired
result at the lowest reasonable cost consistent with good business practices,
reliability, safety and expedition. Good Utility Practice is not intended to be
limited to the optimum practice, method or act to the exclusion of all others,
but rather to be practices, methods or acts generally accepted in the region and
consistently adhered to by the Owner Entity. Good Utility Practices shall
include, but not be limited to North American Electric Reliability Council
("NERC") Criteria & Guidelines, Northeast Power Coordinating Council ("NPCC")
Criteria & Guidelines, and the criteria, rules and standards of the Power Pool,
as they may be amended from time to time including the rules, guidelines and
criteria of any successor organization to the foregoing entities.

      "Governmental Entity" means the government of the United States, or any
political subdivision thereof, whether state or local, and any agency,
authority, instrumentality, regulatory body or other entity exercising
executive, legislative, judicial, taxing. regulatory or administrative powers or
functions of or pertaining to government.

      "Interconnection Agreement" means the Interconnection Agreement by and
between The Connecticut Light and Power Company and NRG Energy, Inc., dated as
of July 1, 1999, entered into by Owner Entity through assignment by NRG Energy,
Inc. of NRG Energy, Inc.'s rights and obligations thereunder.


                                       2
<PAGE>   3

      "Interest Rate" means, for any date, the interest equal to the "Prime
Rate" as may be published on the first Business Day of the applicable calendar
month in The Wall Street Journal under "Money Rates."

      "ISO" means the independent system operator established to sell Power in
the market served by the Station.

      "Lead Participant" means the person responsible for bidding or scheduling
Power of the Station into the ISO and to prepare and submit such documentation
as may be required for Dispatch of the Station.

      "Net Power Revenue" means, for any period, the gross receipts during such
period from sales by Power Marketing of Station Power, including any amounts
paid to Power Marketing during such period under the Standard Offer Service
Agreement, less (i) any payments made by Power Marketing during such period to
CL&P under the Standard Offer Service Agreement, (ii) the amount of any
transmission or other costs incurred by Power Marketing during such period in
delivering Station Power to the point of sale, (iii) the amount of any state or
federal Taxes paid or required to be paid by Power Marketing with respect to the
sale of Station Power or otherwise with respect to the performance of its
obligations hereunder, and (iv) the amount of any other costs paid by Power
Marketing during such period in connection with the sale of Station Power,
including an arms-length, commercially reasonable allocation of overhead and
administrative expense.

      "Operator" means NRG Middletown Operations, Inc., a Delaware corporation,
acting in its capacity as Operator under the Operation and Maintenance
Agreement, dated the date of this Agreement, between the Owner Entity and such
Operator.

      "Power Pool" means the New England Power Pool or its successor.

      "Power" means Capacity. Energy or Ancillary Services or any combination
thereof, as the case may be.

      "Standard Offer Service Agreement" means the Standard Offer Service
Wholesale Sales Agreement dated as of October 29, 1999 by and between The
Connecticut Light and Power Company and NRG Power Marketing Inc.

      "Station" means the generating facilities acquired by the Owner Entity.

      "Station Power" means the aggregate Power generated by the Station from
time to time.

      "Taxes" means any tax, charge, impost, tariff, duty or fee of any kind
charged, imposed or levied, directly or indirectly, by any Governmental Entity,
including any value-added tax, sales tax, stamp duty, gross receipts tax,
property tax, registration fee or license, but excluding any tax on income.

      "Unit" means each of the operating electricity generating units located at
the Station.

                                    ARTICLE 2
                                  TRANSACTIONS

      2.1 Power Transactions.

            (a) Right to Power. Power Marketing shall have the exclusive right
      to take and sell, trade or otherwise deal in all of the Station Power not
      sold or committed by the Owner Entity.

            (b) Delivery of Power. Station Power shall be taken by Power
      Marketing at the Delivery Point, and the Owner Entity shall take all
      commercially reasonable efforts, in accordance with Good Utility Practice,
      to make such Power available to Power Marketing at the Delivery Point.

            (c) Lead Participant. The Owner Entity shall advise the ISO that
      Power Marketing is the Lead Participant commensurate with the term of this
      Agreement. Power Marketing may designate an agent to fulfill


                                       3
<PAGE>   4

      such role as Lead Participant; provided, however, that Power Marketing
      shall remain responsible for effecting the Dispatch of the Station.

            (d) Dispatch. Power Marketing shall have the exclusive right and the
      obligation to effect the Dispatch of the Station. Power Marketing shall
      effect such Dispatch, either for its own account or as agent for the Owner
      Entity, through bilateral and standard offer contracts, the Standard Offer
      Service Agreement and its bidding into the ISO as Lead Participant, and
      such Dispatch shall be subject to the physical limitations of the Station
      as the Owner Entity may advise the ISO or Power Marketing from time to
      time.

            (e) Standard Offer Service Agreement. Power Marketing shall perform
      all of its obligations under the Standard Offer Service Agreement, and
      assist the Owner Entity in performing all of its obligations under any
      bilateral or other power sale agreements to which it may be a party.

            (f) Metering. For the purposes of determining quantities of Power
      delivered to the Power Pool, metering shall be as provided in the
      Interconnection Agreement to which the Owner Entity is a party or Power
      Pool Agreement. All other metering of Power delivered by the Owner Entity
      pursuant to this Agreement shall be through the meters provided for in the
      Interconnection Agreement.

            (g) Auxiliary Power. Power Marketing shall be responsible for
      negotiating agreements for the provision of Power to the Station for
      auxiliary load and Station start-up as required to support the dispatch
      schedule.

      2.2 Fuel Requirements. Power Marketing shall procure for the Owner Entity
all Fuel required to operate the Units, at such time and in such amounts and
types as the Operator shall advise Power Marketing. The Owner Entity shall cause
the Operator to notify Power Marketing on a regular basis, sufficiently in
advance of the need therefor, of the Station's fuel requirements. Coal, fuel
oil, petroleum, petroleum distillates and out-state natural gas shall be
contracted for directly by the Owner Entity. Power Marketing shall purchase and
sell to the Owner Entity all in-state natural gas necessary to meet the Owner
Entity's Fuel requirements.

      2.3 Emissions Credits. The Owner Entity shall make available and transfer
to Power Marketing, as its exclusive agent, all Emissions Credits owned, earned
or acquired by the Owner Entity that are in excess of the amount of Emissions
Credits required to operate the Units at their scheduled capacity. Power
Marketing shall procure for the Owner Entity all Emissions Credits, in excess of
those generated by the Owner Entity, that are required by the Owner Entity to
operate the Units at their scheduled capacity. The Owner Entity shall cause the
Operator to notify Power Marketing on a regular basis, sufficiently in advance
of the need therefor, of the amount of any emissions Credits that Power
Marketing is to required provide pursuant to this Agreement.

                                    ARTICLE 3
                                    PAYMENTS

      3.1 Payments for Power. Power Marketing shall pay to the Owner Entity for
the amount of the Station Power provided by the Owner Entity to Power Marketing
the Net Power Revenue from the sales by Power Marketing of such Power. By no
later than the twenty-fifth (25th) day of each calendar month, Power Marketing
shall deliver an estimated statement, together with the estimated payment
required pursuant to such statement, to the Owner Entity setting forth,
separately with respect to Capacity, Energy and Ancillary Services, the
estimated Station Power provided by the Owner Entity pursuant to Dispatch
effected by Power Marketing during the preceding calendar month and the total
amount due to the Owner Entity from Power Marketing with respect thereto,
together with any applicable supporting documentation. As soon as possible with
respect to each calendar month, and in any case no later than ten (10) Business
Days after final reconciliation of such calendar month by the Power Pool, Power
Marketing shall deliver a true-up statement to the Owner Entity with respect to
such calendar month, which statement shall set forth, separately with respect to
Capacity, Energy and Ancillary Services, the actual Station Power provided by
the Owner Entity pursuant to Dispatch effected by Power Marketing. If such
true-up statement reveals a shortfall in payment by Power Marketing with respect
to such payment, such true-up statement shall be accompanied by


                                       4
<PAGE>   5

payment for such shortfall, together with interest at the Interest rate from the
date originally due (i.e., the twenty-fifth (25th) day of the month following
the calendar month in which such Power was provided or generated by the Owner
Entity) until paid in full. If such true-up statement reveals an overpayment by
Power Marketing with respect to such payment, the Owner Entity shall refund such
overpayment to Power Marketing no later than ten (10) Business Days following
the delivery of such true-up statement, together with interest at the Interest
Rate form the date such overpayment was originally made until repaid in full.

      3.2 Payments for Fuel. The Owner Entity shall pay to Power Marketing the
All-in Fuel Cost for all in-state natural gas provided to the Owner Entity by
Power Marketing. Power Marketing shall deliver to the Owner Entity on or before
the fifteenth (15th) day of each month a statement of the All-in Fuel Coast for
in-state natural gas supplied in the previous month, together with all
applicable supporting documentation. The Owner Entity shall pay to Power
Marketing the amount of each such statement on or before the last day of the
month in which such statement is delivered.

      3.3 Payments for Emissions Credits. Power Marketing shall deliver to the
Owner Entity on or before the fifteenth (15th) day of each month a statement
with respect to any Emissions Credits sold in the previous month, together with
any applicable supporting documentation. Power Marketing shall remit to the
Owner Entity with any such statement with respect to Emissions Credits provided
by the Owner Entity to Power Marketing and sold by Power Marketing for the Owner
Entity the full amount then due. The Owner Entity shall pay to Power Marketing
the amount of each such statement with respect to any Emissions Credits
purchased by it from Power Marketing on or before the last day of the month in
which such statement is delivered.

      3.4 Overdue Payments; Defaults. If any Party shall fail to make any
payment (including any estimated payment) when due, such overdue payment shall
accrue interest at the Interest Rate plus 2% from the due date to the date of
payment. In addition, if Power Marketing is the defaulting Party with respect to
payments for Power and continues to default with respect to any payment for
thirty (30) days after notice of such default by the Owner Entity, the Owner
Entity may (i) temporarily revoke Power Marketing's designation as Lead
Participant, (ii) sell Power from the Station into the ISO or to another power
marketer, (iii) terminate this Agreement, or (iv) take any other such actions as
are available to it an law or equity with respect to such default. During the
exercise of any remedy, including without limitation any revocation of Power
Marketing's designation as Lead Participant, Power Marketing shall continue to
be obligated to pay the Owner Entity for all Power not otherwise sold by the
Owner Entity. In addition, except for a revocation (either permanent or
temporary) of Power Marketing's designation as Lead Participant. Power marketing
shall remain obligated to pay the Owner Entity for all Power generated by the
Owner Entity pursuant to Dispatch effected by Power Marketing. The Owner Entity
may exercise any one or more of such remedies, and no such exercise shall limit
the Owner Entity's rights to exercise any other remedy.

      3.4 Billing Dispute. If either Party, in good faith, disputes a statement,
the disputing Party shall immediately notify the other Party of the basis for
the dispute; provided, however, that no adjustment for any invoice or payment
will be made unless objection to the accuracy thereof was made prior to the
lapse of one (1) year from the date such amount was paid. The disputing Party
shall pay the undisputed portion of such statement no later than the due date.
If any amount withheld under dispute is ultimately determined to be due to the
other Party, it shall be paid within five (5) Business Days of such
determination along with interest accrued at the Interest Rate from the date
originally due until the date paid. Inadvertent overpayments shall be returned
by Party overpaid upon request or deducted by such Party from subsequent
payments, with interest accrued at the Interest Rate from the date originally
paid until the date paid or deducted.

                                    ARTICLE 4
                               PERFORMANCE EXCUSED

      4.1 Force Majeure. If either Party is rendered unable by an event of Force
Majeure to carry out, in whole or part, its obligations under this Agreement,
then, for only the pendency of such Force Majeure, the Party affected by the
event (other than the obligation to make payments then due or becoming due with
respect to performance which occurred prior to the event) shall be temporarily
relieved of its obligations hereunder to deliver Power insofar as they are
affected by Force Majeure but for no longer period. The Party affected by an
event of Force Majeure shall


                                       5
<PAGE>   6

provide the other Party with written notice setting forth the full details
thereof within two (2) Business Days after the occurrence of such event and
shall take all reasonable measures to mitigate or minimize the effects of such
event of Force Majeure.

      4.2 Scheduled Outages. The Owner Entity shall cause the Operator to
promptly notify Power Marketing of any scheduled outage of any Unit. During the
period of such scheduled outage and any additional time reasonably required to
complete the work for which such outage was scheduled, the Owner Entity shall be
relieved of its obligations hereunder to deliver Power from such Unit.

                                    ARTICLE 5
                     TITLE, RISK OF LOSS AND INDEMNIFICATION

      5.1 Title and Risk of Loss. Title to and risk of loss related to Power
procured by Power Marketing hereunder shall transfer from the Owner Entity to
Power Marketing at the Delivery Point. The Owner Entity warrants that it will
deliver to Power Marketing the Power free and clear of all liens, claims and
encumbrances arising prior to the Delivery Point.

      5.2 Indemnity. Each Party shall indemnify, defend and hold harmless the
other party from any Claims arising from any act or incident occurring during
the period when control and title to Power is vested, as between the Parties as
provided in Section 5.1, in the indemnifying Party. "Claims" means all claims or
actions, threatened or filed and, whether groundless, false or fraudulent, that
directly or indirectly relate to the subject matter of an indemnity, and the
resulting losses, damages, expenses, attorneys' fees and court costs, whether
incurred by settlement or otherwise, and whether such claims or actions are
threatened or filed prior to or after the termination of this Agreement.

      5.3 Duty to Mitigate. Each Party agrees that it has a duty to mitigate
damages and covenants that it will use commercially reasonable efforts to
minimize any damages it may incur as a result of the other Party's performance
or non-performance of this Agreement.

                                    ARTICLE 6
                    REPRESENTATIONS, WARRANTIES AND COVENANTS

      6.1 Representations and Warranties. Each Party hereby represents and
warrants to the other Party that the following statements are true and correct
as of the date hereof and shall be true and correct at all times that such Party
is a Party hereto:

            (a) It is duly formed, validly existing, and in good standing under
      the laws of the jurisdiction of its incorporation or formation; to the
      extent required by applicable law, it is duly qualified and in good
      standing in the jurisdiction of its principal place of business, if
      different from its jurisdiction of incorporation or formation; and it has
      full power and authority to execute and deliver this Agreement and, as
      applicable, the Standard Offer Service Agreement and to perform its
      obligations hereunder and thereunder, and all necessary actions by the
      officers. managers, members or other applicable persons necessary for the
      due authorization, execution, delivery, and performance of this Agreement
      by it have been duly taken.

            (b) It has duly executed and delivered this Agreement and the other
      documents contemplated herein. and they constitute its legal, valid and
      binding obligations enforceable against it in accordance with their terms
      (except as may be limited by bankruptcy, insolvency or similar laws of
      general application and by the effect of general principles of equity,
      regardless of whether considered at law or in equity).

            (c) Its authorization, execution, delivery, and performance of this
      Agreement does not and will not (i) conflict with, or result in a breach,
      default or violation of, (A) its organizational documents, (B) any
      contract or agreement to which it is a party or is otherwise subject, or
      (C) any law, order, judgment, decree, writ, injunction or arbitral award
      to which it or any of its properties is subject; or (ii) require any
      consent, approval or authorization


                                       6
<PAGE>   7

      from, filing or registration with, or notice to, any governmental
      authority (including any approvals required by the Federal Energy
      Regulatory Commission) or other person, unless such requirement has
      already been satisfied.

            (d) It has obtained all Governmental Approvals (including all
      approvals, authorizations or waivers from the Federal Energy Regulatory
      Commission) necessary to perform its obligations hereunder.

            (e) It is not a party to any litigation the outcome of which could
      reasonably be expected to adversely affect its ability to perform its
      obligations hereunder or to have a material adverse effect on its
      properties, business or financial condition.

      6.2 Covenants. The Parties hereby covenant and agree as follows:

            (a) Each Party will timely acquire and maintain all permits,
      licenses, waivers and approvals (including approval to operate as an
      electricity wholesale generator) required by any state or federal
      regulatory authority in order for it to perform its obligations hereunder.

            (b) Each Party will at all times abide by all laws, rules and
      regulations of any state or federal governmental authority applicable to
      the conduct of such Party or the performance of its obligations hereunder.

            (c) Power Marketing will not sell Power to any of its Affiliates
      except in conformity with the laws, rules and regulations of any state or
      federal governmental authority applicable to such transactions.

            (d) Each Party will timely perform its obligations under each power
      sales agreement to which it is a party, and Power Marketing will not enter
      into any material amendment to the Standard Offer Service Agreement
      without the written consent of the Owner Entity.

                                    ARTICLE 7
                                  MISCELLANEOUS

      7.1 Term of Agreement. The Term of this Agreement will begin on the date
of this Agreement and will end on December 31, 2030.

      7.2 Governing Law and Jurisdiction. This agreement and the rights and
duties of the Parties hereunder shall be governed by and construed, enforced and
performed in accordance with the laws of the state of New York. Any lawsuits
arising under this Agreement shall be instituted in the Federal or State courts
of New York located in New York County, and each party hereby irrevocably
submits to the in personam jurisdiction of such courts. Each Party herein waives
its respective right to a jury trial with respect to any litigation arising
under or in connection with this Agreement.

      7.3 Assignment. Neither Party shall assign this Agreement or its rights
hereunder without the prior written consent of the other Party, provided,
however, either Party may, without the consent of the other Party (and without
relieving itself from liability hereunder), (i) transfer, sell, pledge, encumber
or assign this Agreement or the accounts, revenues or proceeds hereof in
connection with any financing or other financial arrangements by or for the
benefit of the Owner Entity or NRG Northeast Generating LLC, (ii) transfer or
assign this Agreement to an Affiliate of such Party if such Affiliate's
creditworthiness and technical ability to perform hereunder is not materially
different than that of such Party, (iii) transfer or assign this Agreement to
any person or entity succeeding to all or substantially all of the assets of
such Party, or (iv) in the case of the Owner Entity, transfer or assign this
Agreement to any person or entity acquiring the Station; provided, however, that
in each such case, any such assignee (other than an assignee in a transaction
referred to in clause (i) above) shall agree in writing to be bound by the terms
and conditions hereof and such assignee's creditworthiness and technical ability
to perform hereunder shall not be materially different than that of such Party.

      7.4 Notices.


                                       7
<PAGE>   8

      If to Power Marketing:

            NOTICES AND CORRESPONDENCE:

            NRG Power Marketing, Inc.
            1221 Nicollet Mall
            Minneapolis, MN 55403
            Attn:
            Phone: (612) 373-5300
            Fax: (612) 373-5430

            INVOICES:

            NRG Power Marketing, Inc.
            1221 Nicollet Mall
            Minneapolis, MN 55403
            Attn:
            Phone: (612) 373-5300
            Fax: (612) 373-5430

            PAYMENTS BY WIRE:

                  Bank:      LaSalle National Bank
                  Address:   Chicago, IL
                  ABA:       071 000 505
                  Account:   NRG Power Marketing LLC
                  Acct. No.:

      If to the Owner Entity:

                  NOTICES & CORRESPONDENCE:

                  Middletown Power LLC
                  1221 Nicollet Mall
                  Suite 700
                  Minneapolis, MN 55403
                  Attn: Commercial Asset Manager
                  Phone: (612) 373-5300
                  Fax: (612) 373-5346

                  INVOICES:

                  Middletown Power LLC
                  1221 Nicollet Mall
                  Suite 700
                  Minneapolis, MN 55403
                  Attn: Commercial Asset Manager
                  Phone: (612) 373-5300
                  Fax: (612) 373-5346

                  PAYMENTS BY WIRE:
                  Bank: LaSalle National Bank
                  Address: Chicago, IL
                  ABA: 071 000 505


                                       8
<PAGE>   9

                  Account: Middletown Power LLC
                  Acct. No.:

      7.5 General. No amendment or modification to this Agreement shall be
enforceable unless reduced to writing and executed by both Parties. This
Agreement shall not impact any rights enforceable by any third party (other than
a permitted successor or assignee bound to this Agreement). No waiver by a Party
of any default by the other Party shall be construed as a waiver of any other
default. Any provision declared or rendered unlawful by any applicable court of
law or regulatory agency or deemed unlawful because of a statutory change will
not otherwise affect the remaining lawful obligations that arise under this
Agreement. The headings used herein are for convenience and reference purposes
only. All indemnity and audit rights hereunder shall survive the termination of
this Agreement for six years. For any period over which interest shall accrue,
interest shall accrue on the first day of such period, but shall not accrue on
the last day thereof.

      7.6 Confidential Information. During the Term of this Agreement and for
three (3) years thereafter, neither Party shall divulge, furnish or make
accessible to anyone or use in any way any confidential or secret information of
the other Party which it has acquired or become acquainted in the performance of
its obligations under this Agreement. Each Party acknowledges that the
above-described information constitutes a unique and valuable asset of the Party
seeking such confidential treatment, and that any disclosure or other use of
such knowledge other than for the sole benefit of such other Party would be
wrongful and would cause it irreparable harm. Both during and after the term of
this Agreement, each Party will refrain from any acts or omissions that would
reduce the value of such knowledge or information to such other Party. The
foregoing obligations of confidentiality, however, shall not apply to any
knowledge or information which (i) is now published or which subsequently
becomes generally publicly known in the form in which it was obtained from the
Party seeking such confidential treatment, other than as a direct or indirect
result of the breach of this Agreement, (ii) is disclosed to any regulatory
authority having jurisdiction over the disclosing party, (iii) is disclosed as
required by law or pursuant to legal process, or (iv) is disclosed to a lending
institution in connection with any financing for the benefit of the Owner Entity
or NRG Northeast Generating LLC subject to the terms of a confidentiality
agreement having provisions substantially similar to this Agreement

      IN WITNESS WHEREOF, the parties have executed this Power Sales and Agency
Agreement in multiple counterparts to be construed as one as of the date first
set forth above.

                                        NRG POWER MARKETING, INC.

                                        By: /s/ Craig A. Mataczynski
                                           -------------------------------------
                                           Name:  Craig A. Mataczynski
                                                  ------------------------------
                                           Title: President
                                                  ------------------------------


                                        MIDDLETOWN POWER LLC

                                        By: /s/ Bryan K. Riley
                                           -------------------------------------
                                           Name:  Bryan K. Riley
                                                  ------------------------------
                                           Title: Vice President
                                                  ------------------------------


                                       9