<Page>
Exhibit 10.3.21
FIRST AMENDMENT TO
AMENDED AND RESTATED
ENERGY PURCHASE AGREEMENT
This FIRST AMENDMENT TO AMENDED AND RESTATED ENERGY PURCHASE AGREEMENT
("Amendment"), is made and entered into on this third day of June, 2002 by and
between Sithe/Independence Power Partners, L.P. ("Independence") and
Consolidated Edison Company of New York, Inc. ("ConEd").
WHEREAS, the September 1, 2000 Amended and Restated Energy Purchase
Agreement ("September 1 Agreement") contemplated that Independence and ConEd
would come to a mutual agreement on the amount of equivalent Installed Capacity
that Independence is obligated to sell and ConEd is obligated to purchase under
the September 1 Agreement, in the event that the Installed Capacity Requirements
in effect as of the date of the September 1 Agreement were replaced with new
Installed Capacity Requirements;
WHEREAS, the New York Independent System Operator ("NYISO" or "ISO") has
implemented a new Installed Capacity Requirements system, effective November 1,
2001, based on a calculation of Unforced Capacity, as that term is defined in
and as such calculation is set forth in the NYISO's July 6, 2001 filing amending
the ISO Services Tariff in FERC Docket No. ER01-2536-000, and as such filing
was accepted for filing by the Federal Energy Regulatory Commission on September
4, 2001 in NEW YORK INDEPENDENT SYSTEM OPERATOR, INC., 96 FERC 61,251 (2001);
WHEREAS, Independence and ConEd entered into a Letter Agreement dated
November 1, 2001 ("Letter Agreement") providing for the interim determination of
Installed Capacity rights and obligations under the NYISO's Installed Capacity
Requirements for the period November 1, 2001 through April 30, 2002, which the
parties intended to reconcile following a final agreement on these issues;
WHEREAS, Independence and ConEd have now agreed on a methodology for
calculating Independence's monthly obligation to sell Installed Capacity under
the ISO's new Unforced Capacity requirements, including the methodology for
reconciling the interim payments for the purchase of Unforced Capacity under
Paragraph 3 of the Letter Agreement; and
WHEREAS, Independence and ConEd do not otherwise seek to alter the terms of
the September 1 Agreement;
NOW, THEREFORE, in consideration of the mutual promises and agreements
contained herein, Independence and ConEd, intending to be legally bound, agree
as follows:
1. Section 1.02(u) of the September 1 Agreement is deleted in its
entirety and replaced with the following:
(u) "Purchased Capacity" means, for each Contract Year: (a)
740 MW of Installed Capacity, determined in accordance with
the Installed Capacity Requirements in effect as of the
effective date of the September 1 Agreement, for the period
from September 1, 2000 through
<Page>
October 31, 2001; (b) beginning November 1, 2001 and for as
long as the quantity of Installed Capacity is determined in
accordance with the ISO's Unforced Capacity methodology (as
implemented on November 1, 2001), the Negotiated UCAP
Amount; or (c) if and to the extent that the NYISO adopts a
new Installed Capacity Requirements methodology to replace
the Unforced Capacity methodology implemented on November 1,
2001, or otherwise materially changes or abandons the
Unforced Capacity methodology, "Purchased Capacity" shall
mean an amount of Installed Capacity equivalent to the
amount of Installed Capacity under clause (a) (as reasonably
determined by mutual agreement of the parties), it being the
intent of the parties that the rights and obligations under
clause (a) will not be materially altered.
2. New subsections 1.02(x) and (y) shall be added to the September 1
Agreement, as follows:
(x) "Negotiated UCAP Amount" means an amount of Unforced
Capacity determined according to the following formula:
Negotiated UCAP Amount = 740 MW X (1 - State Average
EFORd)+10 MW
where: State Average EFORd = New York Control Area average
forced outage rate of
generating resources used by
the NYISO to determine Load
Serving Entities' Installed
Capacity Requirements, as
such rate is determined by
the NYISO for the applicable
period
As an example of how the Negotiated UCAP Amount would be
calculated, the parties agree that the New York Control Area
average forced outage rate applicable for the summer 2002
Capability Period (as that term is defined in the ISO
Services Tariff) is 9.68%, and therefore, the calculation
for the Negotiated UCAP Amount for that summer 2002
Capability Period is 740 MW X (1 - 9.68%) + 10 MW = 678.4
MW.
(y) "Unforced Capacity" has the meaning assigned to that
term in the ISO Services Tariff.
3. Sections 1.02(e) and (k) (defining "Current Installed Capacity
Requirements" and "Future Installed Capacity Requirements") shall each be
deleted in their entirety and replaced with the words "Intentionally left
blank."
4. For purposes of clarification, the words "or Unforced Capacity,
whichever is relevant," are added to Section 3.02(a) of the September 1
Agreement, after the words "Installed Capacity."
2
<Page>
5. The parties agree that, for purposes of the reconciliation required in
Paragraph 3 of the Letter Agreement, the reconciliation amount is $112,800. As
of the execution of this Amendment and Independence's payment of this
reconciliation amount to ConEd, the parties will have fulfilled all of their
obligations under the Letter Agreement.
6. Except as set forth above, the capacity purchase and sale will be
governed by the terms of the September 1 Agreement, including but not limited to
the preservation of Independence's right to obtain Replacement Capacity for the
Purchased Capacity from a source other than the Independence Station, and Con
Edison's right to receive the Price Adjustment, calculated as set forth in
Section 3.02(d) of the September 1 Agreement, upon Independence's failure to
provide the Purchased Capacity (including Replacement Capacity). Furthermore,
except as amended hereby, the September 1 Agreement shall remain unchanged and
in full force and effect.
7. This Amendment constitutes the entire understanding between the
parties, and supersedes any and all previous understandings, oral or written,
with respect to the subject matter hereof. This Amendment may be executed in
counterparts, all of which shall constitute one and the same Agreement and each
of which shall be deemed to be an original. Any term used in this Amendment that
is not defined herein shall have the meaning that is in the September 1
Agreement.
8. This Amendment shall be governed by and construed and enforced in
accordance with the laws of the State of New York applicable to contracts made
and to be performed therein. The parties agree that all disputes between them
which arise under this Amendment and which are not settled, other than disputes
which are exclusively within the jurisdiction of FERC, shall be decided by a
court of competent jurisdiction in the State of New York and the parties submit
to the jurisdiction of the courts of the State of New York and the Federal
District Courts located in New York, New York.
3
<Page>
IN WITNESS WHEREOF, the parties have executed this Amendment by their
authorized representatives as of the day and year first set forth above.
SITHE/INDEPENDENCE POWER PARTNERS, L.P.
By: Sithe/Independence, Inc., its general partner
By: /s/ Sandra Manilla
------------------------------------
Name: SANDRA MANILLA
Title: Vice President & Treasurer
CONSOLIDATED EDISON COMPANY OF NEW YORK, INC.
By: /s/ Joseph P. Oates
------------------------------------
Name: Joseph P. Oates
Title: Vice President, Energy Management
4