Exhibit 4.15-c

                               KEYSPAN CORPORATION
                                    GUARANTY

This  Guaranty  (the  "Guaranty")  is made  and  given  as of this  26th  day of
November,  2003, by KeySpan Corporation,  a corporation organized under the laws
of the State of New York,  having its principal office at One MetroTech  Center,
Brooklyn,  New York 11201 ("KeySpan"),  in favor of the Nassau County Industrial
Development  Agency,  a  corporate   governmental  agency  constituting  a  body
corporate and a public benefit corporation organized under the laws of the State
of New York (the "IDA"),  having its principal  office at 400 County Seat Drive,
Mineola, New York 11501.

WHEREAS, KeySpan-Glenwood Energy Center, LLC (the "Primary Obligor") is a wholly
owned, indirect subsidiary of KeySpan ;

WHEREAS,  KeySpan is desirous that the IDA and the Primary  Obligor enter into a
lease  agreement,  dated as of  November  1, 2003 (the  "Lease  Agreement"),  in
connection with a certain  electric power  generation  facility  operated by the
Primary Obligor; and

WHEREAS, KeySpan is willing to enter into this Guaranty in order to guarantee to
the IDA the  obligations  of the  Primary  Obligor  (i) to make  certain  rental
payments  under the Lease  Agreement,  and (ii) to pay amounts  when due under a
certain  Payment  Agreement (the "Payment  Agreement")  delivered by the Primary
Obligor to the IDA (collectively, the "Guaranteed Obligations");

NOW,  THEREFORE,  in  consideration of the foregoing and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, and
intending to be legally bound hereby, KeySpan covenants and agrees as follows:

KeySpan  unconditionally  guarantees,  subject to the exceptions and limitations
set forth below, the full,  faithful,  and prompt payment by the Primary Obligor
of the  Guaranteed  Obligations.  In the  event of any  default  by the  Primary
Obligor in the payment of the Guaranteed  Obligations,  KeySpan shall  forthwith
pay  the  defaulted  obligation  to the  IDA (or  the  Trustee,  at the  written
direction of the IDA), without requiring any proceedings to be taken against the
Primary Obligor,  or any third party, and without the necessity of enforcing any
remedy available under the terms of the Lease  Agreement.  This is a guaranty of
payment and not collection.

KeySpan's  liability  hereunder  is limited to the direct  monetary  obligations
incurred  by the  Primary  Obligor  under the Lease  Agreement  and the  Payment
Agreement,  provided that, in no event will KeySpan be subject to consequential,
special,  exemplary,  equitable,  loss of  profits,  tort or any other  damages.
KeySpan  reserves  to  itself  all  rights,  setoffs,  counterclaims,  and other
defenses to which the Primary Obligor, or any other KeySpan affiliate, is or may
be entitled to under the Lease Agreement.

This Guaranty  shall become  effective as of the date hereof and will  terminate
without  further  notice as of the date that the payment  obligations  under the
Lease Agreement are paid in full  ("Termination  Date").  No termination of this
Guaranty shall affect any valid and enforceable  obligations incurred by KeySpan
under this Guaranty at the time of termination.  KeySpan's obligations hereunder


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shall  continue  until  the  later  of (x)  the  Termination  Date  or  (y)  the
satisfaction  of  only  those  valid   obligations   existing  at  the  time  of
termination.

KeySpan  shall not  delegate  or assign  its duties  and  obligations  hereunder
without  the  IDA's  consent.  This  Guaranty  shall  not  apply if the  Primary
Obligor's  obligation  arises  pursuant to an  assignment  of  contracts  and/or
agreements to a  non-affiliated  entity for which the IDA's consent was granted.
This Guaranty shall be governed by the laws of the State of New York.

The obligations of KeySpan hereunder shall continue in full force and effect and
be automatically  reinstated,  notwithstanding any termination of this Guaranty,
if and to the extent  that for any  reason any  payment to the IDA in respect of
the obligations  under the Lease Agreement is rescinded by, or must be otherwise
repaid  or  restored  by,  the  Primary  Obligor,  whether  as a  result  of any
proceedings in bankruptcy or  reorganization or otherwise under other applicable
laws or any  settlement  in a  proceeding  therein,  subject in any and all such
cases to the limits on KeySpan's liability hereunder.

KeySpan hereby waives the giving of any notice,  including,  but not limited to:
(i) notice of the  acceptance  of this Guaranty by the IDA; (ii) notice that the
Primary Obligor has entered into the Lease  Agreement and the Payment  Agreement
and that  obligations  of the  Primary  Obligor  guaranteed  hereby  have arisen
thereunder; (iii) notice of the modification or amendment of the Lease Agreement
or the  Payment  Agreement;  (iv)  notice  of any  extension  of time  or  other
modification  of  terms  for the  payment  of any  obligation  under  the  Lease
Agreement  or the  Payment  Agreement;  (v)  notice of  presentment,  demand for
payment,  default,  dishonor,  protest or notice of protest  with respect to any
obligation under the Lease Agreement or the Payment  Agreement;  (vi) any notice
of any defaults by or disputes with the Primary  Obligor with respect to payment
or performance  under the Lease  Agreement or the Payment  Agreement;  and (vii)
notice of any action the  Primary  Obligor  may at any time take  involving  the
sale, exchange, release, surrender, or other action with respect to any property
at any time securing,  directly or indirectly, the Primary Obligor's obligations
under the Lease Agreement or the Payment Agreement.

KeySpan  shall  not  consolidate,  amalgamate  or merge  with or  into,  sell or
transfer  all or  substantially  all of its assets to or  undertake  any similar
event with another entity, unless the resulting,  surviving or transferee entity
is liable for all obligations of KeySpan under this Guaranty.

KeySpan represents and warrants to the IDA that:

(1)  KeySpan is a corporation duly organized and existing in good standing under
     the laws of the State of New York and has full power and  authority to make
     and deliver this Guaranty;

(2)  The  execution,  delivery and  performance  of this Guaranty by KeySpan has
     been duly  authorized  by all necessary  corporate  action and does not and
     will not  violate the  provisions  of, or  constitute  default  under,  any
     presently  applicable  law  or  its  organizational,   instruments  or  any
     agreement presently binding on it;

(3)  This  Guaranty  has been duly  executed  and  delivered  by the  authorized
     officers  of KeySpan  and  constitutes  its  lawful,  binding,  and legally
     enforceable obligation; and

(4)  The  obligations  of KeySpan  hereunder  will result in a direct benefit to
     KeySpan.


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Any provision contained in this Guaranty which is prohibited or unenforceable in
any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of
such  prohibition  or  unenforceability   without   invalidating  the  remaining
provisions  hereof,  and  any  such  prohibition  or   unenforceability  in  any
jurisdiction shall not invalidate or render  unenforceable such provision in any
other jurisdiction.

KeySpan  agrees  that  any  suit,  action,  or  proceeding,   whether  claim  or
counterclaim, brought or instituted by KeySpan, by the Primary Obligor or by any
successor or assign of the Primary  Obligor on or with respect to this  Guaranty
or which in any way relates,  directly or  indirectly,  to the Lease  Agreement,
Payment  Agreement or  obligations  thereunder,  or any event,  transaction,  or
occurrence arising out of or in any way connected with the Lease Agreement,  the
Payment Agreement or the dealings of the parties with respect thereto,  shall be
tried only by a court and not by a jury.

This Guaranty shall be binding upon KeySpan and its successors,  transferees and
permitted assigns hereunder and shall inure to the benefit of and be enforceable
by the IDA and its successors and assigns.









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IN WITNESS WHEREOF, the undersigned has executed this Guaranty the 26th day of
November, 2003.

                                             KEYSPAN CORPORATION

                                             By:   /s/
                                                   ------------------

                                             Name: Michael J. Taunton
                                                   ------------------

                                             Title: VP & Treasurer
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