POWER OF ATTORNEY


		Know all by these presents that the undersigned
hereby constitutes and appoints Paul J. Kaleta and Britta Carlson,
and each of them collectively Or individually, as his or her true
and lawful attorney-in-fact to:

	(1)	execute for and on behalf of the undersigned,
Forms 3, 4, and 5 in accordance with Section 16(a) of the Securities
Exchange Act of 1934 and the rules thereunder;

	(2)	do and perform any and all acts for and on
behalf of theundersigned which may be necessary or desirable to
complete the execution of any such Forms 3, 4 or 5 and timely filings
of such forms with the United States Securities and Exchange Commission
and any other authority; and

	(3)	take any other action of any type whatsoever
in connection with the foregoing which, in the opinion of such
attorney-in-fact, may be of benefit to, in the best interest of, or
legally required by, the undersigned, it being understood that the
documents executed by such attorney in fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in such form
and shall contain such terms and conditions as such attorney-in-fact
may approve in his discretion.

	The undersigned hereby grants to such attorney-in-fact
full power and authority to do and perform all and every act and thing
whatsoever requisite, necessary and proper to be done in the exercise
of any of the rights and powers herein granted, as fully to all intents
and purposes as such attorney-in-fact might or could do if personally
present, with full power of substitution or revocation, hereby ratifying
and confirming all that such attorney-in-fact, or his substitute or
substitutes, shall lawfully do or cause to be done by virtue of this
Power of Attorney and the rights and powers herein granted.  The
undersigned acknowledgesthat the foregoing attorney-in-fact, in serving
in such capacity at the request of the undersigned, is not assuming any
of the undersigned's responsibilities to comply with Section 16 of the
Securities Exchange Act of 1934.

	IN WITNESS WHEREOF, the undersigned has caused this Power
of Attorney to be executed as of the 1st day of May, 2008.

/s/Maureen Mullarkey