Tucson Electric Power S-3ASR Automatic shelf registration

Exhibit 15(a)

May 10, 2012

Securities and Exchange Commission

100 F Street, N.E.

Washington, DC 20549

Commissioners:

We are aware that our report dated April 30, 2012 on our review of condensed consolidated interim financial information of UNS Energy Corporation, formerly UniSource Energy Corporation (the “Company”), for the three month periods ended March 31, 2012 and March 31, 2011 and included in the Company’s quarterly report on Form 10-Q for the quarter ended March 31, 2012 is incorporated by reference in its Registration Statement on Form S-3 dated May 10, 2012.

Very truly yours,

/s/ PricewaterhouseCoopers LLP

PricewaterhouseCoopers LLP