P10 Industries (PIOE) 8-K Changes in Registrant's Certifying Accountant

Exhibit 16.1

July 9, 2010

Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C. 20549

Ladies and Gentlemen:

We have read Item 4.01 of Form 8-K dated July 8, 2010, of Active Power, Inc. and are in agreement with the statements contained in the first, third and fourth paragraphs therein. We have no basis to agree or disagree with other statements of the registrant contained therein.

/s/ Ernst & Young LLP

Austin, Texas