Energy.gov

Renewable energy equipment owned by utilities and other entities operating in Arizona is assessed at 20% of its depreciated cost for the purpose of determining property tax. "Renewable energy equipment" is defined as "electric generation facilities, electric transmission, electric distribution, gas distribution or combination gas and electric transmission and distribution and transmission and distribution cooperative property that is located in this state, that is used or useful for the generation, storage, transmission or distribution of electric power, energy or fuel derived from solar, wind or other nonpetroleum renewable sources not intended for self-consumption, including materials and supplies and construction work in progress, but excluding licensed vehicles and property valued under sections 42-14154 and 42-14156."

Originally set to expire in 2011, the expiration date was extended through December 31, 2040 by [http://www.azleg.gov/legtext/48leg/2r/bills/hb2614s.pdf House Bill 2614], passed in July of 2008.