The Arizona Court of Appeals has upheld the authority of the Arizona Corporation Commission to establish a Renewable Portfolio Standard, or Renewable Energy Standard and Tariff (“REST”) . In somewhat of an oversimplification, the standard was set in 2006 requiring public utilities to produce 15% of their electricity from renewable energy sources such as solar, wind, geothermal, biomass, and biogas. It also allows distributed power generation rather than large-scale centralized power plants.The 2006 decision not only increased the goal but added geothermal for the first time. While Arizona doesn't have any commercial geothermal power plants, there is a growing number of ground source (goethermal) heat pumps in residences that contribute by reducing demands for electricity. [right, geothermal well test at Clifton Hot Springs, Arizona, 2005. Credit, APS]