, a subsidiary of German energy company , plans to build a 10-MWbattery energy storage facility combined with a 2-MW solar array at theUniversity of Arizona Science and Technology Park near Tucson, Ariz., under anagreement with utility TucsonElectric Power Co.

The Iron Horse Battery Energy Storage Project, to be completedin the first half of 2017, will provide frequency response and voltage controlfor Tucson Electric, which is owned by UNS Energy Corp. and is a subsidiary of

The agreement follows the Arizona Corporation Commission'sMay decision toapprove Tucson Electric's plan to acquire two 10-MW lithium battery storageunits, including one that would be paired with a 2-MW solar array. The utilityhas received more solicitations from potential storage developers than itexpected.

The commission has also pushed another major utility in the state, subsidiary Arizona Public ServiceCo., to pursue residential energy storage projectsin order to cut its peak demand.

E.ON will work with Greensmith Energy, a U.S.-based providerof energy storage software, on the design of the energy storagesystem. The goal is for the system to work like a conventional power plant interms of availability and ability to respond to the needs of the grid,according to a statement. The storage system will run under a 10-yearcontract.

E.ONhas built and operates over 3,000 MW of solar and wind projects across the U.S.