Arizona Public Service (APS) and First Solar are to install Arizona’s first solar-battery hybrid power plant as part of plans to boost peaking capacity in the US state.

The two companies have signed an agreement to build the 65 MW solar field and 50 MW battery that will store energy during daylight hours and supply consumers with electricity between 3 and 8pm when energy use is peaking.

First Solar will operate the facility and has signed a 15-year power purchase agreement with APS. It will add to the more than one million solar panels and three grid-scale batteries already operating in APS’ system, the utility said.

APS will have full use of the 50 MW battery and will be able to maximize hourly capacity until it is fully discharged. The facility is set to begin service to customers in 2021 and will be built directly adjacent to the existing APS Redhawk power plant in western Maricopa County.

APS is planning to add more than 500 MW of battery storage to its grid over the next 15 years.