Arizona Public Service (APS) said it will expand the amount of solar energy and battery energy storage capacity on its system through three projects.

The projects will add 850 megawatts (MW) of battery storage and at least 100 MW of new solar generation by 2025.

APS said that it owns and operates large-scale solar plants across the state that will be upgraded with 200 MW of battery storage systems. A team led by Chicago-based Invenergy will install six of the new battery systems at solar plants in Maricopa County and Yuma to be in place by 2020. Two additional upgrades will be completed by 2021, the utility said, without offering details.

The utility said it also plans to build an additional 500 MW of solar storage and stand-alone battery storage by 2025. The first project will be a 100 MW solar-storage plant. APS said it expects to issue a request for proposals for this capacity in the summer of 2019.

When this February 2018 Energy Department map was released, Arizona's energy storage profile was negligible. APS initiatives aim to change the map by 2025. Source: EIAIn February 2018, APS signed a 15-year power purchase agreement with Tempe-based First Solar to build a solar-plus-storage project that will be one of the largest in the country when completed in 2021. First Solar will build and operate the facility that includes a 65-MW solar field to charge the battery. The field will store power when the sun is high in the sky and deliver it to customers between 3 and 8 p.m. when the sun is on its way down, but energy use is peaking.

The utility said it will also use 150 MW of battery storage fueled by solar energy to meet part of the demand when energy usage peaks. A more traditional approach to meeting peak demand would be to install one or more generating units fueled by natural gas.

The new battery storage capacity will come from two projects: a 100 MW battery provided by Virginia-based AES, and a 50 MW battery from Invenergy. Additional natural gas-fired generating capacity will come from a contract with Calpine for 463 MW of energy. The purchase agreement with Calpine extends for seven years, which is less than the 20-year contract terms commonly used in the industry. APS said the shorter term offers it the flexibility to take advantage of future technologies as they mature.

In 2017, AES began operating a standalone battery peak demand facility, a 4 MW energy storage system for APS. The pair of 2 MW Advancion energy storage arrays were deployed as part of the APS Solar Partner Program and deliver energy to as many as 1,000 customers at the time of day when electricity is in greatest demand and most expensive.

APS is not the only Arizona utility to pursue battery energy storage to meet demand during times of peak demand. In May 2018, Salt River Project said that it and AES would build the utility's first standalone battery-based energy storage project. The 10 MW, 40-megawatt-hour energy storage array was to be supplied by Fluence and would provide peaking capacity to the grid.

Nationwide, energy storage got a boost in February 2018 when the Federal Energy Regulatory Commission voted 5-0 to remove what it said were nationwide barriers to the participation of electric storage resources in the capacity, energy and ancillary services markets operated by regional transmission organizations and independent system operators. The vote followed a November 2016 Notice of Proposed Rulemaking by the commission. The FERC at the time said that market rules designed for traditional generation resources had created barriers to entry for emerging technologies such as electric storage resources.