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RWE connects 548MWh battery storage project to California’s CAISO grid


Germany utility company RWE has brought its biggest utility-scale battery energy storage system (BESS) project in the US closer to the start of commercial operations.

The company said yesterday (14 June) that its project, called Fifth Standard, has now been connected to the California Independent System Operator (CAISO) grid.

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The 137MWac BESS is a 4-hour duration asset (548MWh) and will be paired with a 150MW solar PV power plant, currently under construction and expected to be completed by August.

It continues a relatively prolific run of battery storage projects for the company, which is currently executing what are thought to be the biggest projects of their kind under construction in Germany – two systems totalling 220MW/235MWh in the state of North Rhine-Westphalia.

It appears that RWE has not publicly said much about Fifth Standard prior to yesterday’s announcement. That’s perhaps because the solar-plus-storage plant’s development was kicked off by fellow Germany-headquartered energy company E.On’s clean energy arm – the assets of which were transferred to RWE as part of a complicated asset swap deal completed in 2020.

According to a 2018 report from local news outlet The Sentinel, E.On’s EC&R Solar Development subsidiary submitted permitting applications for the solar and storage facility in California’s Fresno County 2018. At that stage, EC&R Solar Development was seeking to build a 150MW solar PV plant, and a separate 20MW PV plant coupled with a 20MW/80MWh BESS.

In 2022, Fifth Standard was included in a list of projects in the service area of California investor-owned utility (IOU) Pacific Gas & Electric (PG&E) that could be connected to the CAISO grid without a requirement for transmission system buildout excepting for relatively minor remedial action scheme (RAS) work, in this case a generation tie-in line.

The BESS is connected to the grid via an existing PG&E substation, while RWE said the solar-plus-storage plant is designed to support biodiversity on the site – in line with the company’s strategy for US solar projects. It will also generate a US$10 million contribution to the local tax base during its lifetime, and around 300 workers employed to work on it during peak construction.

Other recent US projects from RWE include one of the country’s biggest DC-coupled solar-plus-storage systems. Hickory Park in Georgia is a 196MW ground mount solar PV plant with a 20MW/80MWh BESS, which went online in mid-2022. The company is currently also working on Texas Waves II, a 30MW/30MWh BESS co-located with a wind farm in Texas.

Among other notable BESS-related developments for RWE include a recently awarded contract for an 8-hour duration 50MW battery storage project through a state government tender in New South Wales, Australia.

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