While best known for its vehicles, Tesla Inc (NASDAQ: TSLA) is an energy production and storage company. Tesla offers solar panels for energy production, and batteries for storage ranging in size from home backup to full grid support such as the Hornsdale, Australia Power Reserve. 

Tesla and PG&E Corporation (NYSE: PCG) are working toward the largest battery backup in the world in Moss Landing, California, as shared by InsideEVs. The site has 256 Tesla Megapacks totaling 730MWh of energy storage, equivalent to 7,300 Tesla Model S Long Range vehicles. 

At completion, this will be the largest battery storage facility in the world, but there are always bigger systems being built.

"The system will be designed, constructed, and maintained by PG&E and Tesla, and will be owned and operated by PG&E," according to PG&E.  

Construction began in July 2020. 

PG&E expects the Moss Landing storage facility to save more than $100 million over the 20-year life of the project. The system contains the option to upsize if PG&E would like to expand. Tesla can provide more batteries than can relatively easily be added on in the case of an expansion.