next to the Mira Loma substation in Southern California."/>

Late last week, California utility Pacific Gas and Electric (PG&E) asked the state to approve four lithium-ion battery storage projects. Three of which would be owned and operated by a third party, and one, built by Tesla, would be owned and operated by PG&E itself.

One of the projects—spearheaded by energy company Vistra (which recently merged with Dynegy)—could become the world's first grid-scale, lithium-ion battery installations to store more than a gigawatt-hour of energy.

Tesla's project is also huge. It would deliver 730MWh of energy, but Tesla's contract with PG&E suggests the utility could opt to increase the size of the battery to 1.1GWh.

The Tesla installation is expected to discharge 182.5MW for 4 hours (hence, the 730MWh number). But the contract could be bumped up to a discharge duration of 6 hours, which would result in just under 1.1 GWh of storage owned by PG&E. For comparison, last year Tesla completed the largest lithium-ion battery installation in the world in South Australia. That battery system clocked in at 100MW/129MWh of storage.

Storage of this size allows the utility to add more renewable energy because if wind speeds drop or cloud cover hurts solar, a battery can kick in to meet the rest of that load.

The Tesla/PG&E battery would be located at the Moss Landing substation in California, near Monterey Bay (and home to the Monterey Bay Aquarium Research Institute). PG&E said it expects the battery to be completed by 2019, pending the approval of the California Public Utilities Commission (CPUC).

Vistra/Dynegy also bid to build a 300MW battery installation that would be able to be discharged for four hours. At 1.2GWh, the battery would be among the largest in the world and would also be located at the Moss Landing site. A press release from the company projects that the installation would be completed by the end of 2020. The project would be supported by a 20-year contract with PG&E to buy energy from Vistra.

A spokeswoman for Vistra said the company had not yet selected a provider to source its batteries from. The project would use two existing interconnection points at Moss Landing to connect to the grid, as well as "an existing turbine building on the site to house the batteries."

The two other projects are smaller and include a 75MW / 300MWh battery installation from a company called Hummingbird Energy Storage LLC, as well as an aggregation project from Micronoc Inc, which will site 10MW / 40MWh of batteries at commercial locations.

These projects depend on the CPUC's approval to move forward, but the commission directed PG&E to accelerate its solicitation of battery storage in January, so the proposals aren't too surprising. A response from CPUC is expected in 90 days.

Correction: The name of the Monterey Bay Aquarium Research Institute was corrected.