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.