Moss Landing Power Plant

Units 6 and 7 used supercritical steam. These units were retired at the end of 2016. At the end of their life, units 6 and 7 were typically operated as peaking units when demand for electricity was highest. In 2016, the last year of operation, they only operated approximately 3% of the time.[10]

The generation process for units 6 and 7 starts with natural gas injected at one end of the boiler to be burned. Primary water is injected at the other end of the boiler to receive the heat produced. The gas simply comes from a natural gas pipeline, and combustion products go up the stack and into the atmosphere. Water has a much more complicated path, and consists of two distinct systems: coolant water and primary (steam-generating) water. Cooling water is pumped out of the Monterey Bay or the nearby Elkhorn Slough. Then it is purified, used to cool down the water coming from the turbines, and discharged into the ocean. Steam for the turbines is created from the primary water flow, which is preheated before entering the boiler. From the boiler, the superheated steam is directed into a first turbine working at high pressure, then into a low pressure turbine. The turbines drive the generators.

Combustion products drive the gas turbines directly. First, air is drawn from the air intake to the compressor (driven by the turbine axle), then it is burned with natural gas in the combustion chamber. The hot combustion gasses then go through the actual turbine (driving the axle). From a thermodynamic standpoint, this is the standard Brayton cycle. Because the gas turbine does not transfer energy from the combustion process to the turbine via steam, it avoids the cost, energy loss and environmental impact of the primary water cycle.

At the output of the gas turbines, some of the remaining energy (heat) in the exhaust gas is recovered through a heat exchanger and transferred to water that feeds a steam turbine, similar to units 6 and 7.

On a smaller scale than the supercritical units, units 1 and 2 are also more flexible, with a start-up time of only an hour, against 24 hours for units 6 and 7.

On June 29, 2018, Vistra Energy, which merged with Dynegy on April 9, 2018,[15] announced that it will develop a 300 MW / 1,200 MWh energy storage system to be located at Moss Landing, using the existing turbine building and existing interconnection from units 6 and 7, connecting to the 500 kV grid.[16] Vistra Energy expected the energy storage system to begin commercial operation by the end of 2020, pending receipt of approval from California Public Utilities Commission (CPUC). This would be the largest lithium-ion battery energy storage system in the world.[17] The project began construction in December 2019,[18] and Phase 1 began operating at the end of 2020.[19] It is made of LG JH4 cells in TR1300 racks in two storeys in the old turbine hall.[20] Phase 2 adding a further 100 MW / 400 MWh was completed in August 2021, bringing total capacity to 400 MW / 1,600 MWh.[21][22] In September 2021, Phase 1 was shut down after a high temperature event caused by a leak in a liquid cooling hose, while Phase 2 kept operating.[23] In February 2022, Phase 1 remained offline while Phase 2 also went offline after a sprinkler event.[24] Most of the facility was back in operation as of July 2022.[25] In 2023, construction of Phase 3 with another 350 MW / 1,400 MWh was underway to bring total capacity to 750 MW / 3,000 MWh,[26] and commissionned in 2023.[27]

An expansion to 1,500 MW / 6,000 MWh (also connecting to the 500 kV grid) was approved in August 2020, but not decided.[28][29]

Utilities in California are required by a 2013 law to provide significant battery storage by 2024.[30] Pacific Gas & Electric (PG&E) asked the CPUC to approve four energy storage projects located at Moss Landing including another large lithium-ion battery storage system of 182.5 MW / 730 MWh ("Elkhorn") to be provided by Tesla and owned and operated by PG&E, connecting to the regional 115 kV grid.[31][32][33]

The project is designed to improve energy reliability and to allow for more renewable energy sources to be used at the Moss Landing site[34] by increasing electricity storage available in California.[35] The project also aims to save costs by reducing PG&E's reliance on peaker power plants that come online during periods of increased demand.[34]

On July 3, 2019, in accordance with the California Environmental Quality Act, the County of Monterey Resource Management Agency published a Mitigated Negative Declaration, detailing actions that must be taken to mitigate potential environmental impacts of the project.[36] The report concluded that the project would have a "Less than Significant Impact" on the environment, assuming the correct mitigating actions were taken.[36] Specifically, it was found that mitigating actions were required to minimize the environmental impact of the project on "biological resources" such as wildlife habitat, and on "cultural resources", especially culturally-significant archaeological sites at the proposed location of the Megapack deployment.[36]

The project was subsequently opened to public submissions on its environmental impact. California Unions for Reliable Energy argued that the County of Monterey failed to meet the standards of the California Environmental Quality Act when performing its environmental assessment.[37] This same union group, with the same legal representation, used similar arguments against the California Flats solar project in order for organized labor to get concessions from the developer.[37]

In February 2020, the Monterey County Planning Commission unanimously approved the project, which was initially scheduled to start construction in late March[38] and be complete by 2021.[39] However, the COVID-19 pandemic in California and subsequent stay-at-home order forced the project to be delayed.[38] Construction began in July 2020,[40] commissioned in April 2022,[41] and inaugurated in June 2022.[42]