2.1.4. Power Curtailment Data for Wind and Solar Generation (Hourly Resolution)

CAISO curtails power flows across the grid system during system emergencies that can affect reliability and safety of the power grid. The operator provides daily reports for the wind and solar electricity generation curtailed specifying the reasons for the curtailment. Reasons of curtailment can be technical or economic, and at either local or system-wide levels, to mitigate congestion, or to mitigate oversupply (defined as when wind or PV facilities deliver more power than is required). An overview of the power curtailment data from the OASIS historical data archive showed that, in 2018, in no case did curtailment occur to mitigate oversupply.

## *2.2. Current and Future Electricity Generation and Storage Technologies in California*

#### 2.2.1. Nuclear

There is only one nuclear power plant currently operating in California, managed by Pacific Gas and Electric Company (PG&E). The plant totals 2393 MW of installed capacity [36] and uses two pressurized-water reactors (PWRs) to generate electricity [37]. This power plant was modelled here using the Ecoinvent process for PWRs in the Western Electricity Coordinating Council (WECC) region, which includes California [38]. It is expected that both reactors will be decommissioned within the time frame of interest for this study, and specifically in November 2024 and August 2025, respectively [39].

#### 2.2.2. Gas-Fired Electricity

In California, natural gas utilities are regulated by the California Public Utilities Commission (CPUC) and those utilities are managed by several service providers such as Pacific Gas and Electric Company (PG&E), Southern California Gas Company (SoCalGas), San Diego Gas & Electric Company (SDG&E), Southwest Gas. At present, Natural Gas Combined-Cycle (NGCC) plants represent the 41% of the total 42,695 MW installed capacity, and 69% of the total electricity generated by natural gas-fired plants [40]. According to the 2018 California Gas Report [41], gas demand for electricity generation is expected to decline due to California's programs to minimise greenhouse gas (GHG) emissions, with a concomitant increase in renewable energy (RE) technologies. In this study, the life-cycle inventories for NGCC and single-cycle gas turbines (SCGT) operated in California were based on the corresponding Ecoinvent processes for the WECC region [38].

## 2.2.3. Geothermal

California is located within the "Pacific ring of fire" geographic area, where the frequency of earthquakes and volcanic eruptions are highest as a result of the movement of tectonic plates. California is also characterised by a large number of natural geysers which provide a natural resource of geothermal power. There are 43 geothermal power plants in California, totalling 2730 MW of installed capacity [36], which use natural steam to drive turbines which in turn are used as generators to produce electricity for the grid. The life-cycle inventory for geothermal electricity was based on the corresponding Ecoinvent processes for the WECC region [38].
