California Independent System Operator (CAISO), the entity responsible for maintaining the balance between supply and demand for electricity throughout most of the state, had to resort to more power imports this summer as flexible gas generators could not fully balance the system amid fuel constraints.
CAISO imports electricity from nearby regions such as the Northwest and Southwest. On an average summer day, these imports hover around 6.5 GW and have now risen to up to 9.4 GW.
Gas supply restrictions
Caps on California’s gas-burn this summer, imposed due to a month-long leak at SoCalGas’ main storage, have significantly shifted the state’s energy mix towards renewables and imported electricity, which together offset the nearly 20% plunge in output from gas power stations in June, July and August.
On the average summer day in 2016, in-region thermal power output ranged between 7.3 gigawatts and 15.2 GW. Over the entire summer, hourly thermal power output was as high as 25.6 GW at 5:00 p.m. on July 27, when total system demand was high, and was as low as 2.6 GW at 9:00 a.m. on June 12, an hour when demand was relatively low and renewables output was relatively high.
One remaining nuclear plant
Baseload power has provided by Diablo Canyon – the on only nuclear facility in CAISO – which consistently provided about 2.2 GW of power after ramping up following a spring maintenance outage.
Hydropower plants this summer accounted for about 2.3 GW to 4.8 GW of power on a typical day. Hydroelectric facilities, the most flexible renewable sources, were generally dispatched to coincide with electricity demand, meaning output was often highest during hours of peak demand.
Surge in solar PV
Solar power has inherently variable levels of output. On an average summer day, utility-scale solar output ranged from 0 GW to 7.6 GW – the largest range among renewable fuels and the only fuel to have many hours without any output, according to EIA figures.
“Utility-scale solar photovoltaic capacity surged by 1.4 GW since June last year, or 27% yoy; and this steep rise in utility-scale solar capacity has reduced the need for summer thermal generation in CAISO, especially during daylight hours,” EIA energy economist Olivia Nilay Manzagol pointed out. Moreover, distributed solar PV capacity has increased to 3.8 GW, up from levels around 2.8 GW last summer.
Wind generators provided about 2.2 GW on average, but they ranged from near zero (0.06 GW) to more than 4 GW several times during the summer. Wind output is often at its lowest point during the middle of the day, when solar output is near its highest.
Geothermal, biomass, biogas, and small hydroelectric facilities had lower but more consistent output with relatively small differences between their highest and lowest hourly output.