California’s curtailments of solar electricity generation continue to increase – Today in Energy

August 24, 2021

Restrictions on solar-powered power generation have increased in the California Independent System Operator (CAISO) region, the portion of the power grid that covers most of the state. In 2020, CAISO reduced 1.5 million megawatt hours of solar energy in the utility area, or 5% of its solar production in the utility area.

Network operators cut back electricity production from solar and wind generators when supply exceeds demand. In 2020, solar shutdowns accounted for 94% of the total energy lowered in CAISO. Solar restrictions tend to be more severe in the spring months, when electricity needs are relatively low (due to moderate temperatures which reduce heating and cooling needs) and solar power is relatively high. In the early afternoon hours of March 2021, CAISO throttled an average of 15% of its solar power in the supply area.

Solar production and cuts in CAISO

The increase in renewable generation and the restriction of solar and wind power followed an increase in new renewable capacities. To meet California’s goal of 50% renewable generation by 2025, CAISO plans to add an additional 1.6 gigawatts (GW) of utility-scale solar capacity and 0.4 GW of onshore wind turbine capacity in 2021.

Small-scale solar capacities have also continued to grow. The customer-side solar power generation reduces the need for CAISO-operated power generation, which leads to further solar restrictions.

CAISO examines and implements various solutions, including:

CAISO’s Energy Imbalances (EIM) Market: CAISO’s EIM is a real-time market that enables participants outside of CAISO to buy and sell energy to balance supply and demand. In 2020, according to reports from EIM operators, 16% of the total possible cuts were avoided by trading within the EIM.

Battery storage: According to our survey of recent and planned capacity changes, CAISO expects to add 2.5 GW of battery storage capacity in 2021. Renewable generators can charge these batteries with electricity that would otherwise have been cut.

Further options for energy storage: Hydrogen production and hydrogen-based energy storage could also help reduce solar attenuation. The hydrogen is produced by electrolysis from excess renewable electricity that would otherwise be cut and stored for later use. Two projects under development are a power-to-gas-to-power project and a project of the Intermountain Power Project (IPP) called IPP Renewed. IPP Renewed focuses on the development of renewable hydrogen generation and storage capacities as well as the installation of natural gas powered generators that can use hydrogen.

Other solutions that CAISO has identified include:

  • Growing demand response that would adjust consumer demand if justified
  • Encouraging time-of-use tariffs that better match consumer prices with real-time energy prices
  • Reducing the minimum generation level for existing generators, which would open up more opportunities for renewable energy generation

Main contributor: Lori Aniti

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