The mismatch between peak solar generation and peak electricity demand is widening in California, but building energy storage across the US state is balancing the grid.
The “duck curve” phenomenon is an electrical grid operating concept that marks a mismatch between peak solar production (midday to afternoon) and peak electricity demand (late afternoon and evening). A duck-like curve shows the peaks and valleys of this mismatch over a typical day.
The experience of a duck curve can stress the grid and challenge electricity markets, prompting California and other solar-friendly states to increase deployment of energy storage to address these challenges.
The Energy Information Administration (EIA) reported that as solar usage increases in California, the “duck curve” is deepening. The midday drop in net load will decrease, making it more difficult for the California Independent System Operator (CAISO) to balance the grid.
The swing in electricity demand for conventional power plants from midday to late evening, when energy demand is still high but solar production is reduced, means that conventional power plants, such as natural gas-fired peak power plants, must ramp up electricity production quickly to meet demand. . This rapid ramp-up makes it more difficult for network operators to match network supply with network demand in real time, a mechanism that balances the network both physically and in the wholesale market.
Additionally, if more solar power is produced than can be used, operators may need to curtail or intentionally shut down solar resources to avoid overproduction. California Independent System Operator (CAISO) contracted 1.5 million MWh of electricity-scale solar energy in 2020, which is 5% of total production according to the EIA. Solar energy is by far the most dominant energy source to be restricted in the state. According to the EIA, 94% of electricity restrictions in 2020 were related to solar energy.
The cuts reach their peak in the spring months, when demand is relatively low and solar energy production is relatively high. For example, in the early afternoon of March 2021, an average of 15 percent of electricity-scale solar power was curtailed, CAISO data showed as reported by the Energy Department.
The EIA also warned that the duck curve scenario also challenges traditional, dispatchable energy sources, as their use around the clock is uneconomical. This harm to a particular facility’s revenue could result in the facility being decommissioned without a highly dispatchable replacement, the YIA said.
“Due to less electricity being sent, it is more difficult for network operators to balance the supply and demand of electricity in a system where there are large fluctuations in net demand,” the EIA said.
However, the duck curve has opened the door to energy storage to meet the grid balancing needs of California and other renewable energy-based economies.
“The large-scale deployment of energy storage systems, such as batteries, makes it possible to store some of the solar energy produced during the day and save it for later use, after sunset,” the EIA said. “Saving some midday solar power flattens the duck’s curve, and transmitting the stored solar power in the evening shortens the duck’s neck.”
Battery energy storage in California has grown rapidly from 200 MW in 2018 to nearly 5 GW today. According to EIA data, operators plan to add another 4.5 GW of storage capacity to the state by the end of the year, suggesting that the solar-plus-battery boom is just beginning.
Despite higher total project costs, solar-plus-storage has an advantage in recovery cost, said global risk insurer DNV. Storage plants can charge their batteries when there is plenty of sunlight during the day and sell the stored electricity when the price is high. DNV said that by 2038, the price advantage of solar and storage projects will outweigh the cost disadvantage, to make these projects even more attractive.
“PV and storage systems are designed as a ‘package’ that can produce energy on demand, just like hydro, nuclear or combustion plants,” DNV said.
DNV said that in 10 years, about 20% of solar projects worldwide will be built with own storage, and by mid-century such projects will reach about 50%.
