California has experienced a rapid increase in solar power generation in recent years as more homeowners and businesses have installed rooftop solar panels. While this growth in solar power is helpful in increasing renewable energy usage and reducing greenhouse gas emissions, it has also created some challenges for managing the electrical grid. One such challenge is oversupply situations that can occur during midday hours on sunny days.
During the midday hours on clear sunny days, solar power generation may peak when demand for electricity is relatively low as most homes and businesses do not need as much power when the sun is highest in the sky. This can potentially lead to situations where solar power production exceeds the immediate demand and needs to be curtailed or stored somehow to maintain grid stability. If too much power is being generated but not used at a given moment, it can cause issues like overloading transformers or requiring more natural gas plants to remain on but idled just in case their power is needed.
To address this oversupply problem, California regulators and utilities have implemented several programs and policies in recent years. One strategy has been to encourage the deployment of battery storage systems at both utility-scale and behind-the-meter at homes and businesses. Large utility-scale batteries can absorb excess solar power during the middle of the day and then discharge that stored power later in the afternoon or evening when solar production falls off but demand rises again. Over 100 megawatts of utility-scale batteries have been installed so far in California with many more planned.
Similarly, rebate and incentive programs have promoted the adoption of residential and commercial battery storage systems to go along with rooftop solar. These smaller batteries can store midday solar production for use later in the home or business when the sun goes down. About 100 megawatts of behind-the-meter storage had been deployed in California homes and firms up until 2021. The state has set targets to reach 3,000 megawatts of storage deployment across all sectors by 2025.
Utilities have also implemented time-variant pricing and demand response programs to help align solar generation with demand patterns. Dynamic pricing rates that are higher during mid-afternoon create an economic incentive for customers to shift discretionary electricity usage to morning or evening hours. Meanwhile, demand response programs pay participants to voluntarily reduce or shift their power consumption during times of predicted oversupply. This could involve actions like pre-cooling buildings earlier in the day.
On the supply side, California’s main grid operator (CAISO) has developed processes to curtail solar generation when necessary to prevent oversupply situations. Curtailment is considered a last resort option due to the lost renewable energy production. CAISO’s market design also facilitates exporting excess solar power to other western states during oversupply events. Interstate transmission lines allow California to ship midday solar surpluses to nearby states with higher afternoon demand.
An emerging approach is boosting electricity demand specifically during the midday solar peak. One strategy is encouraging the deployment of electric vehicles and incentivizing their charging to occur during midday hours when solar output is highest. Two-way “smart” charging could allow EV batteries to absorb excess solar and later discharge to the grid as mobile energy storage. Another demand boosting concept involves using solar power to produce green hydrogen fuel through electrolysis processes that could run most intensively from midday to early afternoon.
Overall, California is employing a portfolio of technical, market-based and policy mechanisms to more effectively manage the integration of high levels of variable solar power onto the grid. By aligning electricity supply and demand patterns through strategies like battery storage deployment, time-variant rates, interstate trade and intentional midday demand boosting, the state aims to maximize the value of its abundant solar resources while maintaining a reliable and low-carbon electricity system. Challenges remain but California continues to pioneer solutions that can inform best practices for other regions scaling up renewable energy.