California leads the nation in renewable energy production, including wind, solar, geothermal, biomass, biogas, and small hydroelectric facilities. These forms of green energy are essential to provide clean energy to the electric power grid and help mitigate the worst impacts of climate change by reducing our dependence on fossil fuel-based energy production.
Solar panels in California produce more than enough energy to meet electricity demands, and often production is curtailed to avoid overloading the energy grid. However, there is a critical dilemma with renewable energy: peak energy demand time does not often coincide with peak energy production time.
Renewable energy is plentiful during times of peak production. Most solar energy is produced in the morning through late afternoon on a sunny California day. The height of electric energy demand, however, is often in the evening, between 5:00-7:00 pm. This is especially true during the summer months when the hottest time of day on the west coast is typically late afternoon, meaning residents are increasing their air conditioning usage, among other home energy demands.
For this article, I reviewed California Independent System Operator (Cal ISO) data to better understand the dilemma facing California. Despite the challenge of meeting energy demands with renewable energy, several solutions exist that can be implemented today to address the issues discussed below. Let’s take a closer look.
California’s Dilemma: Renewable Energy Production Vs. Energy Demand
Figures 1 and 2 compare the Cal ISO supply trend graphs for August 16, 2023, a day with high energy demand, and April 14, 2024, a day with low energy demand. In these graphs, renewable energy production is primarily solar energy and wind energy; biomass and biogas produce comparatively little renewable energy at this time.
In Figure 1, you can see that on peak load days, the amount of natural gas energy production exceeds the amount of renewable energy production, especially later in the day when renewable energy production drops off. Figure 2 shows that the amount of renewable energy production is effectively the same on peak load days and low load days.
The renewable energy dilemma is evident in these figures. While more than enough energy is produced using renewable sources in April, August energy demands are higher later in the day, when renewables are less productive. Even in April, renewables are not reliably providing energy later in the day as energy demand continues. In California today, this gap is filled by burning natural gas. However, continuing to rely on fossil fuel-based energy sources is not a sustainable option as the climate continues to change.
Figure 1 shows the Cal ISO Supply Trend Graph for August 16, 2023, a peak load day (copied from Cal ISO Website).
Figure 2 shows the Cal ISO Supply Trend Graph for April 14, 2024, a low load day (copied from Cal ISO Website).
Timing of Peak Production and Peak Load
Table 1 displays data for a single peak load day in California during calendar years 2019 through 2023. Note that peak renewable energy production these days does not occur at the same time as peak energy demand. Instead, peak renewable energy production typically occurs several hours before peak demand. Reduced renewable energy production in the evening is due to the fact solar energy production drops off.
The increase in energy demand on a summer evening is because consumers continue to use their air conditioners while simultaneously cooking dinner, plugging in electric vehicles after a daily commute, starting a load of laundry, or otherwise increasing their energy usage at home.
To accommodate this increased demand, energy was produced from natural gas facilities; energy production from these facilities peaked around the same time as demand peaked. This resulted in more energy being produced by natural gas facilities than from renewable energy sources on each peak load day.
Although several hundred thousand MWH of renewable energy were produced in August 2023, Cal ISO data reveals that nearly 50,000 MWH of wind and solar energy were curtailed during this time. That means that nearly 50,000 MWH of wind and solar were not harvested in August 2023, despite the availability of this energy. This curtailment is due to system conditions, such as risk of overproducing energy, creating an overfrequency event, and market forces, like lack of energy demand during peak energy production times. Lack of energy storage capability also contributes to energy curtailment.
Later in the Evening Energy Demand
Upon further review of Cal ISO data, I noticed that peak load data can be misleading, so I looked more specifically at data recorded between 6 PM and 8PM, an hour or more after peak load is presented in Table 1. This “later in the evening” data (also referred to as “later” data) was reviewed to determine the appropriateness of peak load data when analyzing renewable energy production levels. In Table 2, the energy necessary to meet a peak demand period between 6 PM and 8PM was mostly produced by natural gas. By this time, renewable energy production was declining.
Because energy is still in high demand later in the evenings, Cal ISO should be concerned about the lack of available renewable energy sources to supply this later peak load. Burning natural gas is not a climate conscious energy source.
This issue exists across the United States and should be a concern of all electric utilities and government authorities as they try to address climate change with renewable energy.
Table 3 compares the percentage of renewable energy capacity that is produced during peak renewable energy production, peak load period, and “later in the evening” when system load remains high. Though renewables can produce 100% capacity at their peak production time, this does provide clean energy during peak demand or later evening demand.
Solutions: Energy Storage, Green Hydrogen, EVs
Several solutions can be used in tandem to address this dilemma. First, substantial amounts of stored energy are needed to counteract the significant reduction in renewable energy production that occurs every evening.
In California, between 6,000 MW and 12,000 MW of stored energy is needed during late evening on most days. Energy storage could be in the form of large-scale lithium-ion batteries, like the big battery in Hornsdale, Australia, or stored hydroelectric energy. More distributed offshore wind farms will also be necessary to help produce enough energy to meet the storage needs, as solar energy is such a variable source.
In addition, large scale biomass and biogas, such as green hydrogen, production facilities will be essential to provide energy that is more climate conscious. Biomass and biogas production can occur at existing fossil fuel production facilities. Existing natural gas burning power plants can be converted to burn biogas products, which will reduce investments in new infrastructure.
Finally, charging electric vehicles during peak renewable energy periods can help to match renewable energy production and energy consumption. This can be done by implementing bidirectional, Level 2 chargers in residences and throughout parking lots, especially those where commuters are encouraged to leave their EVs connected to the charger for entire 8-hour workdays. When used in this manner, EV batteries act as storage facilities for renewable energy, and can provide grid support when a low voltage or underfrequency event occurs.
Prescient provides a more in-depth analysis of renewable energy trends and challenges for our clients. Interested in learning more about how we can help your electric utility prepare to successfully integrate renewable energy into your system? Contact us for a free consultation today.