California Solar Power Market
At the end of 2023, the United States had 162.8 GW of solar capacity installed nationwide. About 25% of the capacity is in California alone with 43.2 GW across almost 2 million installations (residential, commercial, and utility) [Source: SEIA States Map]. The next largest state as measured by total solar capacity is Texas with 20 GW of solar capacity installed. Despite recent headwinds in California, this is going to continue growing.
California has been implementing solar for decades now. In this post, we’ll dive into how far along California is in its solar journey and what the current energy mix is within the nation’s most populous state. This will help you contextualize the energy needs of the country and the opportunity for solar as you look for your next solar job in California
What is the California Independent System Operation (CAL ISO)?
California Independent System Operation (CAL ISO) is a non-profit public benefit corporation that manages the flow of electricity across the 26,000 miles of power lines that serve almost 80% of the state. It is responsible for coordination of different energy sources (e.g. switching from solar to natural gas) and to competitively price electricity.
It was opened in 1998 to help improve efficiency across the electricity grid. Impressively, it is matching buyers and sellers of electricity, facilitating thousands of transactions every day. It is responsible for forecasting demand (it updates its demand forecast dynamically every 5 minutes!) before companies buy and sell power across the market. The ISO is a non-profit that incentives a transparent and efficient energy marketplace.
Now what’s really fascinating is that California ISO makes all of the energy data it collects available online for anyone to monitor and analyze. It gives us a real-time view into the energy supply by source and the state's demand.
California Energy Demand by Hour and by Day
You can access the real-time California ISO demand dashboard here. We’ve pulled screenshots of the dashboard on a winter evening in January to help you understand how to interpret the dashboard.
Remember, 1,000 MW = 1 GW. California’s grid currently has capacity for 41.5 GW of energy and we are currently using 25.5 GW. Evenings use more power when everyone is at home using appliances, watching TV, and heating their homes in the winter. You can see that we expect a peak energy use at 26.2 GW at around 6:15pm, which is a bit lower than tomorrow’s peak. This is no where near the capacity that we have available.
The next chart you’ll see shows the hour-by-hour demand for the entire state. Energy demand is at its lowest levels in the middle of the day (12pm) or in the middle of the night (3am).
California’s Energy "Duck Curve"
Now, we can look at the same chart excluding wind and solar energy consumption during the day. This chart is fascinating for California. During daylight hours, even in the winter time (it’s currently a chilly January evening), California almost entirely runs on solar and wind energy. For example, today, between 10am and 3pm, California only needed between 4.5 GW and 7 GW of additional energy excluding solar and wind.
However, this dramatically changes at nighttime. The energy grid has to shift to other resources dramatically over a 3 hour period from 3pm to 6 pm, which is the peak of energy demand. This is the core reason for why your energy bill is more expensive per hour at night than during the day. You’ll commonly see the day dip referred to as the “duck curve.” Each year more solar comes online, the “duck curve” gets lower and lower as California shifts to run more on renewable energy.
The final chart on the page shows the California ISO’s 7-day forecast. You’ll notice weekends look substantially different than weekdays, when many people are out and about during the day and less likely to be at home in the evenings.
California Energy Supply by Hour and by Day
The energy demand we just reviewed gave you a good sense for how much energy California needs each and every day, but now we can dive into the supply mix of energy sources.
We can break down the 25 GW of energy California is being supplied now by energy source. Only 1.7 GW of this energy is currently coming from renewables given it’s 7:30pm on an evening in January with little wind. The bulk of renewable energy (43%) comes from California’s limited geothermal plants. You’ll see that Solar is even negative. This is because there is some limited (right now, only 55 MW) energy being used by solar auxiliary equipment. Note that batteries that are powered by Solar are included in the “batteries” bucket and are not considered renewables. As batteries become more efficient and are bette integrated into solar systems, we’ll certainly see “Batteries” grow as a % of the evening supply.
California Solar Supply by Hour and by Day
The next chart shows the energy source by hour of the day, where we can see the solar and battery trends throughout the day. The grid has a dramatic shift when the sun rises and sets.
Solar drives the majority of the ~15 GW of renewables energy used during daytime hours. In the evenings, California ramps up Natural Gas and Imports (from other states) to offset the decline in solar power to power all homes and businesses in the state. You’ll see that Batteries shifts negative during the day (as solar recharges the batteries), as do Imports, which also include Battery sources. Hydroelectric power remains an important component of California’s energy grid in the evenings, but is close to 0 during the day. Nuclear power is consistent throughout the day and the majority of it comes from the only functional nuclear plant in California, Diablo Canyon Plant. The rest comes from out of state plants.
What’s next for California’s Energy Grid
California’s energy grid has gone through a significant and accelerating change in the past 2 decades as solar has grown to be a core component of the overall state supply. While we still need many GWs of additional capacity to power the state during the day, what will become critical over the coming years will be pairing solar panels with battery technology to power the state’s needs at nighttime when there is no direct sunlight.
Subscribe to our blog to keep learning more and be sure to check out and familiarize yourself with the intriguing CAL ISO dashboard!
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