A few days ago I wrote a brief article about the recent California heat wave, specifically the rolling blackouts and conflicting announcements from PG&E and the California Independent System Operator (CAISO, the folks in charge of balancing power demand and supply throughout the state). Since then I’ve discovered that CAISO makes very detailed data available on a somewhat obscure part of their website. This is the good, the bad, and the ugly of electricity in California. My case study is a typical day from the recent heat wave.
As always, my methods are transparent. Click here for my Excel workbook.
Wednesday, September 7
In Los Angeles, the high temperature was 98 degrees F. The low was 78. San Jose was 100 and 68. Even the normally chilly San Francisco hit 77. Here’s a quick summary table.
It was hot. Really, really hot. And this lasted from September 1 through 9. The high temperature in Sacramento was over 100 degrees each of those days. September 7 was not the hottest and not the coolest. It was pretty representative of the entire episode. There were FLEX alerts and rolling blackouts (although not in Sacramento where the governor gave a press briefing from his office wearing a fleece jacket).
There must be a few economists at CAISO. Their website gives supply and demand data each day in five-minute increments. The data can be downloaded (although only one day at a time). That’s the source of the data on the graphs that follow.
Demand peaked at 50 gigawatts at 4 pm. That’s 50,000 megawatts. California is a very power-thirsty state.
Demand follows the usual pattern: low overnight, begins to rise about 6 am when people are waking up, increases steadily as the temperature rises until about 5:30 pm, then gradually decreases as the sun sets and things cool off.
I won’t explain the demand response event in detail. Follow the link for a good tutorial. I’ve posted a pdf below that contains the key points. Here’s the really short version.
A demand response event is any of the many programs to induce businesses and homes to lower electricity use. These range from the FLEX program for households to businesses that agree to have their power shut off during emergencies. In return they get lower electricity prices for the rest of the year. (I saw this first-hand when I was a consultant at Visa International in the summer of 2000. One hot afternoon an announcement came over the speakers that PG&E would shut off power to the building in 15 minutes. There were a lot of software developers in my area. I listened to their wailing when the power went off before they shut down their machines.)
Supply comes from a variety of sources:
- Natural gas
- Large hydroelectric
- Battery storage
The graph below shows the percentage of supply that is generated by each source. I’ve omitted batteries because their contribution can be positive or negative (when they are charging). That would mess up my pretty graph. Coal is 0.01% of the total supply, too small to see.
Natural gas generates about half of the power supplied by PG&E. It fills the gaps left by renewables.
Renewables are mainly wind and solar. Their power supply depends on whether the sun is shining and/or the wind is blowing. The shape of the power supply is low during nighttime hours, rising as the sun rises, then gradually declining, with a sharp decrease at sunset.
Large hydro and nuclear supply at fairly constant rates throughout the day. Hydro can be adjusted slightly by changing the flow rate of the water. A more severe adjustment is shutting down or starting up a turbine. That would create a sharp decrease or increase in output. It doesn’t look like either event happened on September 7.
That leaves imports. California buys electric power from Arizona, Nevada, Oregon, and Mexico. This is another source that can be adjusted to fill supply shortfalls. Imports supplied between 25% and 10% on September 7. I have to add that Arizona still has a number of coal-fired power plants. In May 2022 9.2% of Arizona’s electricity came from coal. A whopping 30.7% was from nuclear. Effectively, California is greenwashing electricity by outsourcing coal generation to Arizona.\
California wants to ban sales of gas-powered vehicles by 2035. In one of the great ironies, electric vehicle owners were asked not to charge their cars during the heatwave. California’s politicians seem determined to drive the state off a cliff. That may have worked for Bill Murray (Groundhog Day, 1993). It probably won’e work for the tarnished Golden State.