Enlarge /. On August 14 and 15, a heat wave drive suffered power outages. And then, on August 16, a station in Death Valley hit 130 ° F …
In mid-August, just before dry thunderstorms started a series of fires that would break California records, an intense heat wave resulted in rolling blackouts for two consecutive days. The problem arose in the evening when solar energy was dropping, and some claimed it was the result of reliance on renewable electricity. But it's not that simple, because the failures could have been avoided. A new preliminary root cause analysis report from two state commissions and the California independent system operator who operates the network offers a clearer picture of what went wrong.
The rolling outages affected a few hundred thousand people, beginning around 6:30 p.m. on both August 14 and 15. They were actually the result of the network rules: as soon as the remaining reserve generation falls below six percent of the current requirement, the network operator must initiate rolling blackouts.
The report attributes the need for outages to three things: extreme and widespread hot weather, a failure to update peak load forecasting procedures as solar power grows, and errors in the grid market that caused some facilities to export electricity when it was actually needed -State.
First of all, the weather that caused the shortage: it was remarkably hot indeed, which drove the demand for air conditioning from afternoon to evening. The report assumes a heat wave of around 1 in 35 years. Network planning is extreme to some extent, but oversizing the potential supply for every possible event can bring costs to astronomical levels, so there are limits. And those boundaries are changing as the report describes this as "an extreme heat storm caused by climate change". There is no formal scientific study of this weather event, but the extreme heat trends are clear in a warming climate.
Enlarge /. The average temperatures on August 14th and 15th (and thus the electricity required for cooling) were exceptional.
Equally important is that most of the west was in the same hot high pressure weather system. Since demand had increased everywhere, there was not enough generation available in neighboring countries to import more (more on this in a moment). Hot weather also limits the operation of incinerators – they just don't work as efficiently – and the transmission line capacity.
The second item on the list in the report relates to the demand forecast. Network operators in the past have focused on targeting supply so that it reaches the peak of demand, as that should handle the rest of the day. But the pinch came after the peak in this case, at a time when solar energy was losing its peak for the day but the air conditioners were still rumbling. The report refers to this as “net demand peak,” that is, the peak of total demand minus solar and wind generation. As the share of solar power generation increases in California, this issue becomes increasingly important, but has not been central to planning practices.
On August 14, for example, the peak load just before 5 a.m. was 46,800 megawatts. By 7:00 a.m., demand had dropped by around 4,600 megawatts, while wind and solar power had dropped by 5,400 megawatts.
There's more going on here. The sun and wind production in this window was slightly lower than expected due to the decrease in wind and the high cloud cover. Due to the drought conditions, hydropower generation is declining this year. Natural gas plants generated 1,400 to 2,000 megawatts less than expected due to thermal influences and other problems. In addition, 400 megawatts of pre-planned gas system failures were not replaced.
Enlarge /. Demand (blue) and demand minus solar and wind generation (yellow) on August 14th and 15th. The periods of rolling power failures are shown in the gray bars.
Of course, imports from abroad were also lower than usual, although an additional offer was received when an emergency request was made. Aside from demand elsewhere, this was also due to a failure of a transmission line between California and the Pacific Northwest, limiting transmissions.
Another important strategy for these scarce supply events is to reduce demand. This includes specific agreements that may be drawn upon, as well as the general public conservation demands made in California and some neighboring states. Overall, the energy suppliers were able to achieve around 80 percent of their coordinated demand reduction and thus lower the demand in the early evening by around 1,000 megawatts.
The third focus of the report is on the behavior of the market in the run-up to the rolling power outages. In several ways the market has messed up where it could have helped. The demand forecast made the day before underestimated peak demand by around 3,400 megawatts. And the bidding process that generators use to sell their electricity told some California factories that they could export their electricity to other markets.
A rare bug like this one usually requires many problems to be stacked at the same time, and that appears to have been the case. The report notes that power outages were avoided when the weather in California resumed the heat on August 17th and 19th. This was partly due to some temporary changes in the tendering process, greater availability of imported electricity and greater reductions in demand.
Looking ahead, the report highlights a few things that need improvement. The planning process must adapt to the current network conditions. The daily forecasts and tendering procedures could also be tightened. However, adding a grid-scale storage would make everything a lot easier by smoothing out supplies in the evenings. This will only come true when the share of renewable energies increases – and not just in extreme weather conditions.