Looking into California grid net exports for its relationship to solar curtailment
Last time, I looked into the common spring day cases in California where incredible solar generation is curtailed in the middle of the day and, sometimes, gas is dispatched to meet the load. While there is ample evidence that the curtailment is happening more often — 2024 through March 25th was ~875,000 MWh of curtailment compared to ~550,000 MWh in 2023 — all of the dynamics aren’t clear. I speculated last time that maybe imports — despite the grid exporting at that time — were meeting the load that would have otherwise met by curtailed solar. I now don’t think that’s the case.
Let’s recap. In the middle of the day, California’s incredible solar resources generate more power than can be consumed given transmission constraints. Some other generation source is providing power to the homes and business that couldn’t be reached with cheap solar. But what is it?
One possibility is that imports meet that load. The grid is a net exporter of power during these periods, but it’s possible that some areas are importing power and others are exporting. But that doesn’t look like it’s the case. As solar generation picks up and prices fall, CAISO exports more to every one of its trading partners except one. (Only from IID in southeast California do imports increase.) (Rising numbers in the chart below mean more exports from CAISO to that neighboring grid; when the line goes down it means CAISO is importing energy.)
In fact, “exports” might give the wrong impression about what’s actually happening here. When you look at CAISO’s boundary map, a few of the regions are small and within California itself. In fact two of the three biggest balancing authorities that CAISO is exporting to are population centers within California — LADWP (Los Angeles) and BANC (Sacramento).
In summary, the largest force at play appears to be that high solar generation —> low prices —> CAISO exporting to “neighboring” grids, that may just be a population center in California that operates independently.