Geothermal power is seasonal: more power in winter than summer

Eventually fossil fuels will decline to the point that renewables will have to replace them, and the electric grid become 100% renewable.  One of the factors that will make this difficult is that 50 to 90% will need to come from wind and solar, and both wind and solar are seasonal. And so is geothermal, though the amount of power it does or could provide is so trivial that it doesn’t matter, except perhaps for local areas near geothermal hotspots that also have transmission lines.

What follows comes from: NREL. January 2016. Doubling Geothermal Generation Capacity by 2020: A Strategic Analysis.  National Renewable Energy Laboratory.  Technical Report NREL/TP-6A20-64925

Many geothermal power plants generate less power in the summer.  There are several reasons, but the main one is that there is a smaller brine-ambient air temperature differential.  [ Though evaporative cooling can help (though I wonder how much extra power this takes).]

Figure A1. Comparison of Nameplate to Net Summer Capacity, 1990-2013. Figure shows current discrepancy between installed nameplate capacity (design output of installed projects) to net summer capacity (net output of geothermal power available for sale during the summer). As of 2013, EIA survey data from geothermal generators shows that geothermal nameplate capacity was 3,765 MW in comparison to 2,607 MW reported net summer capacity. Sources: Energy Information Association (2015) Nameplate Capacity: Form 860 Generator Data, State Electricity Profiles (July 2015). Summer Capacity: Annual Energy Review (2015).

Figure A1. Comparison of Nameplate to Net Summer Capacity, 1990-2013. Figure shows current discrepancy between installed nameplate capacity (design output of installed projects) to net summer capacity (net output of geothermal power available for sale during the summer). As of 2013, EIA survey data from geothermal generators shows that geothermal nameplate capacity was 3,765 MW in comparison to 2,607 MW reported net summer capacity. Sources: Energy Information Association (2015) Nameplate Capacity: Form 860 Generator Data, State Electricity Profiles (July 2015). Summer Capacity: Annual Energy Review (2015).

As you can see in figure 2 below, most geothermal power is found in the west, especially California.

Figure 2. Map of United States geothermal regions.

Figure 2. Map of United States geothermal regions.

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