Impacts of Weather-Driven Output Variability on the Value of Geothermal Electricity

Geothermal power is typically represented in electricity system models and planning exercises as a baseload resource with constant power output. While this representation is generally accurate for conventional dry steam and flash power plants using evaporative cooling, it does not accurately reflect the strong impact of variations in ambient air temperature on the power output of air-cooled binary cycle plants, which make up the majority of new geothermal installations in the US today. These variations in output can be significant, at up to 50% of nameplate plant capacity on the hottest summer days, and there is a need to understand their impact on the value of geothermal power plants as electricity systems continue to decarbonize. In this paper we use an electricity system capacity expansion model to explore the impact of temperature-induced output variability on the value and deployment potential of enhanced geothermal systems (EGS) in the western US. Notably, we find that the value of a baseload EGS plant with temperature-dependent output in a decarbonized electricity system is higher than that of one with flat output when EGS market penetration is low (<10% of total generation). However, the opposite is true when large amounts of EGS are deployed in the system. The magnitude of discrepancy between weather-dependent and weather-independent outcomes is larger when EGS plants are assumed to be capable of flexible operations, though the direction is the same as for baseload plants. Our results demonstrate that while a weather-sensitive output profile is more valuable in the early stages of geothermal deployment, it also leads to greater self-cannibalization as deployment scales up.