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Utilizing Enhanced Geothermal Generation as a Load-Following Resource is Examined

Deployment of enhanced geothermal generation could be boosted by using the technology as a load-following rather than baseload system, according to an article in Nature Energy.

The article, The role of flexible geothermal power in decarbonized electricity systems, was written by researchers at Princeton University and Fervo Energy.

Unlike a naturally occurring geothermal systems that tap underground sources of hot water, an enhanced geothermal system injects fluids into hot rocks deep underground to extract steam or hot water.

Conventional geothermal energy’s reliance on naturally occurring hydrothermal reservoirs limits its deployment potential, the report’s authors said, noting that a large portion of the high-quality hydrothermal resources in the United States have already been tapped and geothermal power makes up only 0.4 percent of annual electricity generation.

By eliminating the reliance on pre-existing hydrothermal reservoirs, however, enhanced geothermal systems could unlock more than 5 terawatts of generating potential in the United States, according to the Department of Energy.

However, the report’s authors noted that past studies have assumed that enhanced geothermal systems would operate as baseload resources because that is the preferred operating model for most geothermal power plants because they tend to have high fixed costs and near-zero variable costs and derive few, if any, benefits from curtailing output.

But as the electric grid changes and more variable resources, such as wind and solar power, are available there would be little economic incentive to pay high fixed costs for baseload generators that will be needed only when variable resources are insufficient to meet demand, the authors said.

In part because of this unfavorable economic environment, past energy system studies have concluded that the cost of geothermal drilling would need to decline substantially for baseload enhanced geothermal systems to play a major role in future electricity grids, the authors argue.

In the Nature Energy article, the researchers evaluated the impact of operational flexibility on the long-run system value and deployment potential of enhanced geothermal systems power in the western United States and found that “load-following generation and in-reservoir energy storage enhance the role of EGS power in least-cost decarbonized electricity systems, substantially increasing optimal geothermal penetration and reducing bulk electricity supply costs compared to systems with inflexible EGSs or no EGSs.”

“Flexible geothermal plants preferentially displace the most expensive competing resources by shifting their generation on diurnal and seasonal timescales, with round-trip energy storage efficiencies of 59–93%,” they wrote. “Benefits of EGS flexibility are robust across a range of electricity market and geothermal technology development scenarios.”

“The primary conclusion of this work is that flexible operation represents a viable pathway to large-scale deployment of EGSs in future electricity systems, independent of basic cost reductions,” the report’s author said. “This result suggests that EGS technology development efforts, which currently focus almost exclusively on reducing costs, should place a similar level of emphasis on the development and demonstration of flexible capabilities. We also find that flexible operation would allow successfully developed EGS power plants to deliver substantially greater system-level benefits than had been previously assumed, a finding that may hold relevance for policymakers and analysts focused on identifying suites of technologies to address the broader challenge of energy system decarbonization.”


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