Techno-economic study estimates large EGS potential in continental US
A Stanford study analyzes the techno-economics of enhanced geothermal systems across the continental United States under baseline and advanced scenarios.
The potential for Enhanced Geothermal Systems (EGS) in the continental United States can reach up to 82,945 GW based on business-as-usual scenarios and up to 184,112 GW considering the scenario of flexible geothermal dispatch. This is according to a study done by Mohammad Aljubran and Professor Roland Horne from Stanford University.
The full article “Power supply characterization of baseload and flexible enhanced geothermal systems” can be accessed via this link. The study also has a companion ArcGIS web-based map.
A new approach to EGS modeling
Several studies have been done in the past on the potential of EGS for power generation. The new study proposes to improve on these studies by using a new temperature-at-depth model and incorporating more accurate time-dependent and weather-dependent simulations of the EGS project life cycle, as well as a detailed EGS life cycle simulator called Flexible Geothermal Economics Modeling (FGEM).
Two drilling rate scenarios were considered – a baseline scenario, and an advanced drilling scenario that accounts for the improved performance in drilling rates observed in recent EGS projects.
The EGS supply potential was estimated with respect to capital cost and the levelized cost of electricity (LCOE), with due consideration for the optimal depths required to maximize the economic outlook of EGS and seasonal generation variability of flexible operations.
Modeling parameters and assumptions
Techno-economic analysis was done by assuming that multiple independent projects will exploit the EGS resource, each one occupying an 18 km3 lease (18 km2 areal extent and 1 km thickness). FGEM was used to simulate the life cycle of EGS plants, as well as flexible geothermal operations through wellhead throttling and power plant bypass.
Based on successful EGS implementations, the model considered an EGS systems as consisting of doublets of horizontal production and injection wells each with a 2000-meter lateral section completed with 9.625-inch casing string. Each doublet was set to occupy a hydraulically stimulated reservoir with 1.16 km3 bulk volume and 10% porosity, and a total of 16 doublets will fill each 18 km2 grid cell. Each well was set to flow 125 kg/s.
Only resources with temperature-at-depth of 150 °C or higher were considered as being techno-economically significant for power generation. Resources spanning depths of 1-7 kilometers across the contiguous United States were considered. Power generation was done using Organic Rankine Cycle (ORC) power plants, and each EGS project had a lifetime of 25 years.
EGS potential estimates
The study estimated a total gross EGS capacity potential of 245,032 GW, significantly greater than the most recent estimates of 7469 GW by Augustine et al. Although the estimated EGS power potential is large, it is important to note the amount that can be economically produced is likely to be much smaller. It is also important to note that 78% of that potential was at depth of 6–7 km, where subsurface temperatures were significantly high compared to shallower depths.
The majority of EGS net generation potential per unit area is in the Western and Southwestern regions of the United States. After excluding sensitive land, California showed the greatest capacity potential for EGS, with a total capacity potential of 20,882 GW. Oregon, Nevada, Montana, and Texas followed in rank with relatively high potential of 18,270, 16,484, 15,681, and 14,578 GW, respectively.
Techno-economics of EGS
The study evaluated the economic viability for each 18 km3 EGS project based on capital expenditure (CAPEX), operational expenditure (OPEX), and generation over time, which were represented in terms of LCOE with a discount rate of 7% and investment tax credit (ITC) of 30%.
Considering the business-as-usual (BAU) scenario of baseload dispatch and baseline drilling rates, the study found that LCOE was minimized by drilling to the deepest point (7 km) for 89.3% of the United States areal extent. Meanwhile, drilling to depths of ? 4 km was found optimal only across 0.27% of the United States areal extent, mainly around Western United States.
Advanced drilling rates resulted in 24.3% LCOE improvement, on average, where the baseline and advanced scenarios resulted in average LCOE of 86.1 and 63.4 USD/MWh, respectively.
Considering the BAU scenario of baseload dispatch and baseline drilling costs, a total of 93,176 GW EGS resource capacity was available with LCOE below that of the average geothermal PPA pricing. Compared to LCOE estimates of hydrothermal and biomass resources, the study estimated a total EGS resource capacity under BAU scenario of 82,945 GW and 155,821 GW, respectively. The study also estimated that total EGS resource capacities of 0.65 GW were economically feasible compared to the marginal LCOE of solar PV, but no EGS resources were found viable compared to onshore wind in terms of LCOE.
The study also found that a 6.36% average reduction in LCOE across EGS resources can be achieved by implementing flexible operations where power output was varied to maximize power generation over the project lifetime. Under this scenario, the study estimated total flexible EGS resource capacities of 189,667 GW and 46.16 GW that were economically feasible considering the marginal LCOE of biomass and solar PV, respectively.
Source: Mohammad Aljubran via LinkedIn
