New Mexico Geological Society Annual Spring Meeting — Abstracts

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New Mexico is moving toward a “mostly-electric” future as abundant renewable, carbon-free electric energy is produced in-state, with a substantial portion exported to meet out-of-state demand. Ideally, this energy should be provided on a 24/7, as-needed, base-load resource. The 2019 New Mexico Energy Transition Act (NMETA) requires utilities to generate and distribute 50% of their electric power using renewable sources (primarily solar, wind, and geothermal) by 2030 and 100% by 2045. Fortunately, New Mexico has the nation’s largest combined solar/wind/geothermal energy potential. Because the sun and wind can’t shine or blow 24/7, neither solar nor wind power can generate electricity full-time or on an as-needed basis--two features necessary for a successful energy transition. The solution to this problem is developing utility-scale energy storage technologies such as pumped-storage hydroelectric power (PSH).

Numerous large-scale electric energy storage schemes have been proposed, but most have one or more shortcomings at utility-scale, such as: inadequate capacity (lithium-ion batteries can store only around 4-6 hours of energy at mega-watt levels); environmental impacts (lead-acid batteries produce massive amounts of toxic waste and have limited lifespans); physical limitations (compressed-air storage requires monumental facilities, whether manmade structures or air-tight, impermeable geologic formations); or are economically impractical (a forest of gravity-powered counterweight towers cost billions of dollars). According to DOE’s National Renewable Energy Laboratory, the most dependable, economical, and environmentally-friendly grid-scale electric storage technology available today is proven, centuries-old pumped-storage hydroelectric (PSH).

Employing PSH requires a special combination of physical and geotechnical characteristics, conditions that are seldom present at most locations. However, New Mexico’s existing natural features (especially its geology, hydrology, and topography) provide ideal circumstances for creating PSH facilities at multiple sites around the state. Developing PSH involves construction of a closed-loop water cycling system which can be powered by New Mexico’s abundant daytime supply of low-cost (~2 cents/kwh) solar and wind energy to pump water through penstocks from an existing lower reservoir to an upper reservoir located at least 500 feet above, thereby creating a substantial “hydrologic head” which can later be used to drive electricity-generating turbines. During periods of high-demand for electric power in late afternoon and evening, the process is reversed: water from the upper reservoir is released downward through the same penstocks under high pressure and into the combined turbine/pump equipment to generate high-value, carbon-free electricity. The combined mechanical-electrical efficiency of such systems is typically 85-90%, so that power generated during peak-demand periods can then be sold for ~10-12 cents/kwh, yielding a gross return of 500-600%. A portion of this return-on-investment will be used to offset the significant capital construction costs of building a PSH facility, but is compensated by low operational costs--thus providing substantial profit to the facility owner (utilities and/or investors). The ideal PSH facility will provide at least 100 hours of renewable energy storage at 500-1000 MW power capacity—true utility-scale storage. See Figure 1 for example of a hypothetical PSH facility.

But PSH cannot successfully be developed unless certain key geologic, hydrologic, and topographic features are concurrently present at sites under consideration. The essential site characteristics of a successful PSH facility in New Mexico are: (1) an existing primary/lower reservoir holding at least 100,000 acre-feet of water, with a minimum 1000 acres surface-area; (2) year-round water availability (no new water-rights need be acquired since PSH does not “consume/use” water while being cycled through its closed-loop system; water is merely "borrowed" or leased from the existing water-rights owner); (3) topography suitable for constructing an storage/upper reservoir with at least 1000 acre-foot capacity, ideally within a dry canyon or large off-stream arroyo to minimize excavation/construction costs and environmental impacts; (4) suitable geology and soil conditions (i.e., underlying geologic impermeability) to construct a leak-resistant earth-fill storage dam and buttresses using local geomaterial; (5) at least a 500-foot elevation difference between the upper storage reservoir and existing lower reservoir to create sufficient hydrologic head within the penstocks driving electricity generating turbines located in the lower-reservoir-level powerhouse; (6) sufficient non-turbid water available from the primary reservoir to fill the upper/storage reservoir without creating problematic daily drawdown or environmental effects at the surface of the lower reservoir; (7) at least 1000 acres of land available for purchase or long-term lease at the facility site, preferably for acquisition from a willing public agency or landowner; (8) proximity to nearby existing electric transmission lines for importation of low-cost renewable electricity to power the pumps and for exportation of higher-valued power generated by the turbines back into the grid during peak-demand periods; (9) access to existing surface roads for construction and maintenance of the PSH facility; (10) absence of any “fatal flaw” conditions that might delay or prevent development of the facility (e.g., unsuitable geotechnical conditions for construction/operation, presence of T&E species or sensitive archeological/cultural features at the site, unwillingness of the existing reservoir owner or operator to allow use/cycling of its water for the PSH facility).

All of these conditions/features are present at a minimum of eleven sites within the state of New Mexico. These sites are also located in proximity to existing or planned utility-scale wind, solar, and geothermal generation facilities. The identified sites and their respective owners/operators are: Navajo Reservoir (USBOR), Heron Reservoir (USBOR), El Vado Reservoir (USBR/MRGCD), Abiquiu Reservoir (USACOE), Cochiti Reservoir (USACOE), Elephant Butte Reservoir (USBOR), Caballo Reservoir (USBOR), Bluewater Reservoir (USBOR), Conchas Reservoir (USACOE), Santa Rosa Reservoir (USACOE), and Eagle Nest Reservoir (NMISC/NMPD). To fulfill the NMETA’s mandates, New Mexico’s three investor-owned utilities, seven public-agency electric utilities, two co-op generators, and the more than a dozen merchant power generators--as well as state agencies such as the NMPRC, NMEMNRD, and the Legislature—need to recognize that it will be difficult to achieve NMETA’s lofty goals of achieving a carbon-free, reliable and renewable energy future unless they develop facilities for utility-scale, long-term, high-capacity, dispatchable, and demand-responsive storage of electric power created by the state’s abundant renewable solar, wind, and geothermal energy resources.