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| Fig. 1: Qualitative depiction of daily electricity demand (solid line) and pumped-hydroelectric operation (dashed) for a converted Hoover Dam. During off-peak hours, water is pumped back into Lake Mead to store energy as gravitational potential energy. During peak demand, stored water is released through turbines to create electricity. (Source: N. Ly). |
Pumped hydroelectric storage (PHS) stores electrical energy by pumping water to a higher elevation and releasing it through turbines. It requires two reservoirs at different elevations and consistent water supply, so environmental feasibility is a major challenge. In dry regions, water scarcity has both an ecological and economic value. Hoover Dam, located on the Colorado River between Nevada and Arizona, shows this trade off. The dam provides water and hydroelectric power to millions of people, yet water in the reservoir behind the dam, Lake Mead, has fallen more than 45 meters since the 2000 drought, as shown in Fig. 1. [1]
Given its size, elevation, and structure, Hoover Dam shows potential for converting an existing hydroelectric facility into a pumped-hydro storage system. In this model, water would be pumped from the downstream reservoir back into Lake Mead during off-peak hours, turning the dam into a battery. However, water is scarce in this region, raising the question: does the value of energy outweigh the market of water being cycled?
PHS is currently the most dominant grid-scale storage technology method, accounting for 94% of total energy storage. [2] Modern advances achieved round-trip efficiencies between 70%-85%, comparable to large scale battery storage. [3] In this context, Hoover Dam serves as a potential case study for evaluating the feasibility of turning an existing hydroelectric structure into a closed-loop pump storage system. To solve this, Hoover Dam can be modeled as two reservoirs separated by an elevation head h and connected by reversible turbines and pumps. As shown in Fig. 2, the Hoover Dam structure can be represented schematically with Lake Mead as the upper reservoir and the Colorado River as the lower one. The energy stored in a PHS system is found through the change in gravitational potential energy:
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| Fig. 2: Simplified schematic of pumped-hydroelectric energy storage at Hoover Dam. Water from Lake Mead (upper reservoir) is released through turbines to generate electricity. 160 m hydraulic head is the average elevation difference between the lake and the riverbed. (Source: N. Ly). |
Where E is the energy (J), m is the mass of water (kg), g= 9.81 m/s2 is the acceleration due to gravity, and h is the height of the hydraulic head (m).
According to the U.S. Bureau of Reclamation, the turbines at Hoover Dam operate under an average head ranging from 510 to 530 ft (around 160 m). [4] One cubic meter of water has a mass of 1,000 kg, so the potential energy per cubic meter can be expressed as:
| E | = | 1,000 kg × 9.81 m s-2 × 160 m | = | 1.57 × 106 J |
With a round-trip efficiency of 75%, the recoverable energy per cubic meter can be estimated using the standard pumped-hydro equation:
Where η is the round trip efficiency, ρ is the density of water, g is gravity, h is the hydraulic head, and V is the volume of water displaced. The factor of 1/2 accounts for the fact that water near the bottom of the reservoir has less potential energy than water near the surface. [5]
| Erecoverable | = | 1/2 × 0.75 × 1,000 kg m-3 × 9.81 m s-2 × 160 m |
| = | 5.9 × 105 J m-3 |
This is the usable electrical energy from each cubic meter of water after estimated electrical losses in pumping and generation
In 2022, the total U.S. electricity consumption was about 4.07 × 1012 kWh. [6] The volume of water needed to supply that energy through pumped hydro at Hoover Dam:
| V | = | 4.07 × 1012 kWh ×
3.6 × 106 J kWh-1 5.9 × 105 J m-3 |
= | 2.49 × 1013 m3 |
Given that Lake Mead's total active capacity is around 3.82 × 1010 m3, this means that the U.S. would need over 650 times the total volume of Lake Mead to supply the U.S. through pumped hydro alone, and one day would require 90% of Lake Mead's volume. One day of U.S. consumption would equal about 6.8 × 1010 m3 (≈ 1.8 times Lake Mead's capacity). However, since only about 2⁄5 of daily energy must be shifted to level solar loads, the true storage need is ≈ 2.7 times; 1010 m3, or ~70 % of Lake Mead's capacity. [7] This result highlights the volume required to meet national scale demand, showing the limits of repurposing Hoover Dam.
Wholesale electricity in the western U.S. averages $40 per MWH, or [8]
| $40 MWh-1 3.6 × 109 J MWh-1 |
= | $1.11 × 10-8 per Joule |
The market value of the energy stored behind Hoover dam is thus
| 5.9 × 105 J
m-3 1.11 × 10-8 $ J-1 |
= | $0.0065 per m3 |
The Lower Colorado River Basin System Conservation and Efficiency Program compensates participants at a rate of approximately $400 per acre-foot of conserved water, equivalent to $0.32 per m3. When compared to the recoverable energy value of $0.0065 per m3 derived earlier, this indicates that the market value of water is about 50 times greater than its energy value. [9]
Between 2000 and 2014, the water-surface elevation in Lake Mead declined by more than 140 ft (42.7 m), which was the record lowest level to date. [10]
The 1922 Colorado River Compact and subsequent legal frameworks apportion the rivers flows between the Upper and Lower Basins and impose delivery obligations on the Upper Basin that indirectly constrain large-scale diversions of water. [11]
Reduced lake levels will require greater energy for cyclic pump-storage.
In arid regions such as the American Southwest, water holds a value greater than its monetary equivalent in energy as it is a matter of life and death. This underscores that any policy or technological discussion about pumped-hydro systems at Hoover Dam cannot be separated from the social and ethical realities of water scarcity.
As noted by Bhatt, the state of Arizona has historically resisted California's claims of special entitlement to river water. [12] These disputes reflect tensions between state sovereignty, survival needs, and federal oversight, suggesting that the debate over energy storage in Hoover Dam is inseparable from the century-long struggle over who controls the Colorado River itself.
Based on this analysis, it has shown that converting Hoover Dam into a PHS system is not economically feasible under the conditions assumed. While physically possible, the energy value recovered from each cubic meter of water was found to be lower than its market price, making it financially unsustainable. The amount of water required to meet one day of national energy demand would consume more than Lake Mead's active capacity, so large scale would be impractical. It is also important to note that the analysis was idealized, neglecting losses due to turbine inefficiencies, specific pumping values, and evaporation. Future research could explore smaller renewable systems that minimize water usage.
© Nathan Ly. The author warrants that the work is the authors own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute, and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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[10] M. M. Edalat and H. Stephen, "Socio-Economic Drought Assessment in Lake Mead, USA, Based on a Multivariate Standardized Water-Scarcity Index," Hydrol. Sci. J. 64, 555 (2019).
[11] P. Debaere et al., "Closing Loopholes in Water Rights Systems to Save Water: The Colorado River Basin," Water Resour. Res. 60, e2023WR036667 (2024).
[12] A. Bhatt, "Future Potential of the Central Arizona Project," Physics 240, Stanford Univesity, Fall 2020.