An international study has shown that utility-scale solar combined with hydraulic hydroelectric storage (HHS) could achieve an LCOE as low as $0.022/kWh in certain US regions. The system could provide GWh-scale, cost-competitive and highly reliable long-duration storage that could power large commercial districts with minimal environmental impact.
An international research team has found that combining utility-scale solar with gravity-based hydraulic hydroelectric storage (HHS) could deliver a levelized cost of energy (LCOE) as low as $0.022/kWh in certain locations in the US.
The study analyzed 936 sites across the country using multi-objective capacity optimization to assess the techno-economic feasibility of integrating PV and HHS at gigawatt hour scale.
“This represents the first comprehensive geospatial benchmark for gigascale HHS combined with utility-scale solar,” said co-author Mohamad T. Araji. pv magazine. “Previous research mainly focused on systems under 100 MWh or conceptual models for one location.”
Muhammed A. Hassan, another co-author, noted that the study systematically models the operation of PV-HHS taking into account nighttime power demand, spatial load variability, solar energy sources and regional costs. “Multi-objective optimization allows us to define the precise conditions under which this technology can move from theory to grid-scale reality,” he said.
The system consists of three elements: a PV array as the primary generation source, an HHS unit that serves as an energy buffer, and a total commercial district load representing 2,000 buildings. When PV production exceeds demand, the excess electricity drives a reversible pump turbine, lifting a rock piston and storing energy as gravitational potential. During discharge, the weight of the piston drives pressurized water through the same turbine to generate electricity.
The construction uses standard mining techniques, including cutting the piston from solid rock and installing a rolling diaphragm seal. Storage capacity scales with the fourth power of the piston’s radius, making GWh-scale storage enough to power a city for a day. Unlike conventional hydropower plants, HHS does not depend on elevation changes, increasing its potential deployment, the scientists pointed out.
PV panels were modeled with an efficiency of 20.3%, facing south with a slope equal to the local latitude. It was assumed that the HHS system would have a round trip efficiency of 80% and a storage capacity of eight hours. Load profiles were derived from TMY3 weather data, and MATLAB optimization balanced low LCOE with high reliability as measured by loss of load probability (LOLP).
Araji highlighted that in high-potential regions such as New Mexico, Nebraska and Maine, the LCOE could reach $0.022/kWh as revenues from excess solar exports offset capital and operating costs. “The system can achieve extremely high self-sufficiency at the district level, with a levelized storage cost (LCOS) of less than $0.166/kWh, competitive with utility-scale batteries for long-duration applications,” he said.
Across all climates, storage requirements ranged from 1.012 GWh to 4.232 GWh, with PV capacity generally lower at southern latitudes (0.626–2.305 GW). Approximately 75% of sites achieved an asset-level LCOE of less than $0.093/kWh, and most maintained a LOLP of less than 3.2%, demonstrating robust performance despite variable weather conditions.
“The feasibility of these gigantic projects is strongly influenced by local policies,” the academics emphasized. “State-specific power purchase agreement (PPA) structures and regional PV capital costs are the key determinants of relative system performance. For gravity storage to reach its full potential, site selection must prioritize a convergence of favorable geological conditions and supporting electricity market designs.”
The research results are presented in “Techno-economic analysis of utility-scale photovoltaic installations with hydraulic gravity storage for self-sufficient cities”, published in Energy conversion and management. Researchers from Canada’s University of Waterloo and Egypt’s Cairo University participated in this work.
This content is copyrighted and may not be reused. If you would like to collaborate with us and reuse some of our content, please contact: editors@pv-magazine.com.
