Advocating for Floating Solar
Advocating for Floating SolarAdvocating for Floating SolarAdvocating for Floating Solar
In the Colorado River Basin and beyond.
Mission
Water Wise Solar Solutions was formed to study the application of Utility Scale Floating Photovoltaic Solar Arrays as an effective mitigation strategy for evaporative water loss within the Colorado River Basin.
Colorado River Basin (CRB) Water Supply
Saving Water with Floating Solar
FPV & Water Conservation
May 4, 2025
Utah, New Mexico and Arizona's arid climates and chronic water scarcity makes evaporation reduction the most compelling advantages of floating photovoltaic (FPV) systems. In the context of ongoing negotiations over water allocation within the Colorado River Basin, deploying FPV to cover portions of the region's reservoirs presents a practical and scalable strategy to preserve water supplies for agriculture, municipalities, and ecosystems across the region in combination with other water saving options.
Research conducted by Richter et al. (2024) and aided by Landsat satellite data found that the Colorado River’s major consumptive uses from 2000-2019 of a total of approximately 15 M acre feet per year were Agriculture (52%), evapotranspiration from natural vegetation (19%), municipal, commercial, and industrial (18%), and evaporation from reservoirs (11%). Irrigation for cattle feed was the single largest consumptive use, taking an estimated 32% of the Colorado River’s flow. As of this writing, the two major reservoirs (Mead and Powell) are roughly a third full with approximately 18 M acre feet of capacity in Lake Mead and 15.5 M acre feet of capacity in Lake Powell.
To estimate the water savings associated with covering reservoir surface in each state with a floating photovoltaic (FPV) array, we relied on the evaporation modeling approach outlined in the 2022 National Renewable Energy Laboratory (NREL) report, which utilizes the Penman–Monteith equation. This widely accepted method calculates open water evaporation by accounting for local climate variables including solar radiation, air temperature, humidity, wind speed, and atmospheric pressure. NREL applied this model to weather station data across the continental U.S. to develop a high-resolution map of annual evaporation rates. For Utah, the report identifies a representative annual evaporation rate of approximately 200 centimeters per year (equivalent to 2.0 meters/year), which aligns with arid inland reservoir conditions. New Mexico had an evaporation rate of approximately 245 cm per year and Arizona, approximately 270 cm per year.
Using this rate and Utah as an example, we calculated that each acre of reservoir surface in Utah typically loses about 8,094 cubic meters of water per year to evaporation. When FPV panels are installed, field studies referenced in the NREL report suggest that evaporation can be reduced by approximately 70% beneath the array due to shading and reduced wind exposure. Applying this factor to an installation yields a projected annual savings of 56,660 cubic meters, or approximately 46 acre-feet of water conserved each year for a 10 acre array. This estimate provides a scalable benchmark for assessing the water conservation potential of FPV installations in high-evaporation regions like these three states.
The water savings potential is significant. While site-specific evaporation rates vary, the above method provides a general rule of thumb that suggests that each acre of FPV coverage can save approximately 4.6 acre-feet of water per year. That’s a meaningful gain in a system under increasing stress from overuse and prolonged drought. In New Mexico and Arizona the savings are even more drastic at 5.63 and 6.2 acre-feet of water per year respectively.
All of our reliance on the Colorado River amplifies the urgency of implementing such solutions. Declining river flows have already triggered mandatory water cutbacks and exacerbated competition among users, heightening the burden on water managers to identify new tools for conservation. In 2023 the System Conservation Pilot Program paid farmers nearly $360 per acre foot to leave their water in the Colorado River rather than use it for farming, saving nearly 22000 acre feet at a cost to the State of Utah of $4.4 million.
Floating solar can be one of those tools that doesn’t require difficult to control changes in consumer/farming preferences for meat or landscaping. By limiting surface water loss from evaporation, FPV systems not only preserve water quantity, but also contribute to more resilient and adaptive water management strategies. These benefits extend beyond state borders, offering basin-wide advantages for states that depend on shared water resources.
A U.S. Department of Energy report (August 2022) highlights the broad environmental potential of FPV:
“FPV has the potential to improve several critical factors for reservoirs such as evaporation, water quality, reduced water movement to minimize erosion, and reduced dust accumulation—factors that are especially significant at the United States’ two largest man-made reservoirs, Lake Powell and Lake Mead, both located in drought-prone desert regions of the Southwest.”
The U.S. Bureau of Reclamation estimates that Lake Mead loses 800,000 acre-feet of water annually—around 6% of the Colorado River’s total flow—due to evaporation alone. Lake Powell loses nearly 860,000 acre-feet per year from a combination of evaporation and bank seepage. Although no FPV installations currently exist on either lake, the opportunity has drawn growing interest from researchers, agencies, and developers alike. These two reservoirs account for the majority of the evaporative loss in the Colorado River system and it is a goal of the author to participate in or facilitate the development of FPV of one or both of these critical water bodies.
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