Can floating solar panels reduce reservoir water evaporation?

How much evaporation can floating solar panels actually save?

The biggest, most comprehensive study on this question simulated the Aswan High Dam Reservoir in Egypt — one of the world's largest artificial lakes — and found that covering 90% of the reservoir with floating solar panels would cut evaporation by 49.7%, saving up to 5.9 billion cubic meters of water per year [4]. To put that in perspective, that's enough water to cover the annual domestic needs of millions of people. The same study calculated that each kilowatt-peak of installed floating solar capacity saves about 7.67 cubic meters of water per year [4].

Smaller but tightly controlled experiments back up those numbers. In a Brazilian bauxite mine, researchers built two test reservoirs — one with partial floating solar coverage and one without — and measured a 49% reduction in evaporation from the covered reservoir [2]. Extrapolating to the mine's full 450,000-square-meter water surface, that translates to roughly 466,000 cubic meters of water conserved annually [2]. Another Brazilian study on the Passaúna Reservoir found that a floating solar system covering just 1,265 square meters achieved a 60.2% reduction in evaporation, and estimated that covering the entire reservoir could save 2.69 million cubic meters per year — enough to supply over 196 people for a year [8].

In Northern Cyprus, researchers modeled 15 reservoirs and found that 100% coverage could save up to 621,000 cubic meters of water per reservoir annually [1]. Even partial coverage delivers meaningful savings: a study in Crete, Greece, calculated that covering just 10% of two dams would save 528,000 cubic meters of water per year, and covering 30% would save 1.58 million cubic meters [3]. A study in Uttar Pradesh, India, found that panels mounted 300 mm above the water surface reduced evaporation by 23.44%, and estimated that covering 25% of 28 major dams would save 92.56 million cubic meters annually [6].

What determines how much evaporation is reduced?

The single biggest factor is how much of the water surface the panels cover. Every study shows a clear, direct relationship: more coverage means more evaporation reduction. But the exact savings depend on local climate, panel design, and how the panels are positioned. For example, the Indian study found that raising panels 300 mm above the water surface gave the best evaporation reduction (23.44%), compared to lower or higher mounting [6]. This is because the gap allows some airflow, which can actually increase evaporation if not optimized — so panel height matters.

Wind also plays a role. A wind-tunnel study on floating solar arrays showed that the first row of panels takes the brunt of the wind, while inner rows experience a 'sheltering effect' that reduces wind loads by 45–86% [7]. Less wind reaching the water surface means less evaporation, so larger, denser arrays may actually be more effective at reducing evaporation than small, scattered ones.

The type of floating structure and panel technology also matters. In Northern Cyprus, researchers found that bifacial panels (which capture light from both sides) and a north-facing tilt of 6 degrees produced the best performance [1]. While that study focused on energy generation, the same design choices affect how much of the water surface is shaded and how much airflow is blocked, which in turn affects evaporation reduction.

Are there any downsides or things to watch out for?

Yes, there are trade-offs. Covering a reservoir with solar panels changes the underwater environment. A modeling study on a UK reservoir found that floating solar coverage significantly altered water temperature and light penetration, which in turn affected phytoplankton (the tiny algae that form the base of the aquatic food web) [5]. As coverage increased, phytoplankton biomass generally decreased, but the effect depended on where the panels were placed — deploying them in faster-flowing areas of the reservoir caused less disruption than placing them in stagnant zones [5]. This means reservoir managers need to think about where to put the panels, not just how many to install.

Another practical concern is structural integrity. Floating solar systems must withstand wind, waves, and storms. A wind-load study showed that the outer rows of panels experience much higher forces than inner rows, so the supporting structure needs to be stronger at the edges [7]. The good news is that the same study found that using cheaper materials in the middle of the array could reduce manufacturing costs by 19% for a 2.5 MW system [7].

Finally, the evaporation reduction numbers come from models and small-scale experiments, not from long-term, full-reservoir monitoring. While the models are well-validated (for example, the Aswan Dam study used a hydrodynamic lake model combined with a solar yield model [4]), real-world performance could vary. The Brazilian test reservoirs [2] and the Indian experimental setup [6] provide the most direct evidence, but they are small — the real test will come when large-scale floating solar farms are monitored over years.

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