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A pilot project in California covered sections of irrigation canals with solar panels and the results were surprising: up to 70% reduction in water evaporation, an 85% drop in algae growth, and a 2.5% to 5% increase in energy production from the modules. According to PV Magazine, if applied to the state’s 4,000 kilometers of canals, the concept would generate 13 GW of clean energy and save enough water to supply over 2 million people per year.
California faces a chronic problem affecting everyone from farmers to big-city residents: water scarcity. The state has already lost 40% of its Colorado River allocation this year, and every liter saved makes a difference in a region where severe droughts have become routine. It is in this context that a pilot project called Nexus tested a solution that seems obvious once explained: covering irrigation canals with solar panels to simultaneously generate energy and reduce the evaporation of water flowing through these open-air canals.
The results from the first full irrigation season confirmed that the concept works. The Nexus installation, with a capacity of 1.6 megawatts, was built over canals operated by the Turlock Irrigation District in California, and the covered sections recorded evaporation reductions of between 50% and 70%. Algae growth in the shaded sections dropped by 85%, which significantly reduces canal maintenance and pump cleaning costs. And the solar panels, benefiting from the natural cooling provided by the water underneath, produced between 2.5% and 5% more electricity than equivalent ground-mounted modules.
Why covering canals with solar panels makes sense in California
California’s canal network stretches for approximately 4,000 kilometers, transporting water from regions with greater water availability to agricultural and urban areas that depend on this infrastructure. These canals are open, exposed to sun and wind, which causes continuous evaporation and algae growth that clogs pumps and increases operational costs. Covering these canals with solar panels addresses both problems simultaneously: the shade reduces evaporation and inhibits algae growth, while the modules generate clean electricity.
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A University of California study calculated that covering the entire length of the state’s canals would generate 13 gigawatts of energy annually and save 63 billion gallons of water. This volume of water is enough to meet the residential needs of over 2 million people per year. For a state grappling with rationing, wildfires exacerbated by drought, and increasing pressure on its water resources, the possibility of saving billions of liters while producing renewable energy is hard to ignore.
The cooling effect nobody expected
One of the most interesting findings from the California pilot project is the efficiency gain of solar panels when installed over water. Photovoltaic modules lose efficiency as they heat up, and conventional installations on dry ground or dark rooftops suffer from temperatures that can exceed 60 degrees Celsius on the panel surface. Over the canals, the natural evaporation of water creates a cooler airflow that keeps the modules at lower temperatures during peak solar hours.
The result is a 2.5% to 5% increase in electricity production compared to ground-mounted panels, according to Nexus Project data. It might seem small in percentage terms, but when multiplied by the 4,000 kilometers of canals and the estimated 13 gigawatts of total capacity, this efficiency gain represents additional gigawatt-hours of clean energy produced every year with no extra equipment cost. The water that evaporates and cools the panels would be lost anyway; with solar coverage, part of this evaporation is retained, and the rest contributes to the modules’ performance.
Algae: the silent problem that panels solve
Algae growth in irrigation canals is an operational problem that costs millions of dollars annually in maintenance in California. Algae proliferate in water exposed to direct sunlight and clog filters, pumps, and gates, requiring constant cleaning and reducing the efficiency of the water distribution system. By covering the canals with solar panels, shading drastically reduces light incidence on the water, cutting algae growth by 85% according to data from Project Nexus.
This reduction is not just an environmental benefit, but a concrete operational saving. Fewer algae mean fewer maintenance shutdowns, longer lifespan for pumping equipment, and lower consumption of chemicals used in water treatment. For irrigation districts operating these canals, maintenance savings can help offset part of the initial investment in panel installation, making the project more economically attractive over time.
The main obstacle: the cost of support structures
Despite promising results, the project faces resistance, and the main argument against it is financial. The installation of solar panels over irrigation canals requires heavy steel support structures that must span the entire width of the canal, and these structures alone can account for up to 40% of the total project cost. This value is significantly higher than that of ground-mounted solar farms, where panels are fixed on simpler structures on flat terrain.
Critics argue that California has vast expanses of cheap desert land where traditional solar panels can be installed at a much lower cost. A desert solar farm avoids the engineering complications of building over canals and does not interfere with the operation of the irrigation system. However, this argument ignores a factor that project proponents consider essential: desert solar farms generate energy but do not save a drop of water, and in California, water is as valuable as electricity.
The ecological questions that still have no answer
Shading the canals solves problems, but it can also create new ones. Reducing evaporation means less local humidity being released into the atmosphere, which will likely have minimal impact on the region’s climate, but it could disturb aquatic ecosystems by decreasing dissolved oxygen in the canal water. Organisms that depend on sunlight and natural oxygenation may be negatively affected by permanent coverage.
Maintenance teams also need regular access to the canals for desilting and repairs, and suspended panels significantly complicate this work. Any structural intervention in the canal requires temporary movement or removal of the modules, which adds cost and operational complexity. Project Nexus will continue collecting data in the coming seasons to determine whether California will expand the concept or conclude that the ecological and operational trade-offs do not justify the energy and water gains.
What India has already proven about solar canals
California is not the first region in the world to test solar panels over irrigation canals. India has already built similar solar projects on its canals, proving that the concept works in different climates and geographical regions. The Indian experience demonstrates that the technology is viable in both tropical regions with high solar radiation and temperate zones, and that the benefits of water saving and energy generation are maintained in varied contexts.
For California, the Indian reference serves as proof that scaling the project is not a theoretical gamble, but a decision with real precedents. The difference is that the proposed scale for the American state is much larger, with 4,000 kilometers of canals and a potential of 13 gigawatts, which would require proportional investments and face regulatory, environmental, and political challenges that smaller projects do not encounter. The economic calculation only changes when the saved water receives a real monetary value, something that California’s chronic drought makes increasingly urgent.
Energy and water at the same time: the decision California needs to make
Project Nexus has demonstrated that covering irrigation canals with solar panels works. Evaporation drops by up to 70%, algae decrease by 85%, energy produced is up to 5% higher than in conventional installations, and the water saved would be enough to supply millions of people. The concept is validated. The question now is whether California believes that the water and energy benefits justify the higher cost of support structures and the operational complications the project entails.
Do you think covering canals with solar panels is the best solution for the water and energy crisis, or would it be more practical to invest in solar farms in the desert? Tell us in the comments what you think about California’s project, if Brazil could adopt something similar in its irrigation canals, and what caught your attention the most: water savings, the reduction of algae, or the natural cooling of the panels.
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