Installing solar panels over canals could yield water, land, air and climate payoffs

Climate change and water scarcity are in the foreground in the western United States. The climate in the region is warming, there is a drought of several years and in many places the groundwater supply is overflowing.

Western states are pursuing many strategies to adapt to these pressures and prepare for the future. This includes measures to promote the development of renewable energies, to save water and to manage natural and work areas more sustainably.

As engineers working on climate-friendly solutions, we have found a simple win-win situation for water and climate in California with the so-called “solar duct solution”. Around 4,000 miles of canals carry water to around 35 million Californians and 5.7 million acres of farmland across the state.

Covering these channels with solar panels would reduce the evaporation of precious water – one of California’s most important resources – and help meet the state’s renewable energy goals while saving money.

Save water and land

California is prone to drought and water is a constant problem. Now the changing climate brings hotter, drier weather.

Severe droughts over the past 10 to 30 years have dried up the wells, prompted officials to introduce water restrictions and led to massive forest fires. From mid-April 2021, the entire state was officially affected by drought conditions.

At the same time, California has ambitious conservation goals. The state has the mandate to reduce the pumping of groundwater and at the same time reliably guarantee the supply of farms, cities, wild animals and ecosystems. As part of a comprehensive initiative on climate change, Governor Gavin Newsom instructed the California Agency for Natural Resources in October 2020 to accelerate efforts to conserve 30% of land and coastal waters by 2030.

Most of California’s rain and snow falls north of Sacramento in winter, while 80% of southern California’s water use occurs, mostly in summer. That’s why channels meander through the state – it’s the largest such system in the world. We estimate that approximately 1 to 2% of the water they carry is lost to evaporation under the hot California sun.

In a recent study, we showed that covering all 4,000 miles of California’s canals with solar panels could save more than 65 billion gallons of water annually by reducing evaporation. That’s enough to irrigate 50,000 acres of farmland or meet the water needs of more than 2 million people.

By concentrating solar panels on land that is already in use, rather than building them on vacant land, this approach would help California achieve its sustainable management goals for water and land resources.

Artist rendering of a solar duct system for California. Solar Aquagrid LLC, CC BY-ND

Climate-friendly force

Shading California’s canals with solar panels would generate significant amounts of electricity. Our estimates show it could provide 13 gigawatts of renewable energy capacity, which is roughly half the new sources the state will need to add to meet its clean power targets: 60% from carbon-free sources by 2030 and 100% % renewable by 2045.

Installing solar panels over the ducts makes both systems more efficient. The solar panels would reduce evaporation from the canals, especially in hot California summers. And because water heats more slowly than land, the canal water flowing under the panels could cool them down by 10 ° F and increase electricity production by up to 3%.

These panels could also generate electricity locally in many parts of California, reducing both transmission losses and costs for consumers.

The combination of solar energy with battery storage can help build microgrids in rural areas and underserved communities and make the power grid more efficient and resilient. This would reduce the risk of power outages due to extreme weather, human error, and forest fires.

We estimate that the cost of bridging channels with solar panels is higher than building floor-mounted systems. However, when we added some of the side effects like avoided land costs, water savings, water weed control and improved PV efficiency, we found that solar ducts are a better investment and provide electricity that costs less over the life of solar installations.

Solar collectors installed over channels increase the efficiency of both systems.
Brandi McKuin, CC BY-ND

Benefits for the country

Solar ducts are about much more than just generating renewable energy and saving water. Building these long, thin solar panels could prevent more than 80,000 acres of farmland or natural habitat from being converted into solar parks.

California grows food for an ever-growing world population and produces more than 50% of the fruits, nuts, and vegetables that US consumers eat. However, up to 50% of the new renewable energy capacity to meet the decarbonization goals could be located in agricultural areas, including large parts of prime farmland.

Solar canal systems will also protect wildlife, ecosystems, and culturally important land. Large solar developments can cause habitat loss, degradation, and fragmentation, which can damage endangered species such as the Mojave Desert turtle.

They can also damage plant communities in the desert, including plants that are culturally important to indigenous tribes.

For example, the construction of the Genesis Solar Energy Center in the Sonora and Mojave Deserts in 2012-2014 destroyed hiking trails and burial sites and damaged important cultural artifacts, leading to protracted litigation.

Purify air

By producing clean electricity, solar ducts can improve air quality – a serious problem in central California, which has some of the dirtiest air in the US. Solar power could help remove particulate-spewing diesel engines that pump water through California’s agricultural valleys.

It could also help recharge a growing number of light and heavy-duty electric vehicles that move people and goods across the state.

Another benefit would be to contain aquatic weeds that clog canals. In India, where developers have been building solar ducts since 2014, the shade of the panels limits the growth of weeds that block sewers and restrict water flow.

Control of these weeds with herbicides and mechanical equipment is expensive, and herbicides pose a threat to human health and the environment. For large, 100 foot wide canals in California, we estimate that shading canals could save about $ 40,000 per mile. Nationwide savings of $ 69 million per year could be achieved.

Artist rendering of a solar duct system for California. Solar Aquagrid LLC, CC BY-ND

Bring solar ducts to California

While India has built solar systems over canals and the USA is developing floating solar projects, there is a lack of prototypes in California to study on site.

Discussions are ongoing on large and small demonstration projects in the Central Valley and Southern California. Building prototypes would help operators, developers, and regulators refine designs, assess environmental impacts, measure project costs and benefits, and evaluate the performance of these systems.

With more data, planners can work out strategies for expanding solar ducts nationwide and potentially across the west.

It will take a dozen or more partners to plan, fund, and execute a solar duct project in California. Public-private partnerships are likely to include federal, state, and local government agencies, project developers, and university researchers.

California’s aging energy infrastructure has contributed to catastrophic forest fires and multi-day outages.

The construction of intelligent solar developments on canals and other disturbed areas can make the electricity and water infrastructure more resilient, save water, reduce costs and help combat climate change. We believe this is a model that should be considered across the country – and across the planet.The conversation

Authors: Roger Bales, Distinguished Professor of Engineering, University of California, Merced and Brandi McKuin, Postdoctoral Fellow in Environmental Studies, University of California, Santa Cruz

This article is republished by The Conversation under a Creative Commons license. Read the original article.

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