Saturday, April 17, 2021

Why covering canals with solar panels is a movement of power

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Peanut butter and jelly. Hall & Oates. Now, there is a duo that could be even more powerful literally and figuratively: solar panels and canals. What if instead of leaving the channels open, letting the sun evaporate the water, we covered them with panels that would both shade the precious liquid and suck in solar energy? Maybe mankind can go for that.

California scientists just ran the numbers on what would happen if their state slapped solar panels across 4,000 miles of its canals, including California’s main aqueduct, and the results point to a potentially magnificent partnership. Their feasibility to study, published in the journal Sustainability of nature, finds that if applied statewide, the panels would save 63 billion gallons of water from evaporating each year. At the same time, solar panels on California’s exposed canals would provide 13 gigawatts of renewable energy per year, about half of the new capacity the state needs to meet its decarbonization goals by 2030.

California’s water system is the largest in the world, serving 35 million people and 5.7 million acres of farmland. Seventy-five percent of available water is found in the northern third of the state, while the lower two-thirds of the state accounts for 80 percent of urban and agricultural demand. The shuttle of all this water requires pumps to make it flow uphill; as a result, the water system is the state’s largest consumer of electricity.

The solar panel channels would not only produce renewable energy for use across the state, they would run the water system itself. “By covering the channels with solar panels, we can reduce evaporation and avoid disturbing natural and working land, while providing renewable energy and other related benefits,” says environmental engineer Brandi McKuin of the University of California, Merced and the University of California, Santa Cruz, lead author of the article.

Ironically, the performance of solar panels decreases as temperatures rise. In a solar cell, photons from the sun drive electrons from atoms, producing an electric current. When a panel gets too hot, it puts the electrons in an already excited state, so they don’t create as much energy when dislodged by photons. Covering panels on canals would, in a sense, make them water-cooled, thus increasing their efficiency. “And further,” adds McKuin, “the shade of the panels mitigates the growth of aquatic weeds, which is a major canal maintenance problem.”

Engineering wouldn’t be that complicated either. You can throw a steel truss over a canal and cover it with panels. India actually experimented with solar canals like this and ordered a 25 mile long stretch. at an estimated cost of $ 14 million.

To be clear, this new document is not a pitch for state officials to immediately cover all channels with solar panels. “Our paper is not a detailed engineering design or conceptual design – it is a feasibility study, a proof of concept to move to the next phase of investing in a demonstration project,” says engineer Roger Bales of the University of California at Merced. “But I think the amount of electricity could be significant, both statewide and locally.”

Bales and McKuin calculated all of this by incorporating a variety of models. Evaporation rates, for example, were taken from hydrological models. They have also integrated into climate models to predict how the state will warm in the years to come. They got so granular that they also calculated how the cooling effect of the canal water would improve the efficiency of generating the panels.

In the end, they landed on a potential annual saving of 63 billion gallons of water across California. But they also took into account the human benefits of such a project, which are more nebulous. For example, many farmers pump their water with diesel generators. If solar panels provided this energy instead, it could reduce local emissions, thereby improving air quality. “You can look at the economic costs, but you can also look at the social benefits,” Bales says.

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