Friday, December 9

Someone has had an idea to mitigate the droughts of the future: cover the ditches with solar panels


California has a problem. A serious one that threatens to become entrenched with global warming. In 2021 it suffered one of the driest years of the century, so much so that at the gates of autumn it was facing an extreme shortage that affected around 90% of the entire territory. In addition to a greater risk of fires, the lack of rainfall translates into low dams, restrictions on consumption and problems in hydroelectric plants. To tackle at least part of the challenge, the state has developed a vast 6,400-kilometre network of canals. The big question is: Can you get more out of it? What if in addition to using it to transport water, it was used to generate electricity?

At the University of California (UC) there are technicians who are convinced that it is. And they put on the table a proposal that would serve both the California drylands and any other region crossed by ditches or aqueducts: solar channels. The idea is relatively simple: cover its channels with photovoltaic panels. There, explains Roger Bales, engineer and professor at UC, they are about to be tested; but the proposal has already been tested in some parts of India.

Two challenges, one solution

Why cover the canals with solar panels? Bales and the rest of the proponents of the proposal, such as the firm Solar AquaGrid, also based in California, argue that it would have two great advantages. First of all, I would allow stop part of the evaporation of water, a process that, they say, “charges” approximately between 1 and 2% of the transported liquid. It may seem like a smaller percentage, but —according to his calculations— if the 6,437 kilometers of canals in the state were covered and this effect was stopped, California could save 65,000 million gallons of water each year, about 295,500 million liters. Enough to supply more than two million people.

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In a scenario like California, where most of the rain and snow is collected in the north of Sacramento during the winter and around 80% of the consumption is concentrated in the south of the state in the summer, these savings can be key. Bales also warns of the overexploitation of underground springs. In the west of the country there are already dry wells and the State has even set itself the goal of reducing the pumping of reserves that are kept underground.

The other big advantage is that the panels would generate electricity. How much, exactly? In an article published in The ConversationBales calculates that the system would provide 13 gigawatts of renewable energy capacity, more or less half of the new contribution that California needs if it wants to meet the goals it has set for decarbonization and green energy. The expert also estimates that, by taking advantage of existing pipelines, some 32,400 hectares could be prevented from becoming solar farms.

Channel

Beyond providing an extensive tongue of land in which to install panels, Bales reveals some extra advantages. For example, the wide distribution of the canal network throughout the state would facilitate supply in rural areas and areas that are currently neglected. By rising above moving water and in the shade, the panels could additionally cool down by around 12ºC, which in turn would increase electricity production by 3%. Since they would be protected, the ditches would also accumulate less vegetation and there would be less risk of frequent blockage.

Perhaps we will not have to wait long to go from theory to facts. In the USA the first prototypes for channels are being developed. The initiative is located in the Central Valley of California and its objective, acknowledges the engineer, is to help the proposal become “a large-scale solution”. Where the system has already been tested is in India, a country that in recent years has stepped on the accelerator of renewables, especially solar.

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Long periods of drought are going to be more and more normal.  It's time to get used to them

The objective they were looking for in the Asian power is also twofold: to locate land on which to expand the panels – a task that is not easy in India, given the density of the population, the price of land and that often the same plot can be in the hands multi-owners—and improve duct efficiency by reducing evaporation. Its data is similar to that of UC. In 2020, the BBC detailed how the flow of water there allowed the panels to stay cool and increase their energy efficiency in a range that, at least, moves from 2.5 to 5%.

The first pilot section was launched in the middle of the last decade in the Gujarat region, on the western coast of India, with an extension of 750 meters. The solar installation was located on a canal in the Vadodara district with the purpose of supplying electricity to farmers during the irrigation season and supplying it to the state network or to the canal itself the rest of the year. After that experience, the country has been incorporating others, such as the one located in the secondary channels of the Namada River.

Not all are advantages, of course. One of the great handicaps of solar channels, recognized by Bales himself, is the cost of the infrastructure, which exceeds that of conventional installations that are fixed directly to the ground. Among other issues, the supports must receive a special treatment to prevent them from degrading due to contact with water. The UC engineer is convinced, in any case, that if the value of the land, water savings, improved efficiency and the reduction of weeds that can clog the ditches are also included in the equation, the balance is positive and confirms the profitability of solar channels.

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When planning the installation, however, experts face other equally complex challenges. The width of the channel must be adequate, not excessive, which complicates the process and raises the price; nor too narrow, which could condition the number of honeycombs and their capacity. Furthermore, there is the dimension of the section itself, which must allow the structure to fit. In India, where they have been accumulating experience in its use for some time, they also point out that maintenance is not easy: given the characteristics of the structure, the cleaning staff have needed ramps to work and some companies have opted for sprinklers and robots.

The solution is in any case on the table.

Especially in a context of commitment to renewables and decarbonisation.

And in which the droughts seem to have come to stay. Also in Spain.

Images | Solar Aqua Grid



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