Covering waterways would, in a sense, make solar panels water-cooled, boosting their efficiency.
PEANUT BUTTER AND jelly. Hall & Oates. Now there’s a duo
that could literally and figuratively be even more powerful: solar panels and
canals. What if instead of leaving canals open, letting the sun evaporate the
water away, we covered them with panels that would both shade the precious
liquid and hoover up solar energy? Maybe humanity can go for that.
Scientists in California just ran the numbers on what would
happen if their state slapped solar panels on 4,000 miles of its canals,
including the major California Aqueduct, and the results point to a potentially
beautiful partnership. Their feasibility study, published in the journal Nature
Sustainability, finds that if applied statewide, the panels would save 63
billion gallons of water from evaporating each year. At the same time, solar
panels across California’s exposed canals would provide 13 gigawatts of
renewable power annually, about half of the new capacity the state needs to
meet its decarbonization goals by the year 2030.
California’s water conveyance system is the world’s largest,
serving 35 million people and 5.7 million acres of farmland. Seventy-five
percent of available water is in the northern third of the state, while the
bottom two-thirds of the state accounts for 80 percent of urban and
agricultural demand. Shuttling all that water around requires pumps to make it
flow uphill; accordingly, the water system is the state’s largest single
consumer of electricity.
Solar-paneling canals would not only produce renewable
energy for use across the state, it would run the water system itself. “By
covering canals with solar panels, we can reduce evaporation and avoid
disturbing natural and working lands, while providing renewable energy and
other co-benefits,” says environmental engineer Brandi McKuin of the University
of California, Merced, and the University of California, Santa Cruz, lead
author on the paper.
Ironically enough, the performance of solar panels falls as
temperatures rise. In a solar cell, photons from the sun knock electrons out of
atoms, producing an electric current. When a panel gets too hot, that puts
electrons into an already excited state, so they don’t create as much energy
when dislodged by photons. Spanning panels over canals would, in a sense, make
them water-cooled, boosting their efficiency. “And additionally,” McKuin adds,
“shade from the panels mitigates aquatic weed growth, which is a major canal
maintenance issue.”
The engineering wouldn’t be all that complicated, either.
You could throw a steel truss over a canal and cover it with panels. India has
actually been experimenting with solar canals like this, and it has
commissioned one 25-mile-long stretch for an estimated cost of $14 million.
To be clear, this new paper is not a full-throated pitch to
state officials to immediately cover all canals with solar panels. “Our paper
is not a detailed engineering design or conceptual design—it's a feasibility
study, a proof of concept for taking it to the next phase of investing in a
demonstration project,” says engineer Roger Bales of the University of
California, 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 instance, came from hydrological
models. They folded in climate models, too, to predict how the state will warm
over the coming years. They got so granular that they also calculated how the
cooling effect of the canal water would improve the panels’ generating
efficiency.
Ultimately, they landed on a potential annual savings 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 that
energy instead, that could cut local emissions, thus improving air quality.
“You can look at the economic costs, but you can also look at the social
benefit,” says Bales.
An added social benefit could be that by situating the
panels over canals, the state wouldn’t have to convert croplands or disrupt
natural habitats to set up sprawling solar farms—a canal is already on
long-disturbed land. Think about how you’d install a solar array in your own
home. “I can put it on my roof, rather than mowing down the yard next to my
house and putting panels there,” says Michael Kiparsky, director of the Wheeler
Water Institute at the UC Berkeley School of Law. “You're taking something
that's already been altered by human activity and doubling up on the benefits
it provides. That's the profound piece.”
Solar-paneling California's canals could also prepare the
state for the widespread adoption of electric cars. The California Aqueduct
runs right along Interstate 5, the major artery carrying traffic between the
northern and southern halves of the state. Where there are now gas stations
dotted along the way, in the future there might be car-charging stations that draw
power from the nearby aqueduct.
The plan could also help California prepare for future
climate change. “Droughts are part of our history and part of our future,” says
Kiparsky. “It's just that under climate change, they're projected to become
both more frequent and more severe.” As the state gets hotter, more and more
water will evaporate away from its canals, which the panels can help attenuate.
While the researchers focused on California in this study,
this kind of modeling “could easily be applied to other locations,” McKuin
says. “In water-stressed regions of the world with open canals, it makes a lot
of sense to consider this.” For instance, that might include California’s
neighbors, like the increasingly molten-hot southwestern states and Texas, which
just showed it needs to overhaul its energy system anyway.
There are, of course, some challenges when mulling such a
large infrastructure project. For instance, these researchers didn’t take into
account the potential effects on wildlife—covering canals might cut off access
for waterbirds who depend on it for habitat, especially considering that
California has lost more than 90 percent of its wetlands. Also, situating solar
panels and their trusses over water could lead to rusting of equipment, raising
maintenance costs. And then there’s the cost of solar-paneling canals on a wide
scale. (The study didn’t suggest an overall price tag. McKuin says it will be
hard to estimate without a demonstration project first, and it would depend on
variables like which sites are chosen for development.)
But then again, this isn’t an all-or-nothing idea: Some
canals here and there could be converted, while others remain open. While that
might not provide the full boost of saving 63 billion gallons of water each
year, it would still provide power to water pumps and local car-charging
stations, all while reducing evaporation at a smaller scale. “With or without
climate change, the supply of water in California is tightening, and the demand
for water in California is increasing,” says Kiparsky. “And those two facts
together mean that, indeed, any water savings is good, and it's welcome.”
