Solar Canopies On Irrigation Canals

The idea of ​​pairing solar panels with farming caught fire just a few years ago. The field already has a name — agrivoltaics — and its fans are already reaching for new, next-level variations on the theme. One good example is the Turlock Irrigation District in California, which just announced a new agrivoltaics project that could provide the state with multiple gigawatts of solar power, by outfitting irrigation canals with solar panels.

Agrivoltaics & The Water-Energy Nexus

Until now, the agrivoltaics field has been focusing on the benefits of raising solar panels up off the ground a few extra feet, providing farmers with a twofer. They get new revenue by leasing their land for power generation, and they can still do some farming under the solar panels.

That’s a significant improvement over conventional farm-to-solar practices, in which solar panels are parked closer to the surface, on a bed of gravel or some other non-crop ground cover.

The field of agrivoltaics also dovetails with regenerative agriculture, which is a science-based sustainable farming practice that focuses on conserving soil and improving soil health. In effect, raised solar panels provide the farmer with a sustainability and bottom line three-fer.

The addition of solar panels can turbo-boost regenerative goals, by shading the soil and preventing excess evaporation. That’s a new twist on the water-energy nexus. Instead of exploiting water resources to generate power, agrivoltaics enables solar energy harvesting to conserve water resources.

Mother Of All Agrivoltaics Projects

That brings us to the Turlock Irrigation District project. Earlier this week, TID announced that it had been selected to pilot the first-in-the-nation water-energy nexus system to involve constructing solar canopies on canals.

In addition to generating sustainable electricity, the solar canopies would reduce evaporation from the canals.

“The pilot project is called Project Nexus as a nod to the water-energy nexus paradigm gaining attention among public utilities,” TUD explains. “Utilities are recognizing the symbiotic relationship between water management and energy management, and are finding ways to design projects and actions that benefit the management of both resources beyond what has been done historically.”

The new TID project certainly would make history in terms of size and impact. If all goes according to plan, a 2021 study indicated that California’s 4,000 miles of public water infrastructure could support a capacity of 13 gigawatts in solar energy saving 63 billion gallons of water annually, which is equivalent to the irrigation needs of 50,000 acres of farmland .

That figure of 50,000 acres is just a drop in the bucket of California’s prime, irrigated farmland, which totals approximately 9 million acres. Still, 63 billion gallons of water saved represents a significant gilding of the zero carbon energy lily.

Agrivoltaics, Canals, & Water Conservation

That thing about reducing evaporation should attract the attention of other water districts in California, across the US, and around the world. The solar canopy idea could provide a cost-effective pathway for canal owners to offset the water lost through seepage.

The US Department of Agriculture has been trying to get canal owners to line their canals, in order to prevent seepage-related water loss. However, the idea has not been catching on for obvious reasons.

“Lining water canals with quasi-impermeable materials, such as concrete or plastic membranes, can reduce conveyance losses as less water is lost to seepage. However, the cost of lining canals may be prohibitively high for many irrigation organizations,” USDA explains. “According to data collected in the USDA’s 2019 Survey of Irrigation Organizations, almost 76 percent of water delivery organizations cite expense as a reason for leaving conveyance infrastructure unlined.”

More Solar Power For The US

Aside from the water conservation angle, the Nexus project is yet another demonstration that the US has enormous reserves of renewable energy that can be tapped without destroying habitats or taking farmland out of production.

Back in 2010, the US Department of Energy estimated that 14 million acres of brownfields and other pre-developed sites are potentially available for wind or solar development in the US. The nation has also barely touched its rooftop solar potential, and new solar window technology will enable the nation to extract even more clean kilowatts from buildings.

Meanwhile, the National Renewable Energy Laboratory estimates that the nation could provide for 10% of its overall electricity demand with floating solar panels, placed over a selected group of human-made reservoirs and other bodies of water infrastructure.

The TID project adds a new stock of potential solar sites, along with the agrivoltaics angle.

Next on the list could be Arizona, where the 336-mile Central Arizona Project canal was the subject of an NREL study back in 2015. Advocates have been pressing for solar coverings, but things didn’t look so rosy back then. Based on a similar canal-plus-solar installation in India, NREL estimated that the over-the-canal configuration would be 24% more costly than alternative sites.

Covering the CAP canal with PV panels has the possible benefit of reducing evaporation because of the cooling associated with shading. However this savings is small, 6 acre-ft per year, relative to the costs associated with placing solar over the CAP canal,” NREL concluded.

Solar-Plus-Canals Idea Still Alive & Kicking

CAP stuck a knife in the whole idea of ​​solar-plus-canals and twisted it as recently as 2020. It presented a rundown of obstacles involving construction, sun tracking, canal maintenance, gaps in the transmission system, and prohibitive overall costs.

“The US Bureau of Reclamation, which originally constructed CAP, has conducted studies of this possibility and also found the cost to be prohibitive. Covering the canal would have quadrupled the $4 billion the project originally cost,” they explained.

Part of the problem is location, location, location. The CAP route does travel through some remote and rugged territory.

On its part, TID is ready to give it a try. Project Nexus is a public-private-academic partnership that pairs TID, California’s Department of Water Resources, and the University of California – Merced with a company called Solar AquaGrid, which appears to have the solution to some of the construction issues cited by CAP.

Solar AquaGrid is supported by the marketing and social impact agency Citizen Group, which commissioned the 2021 study conducted by researchers with the University of California at Merced and Santa Cruz, and published in the journal Nature Sustainability.

“We find that over-canal solar could reduce annual evaporation by an average of 39 ± 12 thousand m3 per km of canal,” the research team concluded.

“Furthermore, the financial benefits from shading the canals outweigh the added costs of the cable-support structures required to span the canals,” they added. “The net present value of over-canal solar exceeds conventional overground solar by 20–50%, challenging the convention of leaving canals uncovered and calling into question our understanding of the most economic locations for solar power.”

TID also notes that the covered canals will help improve water quality and reduce canal maintenance costs, by reducing the growth of excess vegetation in the canals.

So. There.

Follow me on Twitter @TinaMCasey.

Image: Project nexus: agrivoltiaics gets a whole new twist with plan for covering irrigation canals in solar canopies (courtesy of TID).

 

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