Arizona residents often suggest — to their utilities, the media, their neighbors — that the canals that deliver water from the Salt and Colorado rivers to the big cities ought to get covered with solar panels.
The idea just seems like a natural fit for a place with nearly 300 days a year of sunshine and crisscrossed by wide, uncovered canals carrying precious water that can evaporate under the hot sun.
Utilities have mostly balked at the idea, saying that coverings of any kind on the canals would hinder maintenance on the ditches, and that solar is cheaper and easier to build over solid land. First responders also regularly need to get in those waterways to rescue people and animals.
Salt River Project, which operates most of the canals in metro Phoenix, also has shared concern over installing expensive and potentially dangerous power-generating equipment along canals that are open to the public. Most large solar plants are fenced off.
But the tide might be shifting. The public utility is partnering with Arizona State University to collect data from two sites along its canals to determine how much electricity they might generate and how much evaporation installing solar panels over the water might prevent.
SRP also is considering issuing a request for proposals for a design of how panels might be built over canals.
That would leave it to designers to create something that is safe for the public, cost effective, doesn't interfere with canal work and allows emergency crews access when needed. That likely would mean something high over the entire right of way, but that's yet to be determined.
That design might include panels held by cables, rather than posts in the ground, SRP Director of Water Engineering and Transmission Robert Pane said last week while talking to a group of the utility's board members.
The federal Inflation Reduction Act earmarked money specifically for solar on canals, which doesn't hurt, either.
"We're a perfect candidate for it," Pane said. "We are a water and power utility."
Also of interest to SRP is whether the shade will reduce algae growth in canals as an additional benefit. But Pane said there also is concern the shade could fuel invasive quagga mussels, which can clog water infrastructure.
Once the ASU data is collected and analyzed, and SRP has a design proposal in hand, officials will re-evaluate whether the idea has merit.
"We want a cost-benefit analysis," Pane said.
Why hasn't this happened already?
Pane cited several reasons utilities have dismissed the idea.
One is that building solar panels over canals would require substantially larger structures than the metal posts commonly used to mount solar panels. That will make solar projects built over waterways less cost effective, even taking into consideration the land-cost savings compared with building them over open land.
Pane shared estimates from SRP that indicate the structures to hold solar panels over canals alone would cost more than the photovoltaic solar panels themselves, which is not usually the case when building a solar power plant.
And large solar plants often take advantage of tracking systems that allow the panels to face the sun as it moves across the sky, increasing the amount of electricity they generate to maximize their efficiency.
Pane said the assumption is that solar panels mounted over canals could not use such tracking, which means the system would generate less electricity than a traditional solar plant.
Another big concern for SRP is that having solar panels along canals will make it more difficult and expensive to monitor and maintain the canals themselves, particularly if the utility can't get heavy equipment under the solar panels.
Some board members echoed these concerns.
SRP board member Jack White asked if Pane was taking into consideration how emergency crews would rescue the people who fall into canals "a few times a year."
Board member Steven Williams was more blunt, asking if "bums" would find the shady places under solar panels a comfortable place to loiter, or if people might hurt themselves on solar equipment.
"You don't want a playground for them to climb all over," Williams said.
Pane said that solar equipment would have to get built high enough to allow emergency vehicles to pass, and that because SRP canals are open to the public, safety is a major consideration.
He said ASU will work with the utility to evaluate the potential at the Arizona Falls water feature near Indian School and 56th streets in Phoenix, and behind the utility's PERA Club near 68th Street and McDowell Road in Scottsdale.
Other entities also are moving ahead with solar canal projects. The Gila River Indian Community announced last year it was building a pilot project to cover part of its canals with help from the U.S. Army Corps of Engineers.
Then this year, the Turlock Irrigation District in California announced it would also develop a $20 million pilot project testing solar on a canal. Both the Gila River and Turlock projects bill themselves at the first-of-their-kind in the U.S.
The Turlock project is a partnership with the University of California, Merced, which produced a report on the subject indicating water evaporation savings would be worth the effort.
Pane cited all of these projects when briefing the SRP board.
CAP historically opposed to covering canals
One SRP board member asked Pane why the Central Arizona Project canal that delivers Colorado River water to Phoenix and Tucson wasn't a good candidate for solar, because unlike SRP canals in metro Phoenix, the CAP is closed to the public.
That utility seems to have a softening posture on solar over canals as well.
"CAP’s leadership is very interested in the measured results of the two committed pilot projects (Turlock Irrigation District and GRIC) and has been communicating with SRP’s leadership as they contemplate a pilot project or study within their urban canal," said Darrin Francom, a CAP assistant general manager
"Of specific interest to CAP is an accurate measurement of the decreased evaporation and the impacts to water quality, biology and maintenance, as well as the effectiveness of inspecting a covered canal."
CAP has addressed the issue before, sharing many of the same concerns as SRP.
When officials studied the issue in 2016, it determined the water savings were negligible and that the cost to build solar over the canal was prohibitive.
This article originally appeared on Arizona Republic: Should solar panels cover Arizona canals? SRP, ASU looking at effects