The southwestern U.S. is in the throes of a “megadrought” so severe that we’ve broken the record — all 1,200 years of it. According to a study published earlier this year, soil hasn’t been this dry since the scientific record began around the year 800.1 This has major implications for the country’s food supply, as we rely on the west coast state of California to produce over a third of the U.S.’s vegetables and three-quarters of its fruit and nuts.2

Researchers from the University of California, however, have proposed a solution that could potentially address both water and energy crises at the same time: covering irrigation canals with solar panels. But is this just another renewable gimmick, or does it hold a little more water? Let’s take a deeper dive to find out.

We talk a lot about solar, and for good reason: it’s a strong contender in the renewable energy race. That said, we’d be remiss if we didn’t acknowledge its drawbacks. For one, those photovoltaic panels have to go somewhere, and the available room is finite. We’ll get to how solar can help with water in a minute, but the challenge around space is important for context.

Take India, for example: coal-fired plants generated 72% of the country’s electricity between 2018 and 2019. At the same time, the country has 300 sunny days in a year, and a large population that could benefit massively from a reliable, abundant source of clean energy.3

The problem is … there’s not a lot of places to collect it. Land is relatively expensive in India, and its high population density (with an average 464 people per square kilometer) further complicates this. Rooftop solar can only go so far with limited sunny building space.3

But when implemented strategically, dual-use options like agrivoltaics show that symbiotic relationships between solar panels and their surrounding environments are possible. We’ve seen this play out in farms where plants grown directly beneath solar panels are not only shielded from wind and storms, but use significantly less water in the shade. In turn, the crops themselves actually keep the panels cooler, which helps them run better.

That’s because despite their purpose, solar panels don’t like it hot. Their electrical components perform their best at or below 25 C (77 F), and have an efficiency rate of about 20%. Solar panels lose about anywhere from 0.3% to 0.5% efficiency for every degree over 25 C. As a result, the negative effects on efficiency worsen significantly in areas where temperatures can climb into ranges as high as over 50 C (122 F).4

What does this have to do with canals? This is where water comes into the picture. As you might imagine, sticking a solar farm over open water takes temperature optimization to the next level. In fact, the resulting cooling effect means efficiency up to 15% higher than that of classic land-locked solar, according to the Environmental and Energy Study Institute.4 Welcome to the world of floating photovoltaic panels, or “floatovoltaics”; AKA floating solar farms.

Floatovoltaics are kind of like the Murphy beds of the solar world … just not as comfortable. When you add solar panels to open water, you get all the perks of renewable energy while using previously squandered surface area. And as for the placement of floating solar farms, man-made bodies of water like aqueducts, canals, and reservoirs are what you want. This is because they’re generally calm, relatively easy to access, and less disruptive to aquatic life.5

Most importantly, these pools of water offer unused workspace. No one wants to build condominiums on top of these conveyances — at least, not yet. Don’t give them any ideas!

Combining hydropower with floating solar is one example. Most hydropower dams have a nearby lake to hold excess water. Floating solar can be installed on these lakes and directly send electricity to the already existing infrastructure at the plant, meaning you get more energy production with just a few tweaks.5

The potential impact of using floatovoltaics in tandem with hydro is nothing to sneeze at. In a Nature article published in June, researchers estimate that covering just 10% of the world’s hydropower reservoirs with solar panels would create almost 4,000 GW of solar capacity. This is equivalent to the electricity-generation capacity of all the fossil-fuel based plants in the world.6

Nevertheless, it’s important to note that floatovoltaics aren’t completely appropriate for every biome and might still need to be supplemented with other sources of renewable energy, depending on their location. But where they do work best, a little goes a long way: research based on the projected demand for solar energy by 2050 estimates that countries like Brazil and Canada would only need about 5% of their reservoirs covered by panels to meet their needs.6

But how exactly can floating solar help solve the water crisis?

Canal-top floatovoltaics in particular are especially advantageous under hot conditions, which are of course intensifying thanks to climate change. Remember our conundrum with solar energy in India that we talked about earlier? In the state of Gujarat, rising temperatures are causing increased “water stress” as irrigation canals dry up. Covering a canal in solar panels, though, not only produces clean energy and saves space, but helps protect the water from evaporation.3

That’s why engineers began to capitalize on the space atop canals along the state’s Narmada river during a floating solar pilot project launched in 2012. By its completion, solar panels covered a 750-meter stretch of the canals. This led to the first large-scale canal-top solar power plant in the Vadodara district in 2015 for $18.3 million.3

Since that first foray into floatovoltaics in Gujarat, at least eight Indian states have commissioned canal solar projects. This includes a 100-MW farm that covers about 40 kilometers at an estimated cost of 1 billion Indian rupees (or $13.9 million USD).3

The United States has also dipped its toes into floating solar. In 2018, the Ciel and Terre company completed installation of the country’s first public floating solar array in Kelseyville County, California. This 252-kW farm consists of 720 solar panels that float on a man-made wastewater treatment pond.5

On the opposite coast, the Big Muddy Lake solar farm in Fort Bragg was the US Army’s first floating structure. Installed in June of this year, this 1.1 MW set-up is the largest of its kind in the southeastern US and currently powers 190 homes and 2 MWh of battery storage.7

Currently, the largest floating solar farm in the states lives in California: the Healdsburg Floating Solar Farm. This 44.8 MW farm sits on two ponds that span 15 acres, and provides 8% of Healdsburg’s annual electricity requirement. It also uses double-sided solar panels to catch the overhead sunlight and the rays that reflect back off of the water.5

As the southwestern U.S. faces a megadrought, the water-conservation aspects of floating solar are particularly relevant to California. When you consider its water insecurity and notoriously polluted air, the state has a lot to lose. At the moment, it’s gradually taking steps to run on carbon-free electricity by 2045.8

It also happens to have the world’s largest water-conveyance system, where 4,000 miles of irrigation canals distribute water to farmers across the state.9 In a 2021 study, researchers from the University of California determined that covering those miles with solar panels could save upward of 63 billion gallons of water each year through reduced evaporation. This is equivalent to the residential water needs of about 2 million people, or enough to irrigate about 50,000 acres of farmland.10

On top of this, it’s estimated that if all of California’s canals and aqueducts were covered with solar panels, they could generate 13 GW of solar energy, which is about half of what it needs to meet its clean energy goals.10

That’s a great sentiment, but how do we know it’s practical? That’s where Project Nexus comes in. As the first venture of its kind in the states, Project Nexus is actually the real-life testing phase of the University of California’s research. Taking direct inspiration from Gujarat, the plan is to install open-sided solar panel canopies over California’s canals in the Turlock Irrigation District by the end of 2023. This pilot phase is meant to prove the viability of the concept, and the project now has a $20 million backing in the state’s current budget, with construction expected to start this fall.8 11 12

As for how testing will work, the goal is to install about 8,500 feet of solar panels over three sections of the Turlock Irrigation District’s canals. The canals range in width from 20 to 100 feet. Researchers will monitor factors that impact productivity, like the difference between cable suspension and steel truss support mounting and the performance of monofacial versus bifacial solar panel designs. They’ll also examine storage solutions to support the local electric grid during outages or cloud cover.12

The project uses existing infrastructure on already-disturbed land to keep costs low and efficiency high, all while supporting the region’s sustainable farming tradition. Plus, the new canals in California can use 50% less raw materials than the ones in India, and they can also be designed to allow more space around the panels for easier maintenance.8

The actual scale of these installations is pretty small in the grand scheme of things. Of the 4,000 miles of canals statewide, the panels for Project Nexus will only cover about two of them, producing about 5 MW of power.8 12 Still, this sets the perfect stage for researchers to watch how the benefits of this technology develop in real time.

So what are the pros and cons?

Well, let’s start with the good. There’s no doubt floating solar is a viable way to install panels in a way that’s less intrusive upon local ecosystems and residential areas. Normally, solar farms take at least 20 times more land as a fossil fuel power plant to produce a single gigawatt of electricity.6 But in the case of floating solar, you don’t need to clear a bunch of trees or otherwise disturb large swaths of land to install your panels.4

Just look at Gujarat. According to the Gujarat State Electricity Corporation, if just 30% of its 80,000 km of canals were converted to solar, you could produce 18,000 MW of power and save 90,000 acres of land at the same time.3

The adaptability of floatovoltaics is what really makes them stand out. You can technically put solar panels in any body of water you want: oceans, lakes, reservoirs, a particularly large puddle. The opportunity cost of building solar panels on some of these sites can be relatively low, especially on reservoirs or surfaces that don’t get used for much of anything else.4 If it sits idle and doesn’t have other attractive uses (like recreational fishing), then you’re practically wasting watery real estate otherwise.

Making use of existing structures is even more impactful when you take into consideration the fact that developers can skip extensive environmental permitting and right-of-way issues. That means they can install these systems more quickly (and cheaply) without as much red tape in the way.13

There’s a boost to the overall infrastructure as well. The energy generated from canal-top solar can provide electricity for farmers during the energy-intensive irrigation season, and the out-of-season electricity can be fed into the state grid, reducing transmission losses and strengthening the local grid.3

Covering the canal surface also doesn’t just help conserve water; it can also improve the quality of that water underneath, too. The shade from the panels can reduce weed growth and algae blooms by blocking sunlight from penetrating the surface.14 These algae blooms are a common headache for the companies that manage the water delivery gates, as weed and algae overgrowth can clog the water pumps and raise maintenance costs.3 Reducing weed growth in the canals could lead to saving as much as $40,000 in maintenance costs per mile of canal.13

Algae and weeds aren’t the only unwanted guests floating solar panels can keep at bay. The shade beneath the panels lessens the number of microorganisms swimming below, improving overall quality and increasing the safety of potable water.14

Installing floating solar panels is also relatively easy, sometimes more so than land- or roof-based systems. All you have to do is assemble and anchor them in place.15

So here’s the multi-million dollar question: what’s the catch?

As good as all of this sounds, there are some challenges. For one, not any canal will do. Factors like wind speed, water currents, and the direction of sun all need to be considered when you install your floating solar. Meandering canals can be especially tricky for this, because you ideally want your solar panels to face south, but a canal’s direction is already set.3

The dimensions of the canal you use matters too: too wide of a stretch, and construction becomes much more expensive and challenging. Too narrow, and the amount of panels you can install is reduced, restricting your production off the bat. You can make some physical changes to the area — for example, trees along the canal often have to be cut down to keep the area free from shade. Naturally, that adds to environmental and cost concerns.3

And, like any other solar panel, floating arrays need to be cleaned regularly. Any gunk that accumulates on top can lead to a decrease in production, and you run the risk of silt buildup from the water itself, depending on where you install them. With this extra exposure to the elements, you need to build in a way to easily access these floating panels — like ramps in select locations — in order to allow for regular access. In more remote areas, some companies have used sprayers and robots to clean the panels on a regular basis.3

Floating solar panels also share the same disadvantages as their terrestrial counterparts: namely, the intermittency of solar access, the not-so-clean extraction and production of the materials used to make them, and the need to keep them well-maintained in order to glean enough energy to keep them productive for their entire lifespans.4

Worst of all, canal-top plants are more expensive to build than normal solar plants at this point in their development. Estimates vary, but costs can be as much as 10-15% higher than land-based panels.4 The bill for installation is generally higher due to the special materials, like galvanized supports to prevent corrosion, the floats themselves, and the niche installation techniques needed to get everything working properly.3

Once you consider operation and maintenance costs, though, things even out a bit. Floating solar involves more complicated maintenance; after all, you have to get to these arrays with appendages like anchors and mooring set-ups that will need extra attention. Still, with all that water around, you don’t need extensive fencing or specialized vegetation, which is often installed for terrestrial solar to keep the panels cool.4

In the end, Project Nexus and similar experiments are putting the potential long-term cost savings of canal-top solar to the test. This magic number can be represented by a net present value, or NPV. At its simplest, NPV is a measure of the financial worth of an investment. And University of California researchers calculated that the NPV of canal-top solar potentially exceeds conventional terrestrial solar by 20-50%.16

That figure changes depending on the exact type of canal-top solar you use. Plants built with tensioned cables, for example, may have a higher NPV than a ground-mounted facility when you consider the additional costs that can be offset by water conservation, decreased land use, and reduced aquatic weed maintenance. Researchers found that you can’t say the same for a plant built with a steel truss.17

Some experts aren’t quite so convinced about canal-top solar. Ellen Bruno, an economist in the Department of Agricultural and Resource Economics at the University of California, believes that the cost of building solar over California’s canals would still add up to be larger than the potential savings made through reduced water evaporation.14 Whether or not the cumulative impact of water conservation and clean energy production would do the trick is still to be determined.

There is some hope on the horizon. Over the array’s lifespan, the Turlock District anticipates that it will recoup the installation costs of the canal-top solar within eight years of operation. There are also other ways to mitigate these costs, like tax breaks and cash rebates.15 Regardless, one thing is certain: to compete with the large-scale terrestrial installations in the long run, canal-top solar needs to achieve a similar levelized cost of energy in order to be a feasible way forward.

So with all of this in mind, is floating solar the best of both worlds? Well, Californians might be able to cash in on a three-for-one deal: an estimated reduction in evaporation of up to 82%, clean energy, and maximizing precious space.13 The benefits are intriguing, especially in locations facing increased drought seasons and tighter squeezes across terrain. It’s certainly not a “one size fits all” type of solution. But in places like California and India, canal-top solar promises a win-win-win: a valuable source of clean energy that can conveniently integrate into the environment and improve it.

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