A reservoir is many things: a source of drinking water, a playground for swimmers, a refuge for migratory birds. But if you ask solar enthusiasts, a reservoir is also not realizing its full potential. That open water can be covered with floating panels, an emerging technology known as floating photovoltaics, also known as “floatovoltaics.” They could simultaneously collect energy from the sun and shade the water, reducing evaporation – a particularly welcome bonus where droughts are worsening.
Now scientists have crunched the numbers and found that if people deployed floatovoltaics in a fraction of lakes and reservoirs around the world – covering just 10 percent of the surface area of each – the systems could collectively generate four times the amount of power that the UK used in a year. The effectiveness of so-called FPVs will vary from country to country, but their research found that some could theoretically provide all their electricity this way, including Ethiopia, Rwanda and Papua New Guinea.
“The countries around the world that we saw the most from these FPVs were these low-latitude, tropical countries that didn’t have a high energy demand in the first place,” said Iestyn Woolway, an Earth system scientist at Bangor University and leader said. author of a new paper described the findings in the journal Nature Water. “This meant that if only a small percentage of their lakes – this 10 percent – were covered by FPVs, it could be enough to fuel the energy demand of the entire country.”
For developing countries, floatovoltaics can be especially powerful as a way to generate clean electricity. Instead of building more planet-warming infrastructure that runs on fossil fuels, such as gas-fired power plants, young economies can use panels on land and water, in addition to other renewables such as wind and hydropower. With solar comes autonomy: utilities don’t have to rely on fossil fuel shipments, but can harness the abundant power of the sun.
Floatovoltaic solar panels – which have increased worldwide, from California on France on Taiwan – is the same that occurs on a roof. “It’s the same electrical system, the same panels, the same inverters,” said Chris Bartle, director of sales and marketing at Ciel and Terre USA, which deploys float-voltaic systems. “We’re just providing a structure that floats to mount that electrical system.” The solar rafts are anchored either to the bottom of the water body or to the shore, or both, to prevent them from wandering.
In many ways, solar panels and bodies of water can benefit each other. Photovoltaics become less efficient the warmer it gets, so floating them on a lake or reservoir helps cool them down. “Because of the cooling effect, we see increased efficiency of the systems,” says Sika Gadzanku, a researcher at the National Renewable Energy Laboratory in Colorado, who studies floatovoltaics, but was not involved in the new research. To return the favor, the panels provide shade, which reduces evaporation. If floatovoltaics are distributed over a reservoir, it could mean that more water will be available for drinking.
If a reservoir is equipped with a dam for hydroelectric generation, the floating power can hook into that existing transmission infrastructure. (Countries like Kenya, for example, are build more of this hydroelectric infrastructure already.) This can save local governments money because they do not need to string new transmission lines from the floatovoltaic to the nearest city. In the event of a drought, when water levels drop too low to generate hydropower, the panels can still function as backup power.
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To do their new modeling, Woolway and his colleagues started with more than a million lakes and reservoirs around the world big enough and deep enough for floatovoltaics. Then they scaled it down based on critical attributes. For one, the water mass could not dry up, stranding the panels or freezing more than six months a year, burying the panels in ice and damaging them. Nor could the lake be protected by law, like a natural refuge. And the site had to be near a human population that could use the generated power.
A remote lake, on the other hand, would require long transmission lines to connect a distant city to the floatovoltaics. This does not necessarily preclude the technology for more remote communities of people living near an otherwise suitable lake. In fact, floatovoltaics can be especially powerful there as a way to provide clean energy. These cases were just not included in the scope of this modeling.
Regardless, taking all these attributes into account, the team ended up with 68,000 viable locations in 163 countries. They found that countries can meet an average of 16 percent of their energy demand with floatovoltaics, but some places can generate much more. In Bolivia, for example, floating photovoltaics can meet up to 87 percent of the national electricity demand, and in Tonga they can meet 92 percent. The potential is much lower in the United States, meeting just 4 percent of energy demand—even though the country has an abundance of large lakes and reservoirs, overall energy consumption is extremely high. In less sunny regions, such as northern Europe, the efficiency of floating photovoltaics drops, but Finland can still meet 17 percent of its electricity demand with floating panels.
“The regions or the countries that we saw that had the highest potential had these two critical variables, in that they were close to the equator, or at high altitudes, so they received large amounts of incoming solar radiation,” Woolway said. . “And secondly, they had large bodies of water.”
For example, covering 10 percent of a 100-square-mile lake would end up with many more solar panels than covering the same percentage of a 10-square-mile lake. “We considered 10 percent to be a reasonable area cover without having a devastating impact on the ecology and the biodiversity,” Woolway said. “If you were to cover the surface 90 percent with solar panels, no light would enter the water itself.”
This is where the new science of floatovoltaics gets tricky, as there is still little data on the potential environmental and social downsides of these floating systems. Scientists are investigating, for example, whether the floats may contain harmful chemicals or microplastics in the water.
And keep in mind that these ecosystems are also solar-powered: Light fuels the growth of aquatic vegetation, which feeds all sorts of other organisms. If a floatovoltaic system cuts off too much of that light, it can reduce the food supply and hinder plants’ ability to produce oxygen. “You’re changing light penetration, and that’s the most fundamental physical variable for an aquatic ecosystem,” said Rafael Almeida, a freshwater ecosystem scientist at the University of Texas Rio Grande Valley, who study floatovoltaics but was not involved in the new study. “If you don’t have enough light, and you reduce oxygen concentrations in that system, and that can flow through the food web, that can potentially affect fish.” At the same time, early research suggests that the panels may counteract the growth of harmful algal blooms that make water dangerous for people to drink.
Scientists are still trying to figure out what amount of coverage can still produce enough power to justify the monetary cost of deploying floatovoltaics, while not incurring ecological costs. Each body of water is its own unique universe of chemical and biological interactions, so the same cover on two different lakes can have dramatically different effects. “Will 10 percent be enough to fall into system-wide changes?” asked Almeida. “These are things we really don’t know.”
Researchers also need more data on how effective the panels are at reducing evaporation, and thus how much water a given system can actually save. “What we have yet to fully understand is that so many of the existing floating solar systems that have tried to collect data on this have been smaller,” Gadzanku said. “So it’s more: How do potential evaporation savings scale while building larger systems?”
People rely on bodies of water in many ways other than drinking. Subsistence fishermen rely on them for food. And waterfront property owners may panic if they think floating solar panels will reduce their property values.
Still, says Almeida, this new research identifies where floatovoltaics can work, and how much energy they can provide given local conditions. “I think what we need now,” Almeida said, “is to understand — from these suitable sites — what the low-hanging fruit really is.”
