Coming soon to a lake near you: floating solar panels

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 tank doesn't realize its full potential either. This open water could be covered with floating panels, a burgeoning technology known as floating photovoltaics, aka “floatvoltaics.” They could simultaneously capture the sun's energy and shade the water, reducing evaporation – a particularly welcome bonus where droughts are worsening.

Now, scientists crunched the numbers and found that if humans deployed ovoltaic floats in a fraction of the world's lakes and reservoirs – covering just 10% of each's surface area – the systems could collectively produce four times the amount of energy in the United Kingdom. used in one year. The effectiveness of so-called FPVs varies from country to country, but their research found that some could theoretically supply all their electricity this way, including Ethiopia, Rwanda and Papua New Guinea.

“The countries around the world that we think benefited the most from these FPVs were these low-latitude tropical countries that didn't have high energy demands in the first place,” said Iestyn Woolway, an Earth system scientist at the Bangor University and leader of the study. author of a new article describing the results in the journal Nature Water. “This meant that if just a small percentage of their lakes – that 10% – were covered by FPVs, that could be enough to power the energy demand of the entire country. »

For developing countries, floatovoltaics could prove particularly powerful for producing clean electricity. Instead of building more global warming infrastructure that runs on fossil fuels, like gas-fired power plants, emerging economies could run panels on land and water, in addition to other renewables like energy wind and hydroelectric. With solar power comes self-reliance: Utilities don't need to rely on fossil fuel shipments, but can harness the sun's abundant energy.

Floating solar panels – which are proliferating around the world, from California to France to Taiwan – are the same as those found 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 et Terre USA, which deploys floatovoltaic systems. “We're just providing a structure that floats to mount this electrical system.” Solar rafts are anchored either to the bottom of the body of water or to the shore, or both, to prevent them from wandering.

In many ways, solar panels and water features can benefit each other. Photovoltaics become less efficient as they heat up, so floating them on a lake or reservoir helps cool them. “Because of the cooling effect, we see increased efficiency of the systems,” said Sika Gadzanku, a researcher at the Colorado National Renewable Energy Laboratory who studies floatovoltaics but was not involved in the new research. In return, the panels provide shading, reducing evaporation. If the floatovoltaics were distributed across a reservoir, this could mean that more water would be available for consumption.

If a reservoir is equipped with a dam for hydroelectric generation, floatovoltaics could hook into this existing transportation infrastructure. (Countries like Kenya, for example, are already building more of this hydroelectric infrastructure.) This could save local governments money, because they would not need to install new transmission lines between the floats and the nearest town. In a drought, when water levels drop too low to produce hydroelectricity, the panels could still function as backup power.

To carry out their new modeling, Woolway and his colleagues started with more than a million lakes and reservoirs around the world, large enough and deep enough for flotovoltaics. Then they narrowed them down based on their critical qualities. For one thing, the body of water could not dry out, fail the panels, or freeze for more than six months a year, burying the panels in ice and damaging them. Nor could the lake be protected by law, as a natural refuge. And the site had to be near a human population capable of using the energy generated.

On the other hand, an isolated lake would require long transmission lines to connect a distant city to the floatovoltaics. This does not necessarily exclude the use of the technology for more remote communities living near an otherwise suitable lake. In fact, floatovoltaics could be particularly powerful there as a means of providing clean energy. These cases were simply not included in the scope of this modeling.

Regardless, with all of these features taken into account, the team came up with 68,000 feasible locations across 163 countries. They found that on average, countries could meet 16% of their energy demand with floating fleets, but some places could produce much more. In Bolivia, for example, floats could supply up to 87 percent of national electricity demand, and in Tonga they could meet 92 percent. However, the potential is much lower in the United States, where they only meet 4% of energy demand. Even though the country has a plethora of large lakes and reservoirs, overall energy consumption is extremely high. In less sunny climates, such as northern Europe, the efficiency of float-voltaics decreases, but Finland could still meet 17 percent of its electricity demand with floating panels.

“The regions or countries that we saw had the highest potential had both of these critical variables, in the sense that they were close to the equator or were at high altitudes, and therefore received large amounts of solar radiation incoming,” Woolway said. “And secondly, they had large bodies of water.”

For example, covering 10% of a 100 square mile lake would require many more solar panels than covering the same percentage of a 10 square mile lake. “We considered an area of ​​10 percent to be reasonable coverage without having a devastating impact on ecology and biodiversity,” Woolway said. “If you were to cover 90% of the surface with solar panels, no light would penetrate into 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 studying, for example, whether floats could release harmful chemicals or microplastics into the water.

And keep in mind that these ecosystems also run on solar energy: light fuels the growth of aquatic vegetation, which feeds all sorts of other organisms. If a flotovoltaic system cuts off too much light, it could reduce the food supply and hinder the ability of plants to produce oxygen. “You change the penetration of light, 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 studies floatovoltaics but was not involved in the new study. . “If you don't have enough light and you reduce the oxygen concentrations in that system, that can ripple through the food web, which could impact the fish.” At the same time, early research suggests the panels can counter the growth of harmful algae blooms that make the water unsafe to drink.

Scientists are still trying to determine how much coverage can still produce enough energy to justify the monetary cost of deploying float-ovoltaics, without incurring ecological costs. Each body of water constitutes its own universe of chemical and biological interactions, so the same coverage on two different lakes can have radically different effects. “Would 10% be enough to drive system-wide change? Almeida asks. “These are things we really don’t know.”

Researchers also need more data on how effective the panels are at reducing evaporation, and therefore how much water a given system could actually save. “What we haven't fully understood yet is that most of the existing floating solar systems that have attempted to collect data on this have been smaller,” Gadzanku said. “So it’s more: how the potential savings from evaporation ladder as you build larger systems?

Humans depend on bodies of water for many purposes other than drinking. Subsistence fishermen depend on them for food. And owners of lakefront properties might chafe if they think floating solar panels would reduce their property values.

Nonetheless, Almeida says, this new research identifies where floatovoltaics could operate and how much energy they could provide given local conditions. “I think what we need now,” Almeida said, “is to understand — among these suitable sites — which ones are really the low-hanging fruit.”