Solar Panels Floating on Water Will Power Japan's Homes

More solar power plants are being built on water, but is this such a good idea?
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Floating solar arrays take advantage of open water where land space is constrained.


Nowadays, bodies of water aren't necessarily something to build around—they're something to build on. They sport not just landfills and man-made beaches but also, in a nascent global trend, massive solar power plants.

Clean energy companies are turning to lakes, wetlands, ponds, and canals as building grounds for sunlight-slurping photovoltaic panels. So far, floating solar structures have been announced in, among other countries, the United Kingdom, Australia, India, and Italy.

The biggest floating plant, in terms of output, will soon be placed atop the reservoir of Japan's Yamakura Dam in Chiba prefecture, just east of Tokyo. When completed in March 2016, it will cover 180,000 square meters, hold 50,000 photovoltaic solar panels, and power nearly 5,000 households. It will also offset nearly 8,000 tons of carbon dioxide emissions annually. (Since the EPA estimates a typical car releases 4.7 tons of CO2 annually, that's about 1,700 cars' worth of emissions.)

The Yamakura Dam project is a collaboration by Kyocera (a Kyoto-headquartered electronics manufacturer), Ciel et Terre (a French company that designs, finances, and operates photovoltaic installations), and Century Tokyo Leasing Corporation.

So, why build solar panels on water instead of just building them on land? Placing the panels on a lake or reservoir frees up surrounding land for agricultural use, conservation, or other development. With these benefits, though, come challenges. (See related story: "How Green Are Those Solar Panels, Really?")

Solar Enters New Territory

"Overall, this is a very interesting idea. If successful, it will bring a huge impact," says Yang Yang, a professor of engineering at the University of California, Los Angeles who specializes in photovoltaic solar panels. "However, I do have concerns of its safety against storms and other natural disasters, not to mention corrosion."

Unlike a solar installation on the ground or mounted on a rooftop, floating solar energy plants present relatively new difficulties. For one thing, everything needs to be waterproofed, including the panels and wiring. Plus, a giant, artificial contraption can't just be dropped into a local water supply without certain precautions, such as adherence to regulations on water quality—a relevant concern, particularly if the structure starts to weather away.

"That is one reason we chose Ciel et Terre's floating platforms, which are 100 percent recyclable and made of high-density polyethylene that can withstand ultraviolet rays and corrosion," says Ichiro Ikeda, general manager of Kyocera's solar energy marketing division.

Another obstacle? Japan's omnipresent threat of natural disasters. In addition to typhoons, the country is a global hot spot for earthquakes, landslides, and tidal waves.

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The planned floating solar array for Japan would sit atop the Yamakura Dam, east of Tokyo.


To make sure the platforms could withstand the whims of Mother Nature, Ciel et Terre's research and development team brought in the big guns: a wind tunnel at Onera, the French aerospace lab. The company's patented Hydrelio system—those polyethylene "frames" that cradle the solar panels—was subjected to very high wind conditions that matched hurricane speeds. The system resisted winds of up to 118 miles per hour.

Why Japan Could Be the Perfect Spot

Given its weather, why build floating solar panels in the storm-filled, Ring of Fire-hugging Land of the Rising Sun? The reason: Many nations could benefit from floating solar power. And Japan is their poster child.

The largely mountainous archipelago of Japan suffers from a lack of usable land, meaning there's less room for anything to be built, let alone a large-scale solar plant. However, the nation is rich in reservoirs, since it has a sprawling rice industry to irrigate, so more solar energy companies in Japan are favoring liquid over land for construction sites. Suddenly, inaccessible terrain becomes accessible.

Kyocera's Ikeda says available land in Japan is especially hard to come by these days, as the number of ground-based solar plants in the country has skyrocketed in the past few years. (See related story: "Japan Solar Energy Soars, But Grid Needs to Catch Up.")

But, he added, "the country has many reservoirs for agricultural and flood-control purposes. There is great potential in carrying out solar power generation on these water surfaces."

In Japan's case, Ciel et Terre says that the region's frequent seismic fits aren't cause for concern, either. In fact, they illustrate another benefit that floating solar panels have over their terrestrial counterparts, the company says.

"Earthquakes have no impacts on the floating photovoltaic system, which has no foundation and an adequate anchoring system that ensures its stability," says Eva Pauly, international business manager at Ciel et Terre. "That's a big advantage in a country like Japan."

Solar's Potential Ecological Impact

Floating solar panel manufacturers hope their creations replace more controversial energy sources.

"Japan needs new, independent, renewable energy sources after the Fukushima disaster," says Pauly. "The country needs more independent sources of electricity after shutting down the nuclear power and relying heavily on imported liquid gas."

This up-and-coming aquatic alternative impacts organisms living in the water, though. The structure stymies sunlight penetration, slowly making the water cooler and darker. This can halt algae growth, for example, which Ciel et Terre project manager Lise Mesnager says "could be either positive or negative." If there's too much algae in the water, the shadow-casting floating panels might be beneficial; if the water harbors endangered species, they could harm them.

"It is really important for the operator to have a good idea of what kind of species can be found in the water body," Mesnager says.

Since companies must follow local environmental rules, these solar plants are usually in the center of the water, away from banks rich with flora and fauna. Plus, companies might prefer building in man-made reservoirs instead of natural ones, as the chances of harming the area's biodiversity are smaller.

Could the Future Include Salt Water?

More than three-quarters of our planet is ocean, which might present alternative energy companies a blank canvas on which to dot more buoyant energy farms. But moving floating panels to the open sea is still in the future. Kyocera's Ikeda says it would bring up a whole new realm of issues, from waves to changing water levels, which could lead to damage and disrupted operations.

Ciel et Terre is experimenting with salt water-friendly systems in Thailand, but ocean-based plants might be impractical, as offshore installations are costly, and it's more logical to produce electricity closer to where it'll be used.

For now, companies are aiming to build floating energy sources that conserve limited space, are cheaper than solar panels on terra firma, and are, above all, efficient. Ciel et Terre says that since its frames keep Kyocera's solar panels cool, the floating plant could generate up to 20 percent more energy than a typical ground system does.

The Yamakura Dam project might be the world's biggest floating solar plant, but it wasn't the first-and it almost certainly won't be the last.

The story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

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