Why Has Floating Solar Become so Popular?

Jason Lomberg, North American Editor, PSD



Healdsburg, CA just switched on a 4.78 megawatt floating-solar array, the largest in the United States, calling attention to a new trend in photovoltaics.

In our rush to fulfill renewable energy mandates (and the steady march of innovation), we’ve been trying our best to reserve as much land as possible for solar farms. But space is finite, not all land is up for grabs, and land-based photovoltaics is intricate and pricy.

Greencoast.org does a good job laying out the pros and cons of setting up a solar farm. Ideally, you’d want to shoot for something at least 1 MW in size (enough to power up to 200 households), and the costs add up from there.

While the relative cost -- $1 per watt – might seem cheap compared to $3-4 for residential solar, you’re aiming much higher with a solar farm. Also, the initial solar farm costs don’t include licensing fees and the value of the land.

To produce 1 MW, and when using crystalline technology, you’d need to reserve 4 acres of land. With thin-film technology, it’d be 4.5 to 5 acres. At $500 per acre, your monthly costs for a 1 MW solar farm would be a bare minimum of $2,000.

And that doesn’t take into account overall efficiency. Crystalline solar panels work out to around 18% efficiency, while thin-film technology is a mere 12%. Overall, “for every acre, the plant produces an average of 0.357 GWh or 357 MWh of energy per year.”

Solar is booming around the globe, and residential solar installation is one of the fastest-growing businesses in the U.S. But the most efficient photovoltaic avenue – solar farms – is prohibitively expensive, a land hog, or both.

Thus, floating photovoltaic (FPV) systems have surged in popularity since at least 2007, when the first one came online at the Far Niente Winery in California, and it’s mainly grown in China, Japan, and the U.K.

Japan currently boasts 70 of the largest FPV systems in the world, and the biggest one – a 40 MW goliath – resides in Huainan, China.

So the U.S. isn’t breaking any records, but circumstances are colluding in favor of FPVs.

Healdsburg, CA’s 4.78 megawatt floating-solar array – for the recycled-water ponds at its Wastewater Treatment Facility – will provide 8% of the city’s electric needs and go a long way towards fulfilling their 50% renewable energy mandate by 2025 and 60% by 2030.

It also taps into the intrinsic advantages of FPVs.

The Florida Solar Energy Center (FSEC) notes that limited land availability (for solar farms) and reduced site-preparation costs (for FPVs) support floating solar. And because photovoltaic systems perform better when they’re cooler, and evaporative cooling could result in lower cell temperatures for FPVs, floating solar is potentially more efficient than its land-based cousin.

FPVs also reduce light exposure and lower water temperatures, with the fringe benefit of reducing harmful algae growth.

It’s an intriguing twist on a renewable energy mainstay.