Technology

Floating Solar PV brings efficient twists

 By RP Siegel

The energy contained in the sunlight hitting the Earth every hour is enough to potentially meet the world’s energy needs for a year. The energy is clean, quiet and essentially free, which is why considerable effort is being made to capture and utilize it. There are, however, a few challenges. For one thing, the energy contained in sunlight is relatively diffuse, which means that a large collection area is required to capture significant quantities. Rooftops provide an excellent location for solar collectors, but all the available rooftop area is not enough to keep up with growing demand, even at today’s improved conversion efficiencies. That means that solar panels and solar farms have to compete with other uses of land, be it development, agriculture or even forests…

NASA solar farm

When Water Met Solar

One emerging solution to this challenge is the idea of floating solar farms. Not only does putting solar collectors in water save room for other endeavors on land, it also has an additional benefit. Solar panels tend to become less efficient when they get very hot, which, being in the sun all day, they often do. Placing the “floatovoltaic” panels in water provides cooling, which helps to keep the panels running at the highest possible efficiency.

Back in 2008, the Far Niente winery in Oakville, California, installed 1,000 solar panels, floating on pontoons in their irrigation pond. Besides providing essentially all of the winery’s power (supplemented by additional solar panels on land), the panels help to suppress the growth of algae and reduce evaporation. The owners were attracted to floating solar because of the high value of vineyard land. That Napa Valley facility was later joined by a larger facility purchased by the Sonoma Clean Power utility in Sonoma County that is floating solar panels on wastewater ponds. This 12.5 MW system is currently the largest in the US.

Far Niente floating PV

Around the World

Beyond the US, floating solar installations can be found in Japan, Australia, South Asia and across Europe. Japan is particularly hungry for new sources of electric power after the failure of the Fukushima nuclear plant. The country is building what is expected to be the world’s largest floating solar plant in a reservoir in Chiba prefecture, just above the Yamakura Dam. This facility will contain 50,000 solar panels that will produce 13.7 MW.

The French company, Ciel & Terre, is responsible for the Yamakura Dam project, one of 43 floating solar projects the company has built around the world. At this point the huge array has been completed, and the system will become operational once the electrical connections have been upgraded early next year. According to Eva Pauly, Ciel & Terre’s International Sales Director, this installation represents the convergence of two trends: scarcity and geography, which combine to make Japan an ideal location for floating solar. First, as was already mentioned, there has been an urgent need for an additional generation capacity in the wake of the Fukushima shutdown. Second, Japan is a small island with limited available land area, but lots of inland ponds and irrigation reservoirs that could be utilized in this manner. According to a GIS study conducted by Ciel & Terre, floating solar could provide as much as 3 GW of electric capacity in Japan alone.

Okegawa floating PV (source: ciel-et-terre.net)

Furthermore, Pauly explained, hydroelectric dam projects are a great fit for floating solar, since the electric utility infrastructure is already there, and in most cases, is oversized to account for variations in water level. Since the company’s inception in 2006, it has been mindful of the need to preserve land. A number of its earliest projects were located in brownfield zones. From there it was a relatively short leap to locating the panels on the water. Ciel & Terre has designed and developed the floating structure and anchoring system for their Hydrelio® system for which they now hold seven patents. Their system can be used with any standard sized solar panel.

The company limits the size of the floating arrays to approximately 1 MW per three acres. The exact limit depends on a variety of location-dependent factors including water depth, wind conditions and wave action. The most recent project, the Alto Rabagão dam in Portugal, is nearly complete. While other floating solar arrays have been installed in reservoirs above dams, this new hybrid system is the first to combine the solar and hydro capabilities. The system allows solar power to be generated during the day while hydro power is reserved for use at night and during peak demand periods. Between the two, clean, continuous, reliable power can be assured, while taking advantage of the built-in storage provided by the hydro. In-house studies have estimated that this approach, installed on just 10 percent of the world’s 50 largest dams, could generate 400 GW of solar electricity. That’s nearly 40 percent of the total capacity supplying the US electric grid. In this particular installation, the 220 kW solar array will supplement the 68 MW hydropower capacity of the dam.

According to Pauly, it is theoretically possible to put floating solar out on the ocean, though it would have to withstand some very challenging conditions that would require considerable expense, not to mention the electrical losses from the long cable runs. Still, given the considerable potential that already exists on inland bodies of water, it’s clear that floating solar is here to stay.

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about the author
RP Siegel
Skilled writer. Technology, sustainability, engineering, energy, renewables, solar, wind, poverty, water, food. Studied both English Lit.and Engineering at university level. Inventor.