From land to water04 / 2012, Applications & Installations | By: Charles W. Thurston
Floating PV systems: Photovoltaic systems have been successfully deployed on land and in space for many years, so it was only a matter of time before water-based PV systems emerged on larger scales. Over the past five years, a myriad of floating systems have evolved in varying degrees for use in ponds, reservoirs, canals, rivers and oceans.
Among the benefits of using floating PV systems is the water-cooling effect on silicon solar cells, the natural reflectivity of the water surface, the potential reduction in algae growth due to reduced sunlight penetration, and a lower water temperature in the areas below the arrays.
What was claimed to be the world’s first floating photovoltaic system was installed in 2007 by SPG Solar, of Novato, California, on a pond at Far Niente Winery in Napa. Land in Napa, famous for its wines, can cost US$300,000 per acre, so land use is at a premium. The 1,000 floating panels in the system were linked to 1,300 stationary panels on land to produce 4,000 kW total, utilizing Sharp flat panels and a proprietary mooring system.
Saving vineyard land
SPG dubbed the system Solar Floatovoltaics, and has been testing the system elsewhere since then, including a 30 kW array at Gundlach Bundschu Wineries, in Sonoma, also a major California wine-producing area. This winery array includes 162 Sharp modules on tethered pontoons.
In April, 2011, SPG Solar CEO Chris Robine announced a second generation of the company’s system including reflectors, saying: “Now, customers around the world can install a floating system that is priced competitively to ground-based, single-axis tracking solar systems.” The latest version includes a SunSeeker single-axis tracker produced by SPG sister company Thompson Technologies Industries, also based in Novato. The cooling effect of the water increases the energy production of the units by up to one percent, the company suggests. SPG says that the pond array helps reduce water evaporation by 70 percent, which is valuable in areas with erratic or limited rainfall.
Among other locations where SPG has begun installing the newest version of its system is Petaluma, California, where there will be 2,000 Suntech solar panels mounted on pontoons with steel lattice frames at 14 degree inclines, on a municipal irrigation pond. Among prospective SPG clients is said to be MDU Resources Group, based in Bismarck, North Dakota, which is considering the array for mine settling ponds in California.
Larger systems emerge
Perhaps the largest flat panel floating system under development now is a SG$11 million, two megawatt system planned by Singapore’s Economic Development Board (EDB) for the Tengeh Reservoir. The project developers, which have examined the SPG Floatovoltaics projects, include the Solar Energy Research Institute of Singapore.
At the time of the November 2011 announcement of the project, Beh Swan Gin, the Managing Director of EDB, said, “This pilot project exemplifies Singapore’s continuing efforts to overcome our resource constraints through innovative renewable energy solutions. The project also enables clean tech companies to address a sophisticated need, which if successful, can be scaled up and commercialized globally.”
Double tracking reflectors
Another approach to pond-based systems is one that utilizes two single-axis reflectors for flat panels, named the Floating Tracking Cooling Concentrator (FTCC) system, by developer Marco Rosa-Clot, a professor at Florence University. Scienza Industria Tecnologia (SIT) is now testing the design in Italy and South Korea. SIT calculates that the water circulating over the panels will permit an increase in energy production of about ten percent, since the heat from mirror-reflected light will not overheat the silicon photovoltaic cells.
Professor Rosa-Clot has been quoted suggesting that his water-based design, which floats on polyethylene tubes, would cost 20 percent less than a similar land-based configuration. He conceived the array of the system as either being circular or square rafts hosting two modules each. A 30 kW pilot plant was completed at Colignola, near Pisa in September 2011, and a 200 kW unit was installed at Terra Moretti’s Petra winery in Suvereto, Italy. Samsung’s Techwin also has built a pilot plant using the technology in Cheongju, South Korea, which is surrounded by ice during the winter.
Designing for ice
Coping with ice is a particular wrinkle in floating PV systems for many regions. To study the effects of heavy ice, in late 2011, New Jersey American Water, of Voorhees, New Jersey, tapped Eneractive Solutions of Asbury Park to install a US$1.35 million water reservoir-based system at the Canoe Brook Water Treatment Plant. Specially designed to withstand a freeze/thaw environment, the 135 kW floating installation is comprised of 538 modules, fixed at a 14 degree angle, that will rise and fall with the reservoir water level. In 2010, New Jersey American Water installed solar “water bees” to churn the water at the reservoir to improve water quality.
Concentrating PV cools in pools
Apart from reflective enhancements to floating PV systems, concentrators are also under development. “The great advantage of concentrated PV (CPV) technology in general is that it switches the cost burden from PV materials – where there are limited materials and opportunities for cost reduction – to concentration optics and tracking controls – where there are numerous opportunities for cost reduction,” says Pyron Solar CEO Stephanie Rosenthal, in San Diego.
San Diego Gas & Electric has been testing a 20 kW peak floating lens concentrating solar system designed by Pyron Solar, and dubbed “Power Reef.” The arrays are 15 meter wide circles with a dual axis lens positioned over proprietary glass optics, floating on eighteen-inch deep pools of water installed for the solar project. Pyron suggests that 3.1 square acres of water could produce one megawatt of power, using the company lens that increases light concentration to a level of 1,200 suns.
According to Rosenthal, “The synchronization of our modules to the daily and seasonal movement of the sun and the cooling and balance advantages delivered by our floating power-production arrays demonstrate an output per cell improvement of more than 19 percent over other commercially available CPV systems for utilities and commercial applications.” She says that her company’s arrays are operating at close to 28 percent efficiency compared to 12 to 15 percent at the array level for conventional flat panels. The system operates at a reported cost of ten U.S. cents per kilowatt hour before government incentives.
“We are operating at only 25 degrees Celsius, and are the only ones we know that operate at that low a temperature. Other CPV systems are operating at 55 degrees Celsius and higher,” Rosenthal says. “We are also using the water as a structural support, so we don’t have a lot of stainless steel, we need no concrete or posts in the ground, no posts, and the system is neutrally buoyant,” she explains.
Open water CPV experiments
In February 2011, Solaris Synergy installed its first floating concentrated photovoltaic (F-CPV) system, connecting it to the Israel Electric Corporation grid. The “Aquasun” system is located at the Arava Institute for Environmental Studies’ Center for Renewable Energy and Energy Conservation located on Kibbutz Ketura, north of Eilat, Israel.
Solaris, in cooperation with France’s EDF, also began testing a system in September 2011 at Cadarache, Provence, close to a local hydroelectric facility and the grid. And in 2010, Solaris signed an agreement with Israeli national water company Mekorot to install the floating concentrator system on a water reservoir during 2011, involving a 50 kW pilot project that could expand to three megawatts, according to Solaris CEO Yossi Fisher.
“Mekorot, which owns the majority of Israel’s more than 400 reservoirs, will initially test the system’s ability to deal with environmental factors such as wind, waves and live organisms. Israel’s largest consumer of electricity, Mekorot will also evaluate the impact of the system on water quality, as well as the impact of the system’s water cover on temperature, evaporation, oxygen, fish and algae growth,” Solaris indicates.
“This agreement is a major step forward for both sides,” said Fisher. “We view Mekorot as a strategic partner that will not only help us evaluate and improve our system under real-life conditions, but also open up the water utility market in Israel. At the same time, the agreement enables Mekorot to fully leverage its resources.”
Australia and India
Tata Power, a unit of Tata Group, has partnered with Australia’s Sunengy Pty for a pilot installation of its patented “Liquid Solar Array” technology, which uses traditional concentrated photovoltaic technology consisting of a plastic lens and plastic concentrators that track the sun. In this system, to be installed near Mumbai, the lens rotates to submerge during bad weather.
Construction of the pilot plant in India began in August 2011 and Sunengy plans to establish a larger system in the New South Wales Hunter Valley, in Australia this year before going into full production. Sunengy lists Rahul Shah as a Director of the company, who also is the Vice President of strategy and business development for Tata Power.
In India, the Gujarat state government has contracted Sun Edison to install solar panels on a one kilometer stretch of the Narmada canal, near Sanand. While a Sun Edison source could not say whether the panels would float or be fixed, the aimed one megawatt scope of the project will attract attention. The Gujarat Electricity Regulatory Commission, the state power regulator, has set a feed-in tariff of 15 Indian rupees for power purchased from solar PV generators.
In Europe, one small output canal project in test was designed by ZM Architecture, of Glasgow, which developed floating “Solar Lily Pads” with motor driven rotators on the Clyde river. Glasgow’s City Council is considering testing a small pilot project in conjunction with the Glasgow Science Centre.
In addition, a variety of companies have proposed that the California State Water Project cover its 400 mile aqueduct network with floating photovoltaic panels, which could help generate electricity for pumped water from the canal system to the agricultural water consumers it serves.
Moving river, rising ocean
Some water-based systems have also been proposed for bodies of water with more rapid or erratic movement, including large rivers and the ocean.
In Seoul, on the river Han, three municipally-owned man-made floating islands utilize solar modules to generate six kilowatts of daily power for the island’s visitors. One of the three-story islets, named Viva, measures 85 meters by 49 meters, and weighs 2,000 tons. The islands will be used mainly for entertainment and cultural events.
Finally, British designer Phil Pauley has proposed ocean-based floating PV systems, which could be moored to the bottom and feed energy to submarine power lines. His hybrid solar concentrator pods would be dome-shaped to collect direct and reflected light from the ocean surface, and include a mechanism to capture the motion produced by waves as well.