You´ve seen them on rooves; you´ve seen them in pastures. How about an island of photovoltaic panels floating in your neighborhood pond? Floating photovoltaic systems, or “floatovoltaics”, may well become a more common sight, as they offer an array of benefits compared with their terrestrial brethren.
Though they are a relatively new application of photovoltaic technology, solar arrays designed to float on water are attracting attention in certain niches, such as mining, agriculture and municipal water management. Projects in various corners of the globe are already being planned and developed, including in Japan, the UK, Australia, India, Italy and the US. The reason for this attention is the range of specific benefits that floating systems can offer compared with land-based systems and their ability to add value to otherwise lacklustre bodies of water.
Photovoltaic systems and valuable tracts of land
Deep in California’s wine country, Napa Valley vintner, Far Niente, has covered its irrigation pond with 994 floating solar panels, a complementary addition to the vinyard’s existing land-based PV installation. Together, the two systems total 400 kilowatts and have enabled the company to offset its consumption of grid electricity. To make room for the original standing system, one acre of grapevines had to be sacrificed. In an area where land sells for US$200,000 to $300,000 an acre, the standing installation came at a significant cost. Thus when Far Niente decided to expand its system, they thought outside the box. “We wanted to go solar, but we didn’t want to pull out vines”, the winery’s chief executive, Larry Maguire, explains in an interview. The floating photovoltaic system, designed and installed by SPG Solar and its sister company, Thomson Technology Industries, spared Far Niente nearly an acre of grapvines, which would have cost them upwards of $150,000 worth of wine per year.
Floating PV systems may offer certain businesses an innovative solar option, but floating arrays also make sense on a larger scale. Across the Pacific in Japan the world’s largest floating photovoltaic plant is soon to come online. Being built on the reservoir of Yamakura Dam just outside Tokyo, the 13.4 megawatt floater, when completed, will power around 4,700 households and offset 7,800 tons of carbon dioxide emissions annually. Japan, a major net importer of energy and renewable energy pioneer, has been under increasing pressure to increase the share of renewable electricity in its energy mix, particularly in the wake of the 2011 Fukushima nuclear disaster. However, open space is at a premium in Japan due to mountainous terrain, built-out urban development and the recent explosion of ground-based solar installations. But what Japan lacks in developable land, it makes up for in a wealth of reservoirs maintained by its large rice industry and flood-management authorities. Their flexibility and cost effectiveness make floating PV systems an attractive, even essential, option in Japan and many other countries.
Japan’s Yamakura Dam flotilla may not hold the title of “world’s largest” for very long. In India’s southern state of Kerala, a 50 megawatt system is being planned, which would become India’s second major floating photovoltaic system. In addition to the fact that project developers avoid costs associated with land leasing or purchase, a floating PV plant also offers a key technical advantage over terrestrial systems. A solar array is greatly affected by heat, which causes a decrease in efficiency. This is particularly important in hot climates, for example in India where temperatures in some areas can reach 50ºC (122ºF). Panels floating in water are naturally cooled, ensuring a higher generation yield, a little fact which is likely very interesting to current or potential PV investors. In addition, floating arrays are relatively simple to orient with the sun because their position can be easily modified.
Underutilized bodies of water and environmental impact
The environmental trade-offs involved with floating photovoltaic systems appears to be low, especially when compared to other types of generation systems. After all, there is no need to clear land and the systems themselves do not substantially affect the water quality. In fact, floating PV systems have been highlighted for their ability to help maintain the quality and quantity of water. A body of water is naturally prone to evaporation; an array of floating PV panels shades portions of the water’s surface, reducing its temperature, thereby diminishing the rate of evaporation. Floating systems also inhibit the growth of algae, which “can cause all sorts of issues” for irrigation ponds, according to David Sedlak, co-director of the University of California’s Berkeley Water Center.
However, it is clear that the environmental impact of floating PV systems is not zero, given the diversity of species that live on and under the water’s surface. This makes floating PV particularly applicable to underutilized bodies of water which are part of the built environment. Wastewater ponds have great potential, for instance. In California, a 15-megawatt system is being developed to float atop six wastewater ponds under the care of the Sonoma County Water Agency. The agency’s deputy chief engineer, Cordel Stillman, said that since the reservoirs are constructed rather than natural, many of the environmental impacts have already been taken into account, though allowances woud have to be considered for aquatic birds, he added.
Several solar entrepreneurs are even eyeing large moving bodies of water, such as the California Aqueduct, the massive canal that stretches 400 miles from the relatively water-rich North to the agricultural and populated South. Though more technically demanding than installing an array in a still body of water, the idea is to cover portions of the open aqeuduct with anchored, floating PV systems. Israeli firm Solaris Synergy estimates that a chain of floating systems would yield up to 2 megawatts of electricity per mile. Ralph Torres, deputy director of the California State Water Project, is a bit less optimistic, commenting that, “A better application would be on a reservoir”, citing potential technical and emergency response challenges involved.
It is clear from the limited number of existing case studies, that, appropriate environmental considerations notwithstanding, floating photovoltaic systems have substantial potential, particularly in built bodies of water that can be dual-purposed as power plants, but also… in a pond near you?