Floating solar offers a cool solution to a hot topic

Solar technology companies recognise serious potential in ‘floatovoltaics'.

It may seem paradoxical, but the enemy of efficiency for PV cells comes from the sun itself: heat. That’s one reason for looking into ways of putting the process on water. Another is saving valuable land space – both locally and globally.

David Mackay’s influential book Renewable Energy Without the Hot Air made the land-saving point forcefully, calculating that generating all the power we use in the UK from solar PV would mean using 200 square metres for each individual. Some of that space could have multiple uses – as when panels are mounted on roofs, or integrated into roads [see ‘Photovoltaics: building material of the future’].

Another solution is to put your solar farm on water rather than land. The pioneering ‘floatovoltaics’ installation at the Far Niente winery in California was designed specially by SPG Solar to avoid displacing valuable vines. Two years on, the company’s CEO Tom Rooney noted that floating the panels on the winery’s irrigation pond had brought some other unexpected benefits. Because they stay cooler than the same panels mounted on land, they’ve generated more electricity. The pond has also lost less precious water to evaporation, and keeping the light off it has stopped the growth of algae – without the use of chemicals.

Another inspiring scheme involves rafts of solar cells shaped into giant lily pads floating in Glasgow’s River Clyde. Cute it may be, but this piece of biomimicry has won an international design award for ZM Architecture, and further praise at New York’s Design Triennial – without actually becoming a source of power in practice.

But where some see a pretty picture, others see serious potential. Israel-based Solaris Synergy is using its patented concentrated photovoltaic technology (CPV) in a floating farm. The design incorporates a patented evaporation cooling technology that keeps the silicon elements at a low and stable temperature (30ºC) however hot the rays. Known as Aquasun, it is being built in the reservoir of a hydro power plant at Caderache in southern France, in partnership with utility company EDF.

Rival claimant to PV’s watery throne is Australian start-up Sunengy. It too is working in partnership with a giant utility: Tata Power of India. And, similarly again, it is using the reservoir of a hydro power plant, in this case near Mumbai.

Sunengy has patented a liquid solar CPV array that will float cunningly around on the reservoir, tracking the sun to maximise energy input while using the water to keep its silicon cool. It keeps installation costs down by sharing transmission lines with the hydro plant, which is only actively generating for about a third of the time due to limited water availability.

Power from the solar array, produced in the daytime, can be dovetailed nicely with hydro power from water released in the evening. Or the PV power can even be stored (the holy grail for intermittent renewables) by using it to pump the water back up. – Roger East

Photo credit: SPG Solar