Solar array floats toward improvement of silicon cells

A new kind of solar array designed to float on water could improve the efficiency of silicon cells in hot weather.

The Israeli-developed technology concentrates sunlight onto an array of British-made solar cells and uses the water to keep them cool, increasing the amount of electricity they produce.

Solaris Synergy, the company behind the technology, is partnering with energy firm EDF to undertake a nine-month trial of the system in France from September this year.

This trial, funded by the international Eureka network and the Israeli Ministry of Industry, Trade and Labor, follows a prototype demonstrated in Israel last week using cells made by renewable energy technology firm Narec.

Silicon solar cells become less efficient as their temperature increases and concentrating sunlight onto them in hot conditions can increase their temperature to as much as 200ºC.

‘Heat reduces the ouput voltage of the cell and therefore the output power. This leads to cell efficiency reduction,’ Solaris’s business development manager, Dr Elyakim Kassel, told The Engineer.

‘In hot countries such as Israel, in summer regular solar panels actually have lower efficiency because of the heat. If you concentrate the light with mirrors you also concentrate the heat so they don’t work at all.

‘Our core technology is a very efficient cooling system to allow the silicon solar cells to still provide superior efficiency.’

Solaris’s technology is designed to float on industrial sources of water, such as cooling reservoirs for the energy sector or stores for fire fighting. This would allow the arrays to be deployed without impacting on public space or the environment.

The water is used to cool the solar cells by means of a submerged closed-loop heat exchanger. The solar array is positioned facing down above a series of mirrors that float on the water and reflect and concentrate sunlight back up to the silicon cells.

The concentration system adds up to two per cent efficiency to the monocrystalline cells, which operate at a standard efficiency of 17 per cent. Each module produces a standard amount of 200kW of electricity.

The cells’ efficiency falls by approximately half a per cent for every degree above 25ºC by which their temperature increases. Even without the concentrators, the cells’ temperature can rise to around 80ºC.

The heat exchanger maintains a steady temperature of around 35ºC, eliminating fatigue caused by changes in temperature, as well as cutting the heat-related inefficiency.

EDF’s 50kW trial will take place at Cadarache in southeast France at a site close to a hydro-electric facility that will provide the necessary water surface. Another trial will take place in Israel in partnership with Israeli water company Mekorot.

Kassel and his team believe the trials will provide the necessary information to commercialise the technology.