As night falls on the Gulf of Ajaccio, Corsica, the Iles Sanguinaires turn red in the dying light of the sun. But it never really sets on the solar plant on the hillside overlooking the Mediterranean.
Thanks to the use of hydrogen, the electricity generated during the hours of sunlight can be stored and injected into the power grid at any time of the day or night. Though the Renewable Hydrogen for Grid Integration (Myrte) facility is still experimental, it is already the largest of its kind in the world.
"The problem of renewable-energy intermittence is particularly acute on islands," said Philippe Poggi, a lecturer at Corsica University and one of the driving forces behind the project, which also involves France's Atomic and Alternative Energies Commission (CEA) and Helion, a subsidiary of Areva, the nuclear power conglomerate, which specialises in hydrogen processes.
In Corsica the 600 megawatts of installed power capacity are largely dependent on oil-fuelled power stations, backed up by a hydroelectric plant and a power line running across the seabed to Sardinia.
Solar and wind power play a marginal part, but the island is keen to develop alternative energy sources. However, as is the case for French overseas territories, a ministerial decree caps the share of intermittent renewables in the overall electricity supply at 30%. This precaution is designed to avoid the risk of an outage caused by cloudy skies or a lull in the wind.
"The only way round this limitation is to store solar energy," said Poggi. This makes it possible to even out fluctuations in output and cope with sudden spikes in demand.
The farm, set in a hollow and partly grassed over, looks very much like a conventional solar power facility, with a 3,700sqm array of photovoltaic panels. The novel feature is an unobtrusive hydrogen plant, which contains all the smart bits.
Powered by the current generated by the solar panels, an electrolyser splits water into oxygen and hydrogen, which is stored in tanks at a pressure of 35 bar. When required a fuel cell reunites the two elements in a reaction, generating electricity that can be fed into the grid.
No single step in this process is revolutionary. The difficult part is optimising the whole process. For example, operation of the electrolyser must be adapted to an intermittent power source. Similarly the fuel cell has to cope with the grid's fluctuating demand. "The challenge is to find a mix that optimises all the components," according to Poggi.
Corsica sees itself as "a laboratory", setting an example of how the mainland could follow once the system is fully operational.
Work on Myrte started in 2006, with a €21m ($27m) budget funded by the regional council, central government and the European Union. It has been up and running for a few months and is still only at the stage of a small-scale test plant. If it lives up to expectations, an industrial-scale unit will come online in 2014-15.