Geoff, this could be for several reasons.
The location is about 250 miles south of London and we enjoy far milder weather than the lattitude might suggest- Artic it ain't!
France is also a big country with a low relative population. Cheap land is a factor.
Alors, Pays de la Loire is an economically depressed agricultural area and thus ripe for EU regional grants. EDF are constructing photovoltaic farms all over France and beyond - a total spend of about 1,000 million euros 2010-12 on large scale projects wordwide is already funded.
At the same time, EDF is building the two initial 12 MW tranches of the Gabardan photovoltaic power plant, currently under construction, which will be commissioned this year. Located in south-west France in la Landes, the ground-based solar power plant will achieve a total capacity of 76 MW, making it one of the largest solar photovoltaic projects in Europe.
Not only that, but to take Reno's point, they are also marketing thousands upon thousands of house-roof units from 9kW-up too, will lend you the capital over 30 years and pay up to 40+ cents a kWh for your net production, [at least while the funds last!
] Claimed working life for these units is 30 years, [.
..takes pinch of salt!].
France's electicity is almost all made in her 58+ nuclear facilities or from hydro stations. So successful has EDF been, [critics might say that's because it's an unassailable Gummint monopoly, 'philes might say it's run as superbly as any organisation could hope to achieve - I don't knock it, because I enjoy the cheapest electricity anywhere in Europe
], that it now supplies a good % of your electicity in Blighty, along with much of your drinking water and gas!
Maybe pure coincidence, but the new 400,000v Contentin-Maine transmission line taking power south toward Italy from the new 1750MW Flammanville nuclear power station in Brittany will pass within just 5 kilometers of the site....