Jean Oliviéri, a retired scientist from the Centre de Radiométrie of Carpentras (located in the Provence, at latitude 44.05°N) sent me a graph with total solar energy (in kWh/m2, always on a horizontal surface) from 1972 to 2009:
It is interesting to see a well defined dimming period from 1972 up to 1988, followed by an overall brightening. This brightening is not monotonically increasing: first there is an interruption caused by the Pinatubo volcano eruption, and than a diminishing through the years 2005 to 2008. The 2009 solar energy is again on the rise.
For that 2005-2008 period we find a negative trend in all stations analysed so far: Maastricht (NL, 50.5 °N), Trier (DE, 49.5°N), Diekirch (LU, 49.5°N), Findel (LU, 49.4°N) and Carpentras (FR, 44.1°N). Trier and Findel readings are sunshine hours, taken as a proxy for total yearly solar energy. All stations also show (where available) a reversal of that trend in 2009.