Solar maps indicate the average yearly sum of solar radiation in kWh/m2 on solar panels placed in optimal inclination towards the sun.
As we can observe in Europe the variation is large; the radiation in southern areas almost doubles the radiation of some North-European areas.
Of course this means that the energy production of your solar installation is much higher in the south, and the time to recover the investment in solar is much shorter. However, this does not mean that solar is not attractive for north-European countries. Less sun means less energy production, but it still is much less costly then the energy prices of the utilities! In southern Europe you may recover your investment within 3-4 years, while in the North within 6-7 years. But over the total lifetime of a solar installation (30 years), this is not very important; the total energy savings are still enormous!
Fact is that the penetration of solar installations in private households in Germany, Holland and Denmark is much higher then in South-European countries. Particularly Germany is the country with the highest penetration of solar installations in the world!
What are we waiting for in the rest of the countries?