It's not a governmental institution but an NGO which unites many local governments and other participants.

  http://www.zonatlas.nl/home/over-de-zonatlas/

They use high resolution 3d surface information (elevation data) and weather reports to assess the efficiency of solar panels. The map for my house accurately shows how much efficiency can be expected on each part of the house. This takes into account neighboring buildings and trees. The site also calculates a number of scenarios and allows you to easily request offers and show how long it takes to earn back your investment. They cleverly compare this to interest rate. E.g. on my house, investing in solar now would yield 4.5% interest over 20 years (given certain assumptions).

It is a very impressive site.