energie-experten.org offers a simple-to-use search function that will display on a Google Map the nearest renewable energy experts to a searched address in Germany. It is possible to search the map by location and by type of renewable energy. Clicking on the returned map markers opens a tabbed information window with contact details and the areas of expertise of the renewable energy company. Site is GERMAN language.
This website is a very useful tool and well-organized, with thousands of experts in the database.