The feed-in into new and existing block and district heating networks is considered a future market for solar thermal heat. Denmark is a role model where already a number of municipalities are supplied by solar assisted district heating systems. But not only the ground mounted collector fields in Denmark can be a model. The district heating supplier E.ON Hanse in Hamburg is working on a feed-in model with roof mounted solar collectors on residential houses which are owned by district heating customers feeding-in their produced heat into the network and getting refund.