Solar thermal plants in the district heating scale were pioneered in Sweden the beginning of the 80’s. Since then a significant number of plants have been built around Europe, both with diurnal and seasonal storage. The technology was developed to a mature stage during the 90’s when a multitude of plants were built around Europe. Most of the plants today are found in Austria, Denmark and Sweden. Also in Germany there are a number of plants in operation. The difference in land prices between the northern and central Europe is probably the reason, that in Sweden and Denmark the collector arrays have been mostly built as ground mounted, whereas in central Europe they are normally mounted on roofs. The large number of solar assisted block heating plants in Austria is mainly thanks to generous subsidies, which have been around 40% of investment costs. Another fact that has made it feasible there is that traditionally the block heating networks were shut down for the summer to avoid the high heat losses. A new summertime heat supply business could be started when investing in solar and could be seen as extra income. The situation is different from the northern European view, where summertime district heating (even though with bad thermal efficiency) is taken for granted, and solar thermal is seen only as a means to save fuels. [1-12]