According to (the) information from the European Large-Scale Solar Heating Network, (See http://www.hvac.chalmers.se/cshp/), the area of installed solar collectors for large-scale application is in Europe, approximately 8 mill m2, corresponding to about 4000 MW thermal power. The 11 plants of the total 51 plants are equipped with long-term storage. In Denmark, 7 plants are installed, comprising of approx. 18,000-m2 collector area with new plants planned. The development of these plants and the involved technologies will be presented in this paper, with afocus on the improvements for Danish Central Solar Heating Plants, servicing District Heating and related developments in large-scale thermal storage. Central solar heating today is a mature and economic realistic solution for district heating based on a renewable source. The cost for solar collectors has decreased by nearly ¼ during the last 10 years and the corresponding cost per collector area for the final installed plant is kept constant, even so the solar production is increased. Unfortunately large-scale seasonal storage was not able to keep up with the advances in solar technology, at least for pit water and gravel storage technologies. There are severe problems with the tightening of pit and lid constructions. First solutions applying thin stainless steel liners are found and demonstrated for pit lining. Similar solutions based on polymerliners are many times cheaper, but seem not reliable at the moment due to material degradation and resulting reduction of the lifetime. The improvements of polymer liners seem realistic and is expected to be solved in the coming years. Floating pit lid designs are in the phase of being tested this year and first results are expected soon
