Danish R&D activities during the last two decades in the field of Central Solar Heating Plants and Thermal Energy Storage Technologies are presented. The most relevant central solar heating plants (CSHPs), with and without seasonal storage, are examined and essential experiences highlighted. The Saltum and Ry plants represent the type of CSHPs with preheating the return stream of a district heating net and no storage involved. The Marstal plant represents an alternative approach, connecting the CSHP to the delivery pipe for summer operation. Here the plant involves short-term storage and the application of variable flow that lead to novelties in the control strategy. The plant is described and experiences are analysed. The presented cases show that the technology, under special conditions, can be economically competitive with other heating technologies. Under normal conditions, public funding and acceptance of higher energy price are necessary. Further technical development and push towards a market is required. Especially the development of economical storage technologies is decisive. Work with steel tanks, concrete tanks, aquifer storage, bore hole storage and most importantly, from a Danish view, pit water storage is presented and conclusions are drawn. R&D in the field of CSHPs call for international co-operation, knowledge transfer and not least financing. The structural and political climate that shapes the boundaries of the R&D activities and also makes up the dominant barrier for the dissemination of CSHPs is discussed. Conclusions are drawn and future work outlined. (C) 2000 Elsevier Science Ltd. All rights reserved.