This report describes investigations of seven Danish DWH solar heating systems. The systems are produced and installed by:1) Aidt Miljø A/S2) Dansk Solvarme A/S3) Batec A/S4) Solvarme A/S5) Solahart Scandinavia ApS6) Thermo.Sol ApS7) Sol-Energi Kobbervarefabrikken.The DWH solar heating systems are installed and tested side by side under realistic conditions in the test facility for SDHW systems. The systems were installed at New Year 1994/95.Measurements of the thermal performance of the systems have been carried out for one year. Furthermore, calculations of the thermal performance of the systems have been carried out with detailed mathematical models. The models that simulate the thermal behaviour of the systems in detail, have been validated against the measurements of the systems. Good agreements between measured and calculated results have been achieved. The mathematical models simulating the thermal behaviour of the systems have been used to determine the yearly thermal performance of the systems. Weather data from the Danish Test Reference Year is used in the calculations. A daily hot water consumption of 200 l heated from 10°C to 45°C is assumed. The calculated net utilised solar energy of the seven investigated systems lies between 1035 kWh and 1670 kWh corresponding to a solar fraction (net utilised solar energy/energy tapped from storage) between 35.2% and 56.8%. By comparison, the Swiss low flow solar heating system, investigated in the same way earlier, has a net utilised solar energy of 1790 kWh with a solar fraction of 60.9%.Additionally, possibilities of improving the systems have been investigated. The results of these investigations showed that all the systems can be improved. The main reason for the relatively low thermal performances is the relatively large heat losses from the heat storages. Even though the pipe layout has been made in a way to decrease the tank heat loss it can be decreased further by improving the insulating around the electric heating element.Furthermore, the calculations showed that the performance of five of the systems can be increased by replacing the storages with mantle tanks combined with low flow operation of the systems.Thus, it can be concluded that improving the thermal performance of all the tested systems is possible.