CombiSol: solar combisystems for houses, state-of-the-art and potentials for improvements

Evaluation of the quality and efficiency of state-of-the-art installed solar combisystems, potentials for improvements and measures to increase the quality

Short Description




The European market for solar combisystems for domestic hot water preparation and space heating is growing significantly. For such solar combisystems more and more improved components are available on the market, but still the installer is the main responsible person who does the installation and who decides on site what the entire system looks like.

Therefore, quality and efficiency of the solar combisystem on site is not much influenced by the solar industry and can not be checked in each single case by industry experts. It was the goal of the project CombiSol to evaluate the quality and efficiency of state-of-the-art installed solar combisystems. Based on the evaluation results the main potentials for improvements have been described and measures to increase the quality of solar combisystems on site have been proposed. In order to reach these project goals the following work packages were defined:

  • Collection and classification of standard solar combisystems existing on the market Qualitative evaluation of 70 solar combisystems by on site visitations in the four project countries Sweden, Germany, France and Austria.
  • Quantitative evaluation by means of a one year monitoring campaign of 45 solar combisystems in all four partner countries.
  • Elaboration of recommendations for producers, retailers and installers for improved development, planning, installation and operation of solar combisystems.
  • Elaboration of new training material to support existing training activities for solar thermal planers and installers.
  • Measurements on solar combisystems in the laboratory and comparison of the results with the in-situ measurements with the goal to test the quality of the performance prediction of laboratory system tests and to support CEN standardization activities for system tests.

A market analysis showed that the number of offered compact solar combisystems which are sold as complete packages is increasing significantly. In the state of the art report 19 such systems are described.

The qualitative evaluation of the 70 solar combisystems showed a quite differentiated image, mainly influenced by the mostly individually planned and installed solar combisystems based on products of different suppliers. The most important result is that all evaluated solar combisystems were in full operation. The quality in terms of efficiency was often not as expected due to reduced insulation quality of heat storage and piping. Also the integration of the auxiliary heater in terms of hydraulics and control concept showed high potentials for improvements.

In-situ monitoring results of 41 solar combisystems showed mostly well but also some badly operating solar combisystems. Often mistakes in just single points result in a significant reduction of energy savings. This wide range of results is quite equally distributed over the countries, the system types and the products as well. Only solar combisystems with high degree of compactness (i.e. including the auxiliary heater from a single supplier) and prefabrication showed significantly higher efficiency and performance. Three products of solar combisystems were measured in the laboratory and compared to in-situ measurements showing high degree of similarity of the results. Also increased heat losses and the reasons for that could be verified in the laboratory tests.

Summarizing, the project showed that all of the state-of-the-art installed solar combisystems worked in principle, but in almost all installations significant potentials for improving the efficiency and the energy savings exist. Improvements can be expected, if the degree of prefabrication and system integration is increased significantly.

Contact Address

DI Dr. Alexander Thür, Gabriele Kuhness, DI (FH) Johann Breidler
AEE – Institut für Nachhaltige Technologien
Abt. Solarthermische Komponenten und Systeme
Tel.: +43 (3112) 5886 - 0