The computer-programme SAESON-SOL simulates thermal conditions in larger solar heating systems with seasonal storage facilities which can be either in the form of solar ponds or bore-hole storage. The computerized simulation shows that the solar heating fraction of 70% - 80% can be obtained in the case of reasonably dimensioned solar-pond storage, which is higher than in the case of borehole storage. In relation to the latter there occurs a significant temperature loss as heat transfer takes place via conduction through soil which has a relatively low heat conduction capacity so that the system works at a slow pace. It was attempted to investigate the influence on bore-hole storage capacity when heat pumps are utilized to raise the temperature niveau and thus work towards a reduction of heat loss, an improved solar heating fraction and a lessened risk of boiling. Use of this computerized simulation programme showed that an improved solar heating fraction can be achieved in relation to the borehole storage facilities by utilizing heat pumps. The significant measuring results are presented. (AB).