Denmark has set an ambitious long-term future energy goal to become independent of fossil fuel by 2050, depending completely on renewable and alternative resources in the energy and transport sectors. Solar energy is one of the most favourable alternative resources in terms of cleanness, safety and the economic and environmental aspects. However, the intermittent nature of solar energy and the lack of high solar radiation intensities in various climates favour the use of various energy storage techniques to eliminate the discrepancy between energy supply and demand. The current work presents an analysis and evaluation of the performance of an underground soil-based thermal energy storage system for solar energy storage, coupled with a combined heat and power generation system. A combined PV-Air Source Heat Pump (ASHP) system is utilized to fulfil heating and electricity needs of a housing project in Odense, Denmark, in addition to charging the soil storage medium in summer months when excess electric power is generated. The stored heat is discharged in December and January to provide the space heating and domestic hot water demands of the residential project without the utilization of an external heating source. Employing a PV system of 30 kW capacity, it was found that a storage medium of 900 m(3) of soil is capable of providing the heating needs for a housing project of 1000 m(2) internal floor area. The year round transient behaviour of the thermal energy storage medium is reported in addition to the heat losses and the surrounding soil temperature variation throughout the year. It was found that the overall system heating coefficient of performance is around 4.76, where the reported energetic efficiency is 5.88% for the standalone PV system, 19.1% for the combined PV-ASHP system, and 22.2% for the combined PV-ASHP system employing a seasonal underground thermal energy storage block. (C) 2016 Elsevier Ltd. All rights reserved.