Energy efficiency and borehole sizing for photovoltaic-thermal collectors integrated to ground source heat pump system: A Nordic case study

Ground source heat pumps (GSHP), as a renewable energy technology, are highly efficient systems suitable for meeting the heating needs of buildings, particularly in heating-dominated regions like Scandinavia. This study aims to better define the scope of application and sizing of GSHP combined with photovoltaic-thermal (PVT) collectors in Nordic conditions. The study compares seasonal performance factors (SPF), average ground temperatures, and investment costs for heating different numbers of apartment blocks in two distinct Nordic climates: Baltic climate and cold continental climate. To assess the long-term effects on the energy performance of GSHP + PVT systems, dynamic simulations using the TRNSYS software are conducted over a period of 50 years. The results demonstrate that PVT improves the long-term system performance, particularly in large and compact borehole (BH) fields, while in smaller BH fields, natural regeneration keeps playing a substantial role. For instance, PVT added to a GSHP system with large BH field can limit the ground temperature reduction after 50 years by 33 % compared to the configurations without PVT. In contrast, this reduction is only 13 % for systems with small BH fields. Moreover, the results show that GSHP + PVT can lead to a reduction of up to 95 % in the required area for installing the BH field while maintaining (almost) the same energy performance compared to a conventional GSHP. Notably, this study shows that the utilization of GSHP + PVT leads to a substantial reduction in BH length (up to 50 %) while maintaining a similar system SPF. It leads to a decrease in investment costs of up to 9.32 % and 22.92 % for the scenarios located in Norway and Sweden, respectively, compared to the case with PV instead of PVT. These findings suggest that PVT integration holds promise for advancing the GSHP adoption in high-latitude regions, especially in larger installations and colder climates, by mitigating investment costs while preserving the system SPF and ground temperature stability.