Zero energy level and economic potential of small-scale building-integrated PV with different heating systems in Nordic conditions

Solar electricity is growing very popular in the world, but it has some problems in matching of generation and demand both in hourly and seasonal levels. In northern latitudes the problem is especially significant, as the difference between solar availability in winter and summer is very large. Cooling needs do not increase electricity demand in summer as much as in southern locations, while there is a high demand for heating in the winter when solar power is not available. This study looks into the economics and energy matching of photovoltaic (PV) systems for single-family houses in Finland. It also introduces the concept of zero energy level of buildings (ZEL), which can be used as a policy tool for renewable energy support schemes. PV self-consumption is compared between cases with district heating (DH), heat pump (HP) and direct electric heating (EH). Because the price of buying electricity is much higher than selling it, any excess PV power after meeting appliance loads was fed to a thermal storage to be stored as heat. Analysis was done for a single building and a community of ten similar buildings. Excess solar power provided part of the space heating (SH) needs in spring and autumn and most domestic hot water (DHW) needs in summer. Self-consumption was increased by 15.70% with EH and by 20.40% with HP, when a PV system was used for space and DHW heating during summer and midseasons. Thermal storage increased energy matching, but high storage capacities did not provide a significant improvement over lower ones. Levelised cost of energy (LCOE) for PV electricity in a single building almost reached grid parity (11 c/kWh) using EH, but the generation cost for HP and DH remained higher (13 and 17 c/kWh, respectively). Investment incentives reduced the LCOE below grid prices for electrically heated systems. In the community, the economies of scale lowered LCOE, such that in many cases grid parity was reached even without incentives.