round source heat pumps (GSHPs) use the vapour compression refrigeration cycle to extract low-grade thermal energy from the ground for heating purposes. A "hybrid" GSHP system incorporating solar thermal collectors to "recharge" the ground during the cooling season is a potential solution to maintaining the annual average ground temperature and preventing any long-term drop in system performance. 2.75m2 of collector area per borehole was required for a typical Edmonton installation where 1009 kWh of energy was extracted from each borehole. For a single borehole, the hybrid system did not provide any significant economic or performance benefit but as the number of boreholes increased, the ability to recharge naturally the extracted energy decreased. A 10x10 grid of boreholes could have 67 boreholes removed and experience the same minimum fluid temperature each year as a 10x10 grid after 30 years. Instead, recharging the ground with the 10x10 grid could save
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