This paper reports on an experimental augmentation system for ground source heat pumps using solar thermal to recharge the ground with heat. The system is running on a house in Nottingham, England. The house has a 4kW photovoltaic array and a ground source heat pump for heating and hot water, using twin 48 metre boreholes. Real-time, diurnial and inter-seasonal solar charging restores the energy level in the earth, which prevents progressive frosting of the borehole zone. Measurements have been performed over a year, achieving zero carbon emission.