The problem with running heat pumps from renewables

The ‘holy grail’ for integrating heat pumps into the grid

If we ‘spend’ 1 kWh on summer electricity can we reduce winter heat

pump electricity use by 1 kWh?

CHOICES ‘timeshifts’ heat pump electricity use from winter to summer

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Interseasonal heat storage energy centre

Solar microgrid

Owen Square Community Energy

CHOICES developed a TRNSYS model to answer this question

We are modelling very promising active recharge COP

Scenarios 1 – 3Illustrates increase in CoP when the same charge is spread over a longer time period (charging most efficient at low speeds)

But the max economic level of seasonal shift is limited by borehole design

Owen Square park, Bristol (£168,000):● 12 x 150m boreholes (1.8km)● 7m distance between boreholes● 1 u-pipe per string, 12 strings● 50,000m3 volume● Low temperature array● Grid benefits: ~4500 kWh/year

Braedstrup, Denmark (£188,000):● 48 x 50m boreholes (2.4km)● 3m distance between boreholes● 12 u-pipes per string, 16 strings● 19,000m3 volume● High temperature array ● Grid benefits: Potentially much higher

Similar size/cost but very different

designs

Further research will explore other borehole designs seeking further grid benefits