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Case Study: Domestic Retrofit | 3 Bed Detached House - Air Source Heat Pump, Solar PV & Solar Thermal

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Solar PV and Thermal
S/SE facing roof
Solar PV panels on garage roof
Mitsubishi 8.50kW ASHP
Mitsubishi 8.50kW ASHP
Solar PV panels
  • 8.5kW Air Source Heat Pump
  • 2.42m² Aperture Area Vacuum Tube Solar Thermal System
  • 2.58kW Photovoltaic System
  • 1.40kW Photovoltaic System


This West Sussex home resides in a lovely village nestling into the north escarpment of the South Downs. Built in the early 1980’s, its original meagre heat retention capabilities have been improved by cavity wall and loft insulation and replacement uPVC double glazing throughout.

Air Source Heat Pump

The property’s calculated winter heat loss of just over 6kW is replenished by an 8.5kW Mitsubishi Ecodan Air Source Heat Pump. Whilst the first floor radiators were found to be suitable for the new heat source, the ground floor units were upgraded to enable the pump to operate at lower temperatures and therefore much more efficiently.

Solar Thermal

The Schott Solar Thermal system was the first stage of this renewable energy project and has an aperture area of 2.42m². It supplies heat energy to a 210 litre twin coil hot water cylinder and provides the greater majority of the hot water needs of the family of four.

Photovoltaic (PV)

The PV system was installed in two phases, as circumstances allowed. The initial 2.58kWp array, mounted on the south east facing roof of the house employed 12 black framed monocrystalline Sungrid panels. The advantageous dimensions of these units suited the roof size perfectly and resulted in an especially aesthetically pleasing installation. The second 1.4kWp phase used 7 off similarly black framed Ahead panels, again chosen for their size and specification. These were mounted on the south facing roof of the garage bringing the combined system to the maximum allowed for under the government’s domestic Feed-in-Tariff scheme.

Air Source Heat Pump

Property size
Heat Pump
Mitsubishi Ecodan 8.5 kW ASHP
100% Space and DHW Heating
Calculated heat loss
6 kW
Replaced heat source
28 yr old worn gas boiler
Annual energy usage via gas boiler
25,000 kWh
Annual energy usage via Heat Pump
5,400 kWh
Savings in Energy
19,600 kWh (78%)
Savings in CO2
1,735 kg based on data from DEFRA

Solar Thermal

Solar Panels
Schott ETC16
Number of Panels
Total aperture area
2.42 m2
Collector efficiency
Domestic hot water cylinder capacity
216 L
DHW Cylinder dedicated solar volume
119 L
Annual Output - SPA2009
1,089 kWh
Annual savings in CO2
200 kg based on data from DEFRA

Solar PV 1

Solar Panels
Sungrid 215M6
Number of panels
Module efficiency
Annual output - SAP2009
2,122 kW
Annual output - Actual 1st Year
2,505 kWh
Annual output - Actual 2nd year
2,446 kWh
Annual output - Actual 3rd year
2,581 kWh

Solar PV 2

Solar Panels
Ahead Power Pro AHM5G-200W
Number of panels
SMA SB1200
Module efficiency
Annual output - SAP2009
962 kWh
Annual output -Actual 1st year
1,180 kWh
Annual output - Actual 2nd year
1,111 kWh