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Modelling retrofit options for typical house types

Photovoltaic orientation

We worked with Wales & West Housing (WWH) to support their planning of a stock wide whole house energy system retrofit programme, to achieve the carbon saving targets set by UK and Welsh Governments.

Wales & West Housing collected relevant property and location information for three typical properties using the PRESS 1 tool developed by the Low Carbon Built Environment (LCBE) team. Using information collected by WWH staff, the LCBE team created computer models and explored potential low carbon solutions to:

  • reduce energy demand
  • enable on-site energy generation and storage
  • reduce energy costs for residents
  • create better living environments
  • reduce carbon emissions


The objectives were to:

  • enable the collection of relevant data by the WWH team to feed into the LCBE team’s model
  • use modelling to identify, appropriate and replicable retrofit solutions which would achieve reduced carbon emissions and energy costs for residents

As requested by WWH, the modelling assumed that in each house type heating would be provided by an air source heat pump (ASHP). The modelling examined the costs and benefits of the following additional low carbon solutions:

  • loft insulation and external wall insulation to minimise heat loss
  • low energy lighting to reduce energy demand
  • mechanical ventilation with heat recovery (MVHR) systems to manage internal air movement, moisture and smells
  • solar photovoltaic (PV) panels
  • on-site energy storge using battery technology


The project demonstrated that despite the homes being of a similar age and orientation, the opportunity to generate energy from photovoltaics varied significantly – from 3.8kWp to 14kWp.

The modelling demonstrates that all three homes were able to reduce energy consumption by more than 60% despite the variation in the energy generation potential.

Two of the homes would generate more energy than they would need over an annual period, making them energy positive. There is also potential to generate an income by feeding energy back to the grid when an appropriate tariff is available and chosen.

Lessons learnt

Having a consistent data collection process that is quick to deliver but collects relevant information including photographs speeds up the planning process.

Modelling enables comparisons between different options. For example, WWH were keen to push beyond building regulations with the thermal performance of the external wall insulation. Modelling the variation of benefits between the options, including energy bill saving and carbon emission reductions, really helped the decision-making process.

East-West orientated PV panels can really help with maximising energy generation and therefore self-sufficiency. This is even more beneficial now as energy suppliers are starting to pay for energy exported to the grid.

Project team

The project team includes the LCBE team at the Welsh School of Architecture and Wales and West Housing.