Oakfield Farm – The Pocket Power Plant.

September, 2024 |

Lowering our heating bills is something we would all like to do. But what if we could turn that on its head and heat our homes and actually make money? That is exactly what Ric Brown has achieved with his PH15 at Oakfield Farm, Kent.

This extract is taken from a presentation given at the 2024 Passivhaus Conference in Oxford.

Oakfield farm is a compact, simple volume project that mirrors the aesthetic of the original barn, ensuring high airtightness and low energy demand despite a form factor of over 3. Wall, roof and floor U-values are not exceptional for a PH15 i.e. there was no additional insulation to improve performance.

The owners took on the challenge of building the home themselves, constructing the above-ground thermal shell with just one carpenter to assist. Their dedication paid off with an exceptional airtightness result of <0.1 ach@50Pa.

The house has no heat pump and uses very small portable electric heaters for about 2 weeks of the year. The 13.8 kWp solar array, paired with a 13.5 kWh battery, boosts on-site renewable electricity use. Hot water is via a Mixergy cylinder with PV diverter. Using the Mixergy with integrated heat pump would improve things further. We now feel this is the most effective solution.

Since moving in, the house has been very closely monitored with specialist software. This was compared to similar data gathered from the owners previous house. The graph below shows their energy use since 2008. The income that has been generated is in part due to very careful energy management – for example by using the low Octopus Energy EV tariff. This figure can be improved with more battery storage or bi-directional charging of the EV as a larger proportion of the generated electricity could be used with less having to come from the grid. The exercise shows though that the point has been reached where energy self-sufficiency is an attainable goal.