Integrated Combined Energy Management

Our energy is generated on site with the highest efficiency and conservation, and stored electrically and thermally to be used year round. Efficiency is further managed and enhanced with a service tunnel that allows easy and visual connection of all systems, ensuring high integration, quality maintenance and upgrade capability is built in, while obsolescence is designed out.

Electrical Demand

This is difficult to accurately predict as we will have variable occupancy in the four lodges and the variety of guests will use facilities in different ways. We will use efficient lighting and appliances to minimise consumption and variation, but we expect hot water to be a much higher demand, and this has driven the large amount of thermal storage.

Heating, Cooling & Ventilation

Space heating requirement in the lodges will be minimal, if any, due to the insulated high thermal mass, solar gain and residual heat from occupancy. However a radiant heating/cooling loop will be installed in the floor just in case it is needed on occasion, for heating or cooling. We considered earth tubes for cooling ventilation but were concerned about unlikely but potential bacterial issues. However on sunny days our solar PV will be running heat pumps to charge the thermal store, allowing free cooling capacity at the same time. Natural ventilation will also be built in, with heat recovery via a heat exchanger to the GSHP, and of course the front, side and rear glass doors can be opened to bring the outside in.

Solar Gain

The lodges are positioned in a gentle arc facing south, and all feature a sun terrace with an insulated roof and large rooflights (with blinds). This provides user variable shading in the summer and maximum daylight in the winter. The high thermal mass floor can absorb any warmth from the sun during the day and release it in the evening. Excess heat can be harvested by the heat pump and dumped in the thermal store, ensuring a comfortable environment at all times.

Solar Thermal

The sun terrace roof has prime exposure to the sun and will include integrated solar thermal loops that can directly harvest heat to the thermal store, or indirectly via the heat pump. We will also integrate solar thermal collection within the parapet roof, with the additional bonus of cooling the rear of the solar PV panels to increase their efficiency. 

Solar PV

Up to 56 PV panels can fit within each lodge roof, 25 are South facing at about 20° inclination and the rest are shallow North facing so onlly 70% efficient. A further 68 panels may be placed on the barn roof, in total up to 292 panels giving 72kW and providing up to 65,000kWh per year. The challenge is surviving off-grid through the winter where output is dramatically reduced, hence the large number of panels. Winter sun is often diffused and reflected so without much direct sun the difference between North and South facing output is less marked.

Heat Pumps

A ground source heat pump (GSHP) is positioned in the service tunnel of each lodge, supplemented by an additional fan coil within the parapet roof to harvest ambient air temperature. A small air source heat pump (ASHP) is also positioned in the service tunnel to harvest a flexible hot air dumping zone. In combination when there is any spare solar power they will work to harvest every available source of heat within the lodges and service tunnel and store it in the thermal stores.

Masonry Stove

A double sided cast iron insert multi-fuel stove will be built into rammed earth with suitable expansion joints to prevent any cracking issues. The system will promote secondary combustion and masonry heating. A closed loop water boiler is incorporated for DHW.

Electrical Storage

A bank of electrical storage batteries is positioned in the service tunnel. Flow batteries are a new technology that seems particularly applicable, and will be investigated.

Thermal Storage

A pair of huge underground 1000 cubic metre thermal energy stores (TES) are positioned under/between the lodges. With the ambient ground temperature around 10°C we hope to drive the TES up to 40°C by autumn so that energy can be used in the depths of winter to deliver hot water via the heat pumps. In addition each lodge has a large thermal store tank kept to around 60°C that will heat DHW as it is drawn, so there is no separate DHW cylinder.

Idyll Energy Challenge

We have devised an integrated energy system for the site that allows us to be off-grid all year round. We challenge the wider informed community to review, analyse and put forward ideas to ensure the entire system is as good and efficient as it can be.


All our water is harvested on site from rainwater and borehole, it is used and reused, then processed on site, cleaned and safely returned back to the landscape.


Greywater will be collected separately from baths and showers and treatment will be processed by a small reed bed for use in toilets and for irrigation. Waste water heat is recovered by piping it through the heat pump ground loop subsoil, transferring heat to the soil which then incrementally gets picked up by the heat pump.