Self-sufficiency: A Green Dream or Reality?

ABOVE: Monique and Laurence Steijger’s super-insulated eco-friendly timber frame house in Derbyshire cost £190,000 to build and requires no central heating. Sunslates from Solarcentury generate 25% of electricity used, a heat pump provides hot water, and rainwater is recycled. The couple’s total energy bill is a meagre £240 a year. A self-sufficient kitchen garden is the icing on the cake. Read more about this self-build.

Energy self-sufficiency is a bit like The Good Life. You want to produce just enough food to live on and you have the space necessary, but you can’t get all you need at the right time. In energy terms, going self-sufficient presupposes that you know exactly how much energy you will need each year, but producing just enough is tricky. So the first decision is whether to produce less than needed and buy in the extra, or produce more and sell the surplus. But you can’t sell all types of energy.

Household energy divides into two parts: heat energy for hot water and space heating (which can’t be sold) and electricity (which can be sold). The mantra must be ‘conserve before you generate’ — and there is far more opportunity to reduce the amount of energy needed to heat the home than there is to reduce power or hot water consumption.

The first step is design. Putting energy at the centre of the design means that you will know what you are going to need. It provides the opportunity to address insulation, airtightness, hot water use and ventilation — all of which have a huge impact.

Second is to consider what resources you have available. A windy site offers the opportunity to generate sufficient energy for an all-electric house, perhaps using heat pumps for space heating. A sunny site might allow passive and active solar energy. Solar thermal energy will always be essential for self-sufficiency but solar PV (photovoltaic) can be costly and needs a lot of space.

Third is storage. The average household consumes around 6,000kWh of electricity per year. That equates to around 16kWh per day — a bit less in summer and a bit more in winter. A wind turbine, for instance, with average wind speed would need a capacity of around 3kW to produce that. But the average kettle needs 3kW; an electric cooker up to 12kW. Peak household demand can be up to 14kW. Our 3kW turbine is not going to get anywhere near that, even though across the year it produces enough to meet the annual consumption. So we need to store power. Storing heat energy is done on site but typically we ‘store’ electricity on the grid by selling what we cannot use and buying back when we need it.

Fourth is economics. Energy generation is a long-term investment — 20 years at least. Our 3kW turbine might cost £10,000 to install, but it will run for 20 years and in that time produce 120,000kWh. That gives a unit cost of 8.4p per kWh – compared to a current retail price of around 15p – which will still be 8.4p in 20 years time. That is energy security, and it has value.

The opportunity to be energy selfsufficient will vary with the site, what is available, how you live and how much energy you need — and how much money you can throw at the problem. But maybe 100% self-sufficiency is not for everyone. Maybe 50% will be a better target for you.

ABOVE: Self-build Day Out - Hockerton Housing Project in Nottinghamshire is the UK’s first earth-sheltered, self-sufficient housing development. Residents generate clean energy, harvest their own water and recycle waste materials. See hockertonhousingproject.org.uk for details of tours and workshops.

Nearly Self-sufficient Homes:

• A Super-insulated Self-build
• A Sustainable Self-build in Devon
• A Budget Sustainable Self-build

Further reading:

• Saving Energy
• The A to Z of Green Homes
• Renovate or Rebuild: Which is Greener?