Supplementary energy sources

We install Bio-gas digestors in our sustainable homes. In some areas we install a retort for the destructive distillation of wood. The methane that is produced is stored under pressure and used for cooking, powering refrigerators, or boosting the output of a Sterling engine.  Where necessary it has been used for gas lighting. 

Bio gas


A newly established reed bed

We usually install a waste digester to produce Bio-gas.  A mixture of human waste and cow manure is placed in the digester every week.  The waste is warmed by a coil through which hot water flows.  The hot water comes from the heat exchanger that strips heat from the hot air that is produced in the solar collectors.  The warmed waste produces methane which is washed before it is stored.  The liquor produced by the process is diluted and passed through a septic tank and a reed bed.

In the temperate zones we install a retort for the “destructive distillation of wood”. The lighter products that are driven out of the wood when it is first heated are methane, carbon monoxide and hydrogen.  This blend of gases is similar to those which were to be found in Town Gas.


To reduce the demand for electricity we avoid phantom loads by dividing the wiring into sub circuits that can be individually switched.  Artificial light is provided by compact fluorescent lamps and light emitting diode (LED) lamps.  The LED lamps and computers run on a 24V DC supply that is generated on site.  Any surplus electricity that is generated on the site is stored.  Where appropriate we employ Sterling engines powered by heat collected by the solar collectors.  The output of the Sterling engines is enhanced by burning the gas that is produced in the fermentation unit and/or by the destructive distillation of wood.

Where possible we use hot air from the solar collectors to power a Sterling engine which drives a generator.  Hot air engines work because of the temperature differential between the two phases of the cycle.  Cooling for our Sterling engine is provided by the water that is stored on site.



A conventional windmill is not wind speed critical.

Air pumping windmills are not limited to a narrow range of operating speeds like electricity generating wind turbines.  Air lift windmills compress air which can be injected into the bottom of a water column.  The bubbles of air then carry the water upwards.  Air pump windmills can lift water on a bubble of air to a height of 100 m at a rate of 25 to 500 litres per minute over a distance of 400 m.  Air that is compressed by a windmill can also be placed in a compressed air battery.  The compressed air can then be used to generate electricity at night or to power machinery.

Domestic Appliances

We offer a range of washing machines, tumble driers and dish washers that are driven by the vertical axis wind turbines that we mount on the roof of our buildings.  As the wind turbines are not being used for the generation of electricity the speed of rotation of the turbine is unimportant.  The rotational power of the windmills is delivered to the appliances by drive belts.  The solar collectors generate the hot air that is needed for our tumble driers.

The first refrigerators were powered by a small gas flame.  Our refrigerators employ absorption cooling refrigeration units and are powered by heat that is drawn from a solar collector or by a gas flame.  Our refrigerators have a large thermal mass so that they are still effective even if there is an interruption in the energy supply.

Water Supply

We collect any rainwater from the roof and store it in a tank.  After it is filtered the water is used for cooking and washing.  A windmill pumps water from the tank to a holding tank in the roof.  As the speed of rotation of the windmill is unimportant the system works whenever the wind blows.  The tank in the roof is sized to hold a week’s water supply.

Our terraces are used for social purposes but their primary function is to keep the ground near the building dry.  If the ground around the building is dry it is warmer.  We position a gutter around the outside of the terrace and the water that is collected is stored and used for flushing toilets.