Generating Electricity

There are three potential sources of power: sun, wind and water. The equipment needed to generate electricity will cost at least as much as the equipment for heating the home, and may account for only 20% of the overall energy consumption. So getting the right equipment is important, and it is worth getting an expert opinion first.

However, the right system, properly design ed and installed, turns your house into a tiny power station, offers protection from rising electricity prices, adds value to your home and can even provide a small income.

For our purposes we assume that the requirement is to generate enough electricity to meet the ‘standard’ demand. Energy Saving Trust figures suggest that the average house consumes around 5,000kWh of electricity per year.

We will be referring here to 1kW, 2kW or 5kW systems, none of which are capable of producing enough power at any one time to meet the peak demand of the house. If we consider that a kettle is 3kW, an electric shower 10kW, an electric cooker 8kW, lighting, TV etc 2kW, it is quickly obvious that our tiny power station can’t keep up. A 0.7kW hydro turbine or a 2.5kW wind turbine will generate as much electricity as we use across the year because they are running 24 hours per day. But not enough to meet that peak demand. The answer is storage and we assume here that grid connection is available as a ‘storage’ system, and to provide the opportunity to sell surplus production.

Solar PV

Solar photovoltaic systems are rated in kWp (kilo Watt peak) so that a 1kWp system will have the capacity to generate 1kW at any one time. The amount of solar energy falling on the country is fairly well known so we know that a 1kWp system will produce from 700kWh in northern England to 800kWh in the south each year. The average figure is taken as 750kWh per year for a 1kWp system. From this we can calculate that to meet our 5,000kWh demand we need a system of 6.7kWp.

A system of that size will occupy 53m2 and will cost about £5,000/kWp and £33,500 installed and connected to the grid.

Wind Turbines

The size and type of system will vary by site. There are estimations available from berr.gov.uk but the only accurate way to judge your wind condition is to measure it. Buy a Wind Prospector from Wind & Sun Ltd — it will cost a few hundred and may save many thousands.

A good domestic machine would be the Skystream 1.9kW turbine available from Segen. With an average wind speed of 5.5 metres per second (m/s) this will produce enough electricity to meet the annual consumption. Installed cost will be £9,000.

Water Power

A river or stream is an obvious prerequisite, as is ownership of both banks, as otherwise the owner of the other bank could have rights to the turbine.

A stream tends to run 24 hours per day, 365 days per year and so a 0.75kW turbine will produce more than 6,000kWh in a year. The size of the turbine will be determined by the flow and head in the stream. The cost of the system will be affected more by the terrain – the size of the stream, its steepness, the depth of soil, trees, rocks etc – than by the output of the turbine. That might amount to only 20% of the overall cost. So it is worthwhile installing the biggest turbine possible and selling the surplus.

A typical domestic system might cost anything from £10,000 to £20,000 dependent on the terrain and the supplier.

"None of the power from my wind turbine is wasted"

Derek Matthews installed a FuturEnergy (futurenergy.co.uk) wind turbine in his and wife Anne’s rural Bromsgrove home two-and-a-half years ago. The turbine forms part of a comprehensive domestic renewable energy system, integrating with a series of motor-driven solar water heater panels. None of the electricity generated by the turbine is wasted. With priority given to maintaining the charge in the batteries, any excess electricity is used to power a series of specially modified freezers and fridges. After this, any additional surplus electricity is used to assist the solar panel in pre-heating the water feeding the hot water cylinder, and water can be diverted for bathing purposes, or for use with a dishwasher and washing machine both modified to run from the hot tank only.

Further Reading:

• Feed-in Tariffs Explained
• Saving Energy: A Look at Renewables
• Wind turbines: Are they worth it?