In off-grid homes (i.e. homes not connected to mains electricity), small-scale wind turbines and photovoltaic (PV) solar panels can be a good alternative to either grid connection (which can be expensive) or a diesel generator (which wil be noisy and polluting, and have ongoing fuel costs).
The book Wind & Solar Electricity covers in more detail using these energy sources as part of an off-mains electricity supply, but here is some intial advice:
If you’re off-grid and need power all year round, wind and solar complement each other well as there is more wind in winter and more sun in summer. If you just need power in summer (e.g. in a caravan), you may want to use only solar power.
Considerations for siting a wind turbine or photovoltaic panels are the same as with grid-connected systems - an unshaded and roughly south-facing site for solar, and somewhere with a strong, consistent wind speed for a turbine. For more advice on assessing a site, see our pages on wind power and solar photovoltaics.
Sizing a system
The difference with off-grid systems is that you'll need to store electricity in batteries. In order to keep sufficient stored electricity for your needs, you will have to first work out how much energy you will be using. You can do this by estimating the total energy consumption of all the electrical appliances you intend to run. The power rating in watts (marked on the back of the appliance) multiplied by the time (in hours) that it will be used each day, gives the energy (in watt-hours) that you will need per day in order to run that appliance. Add all these figures up to see what size system you require.
The more energy you need, the bigger and more expensive the system becomes. Therefore, make sure you are using energy efficiently, and consider whether or not all the appliances are necessary. Fitting low-energy light bulbs and using sources other than electricity for heat (i.e. heating and cooking with wood fuel or gas) will ultimately make a big difference in the overall cost of the system. See our Energy Conservation section for further advice.
To run some appliances, you may need an inverter to convert from 12 volts DC to 240 volts AC. There are different types of inverters for grid-connected and off-grid systems. They can be expensive, and rise in cost as the maximum power that they need to be able to cope with increases, so it could be worth trying to run DC appliances where possible.
Batteries are essential in most off-grid wind or solar systems, but are expensive and will deteriorate. They store low voltage (up to 48V) DC electricity and need to be protected from over and under charging by using a shunt regulator or similar. Lead-acid batteries are the most cost effective, although other types, such as nickel-cadmium, are available. Do make sure you follow proper safety procedures when dealing with batteries.
Deep cycle batteries are preferable for renewable energy systems, as they are designed to have up to 80% of their charge repeatedly removed and replaced over a period of 5 to 15 years (or 1000 - 2000 times). Vehicle batteries are not suitable as they are designed to give a short burst of high current and be recharged immediately. They will perform poorly if allowed to discharge more deeply.
Solar PV panels and small wind turbines usually operate at low voltages (e.g. 12 or 24 volts). The voltage drop in wires can have a significant effect at these levels. Cables must be thick enough to minimise this drop and carry the required current. As cables are expensive, this can affect wind turbine siting.
Feed-in Tariffs for off-grid systems
In theory, off-grid systems can qualify for feed-in tariff payments - however, there is currently a lack of accredited equipment to actually make this possible. To find out more, have a look at our page Can Off-Grid Systems get Feed-in Tariff Payments?