The Alternative Energy blog – green renewable alternative energy

Wind energy is both green and fun, so the idea of building one’s own wind turbine is a good one. The following will give you an idea of what is involved.

Wind energy on a large scale is now competitive with other sources of electricity on a commercial scale. However, small domestic-sized wind turbines have not yet reached this point. The wind is free, but small wind turbines are expensive in relation to what they produce, and cannot realistically compete with mains electricity. Building your own machine saves some of the cost, but please do not underestimate the difficulty of the task. If it were easy to save money by using small wind turbines, then they would be a major feature of the landscape by now.

Most residential locations are not suitable for windpower as trees and buildings break the force of the wind, and create turbulent gusts which can be very destructive. Open hilltop sites or coastal situations with unobstructed views may be suitable for siting a wind turbine. A very tall tower is helpful, but these are not always appreciated by your neighbours.

What size of wind turbine do I need?

Wind turbines work with thin air, so they need to be large in relation to the power they produce. To power a modern home on a good site, the blades would need to span about 5 metres from tip to tip. This is known as the rotor diameter. With careful conservation of energy a smaller machine may suffice. A rotor diameter of 2 metres might yield about 500 kWh of electricity per year, compared with an average annual household consumption of roughly 4,500 kWh.

What sort of generator should I use?

Most small wind turbines are used for charging batteries, to provide a reliable stand-alone power source where grid power is not available. The obvious choice of generator for self-build is the car alternator. However this has major drawbacks. It must be driven at a high shaft speed (over 2000 rpm) to give full output, so you will need to gear it up or modify it in some way to drive it with rotor blades, which typically only manage a few hundred rpm. This reduces the efficiency. In low windspeeds there is very little power available in the wind, and you need a highly efficient generator to capture it. Most, if not all of the power in light winds will be used up energising the magnetic field in the alternator, so the results are disappointing. Nearly all small commercial wind turbines use purpose-built permanent magnet generators for this reason. The DIY enthusiast can make one too, but this is not simple to do. Or you can reuse a permanent magnet motor as a generator. The generator is the key to success or failure of the project, and by far the hardest part to get right.

Can I make my own blades?

The good news is that yes, many beginners have made very useful wind turbine blades, often carved from wood. Or there are sources where you can buy them ready made. If you plan on making your own, it is well worth doing some research and finding out all you can about it in advance. Not only will this save you from ‘reinventing the wheel’ but it will also be safer. Safety is an important issue even with the smallest wind turbines. Never underestimate the destructive power of a runaway windmill rotor in a high wind. Make sure that you have built-in protection against all eventualities. Control systems are as important as any other part of the wind turbine.

Its not easy building your own wind turbine but with skill and dedication it can be very satisfying.

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