Choosing the right propeller power for your household

A wind-electric system can supply a significant proportion of the electrical needs of a family home, but choosing the right one can be difficult. Follow these simple tips to get started on bring renewable energy into your home.

The amount of electrical energy that can be stored by a turbine system depends on the capacity of its batteries. A typical home system will store enough for three or four days without fresh input, after which a gas-powered generator must be switched on.

• If more batteries are used, more windless days can be handled, but batteries are expensive, and it is cheaper to use an occasional backup.
• A bank of batteries installed in a well-ventilated shed stores excess power that the wind turbine generates during low-demand periods, to be released during windless periods or times of peak demand.
• When the wind blows strongly and few appliances are on, or when there is no wind, the battery current reverses, sending just enough to the electric system to make up the difference between turbine output and appliance demand.
• Batteries come in various storage ratings and are priced accordingly.

• Wind turbines are generally rated according to their maximum output. A turbine with a rating of 1,000 watts, corresponding to its power output when the wind is 10 metres per second (22 miles per hour). Its actual output is considerably lower — perhaps only 500 watts for most regions — because there are very few locations where wind speeds average that speed.
• A battery bank rated at 350 ampere-hours means that if an appliance draws 10 amperes of current from such a battery, the battery will become discharged after 35 hours (10 amperes times 35 hours equals 350 ampere-hours). This calculation can be extended to any amount of current drawn, provided it is not excessive.
• Manufacturers of wind turbines recommend a minimum size of battery bank, but the size you require will depend on your power needs and on the type of inverter used; seek advice when you purchase your turbine.

• Properly maintained, a battery will last about 10 years.
• Distilled water should be added periodically, the terminals must be kept clean and the batteries must not be permitted to become more than 50 percent discharged.
• Maintain batteries at room temperature or above, since cold reduces their effectiveness. Be sure to ventilate the storage room; batteries can emit hydrogen, a potentially explosive gas.