Though wind power is not a new technology, the past decade has seen a large growth in the number of residential windmills. Windmills themselves are traditionally large, expensive affairs. The first wind mills were large structures that really were used for milling. The blades of the wind driven axle were connected to gears inside the structure, and these gears turned large, heavy millstones.
A windmill was an alternative to a water mill, or a mill powered by oxen, which were the primary alternatives for milling at the time. The windmill was considered superior to an animal driven mill because you don't have to feed a windmill. It was also considered superior to a water mill because in colder climates, a water mill couldn't operate year round, the winter freeze could stop the flow, effectively nullifying the power source. Wind on the other hand blows year round, and can be especially poignant in the winter, when wind chill becomes a very real factor in the temperature outside.
The fact was however, that only a moderately wealthy miller could afford to build a windmill, because while the cost of keeping oxen was spread out over the life of the cattle, the cost of a windmill is entirely up-front. That relationship has actually stayed the same when we look at the modern residential windmills. Though they are creating electricity instead of flour now, they still are an up-front cost, or an investment. The investment doesn't pay itself back for 5-10 years. The difference is of course that during those 5-10 years, without a windmill you will pay significantly higher power bills. The windmill is in effect a bet that we don't discover a new, inexpensive energy source in the next decade.
This is a fairly safe bet, given that the vast majority of our power is turbine based. The turbine is over a century old, and the only changes that have really been made have been in the means of propulsion. Older turbines were powered by steam, which was created by burning wood or coal to boil water. Some modern power plants still use steam powered turbines, a nuclear power plant for example boils water with nuclear fission. Coal fired plants also boil water. However we have found that simply running water can spin a turbine, giving rise to the hydroelectric power plant. And of course, the wind can spin a turbine, which is the basis for modern wind turbines, both residential windmills and commercial wind farm varieties.
The past decade has seen an explosive growth of residential windmills. Residential windmills are generally small wind turbines, which have an operating capacity of less than 100 kilowatts. By way of comparison, a large commercial turbine is capable of a peak operating capacity of 2 megawatts. A 2009 study has shown that in the US alone, small wind turbines create an estimated 17 megawatts of power or more. That's a lot of power if you consider that the average size of a residential windmill is usually less than 10 kilowatts. That means that 100 or more are necessary for each megawatt of power.