Selecting a site for a Wind Power System by Lazarus Long lazarusl@vaxxine.com Site selection for a windpowered generating system is one of the most important steps in ensuring that the system will perform at the rated capacity that the manufacturer has designed it for. Available Wind Speed: An obvious factor to consider is; what is the average wind speed at the site? Another less apparrent is what is the range between the low average and the high average wind speed. Generally speaking, areas with wind speed averages of 12-16 mph are excellent sites for windpower generation. Sites with wind speed averages of 10-12 are moderate to good and sites with 8-10 mph speeds are marginal. This average speed must be assessed over the entire year as a site that only averages 10 mph overall may have a 12 mph winter month average. If your highest electrical demand is in the winter, this may be an adequate site. To determine the site conditions you can either measure the average wind speed at the site on a monthly basis and build up a database from which to do your calculations, or take advantage of the work already done for you by Universities, airports, agricultural research stations and other agencies that measure climatic conditions. In the U.S. there is a national compilation of this material at the National Climate Center in Asheville, North Carolina. This data is compiled in the Center's "Comparative Climate Date Manual" The average wind speed figures are based on one minute averages taken every 3 hours and averaged over several years. The best geographical areas in the US for wind generators is in the Oklahoma-Kansas region..where wind power exceeds 300 watts/ sq.meter Wyoming, also is a good site with a small part of the south-central part of the state registering at 400watts/sq.meter. As a general rule of thumb, any of the great plains states make for good sites.. another site for those in the east is the upper New England area, particularly Maine..with a 200watt/sq.meter rating. Areas with less than 100 watts/sq.meter are usually not suitable for wind power generation. This inclese the extreme south-eastern and south-western U.S. except for small coastal areas. Site Selection for Obstacles and Height: Choosing a site for a wind power generator involves consideration of the following factor, obstacles in the direction of the prevaling wind that may cause turbulence. A rule of thumb is to install the generator on a tower that brings the center of the rotor at least 30 feet higher than any obstacle within 300 feet of the tower. The higher the tower the more steady and faster the wind will be, as wind loses speed due to ground drag and turbulence. On level ground, the minimum height of the tower should be 40 feet. Adding 10 feet to the tower may bring an increase of 10 percent of available power. An example: a wind system is estimated to generate 300 kwh per month if installed on a 50 foot tower. If the tower height is increased by ten feet that will give you 330 kwh per month. Generally, towers for home size systems will be 60-80 feet in heighth although to clear obstacles tower heighths of up to 100 feet are not unknown. It goes without saying, that if you have a small hill or ridge on your property that it would be the best site for your tower. It would give you that extra heighth without the expense of extra sections of tower. Sites near water are also good as breezes are created by the differences in water and land temperatures, plus the unobstructed wind as it passes over the water. Estimating the electrical load: Most home sized systems are capable of powering a fairly large range of electrical items, although heavy users of power, such as ovens, clothes dryers and air conditioners will be beyond the capacity of the system. What you can depend on is the ability to power lights, small appliances and even a fridge or freezer. There are load charts available from engineering texts and your local utility company. Here is a sample chart suitable for a family of four assuming no heavy usage appliances: Appliance Approximate Wattage Average Kwh/month Food Blender 200-300 1 Vacuum Cleaner 400 - 1200 5 -10 Clock 3 - 10 2 -8 Coffee Maker 600- 1000 3 - 10 Cooling Fan (Attic) 1/6 - 3/4 hp 60 -90 Dishwasher 1000 - 1,600 30 -45 Food Grinder 500 2 Freezer 30cu. ft. 800 250 Lighting 300-500 50 - 150 Water Pump 1/3 - 1 hp 10 - 60 Batteries: Because the wind doesn't blow continually, you will need to store your generated electricity. Deep cycle storage batteries are the way to go, they last a long time and can be heavily drawn down without harm to the battery. You will need to organise your batteries in a bank(any former navy men will be familiar with this, if they served on the old diesel electric subs). The number of batteries in the bank will be determined by the average number of consecutive windless days multiplied by your daily electrical consumption(in watts). Example: If you have 120 volt bank of batteries with the batteries rated at 180 amphours each, it is capable of storing 21.6 kwh(120x180 /1000) If your daily consumption is 6 Kwh then the storage capacity of the bank would be about 31/2 days. Inverters: Most systems will not be using battery banks that will supply 120V as the cost of such a bank is extremely high. Most systems will run 12v as the availability of 12v appliances and lights is quite high. Ideally 24v would be better, but that voltage range is limited by the scarcity of 24V appliances. Inverters must be used to bring the 12v d.c. current to a usable 120v a.c. current for those appliances that are unavailable in 12v d.c. Lights and stereos are readily available in 12v d.c. current..however...your computer might run a tad slow if fed 12 v. Inverters can be either sine wave or square wave. Square wave inverters are cheaper to purchase but they tend to cause electrical noise when used with stereo equipment.. Sine wave inverters produce "clean" power, something that is to be considered if you are planning on using your computer in a wind generated system. Not only does your inverter have to handle the total load that your house may demand but it should be sized to handle starting loads from heavy motors like refrigerators and freezers and your water pump. Stand by Plants: Engine-driven generators are a good source of auxillary power. For most homes the generator does not have to be large enough to supply all the needs of the house, it should be able to charge the batteries if the wind fails for any prolonged length of time and run the essentials. Generators in the 3000 to 6000 watt sizes would be suitable for a backup system. Choosing a wind system: Wind systems should be sized to fit the load needs of the home and budget. The average home, assuming wood is used for heating and cooking, would need a system capable of generating 300 - 500 Kwh per month.. These systems have 12-18 foot rotor diameters and with (without tower) approximately 400 - 800 pounds. Towers must be carefully selected to withstand the strain of such a load, especially in storm conditions. Smaller, cabin size dwelling can get away with 150- 200 Kwh capacity generators. Unless you are very rich, you should not expect to run an all electric house on a wind generating system. The size of system increases dramatically, as does the cost, when you get up to systems capable of generating the 2000 - 5000 Kwh necessary to run such a house...Here you are talking about 28- 30+ foot diameter rotors and 1000 pound+ generator weights. Not only is the generator big and expensive, imagine the cost of a battery bank capable of carrying the house for a 3 day calm! The wind powered generating system can allow the homeowner to become independent of the public utility system, however, bear in mind that the householder also will be responsible for maintaining the system, and theses systems are not maintenance free. The initial costs are high, but at the current cost of electricity, the average system can be expecte to pay for itself withing ten years. Information for this article was gathered from Wind Power for the Homeowner by Donald Marier. Rodale Press, Emmanus Pa. Alternative Sources of Energy magazine. Distribute freely as WINDPOWR.TXT