                    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
