The answer to your question is the same answer we give to a lot of folks, it depends.  For example, will your house be off-grid or on-grid?

Before continuing I want to make my standard plug for energy efficiency.  I don’t know how far along you are in building your house, but to the extent possible, make it energy efficient.  It’s much cheaper to build in energy efficiency house at the start rather than retrofit later.  Energy efficiency is especially important if your house will be off-grid.  It’s much cheaper to build to minimize your electric load than it is to buy a larger stand alone energy system.

First, you want to evaluate your property to determine if it is feasible to site a wind turbine.  Ideally, your lot is at least one acre in size with good exposure to the wind. 

A related consideration is tower height.  Generally, the higher the better.  Wind speed tends to increase with height, so the taller the tower, the greater the wind speed that your turbine will “see”.  Due to the cubic dependence between wind power and wind speed, even small increases in wind speed yield large increases in the power of the wind.  For example, an increase of 10% in wind speed will cause the power in the wind to increase by over 30%.  Ideally, your turbine should be 30 feet higher than any other objects (trees & buildings) within 500 feet.  This will position the turbine above the turbulence caused by these objects.  

If you are off-grid your best course of action, after reducing your load with energy efficiency measures, depends partly on what is most important to you.  Do you want to minimize cost?  Do you refuse to use a generator?

Most off-grid homes in the U.S. that use wind turbines combine them with photovoltaic panels, batteries, and a generator.  These hybrid systems are often a lower cost option than a grid extension or running a generator 24/7.  With a hybrid system the generator typically runs a few 10s to a few 100s of hours per year.  You can dispense with the generator by either oversizing the renewable energy part of the system or at the risk of occasionally doing without electricity.

If your house will be on-grid, then what you do depends on your personal preference and how much money you are willing to spend on the wind turbine.  You can get a small turbine that meets a small portion of your load, or a larger turbine that meets a large portion of your load.  In general there isn’t much point in buying a turbine that will produce significantly more electricity (on an annual basis) than what you consume. 

Typical turbine sizes for residences range from 1 kW to 10 kW.  Unless your house is very efficient, you’ll need a turbine in the upper end of that range to produce an amount of electricity equal to all or most of your load.  Assuming your site is reasonably windy and has good exposure, you can expect a turbine capacity factor (CF) in the range of 10%-20%.  The CF will be below that range if your wind resource is poor and higher than the range if your wind resource is really good.  Your annual energy production is then the turbine size (rated power) x capacity factor x 8760 hours per year.  Thus the annual production of a 10 kW turbine with a 15% capacity factor is: 10 kW x 0.15 x 8760 hours/year = 13,100 kWh year.

Note that capacity factors for small wind turbines are generally lower than the capacity factors for large wind turbines because; 1) small turbines are placed on shorter towers, and 2) small turbines tend to be located in less windy areas.

The economics of grid-tied wind systems are most affected by:

1) Wind resource

2) The availability of incentives: see http://www.dsireusa.org/

According to the South Dakota wind map the Sturgis area has class 3 and class 4 winds, which are more than adequate for small wind turbines.

Even with a good wind resource, without incentives the payback period for small wind turbines tends to be long, generally over 15 years.  Unfortunately, South Dakota’s only incentive, a three-year property tax exemption on renewable energy equipment, is relatively minor.

A final consideration is the availability of net metering.  Turbine production is often not matched to consumption.  As the turbine size increases relative to the load, the turbine will more often produce more electricity than the house needs.  This excess electricity will go back to the grid.  As turbine size increases a larger fraction of overall turbine production that will go to the grid. 

If your utility does not offer net metering, you will have two meters.  One meter will measure incoming electrons for which you will pay your regular retail rate.  The other meter will measure the electricity that you send to grid.  For this outgoing electricity your utility will pay you a wholesale or avoided cost, which is lower than the retail rate.  It is important to understand that this lower rate applies only to electrons sent to the grid.  Wind generated electricity that you use on-site is worth full retail value because they are displacing electrons you would otherwise buy from the utility.  In the situation where you don’t have net metering, it may be financially advantageous to go with an undersized turbine, compared to your consumption, so that most of the production is used on-site and valued at the retail rate.

Net metering replaces two meters with one meter.  When your system is producing more electricity than you are consuming, the meter will spin backwards.  Thus the financial value of all electrons produced by the wind turbine is full retail rate.  This is true unless the overall production of the wind turbine during the “true-up” period (typically monthly or annually) is greater than your overall consumption.  Typically the “net-excess” electricity is sold at a lower rate or given to the utility.  Net metering allows a homeowner to size the wind turbine closer to their home’s consumption without financial penalty.

Unfortunately, South Dakota has no net metering law or regulation, so chances are your utility does not offer net metering.

For a partial listing of available turbines and general pricing, see my answer to Shuman Moore’s question.

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Dennis Keim

Lincoln, Nebraska

Okay, Trudy.  Try one or all of these.  (Just for fun.  <g>)

Whatever happened to the extremely low solidity two-bladed Gale wind turbines that were being developed by the Fel-Pro gasket people?

What was the very appropriate name of Herman Drees' dog when he was developing the Cycloturbine on Cape Cod in the late 1970s?

Which wind system used tip drags for rotor control first?   (Ventimotor, Gedser or Enertech)

Dennis,

I didn’t know the answers to these questions myself but I asked a friend and colleague, Woody Stoddard.  He had all the answers as he usually does and had a reference for the answers to 2/3 of these questions and offered a question back to you.  But first, I will give his answers.

1)    Ernie Rogers who worked on early small turbine designs decided to build a low solidity, low Reynolds number turbine, called the Gale.  At the time he worked for Fel-Pro gasket company and built one prototype turbine.  Ernie actually consulted with Woody on computer codes that he could use to help him design these low Reynold’s number blades.

2)    Herman Drees’ dog’s name was Rotor.  (At least that’s what Woody and Sandy recollect.)

3)    There were actually several early turbines that used tip drags for rotor control.  The first was Louis Vadot who designed yet never built the Ventimotor.  This was a French design.  The second company was Russian and they designed and built a turbine with tip drags, starting with a fixed pitch turbine design and later changing that to a variable pitch design.  One of these 100 kW turbines was used in Yalta for mining salt.  The third turbine design was the Gedser, which was designed and built pre-World War II.  And then of course the Enertech turbine used tip plates or brakes and there were a number of those turbines built and sold in the US when there was a federal tax program for renewables.

Now, here’s a question for you.  From a physics perspective, is it possible to run a windmill with a hollow blade and use centrifugal force that pushes air out the blade to produce power?

Thanks for the questions, finding the answers was quite enjoyable.

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Dale Eastman