ASK THE EXPERTS: Wind Turbine?

Intermediate

I will be building a new house in the near future and am very interested in obtaining solar and wind technology to power it. I use approximately 20,000 kWh during the year (it is cold here in Wyoming and I only have baseboard heat in my inefficient home). So, with that in mind, what type of wind turbine would I need? I see that turbines are measured in watts, but are those measurements per hour, per month, per year? I would also like to know what type of solar system I can use in conjunction with the turbine.

David Hendrix • Laramie, Wyoming

A wise first move will be to design your new home with energy efficiency and conservation in mind. Focus on low energy use in every building decision you make—the size of your home, its building envelope, insulation levels, heating system (examine the suitability of heat pumps), appliance choices, solar orientation, daylighting, etc. This will make the biggest impact on your energy footprint, and will reduce the cost of the electricity generation system dramatically, since the less energy your home needs, the smaller the system it will require.

It is quite possible to build a “zero energy home”—one that makes all its energy on site. But to do this sensibly, you should focus first on the load end of things, not on generating energy. Shrink your energy usage down to the minimum, and making the energy you need on site will be much easier. See our many articles on home design and construction, energy efficiency, and load analysis.

Watt (power) ratings for wind turbines are almost meaningless, since they describe the peak instantaneous output, not the energy yield. (Wattage is an instantaneous rate of energy generation, transfer, or usage; watt-hours and kilowatt-hours are actual units of energy.) Power ratings can be a bit of a shorthand when comparing wind generators to each other, but since a wind generator rarely works at its maximum output, and because each site has a different wind energy resource, you can’t use turbine power ratings to predict your system’s energy (kWh) yield.

The three things you need to know to size a wind turbine are:

•           The estimated energy consumption, in kilowatt-hours, of your new home

•           The average wind speed at tower-top height

•           The projected kWh at the tower-top average wind speed for each wind turbine you are considering

With this information, you can compare the available equipment and see what will be a good match. Looking at seasonal wind data will be especially helpful if you are considering being off-grid. Wind turbine energy curves (not power curves) show kWh per month or year—read the fine print—in various average wind speeds. Get good data on your site, and then be conservative when applying manufacturer numbers.

Solar site analysis is also needed, including finding out the “peak sun-hours” (the solar equivalent of average wind speed) for your site. Consider the shading on any potential array location from nearby trees, buildings, and landforms, and the orientation and tilt of your roof (if you are considering a roof-mounted PV array). Monthly data will help you estimate your potential production from a solar-electric system, and determine how it could match with wind-energy production. Finding the right balance between the two can be tricky for off-grid systems; on-grid systems are much more forgiving. Often on-grid people will chose to use one or the other instead of both, depending on the quality of each resource and the project budget.

Integrating wind and PV systems in a battery-based system is straightforward—both charge the same battery bank, and downstream equipment is in common for both. Without batteries, you may end up with two separate systems or two systems integrated together, depending on the equipment chosen.

Overall, you’ll need to either find experienced help or educate yourself to design, install, and operate these systems well. In either case, think carefully about who you are working with and buying from, and make sure that substantial support is part of the package—not just low price. Wind especially is difficult to make work long-term, and buying cheap is a big mistake. Check out our website for many articles on all of these topics, and enjoy pursuing your clean energy projects.

Ian Woofenden • Home Power senior editor

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