Cheat Sheet

Wind Power For Dummies

From Wind Power For Dummies by Ian Woofenden

After you decide that your home is a good candidate for wind power, you need to understand the basic parts of wind-electric systems and how they fit together. In addition, you need to evaluate how much energy your home needs and how much wind your site actually gets — a realistic wind resource assessment is key. You also want to make sure to steer clear of "too good to be true" energy estimates from the pros who want to sell you their goods and services.

The Major Parts of a Wind-Energy System

When it comes to power, a wind generator by itself will do absolutely nothing for you. You need a wind-energy system, which consists of most or all of these components:

  • Batteries (for off-grid and backup systems) provide energy storage for periods of calm or during utility grid outages.

  • A charge controller and/or voltage clamp take raw energy from a wind generator and condition it so it can charge batteries safely and effectively or interface with an inverter and the utility grid.

  • Disconnects and overcurrent protection provide safety from overloaded circuits and allow you to isolate different parts of the system.

  • A dump load is a place to divert excess energy in off-grid systems or when the utility grid is down, it's windy, and your batteries are full.

  • An inverter converts direct current (DC) electricity to conventional household alternating current (AC) electricity, and it may "sell" surplus electricity to the utility grid.

  • Loads in a system are energy-using devices, such as lights, appliances, and other electricity users.

  • *Metering gives you data display and logging so you can tell what your system is doing and whether it's performing well.

  • A tower supports a wind generator, getting it up into the smooth, strong wind that's needed to generate meaningful amounts of electricity.

  • Transmission wiring and conduit allow you to transfer energy from where it's made to where it's stored and used.

  • Wind generators (or turbines) collect the energy in the wind and use it to make electricity.

Assess Your Energy Usage to Determine Your Wind-Energy Needs

Doing a usage assessment to determine how much energy you need is a vital step toward getting a successful wind-electric system that meets your power expectations. These steps help you calculate how much energy you're using:

  1. Review all energy bills so you can determine your overall energy use.

  2. List all loads (electrical appliances) with wattage and run time to see specifically where you're using energy and how much you're using.

  3. Measure phantom loads (loads that use energy when turned off) using a watt meter.

  4. Inspect your building envelope (the shell of your house), sealing, windows, and so on by having a professional do a blower door test (which pressurizes your house and measures how leaky it is).

  5. Have an HVAC professional inspect your space and water heating systems.

  6. Consider your energy use habits and goals so you can look for ways to reduce your energy use and plan for future energy use.

Do You Get Enough Wind for a Wind-Energy System?

Analyzing your wind resource (your site's average wind speed, measured in miles per hour) is one of the hardest jobs you face when selecting a wind-electric system; no single method gives you exact numbers. To come up with a good estimate of your site's average wind speed, combine as many of the following strategies as possible:

  • Put up a recording anemometer at the proposed wind generator height to measure your actual wind resource; you often need to do it over the course of a year or more.

  • Use a small test turbine with a watt-hour meter to give you some data while giving you a bit of energy; you can learn important lessons from the experience.

  • Consult wind maps and roses, which show generalized wind resource information for your area.

  • Sift through local weather data, which may be an excellent source of wind resource information.

  • Live on site with eyes and ears open to note seasonal variations in wind.

  • Climb something tall (like a tree that's on a high point on your property) and look at topography and obstructions; this can help you determine your optimum tower height.

  • Study vegetation, which may reflect how much wind you have; by reading the deformation of trees, you may be able to estimate your wind resource.

  • Talk with neighbors; they may give you valuable perspective on wind in your neighborhood, especially if your neighbors are wind-energy users.

Verify Energy Claims from Wind Generator Professionals

Many wind generator inventors, manufacturers, and installers make claims about how much energy you can get from their idea or product, but how can you know whether those energy claims are realistic, ambitious, or outright scams? In all cases, you should seek real-world confirmation of estimates and check your wind power professional's numbers.

To test for "enthusiastic" estimates from inventors, manufacturers, or installers, do the following:

  1. Verify the average wind speed the professional or manufacturer is using as the basis of the claim.

    Without an accurate average wind speed from your actual tower height, you can't get an accurate prediction of wind energy on your site.

  2. Verify the swept area (the area that the blades sweep) of the wind generator.

    For horizontal-axis machines, the swept area equals the rotor radius (half of the diameter) squared times Pi (3.14 if your calculator doesn't have a Pi button). For vertical-axis wind generators, take height times width for swept area; multiply that total by 0.65 for Darrieus-style vertical-axis turbines.

  3. Multiply the swept area (in square feet) by the average wind speed cubed (in miles per hour), and divide that total by 32,000 for an estimate of average daily kWh production from a typical machine.

    Multiply your final total by 30 to get your average monthly energy in kWh and 365 for annual energy in kWh.

  4. Check this prediction against manufacturer claims or installer production estimates.

    If the manufacturer or installer claim is 50 percent or more above your estimate, the machine may possibly be very efficient, but you're probably looking at an exaggerated claim.

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