What is the ideal wind speed for a wind turbine to produce enough electricity for a family of four daily?
Hey FAirY, you won’t find a straight forward answer that you’re looking for because the question is quite open ended, I’ll explain. first, a family of four says nothing to their energy use. We have four in our home, our electric use runs about 300 kwh per month. Our neighbors live in almost an identical home with 4 people as well, they use over 1000 kwh per month. They just live differently than we do. when it comes to wind turbines, they are generally engineered to operate in a range of wind speeds. The Southwest Windpower model H-40 powers our home if it is quite windy, like 20 to 40 mph all day and night. Most people do not have wind like this, but we do most the fall and winter, hence the choice of turbines. They make good ones that run as well on less wind, but at 40 mph, they produce almost nothing because they are in full governing mode, which means the tail has pulled the turbine out of the wind to protect it, so it won’t be overpowered.
There is also the fact that the wind is what it is at your location, and determining what speed is ideal is like determining what length of day is best to grow tomatoes. even if you decided on 21 hours, you won’t be able to talk the sun into your new schedule, you’ll have to grow a different variety of tomatoes to make better use of the sun you have.
A better question, and one that wind turbine installers do battle with each day is, “Which turbine willl work best for this client in this wind?” now that’s information we can use.
Most commerciallly manufactured turbines today all run in the same range of efficiency, about 25 – 35 %, so the only two variables that can determine total power output are wind speed and swept rotor area. Since the average wind speed at any given location is basically known, you simply have to find a turbine with the correct swept area and wind speed range to produce the power you need. all to often this problem is worked out wrong, or not properly worked out at all, and people decide on a given turbine because they read something good about it, or a salesman talked them into it. The vertical axis, or Darrieus Rotor, is a classic example. Many places sell these devices as the be all end all turbine for all homeowners. Unfortunately they aren’t. The vertical axis turbine falls into the 5 to 8 % efficiency range primarily because the downwind blade uses most of its mechanical energy forcing the upwind blade back into position. this is why all the utility companies are installing horizontal axis turbines in their wind farms, they actually produce power for them.
There are some great sources for more information on this, and my favorite one is probably at your local library. I’ll list them below. Probably the most informed person on wind turbines today is Mick Sagrillo, founder of Lake Michigan Wind and Sun, author and teacher. Mick has been designing, building and installing turbines for over 30 years. You can probably find some of his writings at the American Wind Energy website below, including a nuts and bolts explanation of the vertical axis turbine that many are falling in love with today. What you won’t find however, is a good turbine, or wind speed for a family of four, that information has to be exptrapolated from other family data, and is different for all clients and locations. We live in a solar and wind powered home today, has been for 11 years. We are currently on our third wind turbine, the other two didn’t work out as well as we had hoped, the current one is working great, because it is sized and engineered for our winds and home energy use habits. good luck, and take care, Rudydoo
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