Backyard Wind Energy

As my airplane circled over Amsterdam, one of the most notable aspects of the landscape below was the number of modernized windmills dotting the fields. So when I came across the Harmowind project, it got me thinking, why can’t we adapt to this free source of energy and become self-reliant? This particular windmill has been specifically designed for household use and can be installed in the backyard. It has the capacity to generate enough power for a single-family unit to use.

As the designer explains, “Unlike the horizontal axis wind turbines, Harmowind is independent of wind direction. It can make use of wind turbulence to generate power, which happens very often in built-up area. Harmowind runs extreme quietly thanks to not only the vertical axis, but also the small rotation radius.”

  • Wind speed is proved to be the most important element (among wind speed, investment costs, operating cost, interest rate and useful life) in reducing or increasing the electricity production cost.
  • As the wind is stronger higher up, and a wind turbine with a height of max. 10 m is allowed to be built without authorization in most states of Germany; it was designed as 10 m high.
  • Double-blade-rotor decreases (compared to 3-blade-rotor) the demand on the natural frequency of the mast.
  • A helix-form reduces the unevenness of aerodynamic force.
  • The shadow effect of the wind turbine has also been a problem when its built near a house.
  • The blade design was aimed also to minimize the shadow and to weaken disco-effect during the rotation.
  • In consideration of min. 20 years of service life, the design has tried to present the feeling of harmonious, timeless, long lasting functionality.

Designer: Hailan Li


  • Paul says:

    Good looking design. How about efficiency compared to radial turbines?
    Best regards,

  • Quintin says:

    There have been many small and large, vertical and regular horizontal wind turbines for residential use.

    None of them have any hope of generating enough electricity to earn their purchase cost back before they wear out. Windmills have to be really quite large before they become economical. For residential use, solar panels are a far better option.

    Also: where are the figures? This seems like a drawing with some text that someone made up. Has the designer done any research on vertical windmills?

    The scale also seems wrong in the picture with the windmill next to the houses.

  • Hailan says:

    Hi Paul,

    By “radial turbines” you wrote, maybe you meant “horizontal axis wind turbines (HAWT)”. 🙂

    Compared to HAWT, there are some advantages of vertical axis wind turbine (VAWT) for built-up area. Such as VAWTs cause much lower acoustic emission in general, they are independent of wind direction so that there is no need for VAWTs to measure local prevailing wind direction. They also don’t need wind direction tracking system for rapidly changing wind direction. The gravitational load to mast is constant by VAWT.
    Besides that, there is a theory of Betz coefficient (Cp, Betz), which I’ve not totally understood, that saying there’s a limit for the value of the power taken from the wind in relation to the power of the wind. It says that via wind turbine, about only 59% of the wind power can be taken from the wind. But this theory is not suitable for vertical wind turbines. It means vertical wind turbine can make use of more than 59% of wind power.

    But there is a big disadvantage for VAWT, that the start-up wind speed of VAWT is higher than HAWT.

    I hope this is what you wanted to hear. 🙂

    Best wishes,

  • Hailan says:

    Hi Quintin,

    Thanks for your comment.

    There are so many small wind turbines that the German Wind Energy Association (BWE) published a special market review for about 230 pages about them including the information about technology, authorization, economic efficiency etc. (Link :

    You are also right about the economic cost. At the very beginning of a new product before it’s become a massive product, they are usually very expensive.
    To invest in a wind turbine in the backyard, there are not only purchase costs but also costs for grid connection, foundation, installation etc. to consider. So if the governments are interested, there are often some sorts of financial subsidies. In Great Britain there have been “Low Carbon Buildings Programme Phase 1 (LCBP)” since 2006 and one household can get a grand of £2,500 for small power generation plants. In the State of California (USA), there is “Emerging Renewables Program” that promotes small wind turbines and fuel cells. For a 10-kW-turbine the grand is US﹩22,500.
    In the case of Germany, where there’s not so much grand, we could try another way to calculate the economic benefits. German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety carried on a study about VAWT (Here is the report: In the economic efficiency section they tried to calculate the cost of producing electricity pro kWh. They also compared the influences of different factors such as investment cost, wind speed, useful life, interest rate etc. And wind speed appeared to be the most important factor. By raising the wind speed of 10%, it reduces the power generation cost for 0.1 Euro/kWh.

    However, lower economic efficiency doesn’t mean lower mechanical efficiency. Still, it can “generate enough power for a single-family unit to use”.
    They are just two different things.

  • Eddard says:

    Lol, “Disco-effect”.
    There is no value in redesigning the windmill to target aesthetic needs, when the thing hasn’t yet been proven to be overwhelmingly mechanically efficient. If it can’t give you enough power when its form is based purely on aerodynamic/mechanical optimization, redesigning it to be less visually obtrusive will reduce its functionality even further and result in a useless waste of time and resources.

  • Quintin says:

    Hi Hailan,

    Thanks for responding to my comment.

    I’m currently building a passive house that should become a zero energy house in the future (when I have money available for solar panels, construction is costing more than anticipated…).

    Adding a small wind turbine would be very interesting, but it just doesn’t seem economical. I’ve looked around quite a bit at the smaller wind turbines currently available (your design would already be too big..)

    There have been quite a few (long term) reviews of small residential wind turbines (there is a field in the Netherlands where they put them up for over a year and test them). None of them generate the amount of power the manufacturer claims, the best ones cost so much and generate so little power that it would take close to 40 years to recoup the cost of buying one.
    Of course wind speed is the most important factor, but even with the string wind near the Dutch coast, the small wind turbines currently for sale don’t live up to their promises…

    The claims about noise are also nice, they are probably very quiet with they’re new. What about when they’ve been up for a few months? The bearings have been run in and there is probably some dirt (bird droppings, etc) on the blades. Now the blades are not perfectly balanced anymore… It probably won’t affect power generation much (if at all), but I’ve heard many stories about small wind turbines starting to vibrate at speed and making the entire house buzz.

    Compare that to just putting solar panels on the roof. Even without subsidies you can make the cost of purchasing them back within 7 to 8 years. Perhaps even sooner.

    • Tess says:

      Hi Quintin,
      Where are you at? We are also trying to rebuild an old house to achieve zero energy cost…..maybe we can compare notes on how to cost effectively do so? Thanks

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