September 26, 2022


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Generate Your Own Electricity: Are small wind turbines worth it to garden?

Berlin. When the wind blows, you can use it to generate electricity and even heat your home. Because there are wind turbines for the roof or garden – small wind turbines. However, this only pays off in a few locations because the wind is not just wind.

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How do small wind turbines work?

Small wind turbines or small wind turbines, as they are also known, are installed on roofs, but above all on masts in the garden or in the open field. It is driven by the wind, and the energy generated from it is converted into direct current.

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In the case of micro wind turbines, this results in a direct current of 24 or 28 volts – which can be used, for example, for LED lights, battery charging or an electric fence, explains Joachim Sroka. He is the second president of the Federal Association of Small Wind Turbines. Slightly larger systems are more interesting for families. It can be used to generate AC 220V or 400V high current.

“The basic principle of the horizontal axial wind turbine is the same in the micro and micro gigawatt category in the field,” says graduate engineer Soroka. But the size of the turbines varies enormously: “Small and small wind turbines have rotating heads from one to four meters in diameter.” Soroca advises mast heights between 12 and 24 metres. If the height of the system is no more than ten meters, you usually do not even need a building permit.

Can this also be used to generate heat?

Electricity from small wind turbines can be used to power heating rods in a buffer or hot water tank. Or to run a heat pump.

What is the advantage of small wind turbines compared to other heating technologies?

The greatest amount of power can be generated using wind turbines, especially in the colder times of the year – that is, when you also need heating. Here’s the problem with the solar thermal system: You’ll likely need their energy from fall to spring, but they produce about 80 percent of their annual crop from March to October.

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What are the disadvantages of this type of power generation?

the prices. “Wind turbines are a relatively high investment that only pays off over a long period of time,” says Soroka. Interested parties should calculate 5,500 euros per kilowatt output. “If you want to supply an entire house – and initially only electricity for your own needs, without heating – you need a five-kilowatt system in winter alone.” You may also need a building permit — and authorities in many places are skeptical about this, according to Joachim Sroka, whose company sells and installs these systems. Because there were ideas of giant wind turbines, which were previously known from the fields, in the center of the village.

“In addition, there is usually not enough space available in apartment buildings to be able to install such a system,” says Sroka. “Because of the building code, you have to take into account shades, sound insulation and clearance areas. There are currently very restrictive requirements here.” However, there are options for private households: low systems up to ten meters high, which do not require a permit. That the main wind direction at your site is unobstructed so these systems are worthwhile.But this rarely happens,” says Soroka.So he advises mast heights of twelve meters or more.“I prefer up to 24 meters” – however, when this The height of the mast is expensive due to static electricity.

What are the suitable locations for small wind turbines?

What has already been said about smaller turbines less than ten meters high plays a role here: the wind, its direction and strength.

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1. Free main wind direction

The wind needs to increase the wind speed: according to the energy consulting service of the Consumer Advice Center in Baden-Württemberg, even a house or bush located in the main wind direction of the system reduces energy production. And even a forest starting 50 meters from the house can have a similar negative effect on the production of electricity.

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2. Average wind strength

And then, as a matter of principle, the winds in the region should be strong enough. According to Joachim Sroka, the average wind speed in Germany is two to eight meters per second. In the north, especially on the coasts, it ranges from seven to 7.5 meters per second, and inland from only two to 4.5 meters per second. “I would advise against choosing a location where the wind rate is less than three meters per second.”

Moreover German Wind Energy Association The energy consultants at the Consumer Advice Center recommend it wind area of the property to be examined during planning. “In general, proximity to the coast or elevation is an advantage, but there should also be free space in front and behind the wind turbines.” It can make all the difference: A good site offers eight times the yield compared to a bad site with only half the average high wind speed.

Lars Muller, an energy expert at the Consumer Consulting Center in Lower Saxony, came to a similar conclusion: “Small systems make sense only in the open area and then as high as possible and not on the roof and with sufficient constant winds, usually almost never.” For him, this It means the systems are “not an option worth considering” for ordinary families. He would only touch on the topic in a very special environment, such as that of farmers.

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No good place in the garden: are there alternatives?

There are also small roof wind turbines, but the energy consultants at the Consumer Advice Center in Baden-Württemberg do not think this is a good idea. The building will ensure that the wind currents are turbulent and the yield is poor. Rotor vibrations may be perceived as bothersome directly in the home.

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But Sroka knows the solution: “There are initial ideas for sharing heating with larger systems.” So many families in the neighborhood get together and get electricity for heating from a larger system. The advantage: the larger the system, the lower the system costs per kilowatt of output, which are then shared by many households.

Generating electricity or thermal heat using wind turbines?

Expert Sroka recommends covering your electricity needs as a priority for single-family homes, “because electricity costs are currently higher than heating costs.” In the second step, it will cover the heating heat by producing excess electricity.

Either way, he advises a hybrid solution: “If you only rely on wind power, it’s not entirely without risk. Because if you stop for a week, you won’t get any energy. But as a rule, calm is associated with good weather.” Hence the photovoltaic system takes over and completes the energy mix. Energy consultants at the Consumer Advice Center in Stuttgart see it this way: a combination that provides more autonomy, “in summer mainly through photovoltaics, in winter during many winds”.

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How can I identify a good small wind turbine?

“You can run into a big problem if the inverter doesn’t comply with the DIN VDE-AR-4105 standard,” says Sroka. “We recently obtained this technical regulation that requires very specific tolerances for transformers. All electricity producers require this certification in order to connect the system to the power grid.” Sroka also advises clarifying whether all documents required for a building permit are supplied with the system.

The NRW Consumer Advice Center advises a critical evaluation of the nominal production of the system specified by the manufacturer. The critical factor is performance at low wind speeds, not in rare strong winds.

RND / dpa