Energy saving: are small wind turbines worth it for the garden?

You see them all over the country, in fields and at sea: the wind turbines that generate the energy. But only a few homes use this technology to generate their own heat and electricity. Why?

Whenever the wind blows, you can use it to generate electricity and even heat for your home. Because there are wind turbines for the roof or garden – small wind turbines. However, it only pays off in certain places because the wind is not the only air.

How do small wind turbines work?

Small wind turbines or small wind turbines, as they are also known, are installed on roofs, but at the top in gardens or on masts in open ground. The wind sets them in motion, and the energy generated from them is converted into a direct current.

In the case of micro wind turbines, this becomes 24 or 28 volts of direct current – ​​which can be used, for example, for LEDs, battery charging or electric paddock fences, explains Joachim Sroka. He is the second president of the Federal Association of Small Wind Turbines. For homes a slightly larger system is more interesting. These can be used to generate alternating current with 220 volts or high current with 400 volts.

“The basic principle of horizontal-axial wind turbines is small and micro in area, as well as the same in the gigawatt class,” says graduate engineer Shroka. But the size of the turbines varies greatly: “Small and micro wind turbines have rotor heads with a diameter of one to four meters.” And Shroka recommends a mast height between twelve and 24 meters. If the system is no more than ten meters high, you usually don’t even need a building permit.

Can it also be used to generate heat?

The electricity from small wind turbines can be used to power a heating rod in a buffer or hot water tank. Or to operate a heat pump.

What are the advantages of small wind turbines compared to other heating technologies?

Especially in the colder times of the year, the most energy can be generated with a wind turbine – that is, when you also need heating. That’s the problem with solar thermal systems: You’ll need most of their energy from autumn to spring, but they produce about 80 percent of their annual yield from March to October.

What are the disadvantages of this type of energy generation?

prices. “A wind turbine is a relatively high investment that only pays for itself in the long run,” says Sroka. Interested parties will have to calculate with 5500 Euro per kWh of output. “If you want to supply the whole house – and initially with electricity only for your needs, without heating – you need a system with five kilowatts in winter alone.”

In addition, it could be that you need a building permit – and in many places authorities are skeptical about this, reports Joachim Sroka, whose company sells and installs such systems. Because in the heart of the village was the idea of ​​\u200b\u200bthe giant wind turbines, formerly known from the fields.

“In addition, there is usually not enough space available in residential buildings to be able to install such a system,” says Sroka. “Due to construction legislation, you have to take into account shade, sound insulation and evacuation areas. There are currently very restrictive specifications here.”

Nevertheless, there are options for private houses: low systems ten meters high, which do not require a permit. However, for these systems to be worthwhile, the main wind direction at your location must be unobstructed. “But that rarely happens,” says Shroka. Therefore he recommends a mast height of 12 meters or more. “24m even better” – but at this height the mast is very expensive due to statics.

What locations are suitable for small wind turbines?

What has already been mentioned for small turbines with a height of less than ten meters comes into play here: wind, its direction and strength.

1. Free main wind direction

Wind needs a run-up: According to the Baden-Württemberg Consumer Advice Center’s Energy Advice Service, even a house or bush that is in the direction of the system’s main wind reduces energy production. . And even a forest starting at a distance of 50 meters from the house can adversely affect the generation of electricity.

2. Average wind force

And then, in theory, the wind in the area 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 is 7 to 7.5 meters per second, inland only 2 to 4.5 meters per second. “I advise against choosing a place where the wind blows on average less than three meters per second.”

Energy consultants from the German Wind Energy Association and the Consumer Advice Center also recommend checking the property’s wind area 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 turbine.” This can make a significant difference: a good location yields eight times the average wind speed of a bad location that is only half that.

Energy expert Lars Möller of the Consumer Advice Center in Lower Saxony comes to a similar conclusion: “Small systems only make sense in an open area and then as high as possible and not on a roof and with enough sustained wind, so usually Almost never.” For them, it also means that the systems are “not an option worth considering” for typical homes. He will only address the subject in a very special environment for farmers.

If I don’t have a good garden space: are there alternatives?

There are also small wind turbines for the roof, but the energy advisors at the Baden-Württemberg Consumer Advice Center do not think this is a good idea. The building will ensure that the air currents are turbulent and the yield is poor. And the vibrations of the rotors can be directly attributed to the irritant in the house.

But Sroka knows a solution: “There are preliminary ideas for sharing heating with larger systems.” So many houses in the neighborhood mix together and receive heating current from a larger system. Benefits: The larger the system, the lower the cost of the system per kWh output, which is then shared by multiple households.

Should I generate electricity or thermal heat from a wind turbine?

Expert Sroka recommends meeting their electricity needs as a priority for single-family homes, “as electricity costs currently exceed heating costs”. In the second phase, he would cover the heating heat with additional power output.

Either way, he recommends a hybrid solution: “If you rely only on wind power, it’s not without risk. Because if you have a week of peace, you get no energy. But generally, calm weather is associated with good weather.” The photovoltaic system then acts here and supplements the energy mix.

Energy consultants at the Consumer Advice Center in Stuttgart also see it this way: a combination provides more freedom, “in summer mainly through photovoltaics, in winter through a lot of wind”.

How do I Identify Good Small Wind Turbines?

“If the inverter doesn’t meet the DIN standard VDE-AR-4105, you could have a bigger problem,” Schroka says. “Recently there has been this technical regulation that requires very specific tolerances for inverters. All power generators to connect the system to the power grid require this certification.” In addition, SROCA recommends clarifying whether all documents required for a building permit are supplied with the system.

The Consumer Advice Center NRW recommends critically evaluating the nominal output of the system as specified by the manufacturer. The deciding factor is performance at low wind speeds, and not in rare strong winds.

(This article was first published on Sunday, October 02, 2022.)