Onshore wind power

The wind industry has evolved considerably over the past two decades. Both the materials and the designs have changed. Where we used to have rigid structures, today the nacelle on the tower has a rotating design. As such, the rotors are always facing into the wind. Since the individual rotor blades are adjustable along their longitudinal axis, the rotational speed can be kept largely constant even with changing wind speeds. The rated output of wind turbines has roughly doubled over the past ten years as a result of technical progress and structural innovations. Due to the way in which wind turbines have evolved from a technical perspective, wind farms can now be gently started up and shut down. This allows wind energy to be used as an important element of an energy supply system in which the proportion of fluctuating power generation will continue to increase.

EnBW Energie Baden-Württemberg AG endeavors to involve regional companies in the construction of the wind farms. This creates jobs for those involved in supplying building materials, building roads and undertaking other construction work, clearing woodland, preparing expert reports and providing catering services.

The wind energy industry in Germany has now evolved into an independent branch. Numerous companies create secure jobs in Germany by developing, manufacturing, building and operating wind turbines. In 2012, around 117,900 people worked in the onshore wind energy generation sector. By 2030, around 40,000 new jobs could be created in Germany.

Source: German Wind Energy Association

Most studies conclude that wind turbines have no lasting negative impact on property value and no empirically ascertainable link to land value:

• “Activity on the real estate market is determined […] by many different influencing factors. The complexity of the interdependencies makes it difficult to methodically attribute price fluctuations to one single influencing factor.”
• “The demographic trend is the primary factor influencing value, particularly in rural regions […], where the expansion of wind energy capacity is predominantly taking place. In Germany, urban migration is leading to a drop in demand for rural properties and causing prices to fall.”
• “Merely the assumption that wind turbines may pose a depreciation risk to the pricing of land and real estate can have an impact on price trends. Structural changes in the surrounding area, which may trigger short-term price fluctuations, are part of the cyclical nature of market activity.”
• “Studies to date, however, support the assertion that wind turbines have no lasting negative impact on property value.”

Source: “Faktencheck Windenergie und Immobilienpreise: Dokumentation der Veranstaltung” [Fact Check on Wind Energy and Property Prices: Documentation from the Event] (p. 8), published by EnergieAgentur.NRW in 2017 – with Prof. Günter Vornholz (professor of real estate economics at the EBZ Business School in Bochum since 2011, specialist field: economic analysis of the real estate industry and markets), among others.

You can find further details here: EnergieAgentur.NRW

A summary of the current level of knowledge can be found here: Wind energy and property prices | naturwind climate knowledge

EnBW Energie Baden-Württemberg AG will only build wind turbines if efficiency can be demonstrated. Wind measurements are an essential factor in determining whether the site is suitable for the construction of wind turbines. To this end, a meteorological tower is usually erected, which is used to measure the wind speed at different levels. The wind direction, turbulence, temperature, humidity and air density are also recorded. At the end of this investigative process, the raw data is passed on to two independent and certified wind surveyors, who verify and evaluate the data and carry out an efficiency calculation.

Red warning strips on the rotor blades and white flashing lights on the nacelle serve to alert aircraft to the presence of a wind farm at an early stage during daylight hours. At night, red warning lights can be seen on every wind turbine. The rules concerning these are laid down by the approval authorities. The lights are installed at hub height so as not to impinge on people’s field of vision in their everyday lives. When the wind is blowing in certain directions, the rotor blades spinning past the wind turbine’s lights can cause the viewer to see a continuous flashing. The turbines within a wind farm are synchronously controlled so that the viewer sees all turbines flashing at the same time.

New legal regulations and innovative technologies are now putting an end to the permanent lighting of wind turbines in Germany. EnBW’s wind turbines will also no longer have red lights in the future. The only exception being when an aircraft approaches at an altitude below 600 meters within a six-kilometer radius of a wind turbine. Then the flashing lights mounted on the nacelles or on the towers are used to draw attention to the obstacle until the aircraft has left the six-kilometer radius or climbs to a higher altitude. By the end of 2022, the Federal Network Agency states that an ADLS must be installed on all wind turbines in Germany taller than 100 meters. This affects virtually every turbine. (Source: Aircraft detection lighting systems on wind turbines)

Germany has 30 years’ experience of wind energy. Within the local communities, there is no evidence whatsoever of a higher incidence of health problems. Another sign of the acceptance of wind turbines: Approval is highest in the regions that have the greatest experience of wind power.

Wind turbines are subject to an approval process in line with immission control regulations. EnBW builds and operates its turbines in a way that prevents any adverse environmental impact and averts dangers or significant detriment and inconvenience to the general public and the neighborhood.

The latest scientific findings confirm that the infrasound from wind turbines essentially has no harmful effects. Compared to methods of transport like cars or planes, the infrasound generated by wind turbines is low.

This is also the conclusion reached by the LUBW (Baden-Württemberg State Institute for the Environment, Measurements and Nature Conservation). Interim findings from the measurement project “Low-frequency noise and infrasound from wind turbines and other sources” show that the infrasound level in the vicinity of wind turbines is well below the human perception threshold even at a close range of between 150 and 300 meters. It has also been established that when a wind turbine located 700 meters away is switched on, the measured infrasound level no longer increases appreciably. The infrasound is then essentially generated by the wind itself rather than by the operation of the turbine.

“The LUBW’s studies to date prove that the issue of infrasound is not an obstacle to the expansion of wind power capacity,” said Environment and Energy Minister Franz Untersteller.

Source: https://www.lubw.baden-wuerttemberg.de/

A distinction must generally be made between audible sound and low-frequency, inaudible, infrasound.

The “noise” of the rotors can be heard in the immediate vicinity of wind turbines during operation. A wind turbine’s sound radiation is not constant, but heavily dependent on the speed of the rotor and other rotating components. Noise emissions therefore change with the wind speed and wind direction.

The sound power level of a wind turbine relevant for immission purposes (almost maximum sound power level) is measured in accordance with FGW guidelines (Federation of German Wind Power and Other Renewable Energies) at a wind speed of 10 m/s. The report then assumes unimpeded sound propagation on flat terrain. In reality, such unimpeded sound propagation is a rare occurrence and thus represents the “worst case.”

If the wind turbine reaches its rated output and thus its maximum noise immission level, the wind-induced ambient noise at the immission locations is also louder and generally masks the turbine noise.

For wind turbine noise forecasts, the worst-case scenario is assumed to be during the loudest hour of the night with the sound traveling in the same direction as the wind at a temperature of 10°C and 70% humidity.

Guideline values based on how the area has been classified must not be exceeded, in accordance with noise control regulations (TA Lärm). The table below shows the immission guideline values for each usage area. These limits must not be exceeded.

The development plan specifies the kind of area involved in each individual case.

Infrasound is defined as frequencies between 0.1 and 20 Hz (hertz), while low-frequency sound is classified as below 100 Hz.

The shadows cast by the turbines are taken into account in the course of the approval process. This involves an independent surveyor assessing the site when the sun is shining. There are legal limits throughout Germany that must be observed. They state that the shadows cast by wind turbines on residential buildings should not exceed 30 hours per year and 30 minutes per day. These are theoretical figures. In practice, the sun doesn’t shine as often as in the theoretical scenario. Accordingly, the actual impact under “normal” conditions only amounts to around a quarter of the theoretically calculated figures.

If the aforementioned immission guideline values are forecast to be exceeded, the wind turbines can be equipped with a shadow flicker management system, which is deployed depending on the position of the sun and weather conditions. They then automatically shut down if the values are exceeded.

As a standard feature, each turbine can detect when ice has formed on the rotor blades due to poorer aerodynamics. The turbine’s performance curve then deviates from the standard. If both the measured meteorological values and the wind turbine’s changed performance curve indicate ice formation, the turbine automatically shuts down. It can only be started up again by the wind farm manager once he or she has carried out an on-site visual inspection to confirm the absence of ice.

Ice sensors installed on the turbines prevent ice throw while they are in operation.

Frost can form on stationary turbines like it does on streetlamps. This can then fall from the rotor blades.

EnBW commissions the following project-specific reports. Some of these reports are required by law.

• Wind/yield report
• Avifaunal report (a report that examines the behavior patterns of endangered bird species)
• Faunal report (a report that examines the behavior patterns of endangered animal species)
• Bat reports
• Landscape conservation support plan
• Flora, fauna and habitat impact assessment with preliminary assessment
• Visualization report / visual shadow analysis (assessing the turbines in terms of their impact on the landscape)
• Preliminary environmental impact assessment / EIA (if necessary)
• A report on measures designed to offset any disruption
• Noise report
• Shadow report
• Turbulence report
• Stability survey
• Ice throw report
• Soil /building site report
• Information on fire protection and occupational safety
• Archaeological report / supervision during construction
• Ecological supervision during construction

Depending on how they are used, forest areas are just as valuable natural spaces as open land areas. A minimum distance of 200 meters must generally be maintained between wind turbines and protected forests. Nature reserves or forests with certain protective roles may also only be used to a limited extent. Wind turbines can be built in a close-to-nature forest like the Brüchlinger Wald, which has been used commercially for generations. Such locations must be carefully selected and surveyed. This is happening at the moment.

Particularly in Germany’s southern states (Baden-Württemberg, Hesse, Rhineland-Palatinate), more and more wind turbines are being built in forests. The reason for this lies in technical developments. New turbines generally tower above the tree population (total height over 200 meters), which means that there is no conflict between turbines and trees. In addition, forests are usually further away from residential developments, which means that the required distances can be maintained. Another potential for conflict – the bird species that are sensitive to wind energy (such as the red kite) – occurs less frequently in the forest because these birds tend to hunt over open land (e.g., fields). In turn, bats are a more common sight (see the article Wind energy in forests / Source: umweltbundesamt.de).

Forest projects must also be examined for approval in line with immission control regulations. Legal issues surrounding forests, such as reforestation and compensatory measures, are also taken into account. (See Wind energy in forests / Source: FA Wind)

Forest clearance is required for the foundations and crane placement areas. Experience has shown that 0.5–1.0 hectares of land need to be cleared for each turbine, including land for any access roads. It goes without saying that nature conservation is a high priority at EnBW. That is why a prerequisite when planning the layout of a wind farm involves ensuring the smallest possible intervention in the forest land. In accordance with the Forest Act (Landeswaldgesetz), compensatory measures must be taken in the same natural area that has been cleared.

Depending on the type of turbine and manufacturer, around 350–600 square meters of land are needed for the foundation area of a wind turbine. Such foundations have a lasting adverse effect on soil function. However, only around 100 square meters of land – the section on which the tower is built – are visibly sealed. The remaining area will be covered with topsoil or gravel during the operating phase. A partially sealed or graveled crane footprint measuring approximately 0.15 hectares per turbine is also needed for both the construction phase and to carry out any later repairs. In addition, a further 0.25 hectares are needed for access, although existing roads and paths are used wherever possible. A wind turbine requires approximately 16.5 hectares of land throughout its lifetime, although only 3% of this area (less than half a hectare) is fully or partially sealed on a permanent basis. (Remarks on the space needed for wind energy / Source: KNE)

Animals such as deer, foxes and hares are not negatively affected by the wind turbines. A three-year study by the Hochschule Hannover reached this conclusion. Before a wind farm is approved, comprehensive reports on environmental protection and conservation must be commissioned at the potential site. This involves experts conducting an assessment of the fauna. They analyze the site in the course of regular inspections. In the preliminary planning stages, distances to areas particularly worthy of protection such as bird sanctuaries or nature reserves are taken into account. This also covers bats and the red kite. Where there are endangered bat species, the approval authority often stipulates that the turbines must be shut down at certain times of the night. During the migration periods of affected migratory birds, the turbines are also shut down during the day.

Decentralized energy generation is one of the declared aims of the energy transition. That’s because it makes sense to generate as much electricity as possible where it is actually needed. This improves security of supply and minimizes the expansion of transmission lines.

Wind turbines essentially consist of a tower, the rotors and the nacelle in which a generator is installed. The blowing wind sets the specially designed rotor blades in motion. The old flour mills worked in a similar way. In the rotor hub (this is the point where the rotor blades converge), the rotational motion of the rotors is used to drive a generator, which in turn produces electricity. Power generation works in a similar way on a bicycle dynamo. The turbines switch themselves on at a minimum wind speed of between 3 and 4.5 meters per second, depending on the type. They reach their peak output at a rated speed of 10 to 14 m/sec. In stormy weather, the turbine automatically turns the angle of its rotor blades out of the wind and shuts itself down. The rotors nonetheless continue to slowly spin while decoupled from the generator.

Generally speaking, wind power represents one of the most efficient ways to produce electricity. There is an inexhaustible supply of the “raw material” wind and it is free. About 50 percent of the energy that hits the rotor blades is converted into electricity. A gasoline engine in a car only converts a maximum of 40 percent of the energy.

Since the airflow rate is proportional and the wind energy is dependent on the square of the wind speed, the wind power is dependent on the third power of the wind speed.

Pwind = 0.5 * ρ * π * R2 * v3

Thus, the key factor in wind power is its speed.
If there is a threefold increase in the wind speed, the power increases by 3x3x3, or 27 times.

The air density of the air has a linear influence on the power. Cold air is denser than warm air. At the same wind speed, this means that a wind turbine delivers around 11% more energy at -10°C, for example, than at +20°C. Since the air density is also dependent on the ambient pressure, high- and low-pressure areas as well as the altitude of the site have an influence on a wind turbine’s yield.