Reesdorf Wind Farm

Critics argue that, because trees also sequester CO₂, it does not make sense to erect wind turbines in forested areas to generate climate-friendly electricity. As a general rule, we must reforest, to an equivalent extent, any land that we clear – either temporarily or permanently – for the construction of wind turbines. Overall, we actually plant more trees than we fell, because when offsetting, we must take into account that we are replacing mature trees with small, young trees. The forests we are reforesting are ecologically valuable mixed forests. This means that no forest is lost as a result of the wind turbines; on the contrary, wind energy promotes ecological forest regeneration in Brandenburg. Regardless of this, the amount of CO₂ that a wind turbine saves is many times greater than what trees can store.

Infrasound is one of the concerns about wind energy that has been raised most frequently by citizens’ initiatives in recent years. What is infrasound? Infrasound refers to particularly low-frequency sounds that the human ear generally cannot hear. Infrasound is omnipresent in our environment: the wind generates infrasound, as do ocean waves and thunderstorms. Artificial sources of infrasound include road traffic, air-conditioning systems and pumps. The cars and lorries travelling on the A9 motorway produce infrasound. Like most technical devices, wind turbines also generate sounds across a broad frequency spectrum, including low-frequency sound. However, the sound levels are so low that, even at close range, they are well beyond the limits of human perception and pose no potential health risk.

Heinz Rudolph, head of the Brandenburg State Fire Service Academy, recently told the *Märkische Allgemeine* that wind farms actually make forests “somewhat safer” (see *Märkische Allgemeine*). Among other reasons, the expert cites the fact that the access roads to the wind turbines can make it easier for the fire services to reach potential sources of fire in the forests.

Modern wind turbines are equipped with effective and tested fire safety mechanisms. Wind turbines, such as those we are planning at Reesdorf, are designed – right from the choice of materials used in the turbine – in such a way that a fire cannot spread within them. In addition, they are fitted with automatic and double-secured fire warning and suppression systems. If the sensors detect smoke, the turbine shuts down automatically. Furthermore, we must install additional access points for fire-fighting water in the forest – these will also help if a carelessly discarded cigarette triggers a forest fire.

Wind energy has undergone over 30 years of technological development since its inception – just like cars, wind turbines have become safer over this period and are now considered safe in terms of fire safety.

Wind turbines, such as those we are planning at Reesdorf, are fitted with smoke detectors and heat sensors that monitor the turbine continuously. If the sensors detect smoke or an elevated temperature, the wind turbine switches itself off automatically.

At the same time, the site manager is automatically notified, as is the fire service – via a direct line.
To prevent fires in the nacelle, the wind turbines are fitted with an automatic fire-suppression system. This, too, reacts to smoke and heat – and, in the event of danger, floods the interior of the nacelle with a gas that smothers the flames.

Should the fire in the nacelle prove impossible to extinguish, the fire service must prevent the fire from spreading to the surrounding woodland. To this end, we are constructing two new, additional fire-fighting water wells near the wind turbines. Incidentally, these wells also make the woodland safer from other fires, such as those caused by a discarded cigarette.

The wind turbines are fitted with a lightning protection system. If lightning strikes a rotor blade, the current is channelled via the lightning conductors on the rotor blades and the nacelle to the structural components of the nacelle. From there, the lightning is conducted on to the nacelle’s/tower’s lightning conductor, where it is channelled down the tower. Finally, the lightning current is discharged via the earthing system.

There is strong evidence to suggest that the fact that wind turbines act as lightning conductors also makes the forest as a whole safer, as lightning no longer strikes the surrounding trees.

To prevent fires from occurring in the first place, wind turbines have been continuously developed in recent years and have become increasingly safe. To ensure the turbines function properly, we must maintain them regularly.
 

The risk of accidents at wind turbines is very low: wind turbines are serviced every year or even every six months. As with cars, there is a TÜV inspection: every two to four years, the turbines are thoroughly inspected. This includes the supporting structures, the machinery – including the electrical equipment of the control and safety systems – and the rotor blades. The German Wind Energy Association (BWE) estimates that there are around 10 accidents involving wind turbines nationwide each year, including fires and damage to rotor blades or towers. With 30,000 wind turbines installed across the country, this is a very small number. And the impact on the surrounding area is generally minimal – quite unlike, for example, at a nuclear power station. BWE Managing Director Wolfram Axthelm recently illustrated just how small the risk is to *Der Spiegel* using a comparison: the liability insurance premium for a wind turbine is barely any more expensive than that for a moped (*Der Spiegel*, No. 19 / 4 May 2019, p. 20).

All potential bat roosts in the trees that are due to be felled are mapped by experts, and the entrances are sealed with a special device which allows the bats to fly out but prevents them from re-entering. Felling will only take place once there are no longer any bats in the roost in question. Bat boxes will be installed as compensation for all felled trees containing roosts and for all trees with potential to provide roosting sites.

In addition, the wind turbines are designed with automatic shutdown periods. This ensures that the rotors stop during the bats’ active phases. From mid-July to mid-September, the shutdown times are determined by the following parameters:

1. when wind speeds at nacelle height are below 5.0 m/s
2. when the air temperature in the wind farm is ≥10 °C
3. during the period from 1 hour before sunset to 1 hour before sunrise
4. when there is no precipitation

Wind turbines emit infrasound. These are sound frequencies that are so low that they are inaudible to the human ear. Bats, on the other hand, use ultrasound for navigation. This, too, is inaudible to the human ear, but because the frequency is particularly high. To ensure that bats are not adversely affected, wind turbines are designed with automatic shutdown periods. This means that the rotors stop when bat activity is expected. Between mid-July and mid-September, these shutdown periods are determined by the following parameters:

1. when wind speeds at nacelle height are below 5.0 m/s
2. when the air temperature in the wind farm is ≥10 °C, and
3. during the period from 1 hour before sunset to 1 hour before sunrise
4. no precipitation.

The special levy is imposed under the Wind Turbine Levy Act (BbgWindAbgG) of 19 June 2019. It is payable annually, throughout the operational life of the wind turbine, to the local authorities situated within a 3,000-metre radius of the respective wind turbine. The special levy amounts to 10,000 euros per wind turbine per year. It is paid by the wind turbine operator. If there are several local authorities within the 3,000-metre radius, the levy is apportioned according to their respective areas.

Modern rotor blades contain carbon fibres. In the event of a fracture, minute particles may be released and dispersed into the surrounding environment. Potential health risks have been investigated, including in a review study conducted by NASA.

If such particles enter the respiratory tract through inhalation, this can cause irritation. There is no carcinogenic effect. The particles are excreted within a few days to weeks via the body’s natural self-cleansing mechanism. Chronic exposure, however, could be problematic.
It is extremely unlikely that any significant concentrations of carbon fibre microparticles would result from a rotor blade fracture at all. Furthermore, any such exposure – for example, for rescue workers – would only be short-term.

In the event of a fire, toxic fumes may be released, comparable to those produced during the thermal decomposition of plastics. Compared with other technical installations, there is no increased risk. Furthermore, in the event of a fire, it would mainly be the nacelle that would be affected, rather than the blades.
 

This question depends on many factors and therefore cannot be answered definitively with a single figure. When it comes to felling, for example, it depends on what happens to the trees afterwards. If the timber is used in the long term, the carbon is not released as CO₂.

Furthermore, older trees store more carbon than young trees. The newly planted trees must therefore be allowed to grow for several years until they reach the same carbon storage level as the original forest. We must also bear in mind that we are clearing pine trees from a commercial forest, so trees are being removed and replanted here anyway.

In addition, during initial afforestation, a larger area is replanted than is cleared.

Furthermore, deciduous trees can store more carbon overall than conifers. As afforestation schemes primarily involve planting deciduous trees to replace the conifers that have been cleared, we anticipate a positive CO₂ balance overall, solely as a result of these forest conversion measures.

Irrespective of this, wind turbines have an excellent carbon footprint both overall and within the forest: according to the Stiftung Unternehmen Wald, on average one hectare of forest stores between 10 and 13 tonnes of CO₂ per year. [1] With an annual output of 25,680 megawatt-hours, the two wind turbines prevent more than 17,000 tonnes of CO₂ emissions each year (see ‘Emissions Balance of Renewable Energy Sources 2017’, Federal Environment Agency, and the CO₂ calculator, German Wind Energy Association).

[1] https://www.wald.de/waldwissen/wie-viel-kohlendioxid-co2-speichert-der-wald-bzw-ein-baum/
 

Approximately 1,226 m³ of concrete and approximately 165 t of reinforcement are required for a foundation.