Can wind farms and forests mix?

Forests were previously no-go areas for wind developers as trees reduced wind speeds and caused unstable wind conditions, making wind farms less efficient. However, Peter Herbert Meier from TÜV SÜD Industrie Service takes a look at how forestry land in Germany is moving into the focus of wind farm planners as modern technologies enable the environmentally and socially sustainable development of new wind farm sites. He examines what aspects planners, investors and operators must consider to ensure an efficient approval process and smooth operation.
Can wind farms and forests mix?

While forests were considered absolute 'no-go' areas for wind turbines only a few years ago, forest wind farms have now become reality in many German states. Not only does onshore wind power still cost roughly 50 per cent less than electricity from offshore wind farms; in addition, onshore wind farms use field-proven technology, thus involving lower investment risks. Last but not least, onshore wind farms do not face the significant challenges of wind farms located in deep-sea areas, including extreme weather conditions.

On top of these advantages, we need to develop new sites onshore if the targets for the expansion of wind power set by the German government are to be reached. A study conducted by the German Fraunhofer Institute proves that as little as two per cent of Germany's land area would be sufficient to generate around 189 gigawatts of power, enough to cover over half of Germany's electricity demand. To exploit this potential, we must identify additional priority areas throughout Germany.

Wind potential of forest sites

Southern Germany is only just beginning to tap into its wind potential. Many attractive sites can still be found, particularly in commercial forests. The mitigated visual impacts of the turbines and their greater distance from residential areas minimise the impacts of possible noise emissions and shadow flicker. Due to their decentralised locations, connection to the regional grid is cost-efficient and relieves some pressure in the urgency of expanding and extending cross-regional grids. In addition, existing forest roads can be used for site development in many cases, keeping both costs and the required deforestation to a minimum.

High hub heights and large rotor diameters enable wind farms at inland sites in southern Germany to operate profitably. At a height of 120 metres, annual mean wind speeds reach up to between 5.5 and 7 metres per second even in Bavaria and Baden-Wuerttemberg. These high-wind layers of air are also high above the tree crowns of the around 11 million hectares of German forests – mainly spruce, pine, beech and oak with average heights of between 15 and 30 metres. This leaves a large number of possible sites unused so far.

Reliable assessment

Comprehensive and thorough assessment of potential wind-power sites is important for planners and investors to make full use of the available potential. Important aspects that must be considered include the forest growth structure in terms of diversity, average stand heights, tree density, spacing and tree crown width. Exact measurement of wind parameters is possible with state-of-the-art laser systems. Quasi 3D modelling, which considers the wind speeds measured at various altitudes and the air turbulence in different zones, is then used to determine the wind-flow conditions. Seasonal changes, storm damage and pest infestation are other aspects relevant in this context.

Reliable wind reports are indispensable for robust site assessment. TÜV SÜD's experts not only include the type of wind turbine and the geographical coordinates of the planned site in the report, but also the energy yield data of existing wind farms in the vicinity and/or the wind speed measured at the site. The result of the wind report includes the forecast mean wind speeds and the expected annual yield. These two variables ensure reliable assessment of the wind farm potential, taking identified uncertainties into account.

In practice, successful site selection is based on further analyses which TÜV SÜD's wind experts can carry out with an accuracy to one metre. In the next step air-pollution control, nature and landscape conservation laws must be taken into consideration. Operators can cover against possible risks by opting for comprehensive due diligence. Due diligence looks at the economic framework conditions and operating costs but also at contracts, supply commitments and yield forecasts. The ultimately critical question for owners and investors is whether a wind farm can reliably deliver a sufficient amount of electricity.

Legal criteria at a glance

From a legal perspective, the protection of species and forest law in particular must be taken into consideration in forest wind farm approval. Within the context of the German Wildlife Conservation Act, for example, possible impacts on bats, birds and insects are of relevance. While these issues make the approval procedure more challenging, forest wind power stations are not inadmissible per se. In fact, these aspects must be analysed in a site-specific approach as the application of legal requirements is generally case-specific.

According to the applicable forest law, for example, a 'forest conversion permit' is required before a wind farm can be erected on forestry land. Such a permit can be granted for a limited or unlimited period of time and is required for every change in land use, such as from forestry to non-forestry type of use. This applies to the construction of a wind power plant but also to the installation of cable lines, transformer stations and construction-site infrastructure, the construction of access roads and the clearing of areas required for the cranes. Where existing forest roads can be used for these purposes, such a permit is not generally required.

Air-pollution control and state law

Wind turbines higher than 50 metres generally require approval under the Air Pollution Control Act. This requirement basically applies to all modern wind turbines. Approval under the Air-Pollution Control Act normally covers all individual approvals required, e.g. also the conversion permit. Compensatory measures in the area of nature conservation and forestry management also must be taken into account. Possible solutions include compensatory afforestation in other areas, the planting of shrubs and deciduous trees under conifers, management of biotopes and forest conversion.

If access roads, construction site infrastructure or cable routes exempted from approval under the Air-Pollution Control Act are applied for separately, the approval procedure is subject to state law. Access roads, for example, frequently require building permits. While building permits cover all other required permits in some German states, a conversion permit may have to be applied for separately in others.

Consideration of conservation categories

The special issues following from the various forest conservation categories must also given consideration. These too may differ depending on the German state. Generally no two forests are the same. The broad range of forest types and their variety of characteristics must also be taken into account in the use of wind power. Does the forest site under consideration fulfil the function of a conservation or recreation area? Where in the region is it located and what significance does it have for the region?

Environmental and social sustainability considerations of wind farms are moving further into the foreground and are taken into account by experts in planning. As part of the eco system, forests also play a special role in supra-regional climate protection and the environment. They filter dust out of the air, compensate for differences in temperature and offer protection against noise and visual protection. In practice, the significance of a forest area always depends on the specific weighting of individual aspects in the overall context.

Specific conservation regulations play a crucial role in individual assessment. Influencing factors include firstly the wind farms' intensity of action, and secondly the sensitivity of the conservation areas. In this context, the intensity of action of the wind farms depends on factors including turbine design, the number and arrangement of the wind turbines and parameters of wind turbine construction and operation. The sensitivity of the conservation area may depend on factors including the distribution of species in their specific habitat.

Case studies: Bavaria and Baden-Wuerttemberg

The Fasanerie wind farm in the Bavarian Vogtland region, for which the experts at TÜV SÜD provided the relevant expert reports, is one example of a successful forest wind farm project. The first forest wind farm in Bavaria to be connected to the grid, in late 2010, it has since produced 22.5 million kilowatt hours of electricity per year. Five wind turbines with a hub height of 138 metres and rotor diameters of 82 metres supply 7,500 households with electricity, saving around 17,500 tonnes of CO2 per year.

From an early stage, the project planners included the local residents, municipalities, authorities and property owners in the planning of the project.

The success of the project proves that balancing profitability and sustainability is possible if acceptance is high among all stakeholders.For forest wind sites, for example, the required deforestation measures must also always be taken into account. On average, the foundation, crane and assembly require an area of between 1,350 and 2,400 square metres per wind turbine. In addition to compensatory afforestation, bank guarantees for the costs of final dismantling ensure that the original condition of the site will be restored at the end of the roughly 20-year service life of the wind turbines.

At present, experts are assessing around 100 locations in Bavaria alone on land owned by the Bavarian State Forest Enterprise (Bayerische Staatsforsten) for their suitability as future wind farm sites. In addition, an increasing number of German states are opting to draw up a comprehensive inventory of their potential wind-power areas. On behalf of the Ministry of the Environment of Baden-Wuerttemberg, for example, TÜV SÜD's experts drew up a comprehensive wind atlas for Germany's most south-western state. The wind atlas supplies regional planners with the first standardised set of data, helping planners and operators to identify the most suitable sites and ensure reliable yield assessment.


The expansion of wind power capacities in forest areas offers major opportunities and contributes significantly to establishing cost-effective decentralised power supply. According to forecasts of the European Wind Energy Association, onshore wind energy will produce the lion's share of energy from renewable sources in Europe by 2020 and continue to be the most cost-effective of all types of energy from renewable sources. TÜV SÜD's experts have long-standing experience and offer impartial support in all issues of wind-farm development.

[Inset: Photo of the Wind farm Simmersfeld, Northern Black Forest (Germany). Courtesy of Friedemann Lichtner, MFG Management & Finanzberatung AG, Karlsruhe]

[Editor's note: This article was kindly provided by Peter Herbert Meier, Head of Wind Cert Services at TÜV SÜD Industrie Service. Mr Meier has long-standing experience in the assessment of wind-farm sites, wind measurements and the assessment of wind potential on behalf of industry and research. He specialises in the assessment of turbulence and extreme winds and the optimisation of wind-farm layouts.]

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TÜV SÜD Industrie Service

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