Only two per cent of Germany's land area would be enough to meet 65 per cent of the country's electricity needs from onshore wind turbines. But how can planners and operators find the best sites and systematically assess energy yields in practice? To make full use of the existing onshore wind energy potential, more and more German states are commissioning detailed wind mapping.
A study conducted by the German Fraunhofer Institute proves that potentially suitable sites for profitable wind power use are not limited to Northern Germany, but can be found throughout the country. According to this study, as little as two per cent of Germany's land area would be enough to generate around 189 gigawatts of wind power. This is sufficient to supply over half of Germany's electricity. In addition, wind power generated onshore still costs almost 50 per cent less than offshore wind energy. The farther off the shore, the higher both the technological challenges and the investment and maintenance costs. Very deep water of up to 40 metres and exposure to wind, waves and salt content make high demands on both construction and material. Offshore wind farms also need their own transformer stations and staffed service platforms.
While stakeholders engage in further improving offshore technology, the latest generation of onshore wind turbines already offer the possibility to develop new wind farm sites now. However, in practice determining the most suitable sites is frequently perceived as a challenge. Against this backdrop, TÜV SÜD's experts drew up a wind atlas for Germany's most south-western state. The project, commissioned by Baden-Wuerttemberg's State Ministry of the Economy, now offers the first standardised set of data to be used in regional planning.
Two-phase modelling
In contrast to the lowlands in Northern Germany, the near-ground wind field in southern Germany is characterised by a variety of relief structures, making spatial modelling of wind speeds considerably more challenging. Addressing these particular difficulties, TÜV SÜD's experts prepared the model in two phases.
In phase one, they mapped the entire land area at a resolution of 250 x 250 metres. This overview helped them to identify high-wind areas, because wind sites are considered profitable from a wind-speed threshold of 5.3 metres per second, when all other requirements are met such as access routes, grid availability, etc. and easy to build or improve.
In phase two of the project, the specialists then focused on the high-wind regions, preparing a second model at a resolution 25 times higher which permitted even more precise recording of hilltops and hollows. At the same time, the experts determined the wind speeds at two different heights: 100 and 140 metres. A comparison between the two sets of data demonstrates the potential: as little as 40 metres of additional altitude can double the number of sites offering high wind yields.
Using an extensive data base
The data underlying the wind atlas were developed in close consultation with the Ministry of the Economy. The objective was to clarify in the run up to the project which data would be required and who would be able to supply them. Close cooperation with associations, ministries, turbine manufacturers and regional operators ultimately proved critical for the success of the project, as a complex data base renders modelling more robust. In addition, higher data density means more accurate calculations.
In this context, modelling of the topography is of key significance. Digital landscape and topography models, topographic maps, boundaries and major towns offer especially suitable input data. Meteorological measurement stations and services generally provide meteorological data. State institutes, private companies and independent organisations can supply wind measurement data.
Existing wind turbines in the region are another important cornerstone of wind resource assessment. The figures for energy yield provided by operators can be used to validate calculations. In the case of sufficient data density, they can also be used to generate additional input data. On-site inspections permit verification of the gathered information.
High-wind sites in all corners of the German state
The wind atlas has raised the identification of areas in Baden-Wuerttemberg which are particularly suitable for wind farm projects to a new level. It showed that wind speeds of over 5.3 metres per second (measured at a height of 140 metres) exist across 18,050 square kilometres of land, i. e. roughly 50 per cent of the entire area of this German state. Given this, Baden-Wuerttemberg plans to build around 150 new wind turbines, increasing its annual wind power capacity to at least 1.2 terawatt hours by 2020.
In practice, the successful selection of a suitable wind power site is based on further analyses. Within the scope of a wind expert report, TÜV SÜD's experts carry out these analyses with accuracy down to one metre. Once a suitable site has been found, air-pollution control and landscape conservation laws must be taken into consideration. In-depth due diligence, addressing the economic framework conditions and operating costs but also yield forecasts and contracts, protects future operators against the potential risks involved in the construction of a wind farm.
Focus on forest areas
Commercial forests offer particularly attractive sites for onshore wind farms. Wind turbines reaching up to the high-wind but low-turbulence layers of air high above the tree crowns have existed for years. Today, hub heights of over 100 metres and larger rotor diameters generate wind yields which up to some years ago were only reached in coastal regions and exposed high-mountain areas.
At the same time, environmental and social issues continue to move into the foreground. Due to their remote locations, limited visibility and long distances from residential areas, forest sites minimise the impacts of possible noise emission and shadow flicker. The existing network of forestry roads can frequently be used for the development of a wind-farm site, reducing both costs and the level of impact on the forest.
At present, experts are assessing around 100 locations on land owned by the Bavarian State Forest Enterprise (Bayerische Staatsforsten) for their suitability as future wind farm sites. Last year, the largest forest wind farm in Bavaria to date went into operation. Impartial TÜV SÜD experts supported the project, providing third-party expert opinions. Today, the five Enercon E-82 turbines, with a capacity of two megawatt each, meet the electricity needs of 7,500 households, helping to save around 17,500 tonnes of carbon dioxide per year.
The expansion of onshore capacities offers major opportunities and contributes significantly to establishing a cost-effective supply of power from renewable sources. Extensive mapping can be used to make the existing wind potential accessible to both investors and operators. TÜV SÜD's impartial experts have international experience and offer support and assistance throughout this process.
Editor's note: Peter Herbert Meier works for TÜV SÜD Industrie Service GmbH's Wind Cert Services in Regensburg (Germany). Many thanks to him for contributing this article.
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