The costs of onshore wind energy are almost 50 per cent lower than those of offshore wind power. But how can planners and operators identify the most suitable inland sites and reliably estimate energy yields? On behalf of Germany's most south-western state, the experts from TÜV SÜD prepared a wind atlas offering unprecedented data quality.
In spite of the ambitious targets defined by the German government, the expansion of offshore wind energy in Germany is progressing only slowly at present. According to a study by the North German market research institute wind:research, at the current rate of expansion wind power capacity will fall short of the 25,000-megawatt (MW) target planned for 2030 by almost 10,000 megawatts. The slow expansion is due to a host of reasons. In some areas, connection of wind farms to the grid has come to a standstill. This is partly due to a lack of the special ships and experts needed to anchor the foundations on the sea bed. In addition, in Germany offshore wind farms are generally not planned in the vicinity of protected coastal areas, but farther out in deeper waters. However, longer cable routes and transport distances also mean higher costs.
For onshore wind power, by contrast, a current study carried out by Fraunhofer Institut on behalf of the German Wind Energy Association (BWE) demonstrates that suitable wind power sites are available across Germany and are not restricted to the northern German states. According to this study, allocating only 2 per cent of Germany's land area for onshore wind power use would be enough to cover 65 per cent of its electricity demand.
Making full use of the potential of wind
Given this, investors and operators are increasingly focusing on southern Germany, in an attempt to identify sites which offer high wind speeds and environmentally compatible yet profitable wind farm realisation. The necessary technologies have been available for years: turbines with hub heights of over 100 metres can reach layers of air offering high winds but low turbulence, turning even forest areas into potentially attractive wind-power sites.
But how can investors and planners focus on identifying the best sites? Practical experience shows that systematic inventories of existing wind potential are still missing in many instances. Against this backdrop, Baden-Wuerttemberg's State Ministry of the Economy commissioned TÜV SÜD's impartial experts to draw up a wind atlas. The experts mapped the entire area of the German state to a degree of resolution which takes the quality of wind-farm site data to new levels.
Relying on a wide variety of different data sources
Close cooperation with regional operators, wind-turbine manufacturers, associations and ministries is critical for the success of such a project. Within the scope of this cooperation, in the run-up to the project the experts must clarify which data will be required and who can supply them. Landscape models, topographical models and maps are some of the methods used for modelling the topography of the land. The higher the data density, the more precise the calculations.
Meteorological measurement stations generally supply long-term meteorological data that provide valuable information for wind mapping. State institutes, independent organisations and private companies also sometimes provide wind measurement data. The context in which these data were originally collected is of minor importance. They can be compared with the calculations used in wind mapping, thus ensuring additional accuracy.
Wind turbine operators can also supply the energy yields of their wind turbines as further important reference data. Within the context of a wind atlas, the energy yield can be used to validate the determined data. In case of sufficient data density, the energy yield may also be used to generate additional input data. On-site inspections permit wind experts to verify the available information. To do so, the experts use photo documentation and detailed descriptions of the environment, identify site coordinates by means of GPS (Global Positioning System) and document available measurement systems.
However, wind mapping of inland areas also involves special challenges. In contrast to coastal areas, the relief structures have a major influence on the near-ground wind field, adding complexity to the task of spatial modelling of wind speed. To ensure efficient modelling, the TÜV SÜD experts calculated the wind atlas of Baden-Wuerttemberg in two phases.
In phase 1 they prepared a wind map with a resolution of 250 x 250 metres at a height of
100 metres. This map was designed to identify areas exceeding the wind-speed threshold of 5.3 metres per second. Sites offering this wind speed or higher are considered profitable for electricity generation. In phase 2, these areas were then calculated in detail to a more precise resolution of 50 x 50 metres and heights of up to 140 metres. To do so, the experts used two different software models individually aligned to the respective conditions.
Results show high wind sites
As the wind atlas demonstrates, Baden-Wuerttemberg offers wind speeds of over 5.3 metres per second (at a height of 140 metres) over a total area of 18,050 square metres, corresponding to roughly 50 per cent of the entire area of this German state. A comparison of the results achieved at different heights underlines the potential: as little as 40 metres in extra altitude can double the number of sites suitable for wind farms
For specific sites, further analyses and assessments become necessary and are carried out within the scope of a wind report. Following the successful selection of a site, steps must be taken to ensure safe and reliable wind-farm construction and compliance with the legal requirements related to immissions, nature and landscape conservation. Opting for comprehensive due diligence permits operators and investors to cover themselves against possible risks. Due diligence assesses the economic framework conditions, the operating costs and the achieved energy yields and reviews immission forecasts, permits, contracts and approvals.
Baden-Wuerttemberg plans to build another 150 wind turbines by 2020. This expansion is necessary in order to increase annual wind power capacity from 0.6 terawatt hours (TWh) in 2009 to at least 1.2 TWh in 2020, as envisaged by Baden-Wuerttemberg's energy scheme for 2020. Onshore sites offer the additional benefit of taking some of the pressure off the expansion of cross-regional grids and promoting more cost-effective decentralised energy supply. This trend complies with the forecast of the European Wind Energy Association, according to which 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 regenerative energies.
An increasing number of German states are opting to draw up a comprehensive inventory of their potential wind-power areas. Systematic wind mapping offers a standardised data foundation for regional planning, taking the identification of areas which are particularly suitable for wind-farm projects to a completely new level. At the same time, it supports investors, planners and operators in identifying attractive sites and estimating amortisation periods. The independent TÜV SÜD experts have long-standing international experience, supporting wind projects across the world from planning to construction and operation.
Dipl.-Ing. Peter Herbert Meier, Wind Cert Services, TÜV SÜD Industrie Service GmbH, Regensburg
TÜV SÜD Industrie Service GmbH
Wind Cert Services
Tel./Fax: +49 (0)941 460212-0 / -29
About the author:
Peter Herbert Meier, born1970, studied environmental engineering and majored in energy technology. As project manager and lead project engineer, Mr Meier has long-standing experience in the assessment of wind-farm sites, wind measurements and the assessment of wind potential for industry and research. He specialises in the assessment of turbulence and extreme winds and the optimisation of wind-farm layouts, looking back on a successful track record in numerous national and international projects. In 2009 Herbert Peter Meier became Head of Wind Cert Services at TÜV SÜD Industrie Service.