17.01.2019 | The high mountains offer less than ideal conditions for wind power
The Swiss Alps, 4 a.m., a metre of new snow at minus 15 degrees, and an average wind speed of 35 km/h - the windmill stops! The halt is necessary. A major repair under these conditions would otherwise not be possible. Wind power in the high mountains presents special challenges for operators. However, power from the mountains also has its advantages.
Switzerland is not a typical wind country. Nevertheless there are some suitable locations: Mainly in the Pre-Alps and Alps in addition to the Jura Mountains and the Western Midlands. Although wind-rich locations in the high mountains offer potential, they also pose restrictions owing to the challenging topography and weather conditions.
Many roads lead to Rome, but only one to the high mountains
Locations high up on mountain ridges are ideal in terms of wind exposure, but they are often unsuitable due to their inaccessibility - from a technical, economic, and, last but not least, ecological viewpoint.
For construction and major repair work heavy transports by lorry must be possible to the site. The windmill is delivered to the site in sections and erected with the help of a crane. The ring generator alone weighs 63 tonnes in gear-less plants. No helicopter in the world can carry this weight. The rotor blades measuring up to 78 metres in length can be erected thanks to special swivelling devices mounted on the lorries. Transporting the equipment up the curving alpine roads to the top requires absolute driving precision.
Locations that are already accessible for tourism are suitable for wind power plants where it is possible to take advantage of synergies to existing roads, railways and power lines. Tourist regions can use the produced power locally for the operation of mountain railways. Building new access roads that must remain open for maintenance and repair work after construction is a huge effort and very costly - and ultimately requires intervention in the natural landscape. This negatively impacts the economic feasibility of a plant, and diminishes the acceptance of a wind power plant from a land conservation perspective. In contrast, the conflicts in high mountains areas, for example shadow casting, noise or the impact on bat populations, are fewer than in the lowlands because the plants are not near residential areas, or are located above bat habitats.
Wind production in the Swiss mountains is attractive owing to the cold temperatures at high altitudes. Taking physics: Cold air is heavier than warm air, which is positive for wind production. Energy volumes depend on air density in addition to the rotor blade surface and wind speeds. The "heavier" the air, the more energy the plant can produce. Taking into account decreasing air pressure with increasing altitude, the low temperatures have a positive effect.
However, what is good for power production is also a huge challenge for the plants. The harsh, unpredictable weather conditions in the Alps must be taken into account during construction during the summer months. High wind speeds from 8-10m/s or suddenly occurring, thick fog can delay crane work time and again.
In the winter half-year rotor blades can ice up. When this occurs, the turbine must be shut down immediately because the additional weight can cause damaging vibrations. Falling chunks of ice also represent a danger to human beings and the environment. In the course of the year, production outages due to icing can amount to 20% if the appropriate countermeasures are not in place, a phenomenon familiar in wind power plants located in the lowlands in northern regions. There are some solutions. Blade warmers that function like a dryer inside the rotor blades are automatically activated by means of sensor technology as soon as the plant shuts down due to icing. Adding hot air can decrease the outage time. The constant, preventative use of blade warmers would, however, not be feasible because their use massively decreases the performance of the plant.
«Axpo would like to realise more wind projects in Switzerland»Christoph Sutter, Head New Energies Axpo
Major repairs that require an additional crane cannot be carried out during the winter due to the snow. Snowmobiles or snowcats are used for regular service work. Plant reliability is particularly important in alpine locations. As a result, the use of proven plant types is preferred over new prototypes.
The Axpo wind farm "La Peñuca " with an installed capacity of 33 MW is located at 1000 metres in the Spanish mountains - one of the highest wind farms in Spain. There is often up to three metres of snow up there. A snowmobile is used to get to the location to carry out maintenance work.
Axpo has wind farm portfolio with a total capacity of over 400 MW, whereby the focus is on onshore wind farms in wind-rich locations in Germany, France, Italy and Northern Europe.
Axpo is investigating suitable locations at high elevations in Switzerland. According to the Energy Strategy 2050, wind energy plants will be producing 4000 GWh of power by 2050 - about forty times more than today. With these expansion targets in mind it makes sense to use the available potential in alpine regions. "Axpo would like to realise more wind projects in Switzerland. Wind power in the Alps ideally complements hydropower. The energy is mainly produced during the winter, while hydopower is primarily produced in summer," explains Christoph Sutter, Head of the New Energies division at Axpo. However, the permit process in Switzerland is lengthy and the chances of success often difficult to assess. It is often the permit process that makes wind power projects fail, rather than the challenging Swiss alpine topography.
Before an ideal location is evaluated, the actual wind conditions must first be measured. For larger offshore or onshore wind farms, e.g. in Germany, measurements are often carried out solely with computer models without using wind mast measurements. Based on the relatively constant wind conditions (offshore) or the many existing wind power plant locations (onshore), a good location can be extrapolated from one location to the next. This is not possible in the Alps because wind conditions vary strongly in this complex landscape.
Measurements have to be carried out by means of wind measurement masts at the foreseen location and at the precise hub height for at least a year in order to collect reliable data.