Wind turbine and wind farm
A wind turbine usually means the entire wind power plant, with its main components being the nacelle, rotor, blades, tower and foundation. A wind farm is an area with several wind turbines usually connected to one another with underground cables. The turbines are then connected to the electricity network as a single entity.
A wind farm consists of wind turbines, maintenance roads, a 20 kV network of underground cables connecting the turbines to the wind farm’s own electricity substation, a substation, and a 110 kV overhead line built for connecting the wind farm to the national electricity grid.
The size and efficiency of individual wind turbines have multiplied in the past few years. Due to technological advances, improved aerodynamics and higher towers, the output of wind turbines has grown almost a hundredfold in the past 25 years.
To start up, a wind turbine needs a wind speed of 3.5 m/s. The plant’s output grows along with increasing wind speed. At wind speeds of over 25 m/s, the plant is usually stopped to avoid damage to the turbine.
Today, a new wind turbine normally has a horizontal axis and three blades, a nominal output of 2–4 MWh, and its tower height and propeller diameter are about 100 metres or even more. At the same time, the turbines have become quieter, they are able to better utilise weaker wind conditions, and their operational reliability has improved.
The tower of a wind turbine is made completely out of steel or concrete, or it may be a so-called hybrid with the lower part made out of concrete and the top part out of steel. The turbine’s hub height (the point where the rotor connects with the nacelle) is 120–140 m and the length of the rotor blade is about 60 m: the blade tip rises to a height of up to 200 metres.
Wind turbine foundations are designed according to the soil and substrate conditions in the area. The most common foundation method is a cast-in, reinforced concrete slab. The diameter of a concrete slab is about 15–25 metres. If the soil is not firm enough, it may be necessary to replace the mass and/or install piles underneath it. If the turbines are located on an intact rock area, the foundations can be anchored to the rock.
Gravel-surfaced maintenance road 6–12 metres wide are built for the construction and maintenance of wind turbines. Efforts are made to utilise any existing roads. When necessary, the road network is improved and new roads are built. Underground cables within the wind farm are located close to the roads.
The length of the rotor blades in the turbines are taken into account when planning the roads and their transport use. During the operation of a wind turbine, the wind power producer takes care of the maintenance of the roads and keeps them clear of snow. The roads also serve the landowners and other people moving in the area. Wind farms are not fenced off, with the exception of the substation.
The duration of the construction stage of a wind farm depends on the size of the farm. Normally, the construction takes 1–2 years. To start the construction work, trees are removed from an area of approximately 0.5 hectares per each wind turbine and possibly from the site of any new roads and the electricity transmission line.
In connection with the improvement and construction of the road network, installation areas are built adjacent to the wind turbine sites for the cranes required in the erection of turbines and for other equipment. The foundations are also built.
At the same time, the substation, underground cable network and the power line will also be built. Once the foundations and roads are ready, the turbine components can be transported to the site and the turbines can be erected. After that, the turbines will be connected to the network, tested and commissioned.
The technical service life of a wind turbine is 20–30 years, during which the equipment is serviced 1–2 times a year according to the turbine manufacturer’s maintenance plan. In addition to these regular visits, occasional maintenance visits will also be made to the turbines if there are any faults. After its service life, the wind turbine is refurbished, dismantled or replaced with a new one.
When a turbine is decommissioned, it can be dismantled using the same kind of equipment as in its erection. It is possible to remove the turbines from the area including their foundations, and the sites can be landscaped to blend in with the surrounding countryside.
Wind power provides jobs
The construction and operation of wind turbines provide jobs to local residents and bring investments and an added boost to many lines of business.
According to the Federation of Finnish Technology Industries, Finland’s 2,500 MW construction obligation by 2020 will employ 29,500 person-years, i.e. wind power provides 11.8 person-years of employment per every installed megawatt. Wind power pays about EUR 10,000–15,000 in municipal real estate tax per turbine.