ECONOMICS

Installation/Operation/Maintenance


Installation costs
Installation of wind farmInstallation of wind farm        In general, installation costs include:
- Foundations, normally made of armed concrete
- Road construction (for moving the turbine and the sections of the tower to the building site)
- A transformer (for converting the low voltage, 690 V, current from the turbine to 10-30 kV current for the local electrical grid
- Telephone connection for remote control and surveillance of the turbine
- Cabling costs, i.e. the cable from the turbine to the local 10-30 kV power line.
        In the figure the Novar Wind Farm is shown in Scotland, under construction, on July 1997.





Installation costs vary
        The costs of roads and foundations depend on soil conditions, i.e. how cheap and easy it is to build a road capable of carrying 30 tonne trucks. Another variable factor is the distance to the nearest ordinary road, the cost of getting a mobile crane to the site, and the distance to a power line capable of handling the maximum energy output from the turbine.
        A telephone connection and remote control is not a necessity, but is is often fairly cheap, and thus economic to include in a turbine installation. Transportation costs for the turbine may enter the calculation, if the site is very remote, though usually they will not exceed some 10,000 euros (prices 1997).



Economies of scale (installation)
        It is obviously cheaper to connect many turbines in the same location, rather than just one. On the other hand, there are limits to the amount of electrical energy the local electrical grid can handle (look in Power quality page). If the local grid is too weak to handle the output from the turbine, there may be need for grid reinforcement, i.e. extending the high voltage electrical grid. It varies from country to country who pays for grid reinforcement - the power company or the owner of the turbine.


Operation and Maintenance costs
        Modern wind turbines are designed to work for some 120 000 hours of operation throughout their design lifetime of 20 years.Experience shows that maintenance cost are generally very low while the turbines are brand new, but they increase somewhat as the turbine ages. Studies done on the 5000 Danish wind turbines installed in Denmark since 1975 show that newer generations of turbines have relatively lower repair and maintenance costs that the older generations (the studies compare turbines which are the same age, but which belong to different generations).
        Older Danish wind turbines (25-150 kW) have annual maintenance costs with an average of around 3% of the original turbine investment. Newer turbines are on average substantially larger, which would tend to lower maintenance costs per kW installed power (you do not need to service a large, modern machine more often than a small one). For newer machines the estimates range around 1.5 to 2% per year of the original turbine investment.
        Most of maintenance cost is a fixed amount per year for the regular service of the turbines, but some people prefer to use a fixed amount per kWh of output in their calculations. The reasoning behind this method is that tear and wear on the turbine generally increases with increasing production.



Economies of scale (operation and maintenance)
        Other than the economies of scale which vary with the size of the turbine, mentioned above, there may be economies of scale in the operation of wind parks rather than individual turbines. These economies are related to the semi-annual maintenance visits, surveillance and administration, etc.


Turbine reinvestment (Refurbishment, Major Overhauls)
        Some wind turbine components are more subject to tear and wear than others. This is particularly true for rotor blades and gearboxes. Wind turbine owners who see that their turbine is close the end of their technical design lifetime may find it advantageous to increase the lifetime of the turbine by doing a major overhaul of the turbine, e.g. by replacing the rotor blades. The price of a new set of rotor blades, a gearbox or a generator is usually in the order of magnitude of 15-20% of the price of the turbine.


Project Lifetime, Design Lifetime
        The components of wind turbines are usually designed to last 20 years. It would, of course, be possible to design certain components to last much longer, but it would really be a waste, if other major components were to fail earlier. The 20 year design lifetime is a useful economic compromise which is used to guide engineers who develop components for the turbines. Their calculations have to prove that their components have a very small probability of failure before 20 years have elapsed.
        The actual lifetime of a wind turbine depends both on the quality of the turbine and the local climatic conditions, e.g. the amount of turbulence at the site. Offshore turbines may e.g. last longer, due to low turbulence at sea.