Operation and Maintenance Costs for Wind Turbines Modern wind turbines are designed to work for some 120 000 hours of operation throughout their design lifetime of 20 years. That is far more than an automobile engine which will generally last for some 4 000 to 6 000 hours. Operation and Maintenance Costs 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 per cent 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 cent 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, usually around 0.01 USD/kWh. The reasoning behind this method is that tear and wear on the turbine generally increases with increasing production. Economies of Scale 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 per cent of the price of the turbine. Project Lifetime, Design Lifetime The components of Danish wind turbines are 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, as explained in the page on turbine design and fatigue loads. Offshore turbines may e.g. last longer, due to low turbulence at sea. This may in turn lower costs, as shown in the graph on the page on the Economics of Offshore Wind Turbines.
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