How long should the turbine last and how much maintenance is required?

Once installed, the source of the power produced is free. However, it should be remembered that the turbine is not free and the actual unit cost of the electricity produced is equal to the total costs of the turbine over its life-time divided by the amount of useful units it supplies (neglecting any payment for export to the grid).

Clearly it is important to keep a turbine running for as long and as well as possible if the financial and environmental benefits are to be accrued. Maintenance costs are an important factor to remember. In principle, the best quality turbines have a working life of up to 20 years but their actual life expectancy depends very much on design, materials, the quality of the installation and maintenance as well as local wind and atmospheric conditions (e.g. coastal air, turbulence). Poor quality turbines may be destroyed in the first high gust of wind or after 2 - 3 winter storms. Equally, a good quality turbine which is poorly or incorrectly installed could be destroyed or damaged within a short period.

A supplier may offer a maintenance agreement or contract for a set period after the installation. Alternatively they may give an indication of what they might charge for a call out or regular service. Some turbines may not need to be serviced until a number of years (2-3) have passed since the installation. Manufacturer's guidelines should clearly state the maintenance schedule which will be in compliance with a warranty. Routine maintenance may simply be a case of greasing wearing surfaces and checking fasteners. Major maintenance may be required less frequently, for example a blade may need to be replaced after a number of years.

Because wind turbines are erected during the weather and wind conditions existing on the day they may need some fine tuning in the days or weeks following. For obvious safety reasons a turbine may be erected during a period of no wind and the installer or electrician may have to return to commission the system on a windy day to ensure everything is operating as designed. Furthermore some teething problems may be experienced in the weeks after commissioning. You need to be sure that you have chosen an installer that will respond to your requests for a site visit under these circumstances. Getting the view of existing customers is one way of gauging a supplier's customer service.