ISET is responsible for tracking the performance of all turbines installed under Germany's 250 MW wind energy support programme. At the end of 1993 this accounted for some 55% of the turbines installed. In its statistics of downtime, ISET reports that control system failure was the most common problem, but as a rule could be repaired for less than DEM 1000. The expensive problems do not occur as frequently, but among these, lightning strikes resulted in repair bills averaging DEM 10,900 while storms caused an average DEM 12,000 worth of damage.
The institute also gathers data for studying wind energy finances. Average annual operating costs, including repairs, maintenance, insurance and land leases, amounted to 3% of the wind turbine's purchase price.