Replacing old turbines with new units - known as repowering - certainly looks attractive. The document cites data from Germany's wind energy institute DEWI in which ten 600 kW turbines at an average wind location generating about 11.05 million kWh/year are replaced with six 2 MW turbines generating around 35.84 million kWh/year. The old turbines, installed in 1996, receive EUR0.091/kWh. The new ones, installed in 2009, receive EUR0.102/kWh, according to the renewable energy act. The old turbines generated income of just over EUR1 million/year, the new project nearly EUR3.7 million.
Repowering difficulties arise if the old turbines were installed outside the areas that have since been prioritised through planning procedures for wind energy use.
The guidelines estimate that in Germany's three northernmost and windiest states, Mecklenburg-Vorpommern, Lower Saxony and Schleswig-Holstein, around 1 GW of wind turbines cannot be replaced at the same site because of planning conflicts. Repowering may also face hitches where an old wind station is owned by a number of investors with different interests. Turbine operators may resist dismantling a machine on their property for a repowering project elsewhere if site rent then has to be paid. The guidelines recommend that independent planning or legal firms mediate between the various interests.
Repowering starts to become economically interesting once a turbine has clocked up at least 10 years, the document notes. There are more than 6000 wind turbines that were installed before 1999, 55% of which have a capacity of 0.5-0.66 MW, and these are therefore potential candidates. Most of these were installed in coastal regions with the best wind conditions and will therefore achieve the most powerful repowering results. Turbines installed from 1999 tend to be larger, from around 1.5 MW, and are sited in inland areas with less attractive wind conditions, so the impact of repowering when using the currently popular 2 MW and 3 MW machines will be less pronounced.
By spring 2009, says the guide, around 50 repowering projects had taken place in Germany, with 530 machines being dismantled and replaced with nearly 300 new units. These figures reveals that, in the main, 250-600 kW machines were replaced with the larger 2 MW machines.