Before, acceptance of onshore wind and the "not in my backyard" syndrome were widely seen as a limiting factor to onshore wind expansion in the southern states.
But last summer's decision to phase out nuclear power in Germany has gone hand in hand with a shift in opinion for previously anti-wind state governments, who have realised that locating onshore wind within their regions keeps investment, taxes and profits locally and reduces the bill for imported energy such as coal and gas.
Until now, the geographic spread of German onshore wind has been relatively lopsided. Around 80% of capacity is sited in the northern half of Germany and only 20% in the south. But now the southerly states of Bavaria, Baden-Wurttemberg, Rhineland Palatinate and Hesse are keen to become involved.
These regions have fewer wide-open spaces for siting wind farms than states such as Schleswig-Holstein in the north or Brandenburg in the east. But what they do have is forested areas, including large stretches used for industrial-scale wood production. The development of taller wind turbines - with towers of up to 160 metres that reach so far above the tree tops that their extra long blades still do not reach the top branches - the forests open up new onshore wind potential.
Germany's environment, nature protection and landscape legislation is strictly applied to forests as elsewhere, but even the remaining forested areas available allow plenty of potential for onshore wind.
The state of Bavaria has about 4,000 square kilometres of wooded areas that could be used for wind energy. It is aiming to install 1,000-1,500 wind turbines by 2021, according to its energy concept published in May 2011. Around 1,000 of these could be located in state-owned forested areas, says Helmut Brunner, Bavaria's agriculture minister. According to Brunner, the Bavarian forest authority has many suitable areas, and should play a leading role in Germany's switch to renewable energies. The new wind-turbine fleet is expected to generate 5-8TWh a year or 6-10 % of the state's electricity needs.
Bringing more onshore wind to southern Germany by installing wind turbines capable of using lower wind speeds and staying on the grid for longer can help reduce the need for new north-south electricity transmission lines and reduce fluctuations in electricity fed into the grid. The new turbines especially developed for inland sites can manage 4,000 full load hours or more a year, which is comparable with offshore wind, according to Germany's wind energy association, BWE.
Such new models include Vestas V126 3MW turbine with a rotor diameter of 126 metres and Enercon's E 115 2.5MW turbine with a 115 metre rotor, both targeted for low wind conditions. Both were launched at the Husum WindEnergy trade fair in September.
German wind developers are already gaining experience with wind power in forests. Juwi has installed 266MW in 22 forested locations in Germany owned by municipalities or forest authorities, including a 53MW wind farm using 2.3MW E-126 Enercon turbines on 138-metre towers in the Rhein-Hunsruck district in south-west Germany in 2011. Ostwind has installed six wind farms with a total 41MW in forests in Bavaria, and is developing a 50MW forest project in Brandenburg.
It is important to take into account the need to place wind turbines further apart when they are installed on very high towers, Juwi co-owner Matthias Willenbacher pointed out at the recent Husum WindEnergy trade fair. And using large rotor diameters and high towers along with a smaller generator may slightly worsen economic performance - to the tune of EUR0.003/kWh, he noted. But on the positive side, the higher number of full load hours and the longer periods of generation create a big plus for the electricity system as a whole, he stressed.
Wind farms in forests are no more difficult to install than in the open landscape, but the challenges are different, says Christoph Markl-Meider, a spokesman for Ostwind. "There is less space available for the installation work in the forest, but technical developments are under way to deal with these constraints," he points out. For example, cranes can be built into the side of turbines so a mobile crane is not needed.
Bavaria's state forestry authority welcomes the new activity. Wind turbines can be installed well away from housing, eliminating noise or blade shadow nuisance, and the forest byways used for forestry work can double up as access roads to the turbines, reducing the need for tree felling. The landscape is less affected when compared with wind turbines installed in open countryside, and the income from site leases can be ploughed back into forest work or paid to the state of Bavaria to the benefit its citizens, the authority says.
The Institute of Energy and Climate Research in Julich estimates that as well as generating around 18GWh per year, a 6MW wind farm using turbines on high towers can bring in up to EUR50,000 per year in local business tax and land-lease payments of EUR75,000.
But operating wind turbines with very high towers in forested areas is still new terrain for the wind sector. "Astonishing though it may sound, scientists know little about the dynamics of wind conditions up there," says the Fraunhofer Institute for Wind Energy and Energy System Technology (Iwes).
A team of scientists at Iwes installed a 200-metre wind measuring mast on a tree-covered hill near Kassel in central Germany in January to take measurements of wind speeds, turbulence and other meteorological data. It is Europe's tallest measuring mast for wind energy - double the height of conventional masts, according to Iwes. Rotor blades of modern turbines easily reach 200 metres, so this is more appropriate, IWES says.
Germany's federal environment ministry is supporting research on wind turbines in forests which also looks at the potential impact on bird life, such as the scare effect driving birds out of areas where turbines are sited or the danger of collision. Potential danger of bats colliding with the turbines is also an issue, although they usually hunt in open landscapes.
Bavarian government wind energy planning guidelines issued in December set out rules for when turbines must be switched off to reduce the number of bat deaths. Construction permits for turbines in forests must specify that the machines are switched off as necessary to ensure that bat death frequency is less than two individuals per turbine per year. The turbine nacelle must be equipped with monitoring equipment that operates when bats are most active: one hour before sunset to sunrise from April to August and three hours before sunset to sunrise from September to October.
Although Germany seems ahead of the field in using wind turbines in forests, other countries also have big plans in the pipeline. In January 2010, the Forestry Commission of Scotland issued details of four forestry regions to be explored for wind-energy potential. German developer PNE Wind, which won a tender for 150-200MW of wind capacity in central Scotland, reported at the Husum fair that permitting procedures are under way. "We hope to start building in 2014-2016," says PNE Wind spokesman Rainer Heinsohn.
In Norway, state-owned forestry enterprise Statskog signed an agreement with E.on Vind Sverige, the Swedish wind subsidiary of German energy giant E.on, for joint development of wind power in Norway in May. Both forests and mountain areas will be considered. The deal covers 200 turbines with a total capacity of around 600MW. Investment decisions will be taken in 2014/2015 at the earliest, with a view to commissioning the turbines in 2017, says Statskog.
Although there are as yet no wind farms operating in Statskog's forests, it also has a 25% stake in Norwegian wind developer Austri Vind - along with property firm Eidsiva Utvikling (50%) and Norwegian electricity company Gudbrandsdal Energi (25%) - which is also starting to develop projects in forest and mountain areas.
Clearly, the big potential for onshore wind in forests is only just beginning to be explored.