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Bioenergy villages: biogas sets the tone

In 2011 Baden-Württemberg was home to around 37 bioenergy villages, and several others are under construction or in the planning phase. Bioenergy villages produce all of their electricity and energy for heating locally from renewable resources such as maize and wood; electricity is mainly generated from biogas. The expansion of regenerative energies and the establishment of new bioenergy villages are at the forefront of efforts being made in the Lake Constance Bioenergy Region to provide a sustainable and environmentally friendly energy supply. The region’s regional energy concept also aims to increase the efficiency of biogas plants and upgrade them so that they can utilize waste heat. Despite the fact that the energy yield of biogas is lower than that of wind and solar energy, it is nevertheless well suited for supplying local electricity and heating needs. This is one of the reasons why most biovillages use biogas as their major source of energy.

Bene Müller, managing director of Singen-based solarcomplex AG © solarcomplex AG

In 2009, the Lake Constance Bioenergy Region became one of a total of 25 bioenergy regions in Germany, two of which are located in Baden-Württemberg. The Lake Constance Bioenergy Region includes the administrative districts of “Konstanz” and “Bodenseekreis” and is a particularly suitable area for setting up a regional regenerative energies network due to its vast agricultural areas. Eight bioenergy villages have already been set up in the Lake Constance region; they cover 100% of their electricity requirements and at last 50% of their heat requirements with bioenergy that is produced locally and hence they are predominantly CO2 neutral. “For me, bioenergy refers to the use of biogas, wood and rape oil for the generation of energy,” said Bene Müller, managing director of Singen-based solarcomplex AG, which coordinates the Lake Constance Bioenergy Region. The German Federal Ministry of Food, Agriculture and Consumer Protection funds the region with 400,000 euros for communication purposes.

Each biovillage has a block heat and power plant, in which a combustion engine drives a power generator and the waste heat is also used to supply heating to houses. Biogas is the major source of energy. In contrast to wind and sun, biogas is permanently available and can thus guarantee a constant supply of energy. “Our block heat and power plant only fails to produce enough heat for the village’s inhabitants during the winter period, which is why the bioenergy village of Lippertsreute close to Überlingen has installed a wood-chip heating system, thus doubling the village’s heat energy supply,” said Müller. The waste heat from electricity production is used to heat water, which is then piped through a 4-km-long supply line directly into schools, nurseries and 60 households for hot water supply and central heating. Other bioenergy villages have installed oil-heating systems as a backup during periods of high demand, for example the cold winter months, when the heat from electricity generation is not sufficient to meet demand.

Waste heat remains unused

While most biogas plants cover 80 per cent of the electricity requirements of a bioenergy village on average, the biogas plant operated by the village of Mauenheim (pop. 500) close to the city of Engen produces more than 900 per cent of its annual electricity consumption. Bioenergy villages often install solar panels on top of biogas plants, which produce excess energy that can be fed into public power grids. In contrast to electrical energy, heat energy cannot be transported across longer distances and it remains on site. Heat energy is nevertheless regarded as a very efficient means to utilize energy. However, many of the 30 biogas plants in the administrative district of Konstanz let the waste heat escape unused into the atmosphere. “The quantity of heat energy that escapes from a biogas plant every year is equal to the heat energy from several hundred thousand litres of heating oil,” said Bene Müller, going on to point out that it is possible to upgrade existing biogas plants so that the escape of heat is reduced or prevented altogether.

No bioenergy village without farmers

The bioenergy village of Mauenheim produces electricity from biogas and solar energy. The village produces nine times as much energy as it requires and feeds excess energy into public power grids. © solarcomplex AG

“Local farmers who are prepared to operate a biogas plant play an important role in bioenergy villages. They provide the feedstocks for the fermentation plant and the block heat and power plants,” said Müller who has already been involved in the setting up of eight bioenergy villages. Biogas is produced from energy crops that are turned into biogas by bacteria. This process leads to biogas that consists of 60 per cent methane, which is then used for the generation of energy in the villages' block and heat power plants. “In addition to the common maize monocultures, a large number of other plants, including sorghum, clover and alfalfa, can be fermented in biogas plants. An organic farmer from the High Rhine area, for example, grows maize together with sunflowers and peas together with vetches,” said the managing director of the Singen-based company. Müller believes that the use of food plants for the production of energy has rightly been criticized, but also considers it indispensable for the production of biogas.

Biogas plants need space

The huge areas required for the cultivation of the crops for operating bioenergy plants must not be underestimated. For example, the medium-sized 500-kilowatt plant in Mauenheim requires 1,600 tons of energy crops per year. These crops are grown near the village on an area of around 180 hectares. Intestinal bacteria contained in cow dung support the fermentation process. “It is worth mentioning that only the energy of the source substances is turned into biogas; valuable nutrients remain in the fermentation residues that are subsequently used to fertilize fields. Thus, the process is an almost completely closed nutrient cycle,” Müller pointed out. In addition, plants like these do not require us to destroy weeds; they can also be used for the production of energy. In addition to their ability to reduce energy costs, although this only pays off after a few years of operation, the popularity of biogas plants is mainly due to their carbon neutral operation. “The fermentation of plants only leads to the release of as much CO2 as the plants have bound during growth,” said Bene Müller.

Although biogas and wood-chip heating plants form the framework of bioenergy villages, they must not be overestimated. “In the long term, only 10 per cent of total energy requirements can be covered with bioenergy; plants’ ability to turn sunlight into biomass is far too inefficient to be able to achieve a greater percentage,” Müller said explaining that one hectare of maize produces around 20,000 kilowatt hours of electricity, photovoltaics (outdoor areas of solar panels) around 350,000 kilowatt hours and wind power as much as 3 million kilowatt hours per hectare. However, the excessive growth of energy plants would outcompete the cultivation of food. Larger towns that do not have access to large cultivation areas therefore need to tap other sources of energy. “In rural areas, biogas reveals its strengths as an environmentally friendly energy, where excess production compensates for times when wind and sunlight are in short supply. This is what biogas can do, no more and no less,” said Müller summarizing his thinking on the potential of biogas for the production of energy.

Further information:
Bene Müller, Managing Director
solarcomplex AG
Ekkehardstr. 10
78224 Singen am Hohentwiel
Tel.: +49 (0)7731/ 8274-0
Fax: +49 (0)7731/ 8274-29
E-mail: box(at)solarcomplex.de

Website address: https://www.biooekonomie-bw.de/en/articles/news/bioenergy-villages-biogas-sets-the-tone