Biogas / Biomass

The University of Göttingen has a 5 % share in the biogas plant in Rosdorf and operates its own biogas plant on its own experimental farms in Relliehausen. In total, the university accounts for 2 million kWh of heat and 6 million kWh of electricity production flexibly tailored to demand.

The biogas plant in Relliehausen is used, among other things, as a research facility where, for example, application-oriented utilization concepts for the sustainable use of straw pellets for biogas production are tested. In Germany, cereal straw is a residual material with great unused potential. The available technical potential is estimated at around 8.5 million tons. However, it has not been widely used yet due to the additional yield often does not cover the additional costs. A more recent innovative approach is the use of pelletized straw. In some cases, caustic soda is added to the straw pellets to improve decomposition. Pelleting and upstream comminution of the straw initially represents a greater energy and financial outlay but offers a whole range of advantages over previous approaches for using straw in biogas plants. These can be summarized as follows: significantly increased transportability, significantly reduced storage space requirements, easy introduction into digesters with existing technology, no floating layer formation, and improved gas yields due to pre-shredding and pelletization. The use of straw pellets as a co-substrate in most existing plants is straightforward from a technical point of view. On the other hand, a major challenge of using straw pellets in biogas plants is the proper liquid management to avoid process disturbances in the plant. In theory, it can be estimated which straw proportions are possible. However, it is unclear which process biological and process engineering limits are set, so that practical experiments are necessary. Further experiments are described here (https://www.uni-goettingen.de/de/2022/663598.html).

The university, the Studentenwerk Göttingen and the UMG produce a lot of food waste. Therefore, in cooperation with the City of Göttingen, it was examined whether the construction of an own biogas plant for the utilization of the food waste would be economically efficient. This is not the case, because one would only get 7 kW of power from all the waste together. The reason is that our public utilities have such an excellent handle on their volumes that only an extremely small amount of waste is produced at all. For years, however, this waste has been largely used to generate energy in a biogas plant operated by third parties, where waste from the entire region is brought, so that cost-effective operation is guaranteed.

The economic operation of a biomass power plant also requires huge amounts of agricultural and forestry waste. Since the city of Göttingen already operates such a biomass power plant, there is not enough further biomass available regionally for a university biomass power plant. Due to climate change, the forest is under such high stress (drought, etc.) that it is unclear if there will be stable wood yields in the long term. The availability of biomass outside our region might be possible, but long transport distances make the construction inefficient and do not make sense in terms of climate protection. In order to examine this situation in detail, a student thesis was commissioned in cooperation with Prof. Dr. Dirk Jäger, Faculty of Forest Sciences and Wildlife Ecology.

Another possibility would be the procurement of virtual biogas. This is biogas that is fed into the normal natural gas grid somewhere and then allocated to a consumer somewhere else in the balance sheet. In reality, natural gas is burned, but the price paid for it is about eight times higher.