Bioenergy
Biogas ensures stable networks

Biogas plants can flexibly feed in power and heat and in this way compensate for fluctuations. In the FlexFuture research project, scientists developed a biogas plant control system for demand-based electricity production. The control system can create schedules for cogeneration plants based on the electricity market, heat demand and distribution network. These schedules enable generation and grid congestion management that also keeps an eye on the overall efficiency of the biogas plant. At the Zellerfeld biogas plant, it was successfully demonstrated that congestion and overloads in the power grid can be avoided if photovoltaic and biogas plants feed in power in a coordinated manner.

Project context

The increasing share of renewable, fluctuating energy generators, such as wind power and photovoltaics, is already pushing distribution and transmission networks to the limits of their physical performance capability. Particularly the requirements for distribution grids with regard to operation and protection mechanisms are becoming increasingly complex. Congestion must therefore be expected in the future, especially in these networks. Operators are meeting the challenges with load balancing, peak load capping, grid expansion and the use of electricity storage facilities. These measures are both planning and cost-intensive. A promising alternative is controllable, decentralised electricity generation by biogas plants, adapted to the local needs of the distribution grids.

Research focus

Biogas plants can reduce their electricity production during periods of low residual load and supply electricity generation capacity during periods of low infeed from fluctuating electricity generators. During demand-based operation, the total amount of electricity generated in the biogas plant remains constant compared to a biogas plant in continuous operation. So far, timetables for biogas plants have been based mainly on electricity prices.

The aim of demand-based control is to take into account the daily and maximum infeed profiles of adjacent photovoltaic systems on a regional basis. The Zellerfeld biogas plant and the Wolfsgrube open-space photovoltaic plant with a total of 6,438 kilowatts of electrical feed-in power are connected at the Zellerfeld grid connection point (GCP), with a capacity of 5,000 kilowatts of electrical power. This means that on sunny days the feed-in power of the two plants exceeds the AC-side power switch limit of the medium-voltage distribution network. In this case, all plants are disconnected from the power grid. This is due to the output limit on the GCP.

In the course of the project, the research teams developed control concepts for the operation of biogas plants with the support of the Zellerfeld biogas plant and the Lechwerke distribution grid. These support the distribution grid in order to compensate for short-term fluctuations in the power grid via the controllable power production of the biogas cogeneration plants. Daily weather and irradiation forecasts are used for this purpose.