Wastewater treatment plants as control component in intelligent distribution systems with renewable energy generation
The energy sector is currently under reconstruction. Renewable energies have reached in 2013 an overall rate of 23,4 % in the power supply. In the short and medium term the rate of decentralised power generation will increase and contribute significantly to the base load supply. Fluctuating electricity production from wind and solar cannot be allowed to cause lower quality in grid operation, i.e. a deviation of the 50 Hertz frequency stability and voltage stability. In future an according potential of control energy as well as storage capacities are necessary to prevent and compensate the temporary curtailment of electricity from renewable energy sources. The urban water management institutions in Germany can contribute to achieve those objectives by its energy storage and generation possibilities.
Fig.1: Volatile renewable energy plants (wind and solar) and control components of wastewater treatment plants (CHP and gas storage)
The core objective of the joint research project arrivee is the integration of the widely available wastewater treatment plants (WWTP) in Germany with anaerobic sludge digestion into an optimized control energy and storage concept. The research project will develop a system solution for the integration of WWTPs with anaerobic sludge digestion into a storage and control energy concept. Therefore the excellent technical conditions of WWTPs with anaerobic digesters such as combined heat and power plants (CHP) as well as gas storage facilities should be used. With the aid of a specifically developed methodology, system and grid services for distribution and transmission systems should be provided. Those services are necessary today and in future due to the increasing extension of fluctuating renewable energy generation from wind and solar power. To meet these expectations, the digester gas of those plants with a methane content of about 65 % should not only be used – after an intermediate storage - to satisfy the electricity demand on the plant. The power generation in heat-power co-generations in form of CHP, that actually cover the energy needs of the plant for sewage and surplus activated sludge treatment, has to be adapted to the control energy and storage concept. In this context a verification of further components of the WWTP for the contribution of those services regarding the aspects of sustainability and economic efficiency is realised.
Focus of the work
The arrivee project will develop in interconnected work packages an integrated solution at the interface of urban wastewater and energy systems in form of a management strategy. The development will be accompanied by statements for comprehensive use of the technical solutions in Germany combined with recommendations for action. This implies the identification and analysis of control energy modules on WWTPs as well as the calculation of resulting potentials of system services for energy grids and the evaluation of further positive effects, for example avoided grid extensions. Based on various options in WWTPs for storage and conversion of excess energy from fluctuating renewable energy, approaches of control energy concepts will be prepared and technical plant concepts for the implementation will be developed. Furthermore the effects on the operation and energy balance of the WWTP and the upstream distribution system will be analysed for WWTP. Depending on the potential use on the spot as well as the efficiency of conversion stages a stepwise utilization concept for renewable energy surplus will be developed. The WWTP Radevormwald will serve as a pilot plant to provide a closer look at the interactions of market, grid load and WWTP. Using a mathematical model of this pilot WWTP, the effects of external interventions for the supply of system services under different conditions (for example continuing expansion of renewable energies) will be considered. In a further step individual control modules of the WWTP will be integrated into a virtual power plant to demonstrate the feasibility of the foregoing, theoretically examined possibilities. For this purpose, an existing control and communication technology tool for the integration of control energy units will be adapted and tested in the light of specific demands of the WWTP.
By the integration of WWTP an intelligent multiple use of already existing suitable equipment can be achieved. Thus it will be possible to contribute to an optimal use of the energy potentials of the generation of renewable energies. Those possibilities and potentials will be analysed and evaluated in the frame of the arrivee project in terms of economics, efficient energy use as well as plant operation. The procedurally, energetically and economical work packages will be linked with an energy policy and energy legislation work package. Within this package the framework of energy legislation and policy as well as the possibility of change will be analysed. Based on expert interviews and workshops, scenarios with practical solutions for the adaption of the political-legal framework will be developed.
Upon attainment of the project objectives a significant contribution is being made to the content and technical connection of technical wastewater management infrastructures and energy supply. This allows a quantification of the control energy potential of WWTP as already available, public infrastructures and a suitability testing of different control and storage concepts for the demands of future operating states of electric power grids. The new findings will make significant contributions to the integration of WWTP with separate anaerobic sludge stabilization into storage and control energy concepts in the frame of the energy turnaround.
Furthermore, the results are expected to give a substantial contribution to a significant increase of energy efficiency of WWTP – municipal as well as industrial ones. The existing infrastructures can be reshaped in a sustainable, ecological and economic manner for a drastically changed framework. By the gained knowledge from the integration of WWTPs in future energy storage and control energy concepts in the frame of energy turnaround, the joint research project arrivee will contribute to make it possible that municipalities can offer the service of wastewater treatment as welfare service in a long-term, sustainable and energy efficient way.