Motivation and objectives
For the implementation of the European policy decision the Federal Government decided the key points of the integrated energy and climate program on August the 23rd of 2007 in Meseberg. This national package with measures for climate protection, development of renewable energies and energy efficiency is supposed to assure the achievement of the climate protection targets until 2020.
That means that the CHP power generation is to be doubled from currently 12 % to 25 % of the power consumption. In the same time the demand of heat will reduce due to the improved insulation of buildings which results in a falling utilization of district heating networks. In addition to cogeneration of heat and power the share of the renewable energies to heat generation ought to increase to 14 % and to power generation to 30 %. These two developments will degrade the profitability of the CHP, because the share of the non-relocatable - the so-called “must-run”-facilities - increases.
The future challenges of combined heat and power as well as possible solutions and evaluation options are contents of the composite research project “EnEff: city - design and intelligent management of optimized energy supply structures at district level" which was initiated by the Federal Ministry of Economics and Technology (BMWi). In this framework the TU Dresden, the TU Darmstadt and the Research Institute of Energy Economy work together on related topics, as shown in Figure 1.
Figure 1: The composite research project „EnEff: city – design and intelligent management of optimized energy supply structures at district level”
The subproject “Opportunities and risks of CHP within the IEKP”, which is supported by the energy providers SWM and EWE and enhanced by the BMWi, is composed of three parts. These differ in their regional and economic parameters and assure collectively a holistic consideration of the topic, as explained below.
DEA: composite of distributed generation facilities
The subproject “DEA: composite of distributed generation facilities” analyses collective control of distributed generation facilities (DEA) and additional commercialization of this “virtual power plant” (VPP) per electricity trading and system services. The focus is on optimal pool composition, offered electricity products and online regulation of the DEA. To find answers for these questions a simulation environment is created, which allows confronting different methods of optimization and operation control. Next to these specifically implemented methods commercial energy management systems (EMS) serve as references. Figure 2 shows conventional marketing channels of the DEA pursuant to the lawful fee of EEG and KWKG as well as the additional routes “electricity trading” and “system services” that can be used in combination.
Figure 2: Collective control of distributed generation - a “virtual power plant”
flex: flexible operation of CHP
The second project examines different possibilities to a flexible operation of CHP generation in order to increase the CHP share of electricity supply. Figure 3 shows the load profile achieving the aims of the IEKP in case the implementation of the regenerative power generation (green load curve) is mainly supplied by wind power plants. The load profile of general supply, which is compatible with the consumers´ load profile, is partly covered by the CHP power generation and the fluctuating regenerative energy generation. The high power peaks require the use of negative balancing power. In times of high heat demand this problem becomes even more problematic because of cogeneration in CHP plants.
Figure 3: Electric load profiles regarding Germany’s political targets
Various options exist that decouple the power and heat generation:
- Development of alternative heat sinks
On the consumer side additional heat sinks with anti-cyclical load characteristic can be created for the supply with CHP. In case of industry and commercial buildings it may be used specifically for the provision of absorption refrigeration.
- Modulation of the power and heat ratio
By altering the extracted flow of steam mass the possibility occurs to modify the current ratio particularly in extraction condensing turbines.
- Thermal storage as an important element in the energy industry
Heat can be stored without any great technical efforts. Thus one possibility to uncouple the heat- and electricity generation of CHP generation is to use thermal storages. As a result, the plant utilisation period of the CHP electricity-generation can be increased.
Masterplan: optimized power supply
This sub-project composes an “optimal” energy supply structure based on identified consumption clusters with a highly decentralized focus. This serves as a benchmark for existing structures and provides options to improve the current system.
Figure 4 presents a schematic illustration of the node-edge- and region model which can be interpreted by using a geographic information system (GIS) with focus on various criteria. The model is based on several information that are relevant for energy economy and that show the energy demand as well as their covering. For example, to determine the heat density in a region it is required to know the population density and the building structures, furthermore, the knowledge of employment at various regional depths (e.g. local or municipal level) is necessary.
Abbildung 4: Schematic illustration of a node-edge- and region model
The project is enhanced by the Federal Ministry of Economics and Technology (BMWi) and supported by the partners SWM GmbH and EWE AG.