What is Power Generation?
In german, the term power generation is devided into two words: "Energiewandlung" and "Leistungsbereitstellung". The first one, "Energiewandlung", could be translated with energy conversion. The meaning of the second one is the way to provide the power. But anyhow the english word power generation describes the whole process of gaining power at its best. It includes all tasks and operations in the process of gaining power. Furthermore it includes the power supply or the controlling of power plants and grids as well as the storage of energy. In the following the mentioned terms of power generation should be explained.
Energy conversion deals with the transformation of one type of energy into another. Commonly, electrical energy is considered as the most valuable/flexible type of energy in private households as well as industry. Power generation therefore concentrates on efficient ways to transform primary energy sources (for example; wind, biomass, coal, etc.) into electricity.
Another required type of energy in our society is heat. Low level heat cannot completely be transformed back in other types of energy, contrary to mechanical and electrical energy. Therefore it belongs to the category of low quality energies. Heat often is a waste byproduct of the production of mechanical and electrical energy, which can be used for heating tasks.
Due to its unlimited convertibility in each other type of energy electricity is a high quality energy form. Furthermore, the transportation of electricity over far distances is comparatively easy and low-loss. In Germany 19% of the end energy is used in the form of electricity. It is the aim of the Center for Power Generation to provide solutions for highly efficient electricity generation.
Primary energy sources for electricity generation may be conventional (coal, gas, oil) as well as renewable energy sources (biomass, wind, water). At present the share of renewable energy sources in the German energy mix is up to almost 25% (end of 2013). Still, this value could only be raised slowly and at great financial expense. In order to achieve agreed targets for climate protection, the research conducted at the CPG therefore focusses on raising the efficiency of conventional technologies for electricity generation.
Conventional Power Plant Technology
Conventional power plant technologies comprise all technologies producing electricity predominantly from fossil energy sources. Examples are large coal power plants with water/steam cycle, gas and steam turbine power plants as well as nuclear power plants. Also included are technologies like waste incineration plants or biomass power plants using steam generated by the combustion of waste or biomass. Furthermore, plants with steady-state motors using diesel, gas, oil or biogas are counted to conventional technologies.
The common ground of most of the technologies is the fact that they generate steam at high temperature and pressure by combusting a carbon-based fuel. Steam is then expanded in a turbine. Electricity is finally generated by transforming the mechanical energy in a generator. Research on this topic is primarily concerned with efficient combustion technologies, steam generation at high pressure and temperature, power plant dynamics and control, efficient design of water/steam cycles and optimized steam turbine technologies.
With respect to conventional power plants, research currently focusses on combustion in an oxygen atmosphere or gasification of coal and subsequent combustion of the resulting syngas. The main objective of the latter research is a reduction of the energy penalty and cost associated with CO2-removal from the exhaust gas.
Electrical Power Transmission
In most cases, the electricity producer and consumer are located far from each other. The produced electricity thus often has to be transported over great distance before it reaches the consumer.
Reliable grid design and development will become increasingly important in the future, especially with further increasing local electricity production from decentralized renewable energy sources. Only a few European locations technically allow large scale electricity production from renewable sources (for example offshore wind power in the North Sea or solar electricity in the Mediterranean region). Research efforts should therefore alos be geared towards low-loss technologies for energy transportation and of course improved strategies to control the grid.
Going along with grid improvements, storage technologies will gain more importance in the future. In a few years front-end electricity generation will fully depend on weather conditions and thus cannot be controlled. Furthermore the power of conventional backup power plants cannot be modulated as quickly as those changing conditions would require. This is where storage technologies come into play. By storing surplus energy when generation from renewables exceeds energy demand and supporting electricity supply when electricity demand is high, energy storages help stabilizing the grid.
At the moment the most frequently used technologies are pumped hydro storage plants. The combined capacity of those plants is – at least in Germany – geographically and politically limited. Thus, research is looking into new storage technologies, such as thermal storage of solar heat using e.g. molten salt or concrete and compressed air storages.
Flexibility increase by innovative plant control mechanisms and deeper understanding of material behavior
To date, a characteristic feature of most of the existing steam power plants is their design for base load operation. Operational flexibility has often deliberately been limited to 200 cold start cycles throughout plant life time. Driven by an increased share of green (and volatile) power generation plants especially in the German grid, previous base load plants now need the flexibility for frequent load changes as well as cold and warm start-ups. Plant materials have not been designed for such requirements. Especially thermal stress becomes an issue. Therefore exact knowledge of material properties and material lifetime when exposed to this new operation conditions becomes vital.