Energy efficiency in thermal power plants through cogeneration
Cogeneration (CHP) in electricity generation in Austria
In Austria, electricity is generated almost exclusively by hydropower plants, wind power plants and thermal power plants, the latter are predominantly designed as CHP plants. In addition to electricity generation, these cover the district heating needs in metropolitan areas such as Vienna, Graz, Linz, Salzburg, Klagenfurt, St. Pölten and Wels. There, the district heating is produced largely in highly efficient CHP plants and contributes significantly to reducing emissions such as CO2, NOx and particulate matter.
District heating plays a key role in urban areas to cover room heating demands. It requires a cost-effective and well-regulated heat source. This can be achieved effectively by heat from CHP plants (fossil and renewable).
Other technologies for the efficient provision of room heating (heat pump, solar collectors, condensing technology, etc.) can usually only be implemented well in new constructions. However, these technologies cannot be used on a large scale for existing buildings in urban areas.
Electricity demand in Austria is higher in the winter than in the summer months. At the same time, the total production from renewable energy sources (hydropower, wind energy and other green electricity) during the winter months is at a minimum. Consequently, in winter there is an increase in the gap between electricity demand and domestic regenerative generation, which can only be filled by thermal power plants or by importing electricity from abroad. In addition, Austria has a high room heating demand during cold times of the year.
The gap between regenerative electricity generation and electricity demand always increases in relation to the number of heating degree days per month. The amount of heating degree days increases the demand for room heating. In Austria, this gap can only be filled as needed by flexible thermal power plants. For these reasons, it is sensible to couple this electricity generation in the thermal power plants with heat generation. This results in the usefulness of employing CHP plants.
Flexible power and heat generation through CHP plants
CHP is a possibility for flexible power and heat generation. In principle, plants of all sizes can be designed as CHP plants, with outputs of several hundred MW down to micro-plants with outputs of a few kW. In principle, all fuels can be used. As well as renewable energy sources such as biomass or biogas, geothermal energy can also only be used energy-efficiently for green electricity production by CHP.
The operation of CHP plants is possible according to the current needs, i.e. exactly when electricity or heat is needed. Most of the time, industrial cogeneration primarily covers the constant heat requirement of production, thereby opens up an additional, independent power generation source for the sites. The energy companies’ CHP plants feed electricity into the public grid and thus also fulfil the function of load balancing, i.e. the relief and support of the grid. Heat is usually extracted into public district heating networks. For this reason, these CHP plants are usually designed such that far-reaching or even full regulation of the operation is possible.
Efficiency of CHP: Fuel and CO2 savings
With the simultaneous need for electricity and heat, CHP can save a great deal of primary energy. Instead of separately generating electricity in a thermal power plant and heat in boiler plants, the waste heat of the thermal power plant can be used by the CHP to provide useful heat. The primary energy savings from CHP in this area are well over 10 per cent. The saving of primary energy is synonymous with a lower fuel input. This results in CO2 savings of the same amount, i.e. well over 10 per cent.
CHP contributes significantly to an efficient, low-emission and secure energy supply, both to public utility companies and to industry.