Summary
The increasing share of electricity generation from renewable energies not only leads to a reduced use of fossil power plants, but also to more difficult conditions for CHP plants. Falling electricity prices on the liberalised electricity market, relative to the cost of fossil fuels, make the operation of CHP plants unprofitable for an increasing number of annual hours. This not only jeopardises the economic viability of CHP plants, but also the energy policy objective of using cogeneration to help reduce primary energy consumption and CO2 emissions.
The aim of the project is to determine the contribution of heat storage and power-to-heat plants to a more efficient, flexible and economical operation of CHP plants in the public district heating supply. The determination of the additional flexibility through heat storage and power-to-heat is based on the comparison with the district heating system without these components. The investigations are carried out for four types of CHP plants, which differ in the type of heat extraction and the fuel used.
The intermediate storage of district heating allows the operation of CHP plants to be partially decoupled from the demand for district heating, which on the one hand enables an electricity price-oriented operation of the CHP plants and on the other hand increases the share of district heating supply from coupled generation. The results for the four types of CHP plants and the different market conditions show that the economic efficiency as well as the effects on the operation of the CHP plants are partly very different, but that the storage of district heating will become more important in the future. In principle, the potential for heat storage is greater in gas-steam power plants, as their operation is more strongly determined by electricity prices due to a high electricity ratio and higher variable generation costs. At the time of the project, the functional electricity storage by heat storage in the district heating sector amounted to approx. 1.2 TWh/a. With an area-wide expansion this can be increased to almost 3 TWh/a.
The use of heat pumps and electric heaters in the district heating supply is not economically feasible during the project period. For heat pumps, the additional costs (levy for renewable energies, grid fees, etc.) for the use of own and third-party electricity would have to be reduced to enable economical operation.
