Glossary

Maintenance involves carrying out inspections, servicing and repair work. This guarantees that the facility is kept in its desired condition throughout its service life.

Medium load is the amount of power that is consumed by a consumer during the greater part of a day, predominantly from morning until evening.

The merit order is a ranking of generation units that indicates the order in which they should be used. This is determined according to the variable marginal costs of electricity generation. Starting with the generation units with the lowest marginal costs, power plants with increasing marginal costs are fed into the grid one after the other until demand is covered.

The degree of meshing indicates the number of other nodes that an individual grid node in the transmission network is connected to. In a highly meshed network, the grid nodes have a large number of direct connections to other nodes. A higher degree of meshing is the foundation for a high level of supply reliability in the transmission network. As a rule, all circuits in transformer stations and substations are connected to one another (‘coupled’) in order to reduce network losses, provided that other technical reasons such as the level of short-circuit capacity or stability requirements do not preclude this. If, however, specific circuits that are experiencing high loads they can be relieved of this load by a process known as ‘demeshing’, whereby the circuits in question are separated from the interconnections. This can be done in different way, e.g. by opening couplings or by directly connecting selected circuits using separate busbar sections within a facility.

The minimum output of a generating unit indicates a level where output must not fall below, due to facility-specific or equipment-based reasons. If the minimum output does not refer to long-term usage, but rather to a shorter time period, this must be clearly highlighted.

In addition to covering the demand for electrical power, the provision of power from generation facilities can also be determined by other factors. In these cases the feeding of energy into the electricity grid is independent of the actual level of demand. This includes facilities that, due to technical restrictions, must feed in energy at predetermined times – in particular heat-led CHP plants, in which electricity generation is based on the local heat demand. Without the use of options to increase flexibility such as boilers, it is not possible to shut down these facilities without simultaneously restricting the heat supply – in other words, the facilities “must run”. Further restrictions may arise, for example, if facilities supply industrial processes or provide the power plant’s own energy supply (e.g. in lignite mining regions).