Peak load

from Wikipedia, the free encyclopedia
Load profiles on different spring days and power plant use (scheme) using the example: load profile on weekdays. Peak load: marked in light green

Peak load refers to briefly occurring high demand for power in the power grid or in other supply networks ( natural gas , district heating , local heating ).

Demand peaks are often characterized by a sharp increase in the demanded power, so that quickly controllable peak load power plants have to be used for the power supply. These can provide high performance within seconds or minutes. These include pumped storage and compressed air storage power plants , but also modern gas turbine power plants .

Power plant management and peak load

In order to be able to ensure security of supply at all times, even with fluctuating electricity consumption , power plant management with peaks is necessary. From the point of view of power grid management, a distinction is made between three types of power plants that are used in different ways in the course of the load:

  • Base load power plants ( nuclear power plants , run-of-river power plants , coal-fired power plants ) are operated around the clock at full load as far as possible . They can generate electricity relatively cheaply, but can only be regulated slowly. In the event of failures in this power plant area, it must be possible to provide reserve power at short notice until other power plants can take over the generation of electricity. This is not always possible, especially in the event of unplanned failures of larger generating units.
  • Medium load power plants (eg. B. coal power plants , gas and steam power plants ) vary their power according to the predictable current need for a predetermined daily timetable. They have average electricity production costs and can be regulated over a wide power range, but the regulation works with a certain inertia. They can only react to a limited extent to rapid changes in electricity demand; these must be absorbed by peak load power plants.
  • Peak load power plants ( pumped storage power plants , compressed air storage power plants , gas turbine power plants ) can quickly follow changes in performance in the network. Gas turbine power plants reach rates of change of up to 20% of the nominal output per minute and have a start-up time of just a few minutes. The power can be regulated between 20% and 100%. They are used to adjust the fluctuations in the power requirement or the generator feed-in that cannot be compensated for by the other types of power plant or where this is not economically viable. Peak-load power plants are usually only used for a few hours a day: at peak consumption, when there is a strong load increase in the grid and when there are unplanned fluctuations in electricity consumption and generation. Due to the consumption of natural gas or pump energy, the electricity they generate is significantly more expensive than that of other types of power plants.

Renewable electricity generators such as solar systems, wind turbines and the majority of the combined heat and power plants are currently (2012) not included in the active grid control , apart from forced shutdowns by the grid operator in problematic situations. By law, these regenerative producers usually feed all of the electricity they generate into the grid (priority feed-in). As a result, they primarily displace medium-load power plants (photovoltaics at midday also displace peak-load power plants) and thereby lower the price of electricity on the electricity exchanges. However, fluctuations in the electricity generated by these power plants often have to be balanced out with the help of peak load power plants, which in turn causes additional costs. The adjustment of the schedules of the medium-load power plants to the forecast electricity generation has become more complex due to the fluctuating regenerative electricity producers, the forecasts have become more complex.

Methods are currently (as of 2011) being developed to absorb peak loads in a decentralized manner. For example, so-called load managers can be installed in households or short-term generator and load fluctuations in photovoltaic systems can be compensated for using hybrid inverters .

Predictable peak load

The increased demand for power during the day is usually very predictable. The course of demand over the day is known. It reaches its highest values ​​all year round between around 11 a.m. and 2 p.m. (up to 82 GW in Germany, 1 nuclear power plant = 1.3 GW), and from around mid-October to the end of March also often between around 4:30 p.m. and 7 p.m. . There are also quite precise forecasts with regard to the electricity feed-in of third parties (e.g. forecast of the feed-in from wind turbines and photovoltaic systems based on current weather forecasts). Timetables for the medium-load power plants are created from the expected course of the day. Smaller forecast errors are compensated for by the so-called control power , which power plant operators have to keep available in different amounts.

If the expected load profile cannot be covered, or not economically, by medium-load power plants, peak load is used:

  • If such strong increases in load are expected at certain times that medium-load power plants cannot cope with this, peak-load power plants are planned for support during this period.
  • If current peaks are so short that it would not be economical to start up a medium-load power plant, the use of peak-load power plants is planned for this period.

Unpredictable peak load

Due to the failure of a base-load or medium-load power plant or an unexpectedly high load in the power grid, peak load power plants may become necessary. Various power plants are used one after the other to cope with acute failures:

  1. First, pumped storage power plants or compressed air storage power plants are used, as they can provide high performance within seconds.
  2. After a few minutes, gas turbine power plants are started up so that they can take over the load from the storage power plants.
  3. At the same time, medium- load power plants are ramped up from the hot or cold reserve . The duration for this is more in the range of hours. As the medium load power plants can provide the load, the peak load power plants are shut down.

Power exchange

Contracts traded on the electricity exchange

Peak loads are often traded on power exchanges , where in extreme cases they can cost several euros per kilowatt hour . On the power exchange, however, no distinction is made between peak load and medium load . All electricity traded on a daily basis is referred to as peak load, such as any increased electricity demand during the day that is around 50% above the base load at noon.

On the European electricity exchange EEX , peak-load electricity is traded in hourly packages between 8 a.m. and 8 p.m.

See also

Individual evidence

  1. Power outages in Hamburg after a fault in the Krümmel nuclear power plant , BCM News, July 4, 2009, accessed on February 28, 2012.
  2. EOn AG: Compatibility of renewable energies and nuclear energy in the generation portfolio (PDF; 5.0 MB), October 2009
  3. Nuclear power blown on the wall , taz February 3, 2012, accessed on February 28, 2012.
  4. Tennet boss on the risk of blackouts , Manager Magazin, February 7, 2012, accessed February 28, 2012.
  5. PowerGate 100 kW solar PV hybrid inverter, Satcon Technology Corporation, accessed January 28, 2012.
  6. Voltwerk VS 5 Hybrid, fully integrated energy management system  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , voltwerk electronics GmbH, accessed on January 28, 2012.@1@ 2Template: Dead Link /