Base load

from Wikipedia, the free encyclopedia
according to EWE: Course of the spring electricity consumption (load) over different days of the week and use of base, medium and peak load power plants on the load course on weekdays (schematic)

Base load refers to the load on a power grid that is not undershot during a day. The respective base load therefore depends on the day of the observation (seasonal fluctuations) as well as the spatial observation (e.g. coverage area of ​​a network operator or the whole of Germany). In Germany it is up to 40 gigawatts on individual days (2005) in contrast to the annual peak load of 75 to 80 gigawatts.

If the base load is exceeded, additional power plant capacity is activated to cover the additional electricity demand by extending the base load power plants to full load, through medium and peak load power plants .

Since the lowest electricity demand usually occurs at night, the level of the base load depends on industrial plants producing at night, street lighting and permanent consumers in households and businesses. In addition, the base load of energy supply companies can be increased by creating additional electricity requirements during off-peak times. For example, the storage basins of pumped storage power plants are filled at night or night storage heaters are switched on. If necessary, the base load power plants used are slowly throttled at night and started up at the beginning of the day.

Base load power plants

There is no clear definition that distinguishes base load power plants from other power plants. In general, any type of power plant can be used to cover the electricity requirements of the base load. The classification is based on business and technical criteria and is not rigid. Base load power plants are those power plants that are operated as uninterrupted as possible and as close as possible to the full load limit. Nuclear power plants and lignite-fired power plants have high fixed costs and low electricity generation costs (especially fuel costs ) and are therefore usually first named as base load power plants. The power plant operators try to estimate the base load requirement in advance in the long term. If the value falls below the estimated value, they must react: by switching on additional consumers (pumped storage power plants), by supplying electricity to other power grids and / or by throttling the base load power plants during low-load times at night.

Due to the historical development of power generation in Germany, various power plants were not designed when they were built to be quickly controllable or, due to their principle, are not. This does not exclude the possibility of (slow) readjustment of the electricity demand, for example through general seasonal fluctuations in demand.

Base load power plants are not to be confused with base load power plants .

  • The base load power plants include lignite power plants . Due to their low fuel costs, they are typically used around the clock, as is typical for base loads. However, they can be controlled just as well or as quickly as a medium- load power plant, which only has higher fuel costs.
  • Run-of-river power plants also provide energy for the base load. They use the potential energy of the water backed up to a certain level. Often, compliance with the congestion destination is included in the concession regulations . The available energy results from the mass of the water and the height difference between the upper and lower water . Therefore, attempts are made to route the water flowing into the power plant as completely as possible through the turbine and convert it into electrical energy. Run-of-river power plants can be throttled well and have no primary energy costs.
  • Wind turbines can deliver most of the base load energy, depending on the wind speed. Conventional power plants have to reduce their output if more wind power is fed in, because the energy suppliers are obliged to purchase wind energy under the Energy Feed Act. Due to an increasing share of renewable energies, previous base load power plants are being used less.
  • Nuclear power plants are classified as base load power plants for economic and technical reasons. Nuclear power plants have high investment and fixed costs. Decisive for the economic classification as base load power plants are the low electricity production costs , i. H. the costs that have to be expended in converting an energy source (here uranium) into electrical energy. Since these fuel costs are still relatively low, attempts are being made to operate the nuclear power plants continuously at full load.

Suitability of nuclear power plants for load following operation

The articles nuclear power plant # operating mode and base load # suitability of nuclear power plants for load sequence operation overlap thematically. Help me to better differentiate or merge the articles (→  instructions ) . To do this, take part in the relevant redundancy discussion . Please remove this module only after the redundancy has been completely processed and do not forget to include the relevant entry on the redundancy discussion page{{ Done | 1 = ~~~~}}to mark. R.Schuster ( discussion ) 09:14, Oct. 1, 2013 (CEST)

According to the information provided by the operator, at least some nuclear power plants of the pressurized water reactor type in Germany were technically designed for use in load-following operation at the design stage. In load-following operation, the power plant output is automatically adjusted to the changing electricity demand (“load”) and the electricity supply. Examples of this were Neckarwestheim 1, Philipsburg 1, Philipsburg 2, Biblis A in 2009. In the older boiling water reactors, this mode of operation was never the subject of the design criteria, particularly for the pressure vessel and the control technology.

The technically possible rate of change depends on the absolute change in load and is up to 10% per minute based on the nominal power.

Restarting a reactor to full capacity takes at least 2 to 3 hours from a subcritical hot state and up to 10 to 12 hours from a cold state, depending on the operating conditions. "In the event of a rapid shutdown, in particular by 50% of the power or more, the xenon poisoning of the fissile material can lead to a further significant delay in the start-up."

In addition to technical hurdles with regard to the suitability of nuclear power plants for load-following operation, there is an economic problem: the electricity production costs in the nuclear power plant consist almost exclusively of fixed costs. The production costs from a nuclear power plant are almost twice as high at 50% output as at 100% output. In particular, nuclear power plants that have not yet been depreciated in the balance sheet are therefore forced to operate at full load for economic reasons.

"For the pressurized water reactors, which represent around two thirds of the nuclear energy capacity available in Germany, variable operation between 100% and 50% of the output is permitted, for the so-called convoy and pre-convoy pressurized water reactors, in addition, variable operation of up to 20% of the Power. The control range of the boiling water reactors is limited to 100% to 60% of the nominal output (Hundt, 2009). The more the power is changed, the lower the permissible rate of change. "

Suitability of lignite power plants for load following operation

Lignite power plants have cold start times of 9 to 15 hours and are comparatively difficult to control. Today's lignite power plants cannot be throttled below 50% of the nominal output, as otherwise the boiler temperature would drop too much. The aim is to achieve greater controllability, although a regulation down to below 40% of the nominal output is considered uneconomical.


For a future electricity supply based on renewable energies , the Advisory Council for Environmental Issues of the Federal Republic of Germany stated in May 2009:

"The possible uses of base-load power plants are restricted when there is a high proportion of renewable energies; instead, fast-starting power plants and control energy are required."

- Advisory Council for Environmental Issues of the Federal Republic of Germany, May 28, 2009

Power plant units are already being used at short notice, e.g. B. without a longer planned revision shutdown, switched from the grid if enough wind power is available for wind turbines . These standstills are called wind dropouts by the power plant operators and mean economic losses for the operators. Depending on the age and design of the system, it wears more from frequent startup and shutdown than in continuous operation. The higher and more continuous the utilization of a system, the more economically it works.


In Switzerland, the term band energy refers to the basic demand for electricity that is consumed around the clock every day. The band energy is supplied by nuclear power plants and run-of- river power plants . The proportion of electricity consumption that exceeds the base load is referred to as peak energy . Thermal power plants and, above all, the easily controllable storage power plants in the Alps are used for it. In Germany, the peak energy (the term is not used there) is divided into medium load and peak load .

See also

Web links

Individual evidence

  1. See Claudia Kemfert : The other climate future. Innovation instead of depression. Hamburg 2008, Murmann-Verlag, p. 161.
  2. Total hydrographs for energy 2.0. Institute for Solar Energy Supply Technology (ISET), p. 7 above.
  3. Monitoring report of the Federal Ministry of Economics and Technology according to § 51 EnWG on security of supply in the area of ​​grid-based supply of electricity ( Memento from January 31, 2012 in the Internet Archive ) (PDF; 118 kB), accessed August 30, 2010
  4. Cf. Volker Quaschning : Base load power plants: bridge or crutch for the regenerative age. In: Sun, Wind & Warmth. 05/2010, pp. 10-15.
  5. a b cf. areva : Renewable energy sources and nuclear power plants - do they go together?  ( Page no longer available , search in web archives ) In: arguments 05/2010, p. 1 / The design of German nuclear power plants for load change capability@1@ 2Template: Dead Link /
  6. Cf. Deutsche Physikalische Gesellschaft : Electricity: Key to a sustainable and climate-friendly energy system ( Memento from July 13, 2011 in the Internet Archive ) (PDF; 1.8 MB) A study by the German Physical Society June 2010, p. 67 / Rolle of nuclear energy in a future energy supply system with a high proportion of fluctuating electricity supply
  7. See Karl Müller: LOAD SEQUENCE OPERATION AND PRIMARY REGULATION  ( page no longer available , search in web archives ) E.ON Kernkraft GmbH, Isar 2 nuclear power plant@1@ 2Template: Dead Link /
  8. See Matthias Hundt: Compatibility of renewable energies and nuclear energy in the generation portfolio (PDF; 5.0 MB). Technical and economic aspects. University of Stuttgart. Institute for Energy Economics and Rational Energy Use 10/2009
  9. 2009. Example on page 31 ( Memento from October 5, 2013 in the Internet Archive ) In: International Journal for Nuclear Power 2010.
  10. Cf. Renneberg study p. 11. Among other things, it says: "A cold pressurized water reactor must first be brought to an operating temperature of around 260 degrees Celsius by the cooling pumps and the decay heat in order to achieve a state in which it will Ignition of the chain reaction behaves safely (negative coolant temperature coefficient). With a boiling water reactor , this state is reached in a slightly shorter time (approx. 5 hours), since the pressure in the reactor is lower. If, for special reasons, recurring tests are added, the start-up can be a reactor can take up to three days. " ..
  11. ^ Renneberg study p. 11. "Hundt, 2009" = Hundt M., Barth R, Sun N., Wissel S., Voss A, Compatibility of renewable energies and nuclear energy in the generation portfolio , expert opinion on behalf of E.ON Energie AG Munich, Stuttgart, October 2009
  12. Coal-based power generation at times of low electricity prices ( Memento from October 16, 2013 in the Internet Archive ) (PDF; 1.9 MB). Fraunhofer ISE . Retrieved April 3, 2014.
  13. ^ Setting the course for a sustainable power supply ( Memento of May 6, 2015 in the Internet Archive ), Council of Economic Experts for Environmental Issues of the Federal Republic of Germany, May 28, 2009, accessed on August 30, 2010