Full load hours are a measure of the degree of utilization of a technical system. Full load hours describe the time for which a system would have to be operated at nominal power in order to carry out the same electrical work as the system actually carried out within a specified period of time, in which there may also be breaks in operation or partial load operation . The information mostly relates to a period of one calendar year and is mainly used for power plants .

The derived from the number of full load hours annual efficiency or capacity factor ( english capacity factor is) the relative full load usage in a year, so the number of full load hours divided by 8,760 hours, the number of hours in a year with 365 days.

## meaning

As a rule, technical systems are not operated constantly under full load, but at certain times also under partial load or taken out of service for maintenance. The total work done by the system in one year is therefore less than the maximum possible over the same period.

The degree of utilization of a technical system can then be expressed in full load hours if a nominal output can be specified and an adequate conversion from partial load operation to nominal load operation exists (e.g. based on the amount of energy or material converted).

The number of full-load hours of a plant fluctuates from year to year due to different maintenance times , power plant deployment schedules, unplanned malfunctions and failures and due to different weather conditions, especially with renewable energy sources .

The value must not be confused with the operating hours . These describe the entire period in which the system has been operated and can include periods of partial load operation.

## calculation

For a controllable power plant, the number of full load hours calculated as the quotient of the standard capacity W (also referred to as the annual energy production) and the rated power P .

${\ displaystyle {\ text {Full load hours}} = {\ frac {W _ {\ text {electrical}}} {P _ {\ text {electrical}}}}}$

With

${\ displaystyle W _ {\ text {electrical}} \ ldots {\ text {electrical work in Wh or kWh}}}$
${\ displaystyle P _ {\ text {electrical}} \ ldots {\ text {nominal electrical power in W or kW}}}$

It indicates how many hours the system would have been running to achieve the annual energy production if it

• would only have run under full load and
• otherwise would have stood still.

## Full load hours after power plants

The development of the full load hours is very dynamic in the context of technological advancement and the energy transition. The following table shows full load hours and annual degree of utilization for power plants installed in Germany, with the exception of wind power USA from 2014.

Energy source Full load hours Annual efficiency
Geothermal energy (2008) 8300 94.7%
Nuclear energy (2008) 7700 87.9%
Lignite (2008) 6650 75.9%
Biomass (2008) 6000 68.5%
Hydropower 4600 52.5%
Offshore wind power (2011) 2600-4500 29.7% -51.4%
Onshore wind power (US new plants 2014) 3600 41.2%
Hard coal (2008) 3550 40.5%
Natural gas (2008) 3150 36.0%
Onshore wind power (new German plants since 2013) 2150 24.5%
Onshore wind power (10-year average Germany 2016) 1651 18.8%
Mineral oil (2008) 1650 18.8%
Photovoltaics (Munich 2008) 1010 11.5%
Pump storage (2007) 970 11.1%
Photovoltaics (Hamburg 2008) 840 9.6%

In the case of wind turbines and photovoltaic systems, the figures also fluctuate more from year to year than with other technologies due to the changing wind and irradiation conditions.

In wind turbines, the number of full-load hours is heavily dependent on their height, the rotor diameter and the ratio of the rotor area to the nominal power of the generator. The mean rotor diameter of the new turbines built in the respective year increased continuously from 22 m in 1992 to over 115 m in 2015 and further growth is possible. A first test facility with a rotor diameter of 180 m and an output of eight megawatts will be built in 2017 in Bremerhaven. The average figures therefore only give an imprecise measure of the possible full load usage.

The full load hours achieved are not a criterion for the quality of a power plant:

• Base load power plants (coal, nuclear energy) naturally have a high annual utilization rate
• In principle, photovoltaic systems cannot achieve a high degree of annual utilization
• Wind power plants can achieve high annual utilization rates with stable wind or by being equipped with a weak generator
• Pump storage, gas and oil power plants are peak load power plants and, due to their principle, are not run to a high annual degree of utilization

## Forecasts

A forecast made by the BMWi in 2016 for the future development of full load hours assumes the following values ​​for 2025:

Energy source Full load hours Annual efficiency
Brown coal 7503 85.7%
Biomass 6616 75.5%
Hard coal 4466 51.0%
Offshore wind power 3466 39.6%
Onshore wind power 2504 28.6%
natural gas 1972 22.5%
Photovoltaics 990 11.3%
mineral oil 384 4.4%
Nuclear energy 0 0%

## Examples

• The Gundremmingen nuclear power plant achieves around 7,400 full-load hours with around 20,000  GWh of electricity generated annually and its 2 × 1.34 GW output. This corresponds to a degree of utilization of 85%. The time availability was 92%.
• Wind turbines achieve between 7,500 and 8,000 operating hours per year when they feed electricity into the grid. Depending on various factors such as B. Site quality and system design, wind turbines achieve between 1400 and 5000 full load hours. This corresponds to a degree of utilization of around 16 to 57%. The technical availability of wind turbines is over 95% for onshore systems, but some offshore wind parks cut e.g. T. significantly worse. While onshore values ​​of approx. 98% are achieved, offshore it is assumed that the values ​​will not rise significantly above 90% in the long term.
• In southern Germany, photovoltaic systems achieve up to 1300 full load hours per year, but the German average only reaches around 800 to 900 h / a. The degree of utilization is around 10%. In the USA, on the other hand , large solar parks achieve capacity factors of around 20%, corresponding to around 1750 full load hours.

## Individual evidence

1. Maximilian Faltlhauser 2016. Facts and figures on power supply in Germany 2016. Archived copy ( memento of the original dated November 7, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessdate = 2017-05-24
2. Full load hours of different wind farms. (No longer available online.) Fraunhofer / IWES wind monitor, archived from the original on November 13, 2017 ; accessed on November 13, 2017 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
3. ^ Wind technologies Market Report . United States Department of Energy ; Retrieved August 24, 2016. Note: This is the capacity factor of all wind turbines newly commissioned in the US in 2014; however, at that time there were no offshore installations.
4. a b Berthold Hahn, Volker Berkhout, Bernd Ponick, Cornelia Stübig, Sarina Keller, Martin Felder, Henning Jachmann 2015: The limits of growth have not yet been reached . (PDF) Wind industry in Germany; accessed on August 1, 2016.
5. Fraunhofer Institute for Solar Energy Systems ISE ( Memento of the original dated November 11, 2017 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , Data for 2016; accessed on November 13, 2017.
6. Originally cited as energy data . BDEW . Data can no longer be found there in 2017.
7. Oliver Gressieker: The world's largest wind turbine is in Bremerhaven. NDR 2017.
8. https://www.bmwi.de/Redaktion/DE/Publikationen/Studien/entwicklung-der-energiemaerkte-energiereferenzprognose-endbericht.pdf?__blob=publicationFile&v=7
9. As early as 2002, the average of the German wind power plant park was around 7500 operating hours per year, individual plants achieved up to 8000 operating hours. See also: Electricity from wind energy for up to 8,000 hours per year . In: Innovations Report , November 19, 2002; Retrieved December 15, 2012.
10. Martin Kaltschmitt , Wolfgang Streicher, Andreas Wiese (ed.): Renewable energies. System technology, economy, environmental aspects . Berlin / Heidelberg 2013, p. 819.
11. 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. (PDF) for the joint project "Increasing the availability of wind turbines" of the BMUB , p. 9
12. Erich Hau: Wind turbines - basics, technology, use, economy. 5th edition. Springer, Berlin / Heidelberg 2014, pp. 628–630; P. 748.
13. ^ Joel Jean et al .: Pathways for solar photovoltaics . In: Energy and Environmental Science , 8, 2015, pp. 1200-1219, doi : 10.1039 / c4ee04073b .