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Glossary · Energy industry & energy transition

Gross and net capacity

Gross capacity net capacity power plant Auxiliary Consumption electricity generation power power plant fleet

In a conventional power plant, gross capacity refers to the electrical power available at the generator terminals. The electricity the plant needs for its own operation has not yet been deducted. Net capacity is what can be delivered at the point of transfer to the grid or to external consumers after deduction of this auxiliary consumption. Both quantities are stated in kilowatts, megawatts or gigawatts. They describe a power rating, that is, how quickly electrical energy is made available. They do not indicate how much electricity is generated over an hour or a year.

A simple analogy: gross capacity corresponds to gross pay, and net capacity to the amount actually paid out after deductions. For a power plant, the deduction is the electricity the plant itself consumes. Depending on the plant, this includes pumps, fans, mills, cooling, flue gas cleaning, control systems and safety systems.

Definitions in German statistics

The Federal Statistical Office (Statistisches Bundesamt) defines net rated capacity as the highest continuous output that a generating unit achieves under rated conditions at the point of transfer. To arrive at it, the auxiliary power consumed during operation is deducted from the gross capacity. Analogously, net electricity generation is gross electricity generation reduced by own consumption. Own consumption is the energy required to maintain the production process, without sourcing from third parties. The Federal Environment Agency (Umweltbundesamt) describes gross electricity generation as the quantity of electricity measured at the generator terminal before feed-in to the grid.

The qualifier 'rated' is important. Net rated capacity is a characteristic value under defined conditions, that is, a capacity figure in the sense of rated capacity. The instantaneous net output in operation can be lower. This is the case, for example, at partial load or when high cooling-water or air temperatures reduce the output of steam and gas turbines.

Order of magnitude for thermal power plants

For coal, gas and nuclear power plants, the difference is clear. The Federal Network Agency's (Bundesnetzagentur) power plant list has separate columns for gross capacity and net rated capacity. Two older hard-coal units show the order of magnitude: for Scholven C it lists 370 MW gross and 345 MW net, for Bergkamen A 780 MW gross and 720 MW net. These are auxiliary consumption shares of roughly 7 to 8 percent. Modern gas-fired power plants are usually below that. The exact share depends on technology, flue gas cleaning, cooling system and operating state.

A worked example shows the effect: a unit with 1,000 MW gross capacity and 70 MW auxiliary consumption makes at most 930 MW available to the grid. Across an entire power plant fleet, such differences easily add up to several gigawatts. This is significant for the capacity balance and for covering residual load.

Renewable plants: register definitions are technology-specific

Caution is needed with renewable plants, because gross and net in the Core Energy Market Data Register (Marktstammdatenregister) are not based on auxiliary consumption everywhere. The Federal Network Agency has defined the terms for each technology. For hydropower, gross capacity corresponds to the generator output and net rated capacity to the net output of the power plant. This corresponds to the classic logic. For wind turbines, gross and net capacity are treated as equal, because both correspond to the rated capacity of the turbine type.

For photovoltaics, gross capacity in the register means the sum of the module capacities in kilowatt-peak, that is, a direct-current quantity under standard test conditions. Net rated capacity is the smaller of the module capacity and the assigned inverter capacity. Because inverters are often sized somewhat smaller than the module array, the net value for PV is usually an alternating-current value limited by the system design. It is not a deducted auxiliary consumption. The common statement that PV gross capacity is present at the inverter terminals is therefore incorrect for German register data.

Physically, wind and PV plants also need electricity, for example for control, pitch and azimuth drives, heating, communication or tracking. Part of this arises during standstill and is then drawn from the grid. In the register's capacity figures, however, this does not appear as a gross-net difference.

Distinction from installed capacity, feed-in and energy

Gross and net capacity are statements about installed capacity with different measuring points. Whether this capacity is actually delivered at a given time depends on maintenance, faults, fuel, weather, grid congestion and market conditions. A 10 MW solar plant does not feed in at night. A coal unit with 800 MW net rated capacity may stand idle because of an overhaul or low prices.

Feed-in is the power or quantity of energy actually delivered to the grid and is thus an operational quantity. It must be distinguished from electrical energy: a plant that delivers 100 MW net for one hour supplies 100 MWh. Auxiliary consumption therefore reduces not only the instantaneous output but also the quantity of electricity delivered over the year. This is why statistics distinguish between gross and net electricity generation.

Typical misunderstandings

  • Mixing gross and net: if gross values of some plants are compared with net values of others, some power plants appear larger than their usable contribution. For capacity figures, it must therefore always be checked which reference quantity is stated. The unit MW alone is not sufficient for this.

  • Including grid losses: net electricity generation means gross generation minus the power plants' own consumption. Losses during transport in lines and transformers of the public grid are not included under the official definitions. Occasionally this is presented differently.

  • Equating net capacity with firm capacity: even a correct net rated capacity says nothing about whether the plant is available when needed. For security of supply, additional quantities such as availability and firm capacity are required.

  • Reading PV kilowatt-peak as grid capacity: for photovoltaics, the module sum in kWp is the gross capacity in the register. The alternating-current power that can be fed in may be considerably lower.

Significance for data, markets and planning

For grid operation, capacity balances and security of supply, net values are usually more meaningful, because they show what actually reaches the grid. The Federal Network Agency's power plant list is therefore based on net rated capacity. Plants with at least 10 MW net rated capacity per site are listed individually; smaller plants appear in aggregated form. Since 2021, the data have been based on the Core Energy Market Data Register. Gross values are mainly useful for the design of generator and plant and for certain statistical balances.

Economically, too, the net value generally counts, because it is the delivered energy that is sold and settled. Higher auxiliary consumption reduces the marketable quantity and worsens the net efficiency.

For industrial power plants and plants with on-site own consumption, a further level is added. The power plant list therefore indicates whether a plant feeds in fully or only partially because it consumes part itself. Net capacity after technical auxiliary consumption is then not the same as the power remaining at the grid connection point after the site's consumption. Anyone using capacity figures should therefore always state the measuring point and system boundary: generator terminal, transfer point of the generating unit, or grid connection of the entire site.

The same applies to international comparisons. Statistics from different countries or institutions may report capacities gross or net and treat renewables differently. Reliable comparisons require that the definitions be disclosed or harmonised.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 16:27

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