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Glossary · Energy industry & energy transition

Curtailment

Curtailment electricity grid generation grid stability redispatch flexibility renewable energies

Curtailment is the deliberate reduction of electricity generation or grid feed-in compared with what a facility could deliver under the prevailing conditions. The term initially describes a technical action, not its cause: curtailment may be ordered by a grid operator, triggered automatically by technical requirements or undertaken for economic reasons. In German grid congestion management, it usually refers to a reduction in feed-in initiated by the grid operator.

A wind turbine can reduce the amount of wind energy it captures by adjusting its rotor blades; a solar installation limits its electrical output through its inverter. A conventional power plant reduces its generation. This does not reduce the facility’s installed capacity. Its actual power output is limited for a specified period. Generation and feed-in are not always identical: if electricity is consumed on site or stored behind the grid connection point, grid feed-in can fall without a corresponding reduction in generation.

Power, duration and energy not fed into the grid

The instantaneous reduction in power is expressed in kilowatts or megawatts. For assessing its impact on the electricity system, the energy not fed into the grid over the duration of the measure also matters, for example in megawatt-hours. In redispatch, this calculated quantity is called curtailed energy. It is based on a comparison with the feed-in that would have been expected without the intervention and is therefore not a quantity of energy that can be read directly from an electricity meter.

An example: if a wind farm could feed a constant 150 megawatts into the grid for ten minutes but is limited to 50 megawatts, the reduction is 100 megawatts. The energy not fed into the grid is 100 megawatts multiplied by one sixth of an hour, or approximately 16.7 megawatt-hours. Over two hours, it would be 200 megawatt-hours. If potential generation fluctuates, the difference must be calculated over time. Rated capacity multiplied by the duration of curtailment would not be a reliable substitute.

Distinguishing grid congestion from surplus generation

A grid constraint exists when an intended electricity flow would breach safe operating limits. Its cause may lie in the transmission grid or the local distribution grid. It is therefore not enough for sufficient demand to exist somewhere: the electricity must be able to reach consumers through the available infrastructure. Curtailment relieves a constraint only if reducing feed-in at the relevant grid location actually reduces the critical power flow or alleviates the critical voltage situation.

This must be distinguished from a temporary surplus of potential generation over demand capable of absorbing it, including storage and exports. In that case too, reducing output may be necessary or economically sensible. A regional grid constraint does not automatically mean, however, that there is too much electricity in the system as a whole. Conversely, a temporary surplus can occur even if no individual line is overloaded. The appropriate countermeasures differ accordingly.

To maintain frequency, generation and consumption must be balanced continuously. Balancing reserves are used for this purpose in particular; a reduction in generation can form part of that balancing. Grid congestion management and frequency control are nevertheless different tasks. A statement that a facility is curtailed for grid stability is therefore not very informative without a more precise reason.

Distinguishing curtailment from redispatch, disconnection and market response

Redispatch is the grid-related adjustment of facility operation, not merely its reduction. Typically, less electricity is fed in at a location where the adjustment relieves the constraint and more is fed in elsewhere. Electricity storage facilities can also be included. Curtailment is the downward adjustment in this process. Since 1 October 2021, renewable energy and combined heat and power facilities have also been integrated into the German system known as Redispatch 2.0; the former term feed-in management is therefore not an appropriate general designation for the current procedure.

Curtailment can reduce output to zero. A complete limit on feed-in does not necessarily mean, however, that the facility has been electrically disconnected from the grid or has failed because of a defect. Conversely, not every stoppage is curtailment: lack of wind, darkness, maintenance and technical faults reduce available generation without deliberately limiting existing generation potential.

The underlying cause must also be stated clearly. If an operator voluntarily reduces generation because of unfavourable market prices, this is not redispatch initiated by a grid operator. In broader usage, it is nevertheless called economic curtailment. This distinction is particularly important when electricity prices are negative: a price signal and a specific grid constraint may occur together, but need not do so. International statistics may include voluntary market responses and are therefore not readily comparable with German redispatch data.

Why wind and solar power receive particular attention

Wind and solar installations use weather-dependent energy sources and need no fuel to generate additional electricity. An hour of wind or sunshine left unused today cannot be recovered later. This makes their curtailment particularly conspicuous. It does not automatically follow, however, that too many renewable energy facilities have been built overall: what matters is how generation, transport, demand and opportunities to shift energy use over time fit together.

For Germany, the Federal Network Agency reports a grid-related reduction in renewable feed-in of 9,379 gigawatt-hours for 2025, equivalent to approximately 9.38 terawatt-hours. The published share of renewable electricity generation is 3.5 percent. Around 35 percent of this redispatch volume was caused by constraints in the distribution grid. These annual figures do not cover every economically or technically motivated limit on generation.

A nationwide average also says little about the risk to an individual facility. Two wind farms using the same technology may be affected very differently because they are connected at different grid nodes. A meaningful assessment therefore requires not only the quantity of energy but also the period, region, facility technology, reason and a clearly identified reference quantity. The total redispatch volume must not be equated with curtailed renewable electricity: it can also include reductions in conventional generation and increases in generation.

Law and financial compensation in Germany

Under Section 13a of the German Energy Industry Act, the adjustment obligation generally covers generation and storage facilities with a rated capacity of 100 kilowatts or more, as well as smaller facilities that a grid operator can remotely control at any time. Section 14 of the Act supplements its application to distribution grid operators. This classification concerns Germany, with the law as it stood on 11 November 2026. It does not mean that every small solar installation automatically participates in the same procedure.

For measures under Section 13a, the law provides for appropriate financial compensation. Taking balancing compensation into account, the operator should generally be left neither better nor worse off financially than without the measure. For renewable generation and combined heat and power, lost revenue and additional expenses are particularly relevant; avoided expenses must also be taken into account. This does not establish a blanket entitlement to compensation for every voluntary, technical or contractually agreed limitation on feed-in.

Financial compensation and balancing compensation are different: the former concerns financial losses, while the latter concerns the allocation of the missing quantity of electricity within the electricity system. Special transitional and implementation rules apply to distribution grids. The amount curtailed, compensation payments and the total costs of grid congestion management must therefore be considered separately. The latter also include, for example, costs for additional power plants brought into operation and are not a direct price for each lost renewable kilowatt-hour.

Flexibility helps only at the right place and time

More flexibility can reduce curtailment: storage facilities absorb energy temporarily, while consumers able to shift their demand adjust their electricity consumption. Options include electric vehicle charging, heat production with thermal storage, electrolysis and suitable industrial processes. Additional transmission capacity and better use of existing grids can also help. None of these options is a universal solution regardless of location, operating mode and costs.

This can be explained using a simplified line between a generating region and a consuming region. If a battery on the generation side charges during a surplus, less electricity needs to flow over the heavily loaded line. If, by contrast, it charges on the consumption side and thereby increases the need to transmit electricity over that very line, it can worsen the constraint. What matters, therefore, is not simply whether storage exists somewhere, but how its operation changes the specific electricity flow.

Likewise, a low wholesale market price does not automatically guarantee behaviour that benefits the grid. Within a single price zone, the market signal does not directly reflect individual local constraints. A consumer technically able to shift demand therefore needs appropriate economic incentives and, where necessary, grid-related control. The question for assessment is whether the additional demand can absorb precisely the generation that would otherwise be curtailed, or whether it creates new pressures elsewhere.

Avoiding curtailment is not always worthwhile

Limited curtailment can be more economical than infrastructure needed solely for rare generation peaks. The goal is therefore not necessarily zero curtailment. The costs of additional lines, storage or shifting consumption must be compared with the benefit of the additional energy that can thereby be used. Frequent, extensive interventions, by contrast, may indicate inadequate grids, insufficient flexibility or unsuitable market rules.

Curtailment is thus both an operating tool and a diagnostic indicator. An increase in its volume alone proves neither that renewable energy has failed nor that grid expansion is uneconomic. It becomes meaningful only when considered alongside causes, costs and realistic alternatives. The guiding question is: what combination of generation, grids, storage and consumption enables a secure supply at the lowest possible total cost?

Sources

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Edited by eCMS on 11.11.2026 06:14

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