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Glossary · Energy industry & energy transition

Flexibility

flexibility power system load shifting storage demand generation grid operation ancillary service distribution grid market rules

In the power system, flexibility refers to the ability to deliberately change electrical power over time in order to respond to technical or economic signals. Consumers, generation plants or storage units can provide it. A load is switched on later, a generation plant reduces its feed-in, a battery storage unit charges or discharges, or a process is interrupted for a certain time. Flexibility is therefore not an amount of energy in itself. It is a controllable change in power over a certain duration that deviates from a baseline schedule.

In European law, the term is defined more broadly. Since the 2024 electricity market reform, the Internal Electricity Market Regulation defines flexibility as the ability of the entire power system to adjust to variable generation and consumption patterns and to grid availability in the relevant market timeframes. Two levels can therefore be distinguished. System flexibility is a property of the overall system. Individual plants whose power can be shifted are flexibility resources. They contribute to this system capability.

Key parameters of flexibility

Several specifications are needed for a technical description. The change in power is usually stated in kilowatts or megawatts. Its duration determines how much energy, in kilowatt-hours or megawatt-hours, is shifted in time. An example: shifting 10 kW for two hours moves 20 kWh. In addition there are response time, availability, repeatability, a possible catch-up phase (the so-called rebound), forecast quality and location in the grid. A battery responds within seconds but is limited by its state of charge. A heat pump can shift load as long as the building and the hot water storage tank provide thermal buffers. An industrial plant can move large amounts of power. However, it needs production windows, contractual certainty and clear cost incentives.

Distinction from storage and efficiency

Flexibility is often equated with storage. This is imprecise. A storage unit is a technical installation that absorbs energy and releases it again later. Flexibility also includes consumption shifting, controllable generation, curtailment, process adjustments and grid-supportive control. A refrigeration system that cools more strongly in advance and then pauses does not store electrical energy in the strict sense. But it uses thermal inertia. An electrolysis plant that runs at low electricity prices and throttles during scarcity is also a flexible load. Storage is thus an important form of flexibility, but not its umbrella term.

Likewise, flexibility must be separated from energy efficiency. Efficiency reduces the energy input for a given useful output. Flexibility changes the timing or level of power consumption. An efficient plant can be inflexible if it must run constantly at constant power. A less efficient plant can be flexible if its operation can be shifted. Both properties are relevant but solve different problems: efficiency reduces quantities, flexibility changes temporal patterns. Flexibly operated plants can also cause losses, for example through charging and discharging losses or through heat losses of preheated buffers.

Why flexibility is needed in the power system

In the power grid, feed-in and withdrawal must be physically balanced at every moment. Deviations show up in the grid frequency. At the same time, lines, transformers and other equipment must not be overloaded. As the share of wind energy and photovoltaics grows, weather-dependent feed-in increases. There are more frequent hours with a great deal of low-cost generation and other hours in which controllable power plants, storage or flexible demand are needed. Flexibility helps to balance these differences without absorbing every fluctuation solely with additional power plant capacity or grid expansion. The EU therefore requires that flexibility needs be assessed at least on seasonal, daily and hourly time scales.

Flexibilities act at different levels. In the overall electricity market, flexible demand can shift consumption from low-price hours to higher-price hours. In the transmission grid, flexibility can reduce balancing deviations or serve as balancing power. In the distribution grid it can ease local bottlenecks, for example when many heat pumps, charging points or photovoltaic systems are connected to the same feeder. These levels do not automatically coincide. What makes sense for the market can aggravate a grid problem locally if many plants react to the same price at the same time.

A key point follows: flexibility has a location. A kilowatt-hour that can be shifted in northern Germany does not without further ado resolve a bottleneck in a southern German distribution grid. Even within a city, the grid connection point decides whether a controllable load helps, remains neutral or places additional strain on the grid. Anyone who views flexibility only as a nationwide quantity of electricity overlooks the grid level at which many practical conflicts arise.

From technical possibility to usable resource

Many devices are theoretically flexible. That does not yet make them a reliable resource for system operation. Flexibility becomes usable only when it can be measured, forecast, controlled, billed and contractually secured. This requires smart metering systems, control technology, communication channels, standardised interfaces and rules for access. It must also be clarified who may market or request the flexibility: the supplier, an aggregator, the grid operator, the plant operator or a service provider. In Germany, grid-oriented control is to run via a smart meter gateway under the relevant act as soon as a smart metering system has been installed.

These responsibilities are not incidental. A flexible wallbox can react to electricity prices, be throttled during grid bottlenecks or be pooled with other plants in a virtual power plant. Each of these purposes follows its own rules. Market-based flexibility is guided by prices, grid-related flexibility by operational security. Balancing energy and other system services require prequalification, reliable callability and proof. Conflicts arise where technical possibility, market rules and responsibility diverge.

Remuneration and risk allocation also decide whether flexibility comes about. Anyone who makes a plant flexible bears investment costs, loss of comfort, process risks or additional wear. If these costs are not covered, flexibility remains unused even though it is technically available. Conversely, wrong incentives can lead to flexibility being used only where it yields private revenue, even though it would be more useful elsewhere in the grid. Flexibility is therefore always also a question of market design and regulation.

Legal framework in the EU and Germany (as of November 2026)

  • EU: Regulation (EU) 2024/1747 amended the Internal Electricity Market Regulation (EU) 2019/943 and applies directly. The regulatory authority or another designated body must regularly prepare a report on national flexibility needs for at least the next five to ten years. The basis is a European methodology approved by ACER and data from transmission and distribution system operators. The report must also assess the potential of non-fossil flexibility such as demand response and energy storage, as well as market barriers. Building on this, Member States set an indicative national objective for non-fossil flexibility. Under conditions, they may use support schemes in the form of capacity payments for this purpose.

  • Germany, low voltage, § 14a EnWG: Since 1 January 2024, newly commissioned controllable consumption devices with a grid connection capacity of more than 4.2 kW must be controllable. These include private wallboxes, heat pumps, air conditioners and electricity storage units, the latter only when charging. If overload threatens, the grid operator may temporarily throttle consumption, but not reduce it below 4.2 kW per device. It may not switch it off completely. The remaining household electricity and PV feed-in are not affected. In return, the grid charge is reduced. Existing installations and night storage heaters are subject to transitional or special rules.

  • Germany, distribution grid, § 14c EnWG: If distribution system operators procure flexibility services in order to make the operation and expansion of their grid more efficient, this must be done in a transparent, non-discriminatory and market-based manner. The Bundesnetzagentur (Federal Network Agency) must approve the specifications and standardised products. It can allow exceptions, for example if market-based procurement would not be economical or would intensify bottlenecks. The redispatch regime and § 14a remain unaffected.

Typical misconceptions

A common misconception is that flexibility can largely replace grid expansion. It can relieve grids and postpone expansion or make it more targeted. But it does not replace a line if more power must permanently be transported into or out of an area. The Bundesnetzagentur also stresses that most low-voltage grids are not yet designed for a rapid ramp-up of heat pumps and wallboxes. They must therefore be optimised, digitalised and expanded. The throttling rule under § 14a is a precaution for the transition period, not a substitute for capacity. Flexibility and grid expansion are not opposites but different tools for different bottlenecks.

A second misconception concerns dynamic electricity prices. Prices can shift consumption if people or automated systems respond to them. They do not guarantee a grid-supportive effect. The Bundesnetzagentur itself gives an example: cheap electricity at a certain time of day can cause many home storage units to charge simultaneously and overload local grid areas. Price signals alone are therefore not sufficient where local grid limits play a role. Market prices, grid charges, connection rules and control options must fit together. Time-variable grid charges under § 14a are one approach to building local grid signals into prices.

A third misconception equates flexibility with doing without. Load shifting does not necessarily mean that users receive less heat, mobility or production. Often the same energy service is simply provided at a different time. This distinguishes flexibility from a shutdown without replacement. In industrial plants, however, flexibility can cause real opportunity costs, because production processes, staff planning, delivery deadlines and plant wear are affected. These costs must be made visible, otherwise the potential is overestimated.

A fourth problem is aggregated potential figures. Studies often cite high flexible capacities from electric cars, heat pumps, home storage units or industrial processes. Such figures are meaningful only if they take into account availability, simultaneity, grid location, technical controllability and user limits. An electric car is flexible only if it is plugged in, the state of charge leaves leeway and the desired departure time is met. A heat pump can be shifted only to a limited extent if outdoor temperature, building envelope and storage size set narrow limits. Installed capacity of several gigawatts is therefore not the same as several gigawatts that can be reliably called upon in a particular hour.

Relationship with residual load, security of supply and system costs

Flexibility becomes particularly important when the residual load fluctuates strongly. It is electricity consumption minus feed-in from weather-dependent renewable energies. With a lot of wind and solar power it can become low or temporarily negative. With little wind, little sun and high consumption it rises. Flexible consumers, storage and controllable generators can cushion these fluctuations by adjusting electricity use and provision over time.

For security of supply, however, flexibility is not a complete substitute for firm capacity. A flexible load reduces demand in critical hours only if it is actually available and callable. A storage unit delivers power only as long as it is sufficiently charged. In longer periods with little wind and sun this is a hard limit. Controllable power plants step in if fuel, technical availability and the market framework are in place. Security of supply arises from the interplay of these resources, not from a single category.

Flexibility also affects system costs. It can reduce expensive peak loads, lower the curtailment of renewable energies, ease grid bottlenecks and reduce the need for reserve capacity. At the same time it has costs of its own: metering, control, digitalisation, contract management and interventions in operating processes. A sensible assessment therefore does not compare flexibility with a cost-free ideal state but with concrete alternatives. These include additional grid expansion, more storage, more controllable capacity, more curtailment or stricter connection limits.

Flexibility shows that a renewable power system cannot be described by annual quantities alone. Its value is determined by timing, duration, location, reliability and access rules. The term therefore stands not for a blanket solution but for a precisely defined system capability: shifting or adjusting electrical power so that the market, grid operation and security of supply work together with fewer unnecessary costs and fewer uncoordinated interventions.

Sources

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Edited by eCMS on 11.11.2026 19:47

© 2026 Erik Schmidt. All rights reserved. Quotations with a link to the source are welcome.