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Glossary · Energy industry & energy transition

Flexibility need

flexibility need flexibility residual load storage load management power system renewable energies

Flexibility need refers to the extent of temporal, spatial and technical adaptability that a power system requires. Its purpose is to keep generation and consumption balanced at all times, to respect grid limits and to ensure security of supply. It does not mean a single technology but a requirement placed on the system as a whole. Electricity must be available, or saved, at every moment where it is needed. However, lines, power plants, storage facilities, consumers and market rules can only respond to a limited extent and at different speeds.

The term describes a gap: between the actual profile of generation and consumption and the profile that would be needed for secure operation. This gap can occur over seconds, hours, days or across seasons. It can affect the whole system or be very local, for example in a distribution grid with many photovoltaic systems. A single figure in kilowatt hours is therefore not sufficient. Depending on the question, several quantities matter: power in kilowatts or megawatts, energy in kilowatt hours or megawatt hours, rate of change (for example megawatts per hour), response time, duration, location and reliability. The Bundesnetzagentur (Federal Network Agency) names similar characteristics to describe flexibility: magnitude of the power change, duration, rate of change, response time and location.

Distinction from flexibility, storage need and residual load

Flexibility need must be distinguished from flexibility. The Bundesnetzagentur understands flexibility to mean that feed-in or withdrawal is changed in response to an external signal, that is, a price signal or a dispatch call, in order to provide a service in the energy system. Flexibility need, by contrast, describes how much of this adjustment is required and under what conditions it must be available. A system can therefore have a high need without sufficient usable flexibility already being in place.

Flexibility need is also not the same as storage need. Storage is one possible answer, but not the only one. Other options can also partly cover the same need: load shifting in industry, controlled charging of electric cars, heat pumps with buffer tanks, flexible electrolysers, dispatchable power plants, grid expansion, curtailment and electricity trading across larger areas. Which solution fits depends on duration, frequency, location and the required reliability. A battery storage system shifts electricity very quickly over minutes and hours, but does not bridge a multi-week period with little wind and sun. A heat store shifts electricity demand in the heating sector, but does not feed electricity back into the grid. A gas-fired power plant provides firm capacity, but does not create room for local PV surpluses in the low-voltage grid.

Residual load is a related but narrower term. It refers to the consumption that remains after deducting weather-dependent renewable feed-in, mainly from wind and photovoltaics. Depending on the study, other renewable or non-dispatchable plants are also deducted. Flexibility need often results from the profile of the residual load, but covers more. Grid congestion, forecast errors, balancing power, voltage control and institutional requirements can also call for flexibility, even if the nationwide residual load looks unremarkable.

Time scales and technical function

In the range of seconds and minutes, the issue is frequency control. Generation and consumption must match almost exactly, otherwise the grid frequency deviates. This task is handled by automatic control mechanisms, balancing power procured on the market, and technical reserves.

In the range of hours, requirements arise from the daily profile. Photovoltaics generate a lot of electricity at midday, while consumption is often high in the morning and evening. Wind power can rise or fall sharply within a few hours. This creates ramps, that is, rapid rises or drops in residual load. The Bundesnetzagentur described this pattern as early as 2017: as the share of renewable energy increases, residual load falls towards zero in many hours and then rises significantly within a short time.

Over days and weeks, the issue is less about speed than about endurance. Storage needs sufficient energy content, flexible consumers must actually be able to shift their processes, and dispatchable generation must remain available. Seasonal questions are added as electricity is increasingly used for heat, transport and industry. In winter, heat demand is higher, PV yields are lower and wind patterns differ from those in summer. A need that looks small on an annual average can become very large under certain weather conditions.

Location also matters. A storage unit behind a grid bottleneck has a different effect on the overloaded section than a storage unit on the other side of the bottleneck. Flexible loads in a wind-rich region can ease bottlenecks if they are controlled in a grid-serving way. If they respond only to nationwide exchange prices, they can also aggravate bottlenecks. Flexibility need therefore always has a technical and an institutional side. Physically, what happens in the grid counts; economically, what counts is which signals plant operators actually receive.

Legal framework in the EU and in Germany

Since the reform of the EU electricity market design, flexibility need has also been a legal concept. Regulation (EU) 2024/1747 of 13 June 2024, in force since 16 July 2024, amended the Internal Electricity Market Regulation (EU) 2019/943. The new Article 19e obliges Member States to adopt a report on the estimated flexibility need for at least the next five to ten years. It is based on data and analyses from the transmission and distribution system operators. The need must be assessed at least on a seasonal, daily and hourly basis. The methodology was proposed by ENTSO-E and the EU DSO Entity and approved by ACER. It is to take into account all available sources of flexibility in a cost-efficient manner, including those in other Member States.

Article 19f builds on these reports. Within six months, each Member State must set an indicative national objective for non-fossil flexibility. This must show the contributions of demand response and energy storage. ACER then evaluates the national reports and issues recommendations on cross-border issues.

In Germany, the Bundesnetzagentur published such a report for the first time in 2026 (status as of August 2026). It is based on calculations by the transmission system operators and distribution system operators and supplements the classic monitoring of security of supply, which focuses on dispatchable generation. Result: for the years examined, the authority saw no reason for additional measures against uncovered flexibility need. Further developments are to be monitored in the following reports. The report expressly does not examine periods of less than one hour. These remain an ongoing task of the grid operators.

The Bundesverband Neue Energiewirtschaft (bne, German Association of New Energy Economy) reads the report as follows: the need for 2030 and 2035 can be met above all if many battery storage systems are added quickly. The association also cites hourly residual load ramps of up to 58 gigawatts per hour upwards and 43 gigawatts per hour downwards in 2030. For 2035 it cites 80 and 60 gigawatts per hour. These are model results under certain assumptions, not forecasts with a guarantee.

Why the need becomes more visible with renewable energy

Systems with many conventional power plants also had a flexibility need. Consumption fluctuates, power plants fail, forecasts are uncertain. In the past, it was mainly the load that was hard to predict. Today, a growing share of generation follows weather and daylight. As a result, the adjustment task shifts more towards flexible demand, storage, grids, dispatchable residual capacity, and imports and exports with neighbouring countries.

A rising flexibility need does not automatically make a system less secure. However, secure operation requires different means. Security of supply then depends more on whether flexibility is reliably available, technically connectable, economically viable and legally permissible. A heat pump only helps the system if the building, storage, controls, tariff and grid connection fit together. An annual balance with enough renewable electricity says nothing about whether enough capacity is available in every hour or whether grid sections become overloaded. Flexibility need forces one to consider time profiles and bottlenecks as well.

Typical misinterpretations

  • Flexibility need equals missing storage: this equation narrows the solutions too early. Storage competes with load management, grid expansion, dispatchable generation and European trading, and complements them. The Bundesnetzagentur considers grid expansion the most sensible solution for grid bottlenecks in almost all cases.

  • National view only: balancing across national borders can reduce the national need. The EU methodology therefore expressly also takes cross-border flexibility into account. European trading, however, does not remove local bottlenecks. A low nationwide price can coincide with a local bottleneck. Market-serving and grid-serving flexibility then differ.

  • Negative prices as a complete diagnosis: negative electricity prices point to a flexibility need. However, they can also be amplified by support rules, technical minimum outputs, grid bottlenecks, bidding strategies or inflexible demand. Anyone who wants to understand their effect must look at the rules that produce them.

  • Curtailment equals storage gap: every curtailed kilowatt hour shows that electricity could not be used or transported at one place at one time. Whether storage is the right answer depends on where the bottleneck lies: in the distribution grid, in the transmission grid, in the market mechanism, in demand or in controllability.

  • Overlooking the seconds range: the German report of 2026 does not cover periods of less than one hour. If it finds no uncovered need, that is therefore not a statement about frequency control or balancing power.

Institutional and economic significance

Flexibility need arises from technology but is assessed through rules. Grid charges, tariffs, balancing group rules, redispatch, support schemes, connection conditions and metering and control technology determine which flexibility becomes economically visible. A heat pump with a buffer tank is technically flexible. Without variable tariffs, suitable controls and clear rules for interventions by the grid operator, however, this flexibility often remains unused. The Bundesnetzagentur fundamentally relies on competitive solutions with price signals and rejects special support for individual actors. At the same time, it wants to discuss whether grid operators should reflect scarce grid capacity through further developed charges.

Flexibility need is thus a test concept for electricity market design and grid regulation. It asks about coordination: who recognises the need, who may call on flexibility, who pays for it, who bears the risk? And how is it prevented that a solution in one place enlarges a problem in another? The term distinguishes between energy quantity, power, time and location. A system with a high share of renewable generation does not need just any flexibility, but suitable flexibility: as fast, as long, at the place and as reliable as the respective situation demands.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 19:47

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