Connection study (Anschlussstudie) · Glossary

A connection study is a technical investigation. It clarifies whether, where and under what conditions a planned installation can be connected to an electricity grid. The electrical design of a project is compared with the actual capability of the grid at the intended site. Typical subjects of examination are the suitable connection point, the voltage level, the available grid capacity, load flows, short-circuit power, voltage maintenance, reactive power behaviour, protection systems, grid feedback effects, possible grid reinforcements and operational restrictions.

In Germany the term is not defined by statute. In practice, similar investigations go by names such as grid connection study, grid study, feasibility study on grid connection or, where many applications are processed together, cluster study. By contrast, individual procedural steps are regulated by law. These include the grid compatibility check under the Renewable Energy Sources Act (Erneuerbare-Energien-Gesetz) and the examination of a grid connection request under the Power Plant Grid Connection Ordinance (Kraftwerks-Netzanschlussverordnung). A connection study can prepare, include or supplement such steps. However, it is not identical to them.

The term is used mainly for larger projects: wind farms, solar parks, battery storage, electrolysers, data centres, industrial plants, charging parks, substations and mixed projects with generation and consumption. For small house connections the check is largely standardised. Large connection capacities, by contrast, can noticeably change the mode of operation of an entire grid section. In that case it is not enough to plan a line to the nearest station. The grid must be able to absorb, transport or provide the additional power without violating limit values. The connection study thus becomes the link between project development and grid planning. Its result is not a mere site assessment. It is a statement about technical connectability under clearly stated assumptions.

What a connection study examines technically

The focus is on the connection capacity. It is stated in kilowatts, megawatts or, for very large projects, gigawatts. It means the maximum electrical power that an installation may feed in or draw. This must be distinguished from the quantity of energy. A battery storage system may, for example, have a power of 100 megawatts and store 200 megawatt hours. For the study, what counts first is the maximum feed-in or draw power, because lines, transformers, switchgear and protective devices are designed for currents and voltages. The quantity of energy rather determines how long this power can be called upon and what the operating profile looks like.

The study also clarifies at which voltage level a project is sensibly connected. Low voltage, medium voltage, high voltage and extra-high voltage differ not only in their voltage values. Responsibilities, protection concepts, costs and permitting effort also differ. Under the German technical connection rule, a medium-voltage grid is a 50-hertz three-phase grid with voltages above 1 kilovolt and below 60 kilovolts. A larger commercial or industrial business can be connected there. A large electrolyser or large-scale storage system, by contrast, usually needs high or extra-high voltage. The size of the installation alone, however, does not decide the voltage level. The local grid structure, existing reserves and the load and generation situation in the surrounding area also matter.

An important building block is the load flow calculation. It calculates how currents are distributed in the grid when the new installation feeds in or draws power. Electricity does not follow contractually desired paths. It distributes itself over all available paths according to electrical impedances. A connection can therefore also load equipment that is spatially far from the project site. Calculations cover not only undisturbed normal operation. Grid operators generally also check the (n-1) criterion: the grid must remain secure if a single important item of equipment, such as a line or a transformer, fails. The transmission system operators explicitly name this criterion as a principle of their grid calculation for new connections.

The study also includes checking the short-circuit power. It shows which currents can occur in the event of a fault and whether switchgear, protective devices and other grid components can safely handle these currents. Too low a short-circuit power is likewise problematic. Protection systems then detect faults less well, and inverter-based installations interact less stably with the grid. Photovoltaics, battery storage, modern wind turbines and converters for electrolysers are coupled to the grid via power electronics. They behave differently from classical synchronous generators. A connection study therefore often also has to examine dynamic and control-engineering properties. Depending on the procedure, this often happens only in a later, more detailed examination stage.

A further core point is voltage maintenance. Every feed-in and every consumption changes the voltage in the grid: feed-in tends to raise it, consumption lowers it. The permissible voltage bands are limited technically and by standards. In distribution grids with a lot of photovoltaics, the voltage on sunny days is often already close to the upper limit. A further solar park on the same grid section then cannot be assessed solely by the free line capacity. It can push the voltage beyond the permissible limit even though the thermal loading of the line would still be acceptable.

Reactive power is also part of the examination. It is stated in var or megavar. Reactive power builds up electric and magnetic fields but performs no usable work. Nevertheless it influences voltages, currents and grid losses. Many installations today must be able to provide or absorb reactive power in order to stabilise the voltage. The study clarifies which requirements for operating point and control apply and whether additional compensation equipment is needed.

For larger projects, grid feedback effects are also examined. These include harmonics, flicker, asymmetrical loading, rapid load jumps and switching operations. Such effects can affect other grid users or disturb protection and metering systems. High-power charging parks, industrial converters, electrolysers and battery storage are often demanding in this respect. A careful connection study therefore looks not only at average power. It also asks in what manner the installation draws power from the grid or feeds it into the grid.

Legal and regulatory framework in Germany

Which rules apply to a connection in Germany depends strongly on the class of installation. Roughly, three groups can be distinguished. The Renewable Energy Sources Act applies to installations generating electricity from renewable energies. The Power Plant Grid Connection Ordinance applies to other generation installations with a rated capacity of 100 megawatts or more connected to grids of 110 kilovolts or above. The general connection obligation under section 17 of the Energy Industry Act (Energiewirtschaftsgesetz) applies to storage facilities, to consumers such as data centres, industry and electrolysers, and to the remaining cases. Under it, grid operators must enable connections in a reasonable, non-discriminatory and transparent manner.

Renewable energies (EEG 2023, section 8): Grid operators must connect such installations without delay and with priority. The decisive point is the point of interconnection at a suitable voltage level with the shortest straight-line distance, unless another point is technically and economically more favourable. Once the grid operator has all the necessary information, it must communicate the result of its grid compatibility check without delay, but at the latest within eight weeks. This includes a schedule, a detailed cost estimate and, on request, the grid data needed for a separate grid compatibility check. Since 2025, a shortened deadline of one month applies to installations of up to 30 kilowatts on properties with an existing connection. The connection obligation also exists where the grid first has to be optimised, reinforced or expanded in order to take the electricity.
Conventional large power plants (KraftNAV): The ordinance applies to generation installations of 100 megawatts rated capacity or more on grids of 110 kilovolts or above. It regulates a formal examination procedure, the connection commitment and the grid connection contract. Since 24 December 2025 it states explicitly that it does not apply to energy storage installations. Large battery storage systems therefore no longer fall under this procedure.
Storage and large consumers on the transmission grid (section 17 EnWG, maturity-level procedure): On 5 February 2026 the four transmission system operators presented a maturity-level procedure based on the principle of "first ready, first served". The first application cycle was planned for April 2026. Applications are collected cyclically up to a cut-off date. The grid operator then checks minimum requirements, allocates capacity by maturity points in the event of oversubscription, and calculates the grid in a joint cluster study that is expected to take around five months. An application fee of 50,000 euros is envisaged and, upon acceptance of an offer, a realisation deposit of 1,500 euros per megawatt.

Alongside procedural law, technical rules shape the study. In Germany, the VDE application rules lay down, as technical connection rules, what customer installations must fulfil. These include generation installations, storage, consumption and mixed installations, and charging facilities. The rules concern protection technology, frequency and voltage behaviour, reactive power provision, active power control, and verification and certification procedures. VDE-AR-N 4110 applies to medium voltage, VDE-AR-N 4120 to high voltage and VDE-AR-N 4130 to extra-high voltage. Individual grid operators supplement these rules with their own technical connection conditions. The rules are continuously revised. A study must therefore state the version that is applicable.

Distinction from grid connection, grid compatibility check and connection commitment

The connection study is often confused with related terms. A grid connection is the actual technical and contractual link of an installation to the electricity grid. It includes lines, switchgear bays, metering, protection technology, contracts, boundaries of responsibility and operating rules. The connection study generally comes earlier in time or accompanies the planning.

The grid compatibility check is more narrowly defined. Within the scope of the EEG, it is a procedural step to be carried out by the grid operator, with a statutory deadline and a defined scope of results. It examines whether a particular feed-in or withdrawal is compatible with existing grid conditions. A connection study can contain such a check or serve as the installation operator's own counter-check on the basis of the grid data released. Often, however, it goes further: it compares variants, outlines grid reinforcements, examines alternative voltage levels, assesses timed expansion paths and derives technical connection conditions.

A grid connection commitment or grid connection reservation, by contrast, is a declaration by the responsible grid operator. Depending on the procedure, it may be binding or subject to conditions. The KraftNAV, for example, provides for a formal connection commitment. In the transmission system operators' maturity-level procedure, reservation offers for capacity and connection point are issued. The earliest possible connection date stated there is expressly only indicative. A study commissioned by project developers does not, in itself, establish any entitlement to a particular connection point, a particular capacity or a particular commissioning date. Bindingness arises only through the relevant rules, procedures and contracts.

A general feasibility study is also something different. It may consider site, permit, subsoil, economic viability, supply chains and financing. The connection study concentrates on the electrical integration into the grid. It can be decisive for economic feasibility, but does not replace an overall assessment of the project.

Why connection studies are central to project development

A project can appear technically mature, permittable and financially attractive and still fail because of the grid connection or be greatly changed by grid requirements. For renewable energies, battery storage, electrolysers and new large consumers, the grid connection often becomes the critical path. The connection study shows early whether the nearest grid point is really suitable, which line route is needed, whether a substation has to be extended and which measures are necessary before commissioning.

For investors and project developers this is economically essential. The costs of a grid connection range from manageable cable work to new substations, high-voltage lines or extensive protection and control systems. The schedule also depends heavily on the grid. A battery storage system can be built on the site comparatively quickly. The grid connection, by contrast, can take several years because of switchgear extension, permitting, delivery times for transformers or grid reinforcement. The transmission system operators report that in their substations it is above all free switchgear bays that are scarce, and that nearly all free connection points on the transmission grid are already reserved for the next five years.

The connection study also feeds back into the plant design. If grid capacity is limited, a smaller connection capacity may make more economic sense than the largest possible installation. For a solar park, a deliberately limited feed-in capacity can reduce connection costs. For a battery storage system, a different operating mode can help avoid grid bottlenecks. For an electrolyser, flexible operation can lower the requirements if the installation does not permanently draw its full power. For the grid connection, therefore, not only the installed capacity counts. It also matters when power occurs, how fast it changes, how it coincides with other feeders and consumers, and how well the installation can be controlled.

Grid capacity is not a fixed number

A common misunderstanding treats grid capacity like free storage space. In reality it depends on the grid state, on switching states, on simultaneous feed-in and withdrawal, on temperature assumptions, safety criteria and the grid operator's operating rules. A line does have a thermal loading limit. But this limit alone hardly says whether a connection is possible. Voltage, short-circuit behaviour, protection coordination and grid stability can limit earlier. Which resource is scarce also differs between grid levels. On the transmission grid, according to the transmission system operators, it is above all indivisible switchgear bays and project resources. In distribution grids, the limiting factor is more often the available power.

The talk of a "free grid connection point" is also misleading. A nearby substation can be electrically unsuitable if the transformers are fully utilised, switchgear bays are missing or the upstream grid level cannot absorb additional power. Conversely, a more distant connection point can be economically better if a higher voltage level is available there or grid expansion is planned anyway.

Connection studies therefore work with assumptions. They take into account existing grids, projects already committed, the expected development of load and generation, planned grid reinforcements and technical standards. How meaningful a study is depends on how robust these assumptions are. When many projects in the same region want a connection, they compete technically for the same reserves. Grid operators are therefore increasingly moving to bundled studies that calculate all applications of a cycle together and take mutual dependencies into account. Individual studies are then no longer processed one after another.

Connection studies between grid operator and installation operator

The grid operator is responsible for secure, reliable and non-discriminatory grid operation. It must enable connections when the statutory and technical requirements are met, but may not endanger grid security in doing so. The installation operator wants a connection that is as cheap, fast and powerful as possible. The connection study stands between these interests. It is meant to make technical limits transparent and show variants, without blurring responsibility for the grid.

This results in a clear division of roles. Project developers can commission experts, have preliminary studies prepared and prepare technical variants. Binding statements about the public grid and its operation, however, can only be made by the responsible grid operator. For connection to the transmission grid different procedures apply than in the distribution grid, and distribution system operators also differ in data situation, grid structure and processing workflows. Large projects often require additional coordination with the upstream grid. A connection in the medium-voltage grid can have repercussions on the high-voltage grid. A large consumer in the high-voltage grid can aggravate bottlenecks in the transmission grid. The electrical effect follows the grid, not the organisational boundary.

Costs, responsibilities and incentives

Connection studies make visible costs that are often underestimated in early project ideas. These include connection lines, switchgear bays, transformers, metering and protection technology, construction cost contributions, land, route rights, permits, installation certificates and, where applicable, grid reinforcements. Which costs the connection customer bears and which are spread across all grid users via grid charges depends on the legal framework, on the type of project and on the delimitation between connection facility and general grid expansion. Under the EEG, for example, the grid operator's cost estimate covers only the costs of the technical establishment of the connection. The right to use third-party land for the connection line is expressly not part of it.

Incentives also arise in dimensioning. Whoever applies for a very high connection capacity secures operational freedom, but causes higher costs and occupies grid capacity. Whoever limits the power or accepts flexible modes of operation can, under certain circumstances, be connected faster or more cheaply. The EEG now expressly provides for flexible grid connection agreements for this purpose. Flexible assumptions, however, do not replace robust planning. If a project is grid-compatible only if it is curtailed in certain grid situations, it must be clarified who controls this limitation, how it is implemented technically and regulated contractually, and what economic consequences it has. Such operating restrictions belong at the core of the study, not in a non-binding footnote.

Flexibility, storage and new electricity consumers

With the electrification of heat, transport and industry, connection studies for consumption installations are gaining weight. For a long time the public debate focused mainly on wind and solar parks. Today the focus is increasingly on data centres, electrolysers, heat pump districts, fast-charging parks, battery factories and industrial process conversions. How great the rush is is shown by figures from the transmission system operators: at the end of September 2025, connection applications for battery storage alone amounting to around 211 gigawatts were pending with them. This is well above the assumptions of grid development planning.

A flexible consumer has to be assessed differently for the grid than an inflexible one. An electrolyser that adapts its power to grid bottlenecks or electricity prices loads the grid differently from an installation running at full load around the clock. A charging park with intelligent control can smooth load peaks, whereas uncoordinated fast charging creates high simultaneity. For storage, the assessment is particularly demanding because it can both feed in and draw. A storage system can relieve the grid if it charges when local generation is high and discharges when load is high. But it can also burden the grid if it operates according to price signals that do not match the local grid situation. Flexibility therefore does not automatically mean being beneficial to the grid. The study must examine according to which rules and within which technical limits an installation is operated.

For generation installations too, installed capacity alone is not sufficient. A wind farm and a solar park with the same connection capacity have different feed-in profiles. A hybrid project of photovoltaics and battery storage can manage with a lower shared connection capacity than the sum of the individual installations. Such concepts use connections more efficiently, but require precise control concepts as well as clear metering and settlement points. In the transmission system operators' maturity-level procedure, the shared use of a connection by generation, load and storage earns additional points.

Typical misinterpretations

"A positive study means build immediately": A study can contain conditions, such as grid reinforcements, a new switchgear bay, a limited connection capacity, particular protection technology, reactive power control, certificate evidence or dependencies on other expansion measures. Only planning, permitting, procurement, contract and construction turn a technical possibility into a real connection.
"The nearest grid point is the best": The nearest pylon or substation is not automatically the right connection point. What is decisive is the electrical integration, free capacity at the appropriate voltage level and a cleanly implementable protection and operating concept. A short connection line can become more expensive than a longer one if extensive reinforcements are needed at the nearby point.
"Different results are arbitrary": If one project receives a connection and another in the same region does not, this can be due to different connection capacities, voltage levels, application dates, maturity levels, interconnection points or operating profiles. Transparency nonetheless remains important, precisely because procedures such as the maturity-level procedure deliberately weight project maturity more heavily than the order of applications.
"A bottleneck is a bottleneck": A grid bottleneck in the transmission grid is something different from a missing switchgear bay, a local violation of the voltage band or too low a short-circuit power. These problems have different causes and require different solutions. A good study therefore states precisely which technical limit is decisive.

Link to security of supply and grid planning

Connection studies are not abstract individual expert opinions. They influence how quickly new generation, new consumers and new storage are integrated into the electricity system. In doing so they touch security of supply, decarbonisation, industrial settlement and regional development. A grid that cannot provide connections in time slows down technically feasible projects. A grid that permits connections without sufficient examination risks operating problems and higher costs for interventions.

For grid planning, connection requests and the associated studies are an important source of information. They show where which capacities are in demand and which grid sections will be more heavily loaded in future. Individual enquiries may be speculative. The transmission system operators even report secondary markets for connection reservations that arose under the first-come, first-served principle. In sum, however, the enquiries nonetheless show spatial patterns. Many conflicts have their cause in temporal asymmetry: a solar park or battery storage system is planned much faster than a new high-voltage line. Connection studies make this time difference visible and help to examine interim solutions. These include temporary connection capacities, staged commissioning, dynamic feed-in limitations, grid-beneficial operating agreements and shared connections of several installations. Such solutions are not always equivalent to a fully expanded connection.

Data, models and limits of the findings

The quality of a connection study depends on the grid model used. A complete model contains lines, transformers, switching states, loads, generation installations, protective devices, controls and planned extensions. Grid operators hold these operating data, but for reasons of security, data protection and competition do not always pass them on completely to external experts. For renewable energy installations there is at least a statutory entitlement to receive, on request, the grid data required for a grid compatibility check. Otherwise, external studies often work with approximations, public information or excerpts provided by the grid operator. More transparency can speed up procedures, but does not replace a robust check in the specific grid model.

A connection study also has methodological limits. It can calculate various scenarios. However, it cannot reliably foresee future project competition, regulatory changes, delivery times or political priorities. It can say which grid reinforcement is necessary according to current knowledge, but cannot guarantee that the framework conditions will remain the same until commissioning. Connection studies should therefore be versioned and documented with their assumptions. In the event of major changes to the project, the grid or the rules, they must be updated.

What the term makes visible

The term connection study draws attention to an often underestimated fact: electricity projects do not arise only on plots of land, in permit documents or in financial models. They arise at a specific point in a physically operated grid with limit values, protection concepts, operating rules, responsibilities and investment cycles. An installation can make business sense and still be unfavourably located in grid terms at a particular site. It can be technically connectable and yet cause such high connection costs that the project does not pay off.

The connection study answers a precise question: which electrical and operational conditions must be met so that a particular installation can be safely connected and operated at a particular grid point? Whether a project is socially sensible, politically desired or viable as a business model, it does not clarify. Debates about missing grid capacity, long connection times or blocked projects become more precise when one distinguishes between connection capacity, actual operation, grid reinforcement, grid compatibility and binding commitment. The connection study neither replaces grid expansion nor guarantees the implementation of a project. But it provides the basis on which an electrical idea can become a robustly planned grid connection.

Sources

Gesetz für den Ausbau erneuerbarer Energien (EEG 2023), § 8 Anschluss — Bundesministerium der Justiz / gesetze-im-internet.de; unbekannt (konsolidierte Fassung, abgerufen November 2026). § 8 Abs. 1, 2, 4, 6 und 7 EEG 2023
Kraftwerks-Netzanschlussverordnung (KraftNAV) — Bundesministerium der Justiz / gesetze-im-internet.de; 26.06.2007 (Ursprungsfassung; geändert). § 1 Anwendungsbereich, § 2 Begriffsbestimmungen, Inhaltsübersicht §§ 3–4
Stromspeicher – FAQ zur Anwendung der KraftNAV auf Großspeicher — Bundesnetzagentur; unbekannt. FAQ „Gilt die KraftNAV für Batteriespeicher …?“
Reifegradverfahren für Netzanschlüsse an das Übertragungsnetz – Konzept der Übertragungsnetzbetreiber — 50Hertz, Amprion, TenneT, TransnetBW; 05.02.2026. Kap. 1, 2.1–2.3, 3.1–3.2, 4.1–4.3, 5.2.4, 6.2; Fußnote 12
VDE-AR-N 4110 – TAR Mittelspannung — Clearingstelle EEG|KWKG; unbekannt. Normbeschreibung

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Edited by eCMS on 11.11.2026 14:23