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Glossary · Energy industry & energy transition

Cable Pooling

Cable pooling grid connection photovoltaics wind energy Battery storage Hybrid power plant Connected capacity renewable energies

Definition

Cable pooling refers to the shared use of one grid connection by several generation plants, storage units or flexible consumers. For example, ground-mounted photovoltaics, wind turbines and a battery storage system can be connected to a common grid connection point. The sum of their installed capacity is often greater than the agreed or technically permissible connection capacity. This is referred to as oversizing of the grid connection point. It is only permissible if, at the connection point, no more power is fed in or drawn than is allowed at any time. Cable pooling and oversizing are closely related but not the same thing. Several plants can also share a connection if the connection capacity is sufficient for all of them together.

Power and energy quantity

The connection limit is determined by power, measured in kilowatts or megawatts. An example: a solar park has 50 megawatts of installed capacity and a wind farm 40 megawatts. Together they could theoretically generate 90 megawatts. If both share a connection at which no more than 60 megawatts may be fed in, the operational management must keep to these 60 megawatts at the connection point. The energy quantity, measured in kilowatt-hours or megawatt-hours, by contrast indicates how much electricity is generated, stored or delivered over a period of time. Cable pooling initially concerns only the power at the connection. Through curtailment, storage and load shifting, however, it also influences the quantity of energy that can actually be generated and sold.

Distinction from related terms

A grid connection is the technical and legal link between a plant and the electricity grid. Cable pooling describes a particular way of using it: several plants are bundled behind a common connection point. The term is also not identical to a hybrid power plant. A hybrid power plant is usually planned and controlled as a single unit, for example wind, solar and storage with a common control system. With cable pooling, by contrast, the plants can remain legally and economically separate and belong to different operators.

Cable pooling is also not the same as curtailment. Curtailment can be an operating option but is not the purpose. The benefit arises when different generation profiles, storage and control complement each other in such a way that the connection capacity is used in more hours of the year. Likewise, cable pooling is not a general term for flexibility, but a concrete connection and operating configuration. It uses the ability of plants to shift feed-in, consumption or storage over time.

Why cable pooling is gaining importance

Grid connection capacity is scarce. Many renewable energy projects fail not because of land or technology, but because of long waiting times in the grid connection queue, limited transformer capacity or a lack of reserves in the lines. Photovoltaics reaches its peak output only in a few hours of the year. Wind follows a different, weather-dependent pattern and often blows at night or in winter. If each plant needs its own connection sized to its rated capacity, part of this infrastructure is only weakly utilised most of the time. Cable pooling therefore treats the connection as a jointly managed resource. Projects can share transformers, switchgear and cable routes. Additional plants also become possible where a separate connection could not be obtained in the short term.

Legal framework in Germany (EEG 2023, as of November 2026)

For plants generating electricity from renewable energy sources, Section 8(2) EEG 2023 expressly regulates cable pooling. Plant operators may choose a connection point other than the one provided for by law. This can also be a point to which an existing plant is already connected, provided its operator agrees to the shared use. Since 25 February 2025, this choice can also be combined with the offer of a flexible grid connection agreement under Section 8a EEG. The amendments stem from the act of 21 February 2025 (BGBl. 2025 I No. 51), usually called the "Solarspitzengesetz" (Solar Peak Act).

A flexible grid connection agreement is concluded between the grid operator and the plant operator. In it, they limit the maximum active power feed-in at the connection. The plant operator must ensure at all times, by suitable technical measures, that this limit is observed. The limit can be restricted to certain time windows and can be set at different levels for each time window. The law specifies minimum contents for the contract:

  • the level of the limited maximum active power feed-in and, where applicable, time windows with different limits,

  • the duration of the limitation and what applies afterwards if it is not intended to be permanent,

  • how the technical requirements for the limitation are ensured and how the plant operator is liable if the limit is exceeded,

  • in the case of cable pooling: the consent of other plant or storage operators at the same connection point, as well as rules on their shared responsibility and on joint and several liability.

Such an agreement is voluntary; the law words it as a discretionary provision ("may" rule). There is no entitlement to conclude one. However, the grid operator must examine the possibility if the technically and economically most favourable connection point is not the nearest one. It communicates the result together with the grid compatibility assessment. Where a flexible grid connection agreement exists, the grid operator only has to take the electricity generated within the agreed maximum feed-in (Section 11 EEG). Electricity above the limit is therefore not the grid operator's problem, but must be stored, consumed or curtailed behind the connection.

Two restrictions are important. First, Section 8a EEG limits only feed-in. For electricity storage units that also draw electricity from the grid, Section 17(2b) of the Energy Industry Act (Energiewirtschaftsgesetz) provides for flexible agreements for feed-in and withdrawal. Second, the law does not prescribe a specific metering concept for separating the electricity quantities of the individual plants from one another. The parties must determine this themselves. The rules apply to German EEG plants and storage units. Other countries have their own rules. At EU level, the reformed Electricity Market Directive provides for flexible connection agreements, but they are implemented differently at national level.

Technical requirements

The benefits arise only if technical responsibility is clearly regulated. At the connection point, a measurement must record how much power is currently being fed in or drawn. If an exceedance threatens, a higher-level park controller decides which generation is curtailed, which storage unit is charged or which load is switched on. Protection technology, provision of reactive power, voltage maintenance and short-circuit behaviour remain requirements of grid operation. Plants behind a shared connection must also meet the technical connection conditions. A shared connection does not lower these requirements. It shifts part of the coordination behind the connection point.

Economic and organisational questions

If several operators share a connection, they must set priorities. Wind, solar and storage operators have different revenue models, support conditions and contractual risks. If all generate a lot at the same time, the question arises which plant is curtailed and who bears the loss of yield. For storage units, there is the additional question of whether they take up only renewable surpluses or also draw electricity from the grid. This affects the metering concept, the allocation to the balancing group, grid charges, eligibility for support and guarantees of origin. Because of the joint and several liability under Section 8a EEG, the operators also need rules in their internal relationship, that is, among themselves.

How high the oversizing should be depends on weather data, market prices, grid restrictions, support rules and investment costs. Because wind and solar generation often complement each other over time, moderate oversizing often loses only peak hours. Additional plants have hardly any marginal costs, so a high oversizing factor can be worthwhile. It becomes expensive if the profiles coincide more strongly than expected, if the storage unit is too small or if contractual priorities lead to conflicts.

Common misconceptions

Cable pooling does not create additional grid capacity. Transformer, cable, switchgear and upstream grid can still absorb only a certain amount of power. Cable pooling generates more benefit within this limit because generation, storage and consumption are better adapted to it over time. It does not replace grid expansion, but it can ease bottlenecks and buy time. A second misconception concerns installed capacity. If plants with a combined 100 megawatts stand behind a 60-megawatt connection, the grid does not have to absorb 100 megawatts. The agreed limit at the connection point is what matters. Battery storage systems also do not generate additional energy. They shift energy over time and lose some of it through conversion losses.

Conclusion

With cable pooling, a grid connection turns from the passive endpoint of a single plant into a jointly managed interface. There, generation, storage and consumption are coordinated with a limited connection capacity. In Germany, the model rests on the freedom to choose the connection point under Section 8 EEG and on flexible grid connection agreements under Section 8a EEG. Whether it succeeds depends on clear control, clean metering and a contractual allocation of opportunities, risks and liability.

Sources

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Edited by eCMS on 11.11.2026 16:39

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