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Glossary · Energy industry & energy transition

Feed-in (grid injection)

Feed-in electricity grid generation photovoltaics wind energy grid connection power system

Feed-in refers to the supply of electrical energy from a generation plant, a storage system or a customer installation into a public or closed electricity grid. It therefore means the flow of electricity towards the grid. It is measured or accounted for at the relevant grid connection point. Large power plants, wind farms, photovoltaic systems, combined heat and power plants, hydropower and biomass plants, and battery storage systems can all feed in. Connections that are actually consumers can also feed in if they temporarily supply more electricity than they draw themselves.

Feed-in can refer to two different quantities. As an amount of energy, it is stated in kilowatt-hours or megawatt-hours. In that case, the question is how much electricity has flowed into the grid over a period of time. As instantaneous or averaged power, it is stated in kilowatts or megawatts. In that case, the question is how strongly a plant feeds in at a particular point in time. This distinction matters for grid operation, billing and political debates. Over the year, a photovoltaic system may feed in only a moderate amount of energy, yet reach a high feed-in power on a clear midday. It is precisely this peak that is decisive for the design of lines and transformers.

Generation, self-consumption and grid feed-in

Feed-in is not the same as generation. A photovoltaic system on a building generates electricity as soon as enough sunlight arrives. Part of it can be consumed directly in the building, for example by household appliances, a heat pump, a charging point or a commercial business. Grid feed-in is only the share that physically flows into the grid via the grid connection. The share used on site is self-consumption or direct consumption behind the meter.

This distinction is often overlooked when the load on the grid is inferred directly from installed capacity or expected annual generation. What counts for the grid is first of all the flow of electricity at the connection point. A large photovoltaic system with high self-consumption may feed in less than a smaller system with no consumers on site. Conversely, even a small system can become relevant if it is connected to a weak low-voltage grid, many systems on the same street feed in at the same time, and consumption is low.

Storage systems also change the meaning of the term. A battery storage system can charge from the grid or from a photovoltaic system and feed the electricity back in later. This feed-in is not separate electricity generation. It releases energy that has already been generated at a later time, minus storage losses. For accounting and grid operation, it nevertheless remains feed-in, because the connection point is supplying electricity to the grid at that moment.

Measuring point, grid connection and balancing

In practice, feed-in is organised through metering concepts, grid connection rules and market roles. The grid connection point defines where a plant is connected to the grid. The measuring point determines which electricity flows are recorded and used for billing, support payments or balancing. For small plants, bidirectional meters or smart metering systems often measure consumption and feed-in separately. For larger plants, registered power measurement, remote control technology and more detailed data reporting are added. Operators of generation plants and electricity storage systems of 100 kW or more have had to transmit master data, information on unavailability and real-time data on current feed-in power to the connecting grid operator since October 2021.

The accounting consequences extend beyond the individual connection. Electricity fed in is allocated to a balancing group, a direct marketer, a supplier or a support rule. This establishes who is economically responsible for the quantity of electricity, who markets it and how deviations between forecast and actual feed-in are settled. For wind and photovoltaics, this forecasting question is particularly important because feed-in depends on the weather. Forecast errors affect balancing energy, intraday trading and the dispatch planning of other plants.

The term thus links physical electricity flows with institutional rules. Physically, electricity must be absorbed and transported at every moment. Economically, it must be assigned to an actor, a price, a support payment or a balancing rule. The two levels do not always coincide intuitively. An electricity flow can cause a voltage problem in a local grid even though the same electricity has long since been sold across regions in accounting terms.

Significance for grid operation

Feed-in affects electricity grids mainly through load flows, voltage and the loading of equipment. In classic distribution grids, electricity flowed predominantly from higher voltage levels to consumers at the lower levels. With many decentralised plants, the direction of flow temporarily reverses. Photovoltaic systems in the low-voltage grid then feed in so much that electricity flows back through the local network transformer into higher grid levels.

Technically, this is possible as long as voltage, thermal loading and protection concepts remain within the permissible limits. Problems arise when lines, transformers or protective devices were designed for other operating states. In weak low-voltage grids, photovoltaic feed-in can raise the voltage. In rural medium-voltage grids, wind energy can cause strong reverse power flows because little is consumed locally. Large power plants affect transmission grids, frequency maintenance, reactive power and grid stability.

Grid operators therefore need to know where, when and at what power feed-in occurs. For this they need connection assessments, technical connection conditions, control options and measurement data. If a grid congestion threatens, feed-in power can be reduced. In Germany, this has been done uniformly in redispatch (Redispatch 2.0) since 1 October 2021. The former feed-in management under sections 14 and 15 of the EEG, that is, the separate curtailment of renewable and CHP plants, has since lapsed and been integrated into this system. Renewable energies and CHP continue to have priority: they may be curtailed only if this is significantly more effective than throttling conventional generation. For plant operators, this concerns revenues, compensation claims and investment security.

Feed-in and market value

Electricity fed in is not worth the same at all times. Its value depends on the market price, the location in the grid, forecast quality, controllability and the form of marketing. A kilowatt-hour of solar power at midday on a sunny spring day is often worth less, in a market with many photovoltaic systems feeding in at the same time, than a kilowatt-hour in the evening. With very high feed-in and low demand, exchange prices can fall sharply or become negative.

This does not make this generation technically worthless. Rather, the price shows that the value of electricity arises from simultaneity, availability and grid compatibility. A plant that feeds in at times of high demand or can control its feed-in fulfils a different function than a plant with a weather-dependent profile that can hardly be shifted. For wind and solar energy, it is therefore becoming ever more important how feed-in interacts with flexibility, storage, controllable consumers and grid expansion.

For supported plants in Germany, statutory remuneration rules partly cushion or redistribute this question of value. The Renewable Energy Sources Act (EEG) has long organised the feed-in of renewable energies through fixed tariffs and purchase entitlements. With direct marketing, market integration was strengthened without solving the physical challenge of weather-dependent feed-in. Since the Solar Peak Act (Solarspitzengesetz) of 25 February 2025, under section 51 EEG the applicable value is reduced to zero for all periods with a negative spot market price, without the former minimum durations of several hours. This applies in principle to new plants. Plants below 100 kW are exempt until the end of the calendar year in which they receive a smart metering system. New photovoltaic systems between 2 and under 25 kWp may also feed in only 60 percent of their rated power as long as no smart metering system with a control device has been installed and successfully tested by the grid operator. The limit applies to feed-in at the grid connection, not to generation. Electricity that is self-consumed or stored therefore does not count towards it.

Common misconceptions

  • Generation equals feed-in: Not every kilowatt-hour generated is fed in. For statistics, billing and grid planning, it makes a difference whether electricity is consumed on site, stored or supplied to the grid. Anyone who blurs this boundary easily overestimates or underestimates the load on individual grid sections.

  • High feed-in equals high security of supply: A large annual quantity says little about whether enough power is available at a particular point in time. Security of supply depends on firm capacity, grid availability, reserves, balancing energy and consumption profiles. Wind and solar power follow the weather and the time of day. To cover the residual load, that is, consumption after deducting weather-dependent feed-in, further resources are needed.

  • The grid must accept every feed-in at all times: Electricity grids have physical limits. Lines have loading limits, transformers have rated capacities, and voltage bands must be observed. Expanding the grid for every theoretical feed-in peak can be expensive for the economy as a whole if these peaks occur only a few hours a year. Grid planning, peak curtailment, storage, incentives for on-site consumption and controllable plants are therefore considered together. Which solution makes sense depends on the grid section, the feed-in profile and the costs of the alternatives.

Distinction from consumption, reverse feed and export

Electricity consumption from the grid is the opposite direction: a consumer or storage system draws electrical energy from the grid. Many connections use both directions today. A household with a photovoltaic system draws electricity at night and feeds in surpluses at midday. Depending on technology and control, an electric car can only charge or also return electricity. With bidirectional charging, the return to the grid likewise appears as feed-in at the connection point.

Reverse feed is often spoken of when electricity flows back from a lower into a higher grid level or when a consumer connection temporarily supplies electricity. The term starts from the original consumption character of the connection. Feed-in is more general and also covers plants that are connected as generation plants from the outset. Electricity export, by contrast, generally means cross-border deliveries between market areas or countries. Feed-in can take place within a local grid without any electricity being exported. Whether a country exports or imports on balance results from the net of many feed-ins, consumption, storage flows and cross-border exchanges.

Role in a more electrified power system

With increasing electrification, feed-in and consumption shift in time and space. Heat pumps, electromobility, electrolysers and the conversion of industrial processes increase electricity demand. But they can also absorb local feed-in. When charging points, heat pumps or storage systems respond to times of high renewable feed-in, the pressure on grids and markets falls. Without suitable control, however, additional consumption can create new peaks that do not match the feed-in patterns.

The annual quantity is therefore not sufficient for assessing feed-in. Location, timing, power, predictability and controllability matter. A kilowatt-hour that flows into a grid section with spare capacity places different demands than the same kilowatt-hour in an already fully loaded grid. Feed-in that can be reduced, shifted or combined with reactive power for voltage maintenance when needed has a different operational quality than an uncontrolled peak.

Feed-in is thus a precise term for the interface between a plant and the grid. It shows which quantities of electricity actually reach the grid, which power levels occur there and which rules govern their technical and economic treatment. It does not by itself explain whether a power system functions adequately, cost-effectively or climate-neutrally. For that, consumption, grid capacity, market rules, storage, controllable power and security of supply must also be considered. Without a clean separation of generation, self-consumption and grid feed-in, these relationships remain blurred.

Sources

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Edited by eCMS on 11.11.2026 19:43

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