Simultaneity (Gleichzeitigkeit) · Glossary

Simultaneity describes the extent to which several electrical consumers, generation plants or storage units draw or feed in power at the same time. For the power grid, what matters is not which devices are installed, but what power they demand at the same moment. A building can contain many devices with a high connected load that never all run at full power at once. Conversely, a street with only a few new installations can place a heavy load on the grid if these installations operate at the same time of day.

What is decisive is power, stated in kilowatts or megawatts. It describes the instantaneous flow of energy. Electricity consumption over a period of time, by contrast, is measured in kilowatt-hours. An electric car that charges 30 kilowatt-hours overnight may need about eight hours at 3.7 kilowatts or just under three hours at 11 kilowatts. The amount of energy charged is the same in both cases. For the grid, however, it makes a big difference whether many vehicles charge at high power at the same time.

Simultaneity factor: definition and worked example

The simultaneity factor makes this relationship calculable. It sets the highest power that a group actually draws or will draw at the same time in relation to the sum of the individual power ratings. An example: ten charging points of 11 kilowatts each add up to 110 kilowatts of connected load. If the planning assumes that at most 55 kilowatts occur simultaneously, the factor is 0.5. The factor has no unit and lies between 0 and 1. It is not a law of nature but a planning assumption. It is based on measurement data, usage behaviour, technical rules and safety margins.

In practice, the terms are not used consistently. Strictly speaking, the simultaneity factor refers to the peak values of the individual loads. The demand factor or utilisation factor, by contrast, refers to the installed rated power. Many planning aids mix both quantities. When comparing numerical values, one should therefore always check what the factor refers to. It is also typical that the larger the group, the smaller the factor, because the peaks of many users offset one another. For residential buildings in Germany, the planning standard DIN 18015-1 shows the power demand as a function of the number of dwellings. It distinguishes between dwellings with and without electric water heating. The factor falls as the number of dwelling units rises.

Distinction from connected load, peak load and load profile

The connected load indicates how much power a device, an installation or a grid connection can technically draw or feed in at most. It says nothing about how often and when this power is used. A instantaneous water heater, heat pump, charging point and electric cooker together result in a high installed power. Grid planning, however, does not necessarily have to treat this sum as a simultaneous load.

The peak load is the highest power actually occurring or expected in a grid section. Simultaneity explains how this peak arises from many individual installations. The load profile shows the course of power over time: in the morning or evening, seasonal, weather-dependent or triggered by prices. Simultaneity is therefore not a property of an individual device. It belongs to a group, a period and specific framework conditions.

Annual energy volume is also something different. A heat pump can consume a lot of electricity over the year and still place little load on the grid if it runs evenly at low power. In frost and with unfavourable control, however, it can contribute to a local load peak. A device with low annual consumption, on the other hand, can briefly draw high power. For cables, transformers, voltage maintenance and protection systems, such power values matter because these items of equipment have thermal and electrical limits.

Why simultaneity is becoming more important in the distribution grid

In classic household grids, simultaneity was easy to manage thanks to statistical diversity. Not all households cook, do laundry or shower in the same minute. With electrification, these patterns change. Heat pumps respond to the outdoor temperature, charging infrastructure to the times people arrive home, and photovoltaic systems to the sun. These installations share common triggers. Their behaviour is therefore more strongly interlinked than that of classic household appliances. The Bundesnetzagentur (Federal Network Agency) expressly points out that charging equipment and heat pumps have higher power ratings than most household appliances and are often used at the same time. Most low-voltage grids are currently not yet designed for a rapid ramp-up.

In the distribution grid, this has a particularly strong effect. A local distribution transformer or a low-voltage cable is not loaded by national annual consumption, but by the power flowing simultaneously in its section. If many electric cars charge in one street in the evening, the local peak can rise even though the overall system has enough generation. If many PV systems feed in on a sunny midday and little is consumed locally, the voltage can rise above the permissible band due to reverse feed-in.

Simultaneity therefore affects both withdrawal and feed-in. For photovoltaics it is often very high, because the same weather situation shapes many installations at once. For wind energy, something similar applies on a larger spatial scale. For storage units, it depends on the control. Home storage units can smooth peaks if they absorb local generation. But they can also create new simultaneity if many devices respond to the same price signal. The Bundesnetzagentur names precisely this risk: cheap electricity at a particular time of day could lead many operators to fill their storage units at the same time and thus overload local grid areas.

Planning assumptions and economic significance

For grid operators, the simultaneity factor is a tool for building grids neither too tight nor unnecessarily large. Assumptions that are too low lead to overloads, violations of the voltage band or frequent interventions in controllable installations. Assumptions that are too high lead to rarely used grid expansion that everyone pays for through grid charges. When sizing a house connection or in the case of a power increase, the calculation for a single-family home differs from that for a charging park, an underground car park in an apartment building or a commercial business. Without load management, planners often cautiously apply a high factor for charging points. The exact values are set by the technical connection conditions of the respective grid operator and the regulatory framework.

Simultaneity in law: § 14a EnWG (Germany)

In Germany, simultaneity has even found its way into regulation. The basis is § 14a EnWG and the determination BK6-22-300 of the Bundesnetzagentur. Since 1 January 2024, every newly commissioned controllable consumption device with more than 4.2 kilowatts of grid connection capacity must be dimmable. These include private wallboxes, heat pumps, air conditioners and electricity storage units, the latter only when charging. Publicly accessible charging points under the Ladesäulenverordnung (Charging Point Ordinance) are excluded. In return, the grid operator may no longer refuse or delay the connection because of possible local overload. If an overload threatens, it may temporarily reduce grid withdrawal to as little as 4.2 kilowatts per device. Normal household electricity and PV feed-in are not affected. Operators receive reduced grid charges for this.

If control is direct, 4.2 kilowatts per device generally remain available. For large heat pumps or air conditioners with more than 11 kilowatts, the minimum power results from the grid connection capacity multiplied by a scaling factor, currently 0.4. If an energy management system controls several devices together, the grid operator determines a joint minimum power using a prescribed simultaneity factor. The formula is: 4.2 kW + (number of devices − 1) × simultaneity factor × 4.2 kW. For two devices, the factor is 0.8. This gives 7.56 kilowatts instead of 8.4 kilowatts with direct control. Grid operators publish a graduated table: the factor falls from 0.8 for two devices to 0.45 from nine devices. In this way, the regulation uses precisely the balancing effect that the term describes. Electricity from one's own PV system is not counted, because the limit applies only to withdrawal from the grid.

The technical possibility of control does not solve the problem automatically. It must be legally permissible, practically implementable, understandable for users and reliable in grid operation. The goal is grid-serving control that limits interventions to genuine cases of risk.

Price signals can reduce or increase simultaneity

Time-variable electricity prices can shift loads away from expensive hours. But if many installations respond to the same signal, the new peak arises directly in the price trough. A control system that only knows the exchange electricity price does not see the load on the local grid. What makes sense for the transmission grid can aggravate a bottleneck in the low-voltage grid.

Typical misunderstandings

Installed power equals grid load: Anyone who adds up all connected loads usually overestimates the real load and plans connections that are too large. Existing grids have always been sized with statistical diversity.
Old factors for new patterns: Values from the era of cookers, televisions and washing machines do not simply fit a commuter street with wallboxes or heat pumps in frost. The more similar the triggers are, such as temperature, end of the working day, sun or price, the higher the simultaneity.
A fixed value: The factor depends on group size, device mix, control and the grid level considered. A value for a house connection does not automatically apply to a local distribution transformer.
A purely technical problem: Simultaneity also depends on tariffs, metering systems, comfort expectations, connection rules and clear rights and obligations.

Simultaneity shows that electrification is determined not only by additional kilowatt-hours. It also matters when and where power occurs and whether many individual decisions reach the same grid limit. The term does not answer whether enough energy is available or whether a grid must be expanded. But it makes the question more precise: what power flows simultaneously through which items of equipment, and which rules amplify or limit this.

Sources

Integration von steuerbaren Verbrauchseinrichtungen — Bundesnetzagentur; unbekannt. Einleitung; Abschnitte zu betroffenen Anlagen, Mindestleistung, Stromspeichern, großen Wärmepumpen und PV
Netzorientierte Steuerung ermöglicht den weiteren Zubau von Wärmepumpen (Factsheet § 14a) — KEDi / Deutsche Energie-Agentur (dena); 2024-02-05 (laut Dateiname). Formel zur Mindestleistung bei Energiemanagementsystem und Rechenbeispiel
Steuerbare Verbrauchseinrichtungen — wesernetz (Verteilnetzbetreiber); unbekannt. FAQ Steuerung, Tabelle Gleichzeitigkeitsfaktor
Leistungsbedarf und Gleichzeitigkeitsfaktor — Elektropraktiker; unbekannt. Abschnitt zu DIN 18015-1, Bild 1

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Edited by eCMS on 12.11.2026 05:05