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Glossary · Energy industry & energy transition

Coincidence Factor

Coincidence factor Simultaneity grid planning Connected capacity peak load charging infrastructure heat pump distribution grid load management Electrification

Definition

The coincidence factor (usually abbreviated g, also called simultaneity factor) relates two values to each other. The numerator is the highest power that a group of consumers or generators reaches together at the same time. The denominator is the sum of the highest individual power values. It therefore indicates what share of many theoretical individual peaks actually becomes effective at the same time in practice. A factor of 0.3 means: of 100 kilowatts of installed or contractually possible power, only 30 kilowatts are assumed as the joint peak in the group under consideration. The value lies between 0 and 1. The larger and more mixed a group is, the smaller it generally becomes. The factor is based on measurements, empirical values and planning decisions. It is not a law of nature.

The technical literature contains related indicators that should not be confused. The reciprocal of the coincidence factor is often called the diversity factor in English and is greater than 1. Demand or utilisation factors, by contrast, usually describe how fully an individual device uses its rated power. Anyone adopting values from different standards, tables or calculators should therefore check which definition is meant there.

Power, Not Energy

The coincidence factor refers to power and not to energy. Power is stated in kilowatts or megawatts and describes a demand or feed-in at a specific moment. Energy, for example in kilowatt-hours, is a quantity over a period of time. For sizing a cable, a transformer or a house connection, annual consumption is not the primary concern. What matters is which power is present at the same time in critical minutes or quarter-hours. How high the factor turns out also depends on the averaging time: peaks over a few seconds yield different values than quarter-hour averages.

Distinction from Connected Load and Peak Load

The connected load indicates how much power a connection, a device or a system can draw or deliver at most. Adding up many connected loads does not yet give the expected grid peak. In an apartment building, all apartments can have an electric cooker and a washing machine without all devices running at full power at the same time. The peak load, by contrast, is a concrete, measured or forecast maximum value in a grid, building or neighbourhood. The coincidence factor describes how this joint peak arises from many possible individual peaks.

Illustrative Example: Residential Buildings

In Germany, the power demand of residential buildings is traditionally determined according to the planning standard DIN 18015-1. It contains a diagram showing the simultaneous power demand as a function of the number of apartments. There are separate curves for apartments with and without electric water heating. A frequently cited example is as follows: an apartment without electric water heating is assumed at about 15 kVA. For three such apartments, however, the diagram provides only about 30 kVA and not the arithmetic 45 kVA. This corresponds to a coincidence factor of around 0.67. For large buildings, the factor falls well below 0.2. The more households are combined, the more their differing habits balance out.

New Loads: Heat Pumps and Electromobility

The electrification of heating and transport is changing these empirical values. A heat pump usually needs considerably less electrical power for the same heating output than direct electric heating. Its operation, however, depends strongly on the outdoor temperature. On cold days, many systems in the same area therefore run at high power at the same time. The situation is similar with electric cars: many are plugged in at home after work. If charging starts uncontrolled, loads concentrate in the evening. The Bundesnetzagentur expressly points out that controllable consumption devices have higher power than most household appliances and are often used at the same time. Most low-voltage grids, it says, are not yet designed for a rapid ramp-up.

It does not follow that every distribution grid must be designed for the full sum of all wallboxes and heat pumps. However, old empirical values must not be transferred unchecked to new load types. A wallbox of 11 kilowatts that charges for several hours on many evenings loads the grid differently than a high-power device that runs only rarely and briefly. An example: a street with fifty wallboxes of 11 kilowatts each arithmetically comes to 550 kilowatts. It does not follow that the local distribution transformer must additionally provide this power. It would be equally wrong to simply keep using the low factors of classic household loads. How high a reliable value is depends on device type, usage pattern, temperature, tariff, controllability and grid area.

Significance for Grid Planning and Grid Connection

For grid operators, the choice of factor has direct economic consequences. If it is set too high, equipment is oversized. This increases capital costs and grid charges. If it is set too low, cables, transformers or switchgear can be overloaded. Grid planning therefore works with safety margins and, depending on grid level, customer group and use case, with different factors. A single house connection is assessed differently from a street, a commercial area or a substation. For connection requests for many charging points, heat pumps or process plants, the grid operator examines what simultaneous power can occur in the affected grid section. The factor alone is not sufficient for this examination, however. Load profiles, grid models, equipment limit values and analyses of the voltage band are also needed.

Coincidence Factor in the §14a EnWG Rules

In Germany, the term has also played a legal role since 2024. The basis is the determinations of the Bundesnetzagentur on §14a EnWG (BK6-22-300 of 27 November 2023). They apply to controllable consumption devices in the low-voltage grid with a grid connection capacity of more than 4.2 kW that have been put into operation since 1 January 2024. These include private wallboxes, heat pumps, space cooling systems and electricity storage when charging from the grid. Publicly accessible charging points and night storage heaters are excluded. Grid operators may no longer refuse or delay the connection of such systems by citing possible local grid overload. In return, they may temporarily curtail power consumption if an overload threatens. With direct control, a minimum power of 4.2 kW per device is retained. For existing systems with already agreed control, transitional rules apply until the end of 2028.

If several devices are controlled together via an energy management system, the determination expressly sets a coincidence factor. The minimum power for all devices together is 4.2 kW plus (number of devices minus 1) times coincidence factor times 4.2 kW. With two devices, the factor is 0.8. With each additional device it falls by 0.05, until it stays at 0.45 from nine devices onward. Two devices are thus together entitled to 7.56 kW, three to 10.5 kW and four to 13.02 kW. For large heat pumps and air conditioners above 11 kW, special rules apply with a scaling factor of currently 0.4. This example shows well how the coincidence factor works: a sum of individual entitlements is not simply added up but reduced depending on the number of devices.

Load Management, Price Signals and New Coincidences

Load management does not reduce annual consumption but distributes the load over time. If electric cars do not all charge at full power at 6 p.m., but spread over the night or controlled in a grid-serving way, the effective coincidence falls. Heat pumps can be shifted within thermal limits if buildings and storage have enough inertia. Flexibility therefore acts in the grid above all as a shift or reduction of simultaneous power. Price signals can, however, also create new coincidences. The Bundesnetzagentur itself cites the example that many electricity storage systems fill up in the same cheap hour and could thereby overload local grid areas. A nationally low exchange price says nothing about whether a particular local distribution transformer currently has free capacity.

Coincidence on the Generation Side

Coincidence also plays a role in generation. Many photovoltaic systems in an area feed in at the same time in strong sunshine. This then concerns feed-in peaks, voltage rise and reverse flow into higher grid levels. Because the weather in a small area is almost the same everywhere, feed-in balances out less there than with household loads. Orientation, shading and the spatial distribution of the systems change the picture only to a limited extent. With wind power, other weather patterns apply. What matters in each case is which joint power arrives at a particular grid point.

Typical Fallacies

  • Sum of installed power equals grid demand: anyone calculating this way usually overestimates the immediate need for grid expansion.

  • Historical factors still apply: anyone relying only on statistical smoothing easily overlooks local bottlenecks caused by temperature- or price-coupled loads.

  • One value for all levels: a factor for a house connection cannot be transferred to a substation and vice versa.

  • Table values are standard values: many guideline values circulating online are rules of thumb. Binding are the currently valid standard, the grid operator's technical connection conditions and coordination in the individual case.

The coincidence factor thus makes tangible a core question of electricity supply: what power must a grid be able to safely absorb or deliver at a given time and place? The answer depends not only on the number of devices but on how strongly their operation coincides in time.

Sources

Related glossary entries

Edited by eCMS on 12.11.2026 05:05

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