Exceeding subscribed power: shaving peaks with a battery

Exceeding the subscribed power happens every time a site draws more power from the grid than its network access contract provides for. Above 36 kVA, it does not cut the supply: it is billed every month. This article explains how the network tariff calculates this charge since 1 August 2026, which responses exist, and how a storage battery is sized to shave the peaks.

What is subscribed power, and when is it exceeded?

Subscribed power is the maximum power the site reserves on the public grid, per time band. It is chosen in the network access contract and sets a large part of the network bill: the annual withdrawal component of the TURPE, the network tariff set by the French energy regulator (CRE), is proportional to the subscribed powers.

The number of powers to choose depends on the voltage level:

• Low voltage above 36 kVA (offices, shops, SMEs): four time bands, peak and off-peak hours in the high season and in the low season. Powers are chosen in multiples of 1 kVA and cannot decrease from one band to the next.
• HTA (industrial sites connected in medium voltage): five time bands, including a peak band.
• Low voltage of 36 kVA or less: power is limited by the circuit breaker or the smart meter. An excessive draw cuts the supply; the Enedis brochure states that overruns do "not apply" there.

An overrun occurs when the power drawn exceeds the subscribed power of the current time band: several machines starting at once, an air-conditioning peak in summer, electric vehicles charging at the end of the day, a furnace or compressor starting up.

How much does exceeding the subscribed power cost?

The cost appears on the bill as CMDPS, the monthly component for exceeding subscribed power. How it is calculated depends on the voltage level. The values below are those of the TURPE 7 HTA-BT in force at 1 August 2026 (Enedis brochure, CRE decision of 21 May 2026).

In low voltage above 36 kVA: duration

The charge is counted in hours. An overrun of a few kilovolt-amperes costs as much, per hour, as an overrun of several dozen. When control is based on active power, the subscribed power taken into account is the apparent power multiplied by 0.93.

The brochure provides for a cap on request to the grid operator: when the month's CMDPS exceeds both 30 % of the monthly TURPE bill and 25 times the tariff for the additional power that would have had to be subscribed to avoid any overrun, it is brought down to the higher of these two limits. It is a safety net, not a way of managing the site.

In HTA: size

In HTA, each overrun ΔP (in kW) is recorded every 10 minutes. The overruns are squared and added up, then the square root of the sum is multiplied by 0.04 and by the power coefficient b of the time band. For the HTA short-use tariff with fixed peak, this coefficient is €14.85/kW/year in peak hours at 1 August 2026.

Squaring has a direct consequence: one high peak weighs more than several small ones. Reducing the height of the peaks is therefore the first lever, before their number.

Raise the subscribed power, shift uses or shave peaks?

Three responses exist, and they are often combined.

1. Raise the subscribed power. The overruns disappear, but the withdrawal component increases all year round, for a peak that sometimes lasts only a few tens of minutes. And beyond the connection capacity, the increase may require works on the connection.
2. Shift uses. Stagger machine start-ups, schedule vehicle charging or preheating. This is the simplest response when the process allows it.
3. Shave peaks with a battery. The battery supplies the part of the peak that exceeds a chosen threshold. Seen from the grid, the site no longer exceeds its power: depending on the shape of its curve, it may even subscribe a lower power.

The choice between these options is made on the load curve, not on a general rule. Long, regular overruns often call for a better-adjusted subscribed power; short, high peaks lend themselves well to peak shaving.

How does a battery shave peaks?

The battery's energy management system (EMS) continuously measures the power at the delivery point. It follows a setpoint: a threshold slightly below the subscribed power of the current time band.

• As long as the site consumes less than the threshold, the battery does nothing, or recharges.
• As soon as consumption crosses the threshold, the battery discharges the difference, within moments.
• When the peak subsides, the battery recharges, preferably in off-peak hours and always below the threshold, so as not to create a new peak itself.

The threshold changes with the time bands, since the subscribed powers differ. The control system follows it automatically.

How do you size a battery to shave peaks?

The method follows our guide to sizing a commercial storage battery, applied to peak shaving.

1. Read the load curve

The load curve in 10-minute steps can be downloaded from the Enedis business customer area. Twelve months are needed to see the high and low seasons, and the time bands where overruns are concentrated.

2. Set the threshold

The threshold is the power the site must no longer exceed as seen from the grid. The lower it is, the more powerful the battery must be and the harder it works. Several thresholds are usually compared.

3. Derive the battery's power

The battery's power is the gap between the highest observed peak and the threshold, with a margin for future peaks (new machines, charging points).

4. Derive the energy

The energy is the largest area of the curve above the threshold in a single day, in kWh, divided by the usable depth of discharge, plus a margin. Worked example: a peak that exceeds the threshold by 100 kW for 30 minutes requires 100 kW and 50 kWh usable; three similar peaks in the day, with no recharge between them, require 150.

5. Check the recharge

Between two peaks, the battery must recover enough energy without itself exceeding the threshold. On a site where peaks follow one another closely, this criterion often sets the size.

Which range for a commercial site?

Peak shaving calls for power more than energy: short peaks are handled by a battery with a high power-to-energy ratio.

• The VenturePro range: one cabinet delivers 125 kW and stores 250 kWh, i.e. two hours at full power (RelyEZ datasheet). Up to twelve cabinets connect in parallel on the same 400 V bus.
• The Fusion 2 range: one control cabinet manages one to eight battery cabinets, from 261 kWh and 130.6 kW up to 3.34 MWh. The system grows by adding cabinets, if the site adds charging points or electrifies a process.

For a charging station whose peak exceeds the available connection, the case is covered separately on our page dedicated to fast charging.

Where to start?

Three documents are enough for an initial assessment:

• the load curve over twelve months;
• recent network bills, which show the subscribed powers and the CMDPS line;
• the list of projects that will change consumption: charging points, new machines, extension.

From these data, we compare the three responses, adjusted subscribed power, shifted uses or peak shaving, and several battery sizes. The value of a peak-shaving battery lies in sizing it right: powerful enough to hold the peak, with no energy tied up needlessly. You can request an assessment with these documents.