Peak shaving calculator: what the red band is worth on your site

Peak shaving means discharging a battery through the hours when network and supplier charges are highest and recharging when they are lowest. On a UK half-hourly meter the biggest single lever is the distribution network operator's red time band: a weekday window of two to three hours in the late afternoon when the unit charge for using the network is tens or hundreds of times the overnight rate. A battery that carries a site's load through that window, and a lower agreed capacity if the peak is gone for good, are the two savings this calculator measures. Our guide to DUoS charges explains where these charges sit on your bill; this page puts numbers on them.

A worked example on the East Midlands 2026/27 rates

Take a manufacturing site on a low-voltage half-hourly supply in the East Midlands whose weekday import sits at 450 kW through the 16:00 to 19:00 red band, and a battery that can hold 150 kW off the grid for those three hours. That is 450 kWh moved per weekday, so the battery needs at least 450 kWh usable. Over 261 weekdays it moves 117,450 kWh. At the published LV red rate of 7.777p/kWh, avoiding those units is worth £9,134; recharging the same energy in the green band at 0.054p/kWh, with 85% round-trip efficiency, costs £75. The DUoS unit saving is therefore about £9,060 a year. If the peak reduction is reliable enough for the site to agree a 100 kVA lower capacity with the network operator, the capacity charge saving is 100 kVA × 7.68p × 365 days, about £2,800. Together, about £11,860 a year from the distribution charges alone, before any supplier time-of-use saving and before grid-services income.

Set that against the published installed-cost bands on our cost page: a 500 kWh system in the £300 to £500 per kWh band is £150,000 to £250,000 installed, so the distribution-charge saving on its own gives a simple payback of roughly 13 to 21 years. That is the honest reading of peak shaving in the Midlands on 2026/27 rates: on its own it rarely carries a battery. It carries one when it stacks with a supplier tariff that follows the same shape, with load shifting on a wide day-night spread, with stored solar, or with grid-services income. In the South West, where the red rate is 14.833p/kWh, the same battery's DUoS saving roughly doubles, which is why the region matters more than the brochure.

How the calculator works, line by line

1. Energy moved per weekday = the kW you hold off the grid × red hours in your area, capped at the battery's usable kWh. Red bands run only on weekdays (including bank holidays) in all four NGED areas, so the year has 261 red-band days in 2026.
2. DUoS unit saving = units moved × (red rate − green rate ÷ efficiency). The battery avoids the red unit charge and pays the green unit charge on the slightly larger amount of energy it has to import to recharge.
3. Capacity saving = the kVA reduction you can agree with the network operator × the capacity charge × 365. This only counts if the operator agrees a lower maximum import capacity; it is not automatic, and exceeding a reduced capacity is charged at the exceeded-capacity rate.
4. Supplier tariff saving = units moved × (peak unit rate − off-peak unit rate ÷ efficiency), if your supply contract has a time-of-use shape. Many fixed contracts do not, in which case leave it blank.
5. Simple payback = installed cost ÷ total annual saving, before tax relief. Our tax guide covers the Annual Investment Allowance and the 50% first-year allowance, and the cost page calculator shows the after-relief position.

What it leaves out, on purpose

• The residual charge. Since the Targeted Charging Review, the residual part of distribution and transmission charges is a fixed daily amount by band. A battery does not change it.
• Amber-band savings. Shifting load from amber to green saves the amber rate (0.958p/kWh LV in the East Midlands) less the green rate, which is real but small next to red; most batteries do not have the energy to cover amber as well. Add it by hand if your case depends on it.
• How often the peak is actually there. The calculator assumes the site peaks in the red band on every weekday. Seasonal sites, shift patterns and shutdowns reduce the real number; a year of half-hourly data tells you by how much. Our guide on reading half-hourly data shows what to look for.
• Degradation, availability and standby losses, which lower the energy moved over the battery's life. Published warranties set the floor; see what eight makers publish.
• Grid-services income, which depends on markets and an aggregator, and solar self-consumption, which depends on your array. Both belong in the full model, not in a tariff calculator.
• Transmission (TNUoS) charges, which have their own structure and are not banded the same way.

Finding your own red band and rates

Red-band hours are set by network area, not nationally, and they change between charging years. Your half-hourly supplier bill or DUoS statement shows the distribution tariff you are on, often as a tariff ID or LLFC, and the network operator's charging statement for the year gives that tariff's time bands and unit rates. The four National Grid Electricity Distribution areas are in the table above with links to the published workbooks. The other operators are UK Power Networks (London, the South East and the East of England), Northern Powergrid (the North East and Yorkshire), SP Energy Networks (Merseyside, Cheshire, North Wales and central and southern Scotland), SSEN (central southern England and the north of Scotland) and Electricity North West (the North West). Each publishes an annual Use of System charging statement with the same table; our guide to finding your network operator explains how to identify yours from the MPAN.

In Northern Ireland the network is run by NIE Networks, regulated by the Utility Regulator rather than Ofgem, and the GB network operator tables here do not apply; enter the rates from your own bill.

If your supplier bills you a single blended unit rate, the DUoS charges are inside it and you will not see the bands. The saving is still real, but it reaches you only if the contract is re-priced on a pass-through or time-of-use basis, which is a question for your broker or supplier before you buy a battery.

How to use the result

Treat the figure as the ceiling the published rates allow, then do three things. First, get a year of half-hourly data and count the weekdays on which the site really peaks in the red band. Second, ask your supplier what happens to your unit rates if the peak is removed. Third, ask the network operator whether a lower agreed capacity is available at your connection and what the exceeded-capacity charge would be if you overrun it. Only then ask installers for quotes, and ask them to show the red-band figure they used. A quote that cannot show it has not done the work; our quote checklist sets out what to ask for in writing.

Cite this calculator

Battery Storage for Business, "Peak shaving calculator: red-band DUoS savings (UK, 2026)", batterystorageforbusiness.co.uk/peak-shaving-calculator/, rates last verified 2026-10-29 against the NGED 2026/27 schedules below. Method: published unit rates and capacity charges; all site figures entered by the user; 261 weekdays; no residual, TNUoS, degradation or availability adjustment.

Sources

• National Grid Electricity Distribution (East Midlands) plc, Schedule of charges and other tables 2026/27, Annex 1 (effective 1 April 2026, Final)
• National Grid Electricity Distribution (West Midlands) plc, Schedule of charges and other tables 2026/27, Annex 1 (effective 1 April 2026, Final)
• National Grid Electricity Distribution (South Wales) plc, Schedule of charges and other tables 2026/27, Annex 1 (effective 1 April 2026, Final)
• National Grid Electricity Distribution (South West) plc, Schedule of charges and other tables 2026/27, Annex 1 (effective 1 April 2026, Final)
• National Grid Electricity Distribution, charging statements and methodology
• NREL Annual Technology Baseline 2024, commercial battery storage (the 85% round-trip efficiency planning assumption used as the default)