Home  /  Glossary  /  What is maximum demand?

Business Energy Glossary

What is maximum demand?

Maximum demand is the highest half-hourly electrical load that a business site has drawn over a defined period, measured in kVA (apparent power) or kW (real power). On half-hourly metered electricity supplies, maximum demand drives the sizing of the network connection and is the basis for the Authorised Supply Capacity and the monthly capacity charge. Reviewing maximum demand against the ASC is the standard test for whether the supply is right-sized.

Maximum demand on most UK business sites occurs during a specific operating moment: a hotel during breakfast service, a manufacturing site at the start of a shift, an office on the hottest summer afternoon. Identifying that peak and understanding why it occurs is essential for managing capacity charges and for planning any capacity reductions or upgrades.

What maximum demand measures

Maximum demand is the single highest half-hourly average load drawn by the supply over a defined window. The standard measurement period is 30 minutes (matching the half-hourly settlement structure of the UK electricity market).

The figure can be reported as:

• Maximum half-hourly kW (real power) for sites measuring active demand only.
• Maximum half-hourly kVA (apparent power) for sites measuring total demand including reactive component.

For sizing purposes the kVA figure is the one that matters, because the network is sized to carry kVA. Some monitoring systems only record kW; converting requires dividing kW by the power factor at the time of measurement.

kVA vs kW maximum demand

The two metrics are linked but not interchangeable:

• Maximum kW demand is the highest real power being drawn at any half-hour. Useful for understanding equipment loading and energy bills.
• Maximum kVA demand is the highest apparent power being drawn at any half-hour. Used for ASC sizing and capacity charge calculations.

The two are related by power factor: kVA = kW divided by power factor. A site with a maximum demand of 180 kW and a power factor of 0.9 has a maximum kVA demand of 200 kVA. The DNO needs to size for the 200 kVA figure, not the 180 kW figure.

How to find your maximum demand

Three methods, in order of reliability:

1. Pull half-hourly data from the supplier or meter operator. Provides the most accurate record. Most HH suppliers can provide 12 to 36 months of data on request.
2. Read it from a smart meter or AMR system. Real-time monitoring systems usually log maximum demand within a defined period.
3. Estimate from equipment loads. Add up the connected kW of all equipment, multiply by a diversity factor (typically 0.5 to 0.8) to estimate likely peak. Only useful where no measured data is available.

For ASC reviews, 12 months of half-hourly data is the standard. 24 months is better because it captures any seasonal variation that a 12-month window might miss.

When peaks typically occur

Maximum demand patterns differ by site type:

Identifying the time of the peak is important because it informs both ASC sizing and demand reduction opportunities. Shifting load away from the peak half-hour, where operationally possible, reduces the maximum demand figure.

How to reduce maximum demand

Three categories of demand reduction:

• Load shifting. Move discretionary loads away from the peak. EV charging, water heating, and process loads can often run overnight or off-peak with no operational impact.
• Equipment efficiency. Replace older inefficient equipment with modern alternatives. LED lighting, modern HVAC controls, variable speed drives on motors can all reduce peak loading.
• On-site generation. Solar PV with or without battery storage can offset peak imports during daylight hours.

The right approach depends on what the peak consists of. Sites where the peak is unavoidable operational equipment have limited reduction options. Sites with a discretionary peak (catering, EV charging, water heating) have more flexibility.

Consequences of exceeding capacity

If maximum demand in any half-hour exceeds the ASC, the DNO charges an excess capacity charge for that excess kVA, typically at 2 to 3 times the standard capacity rate. The charge applies even if the breach is momentary and only happens in one half-hour of the month.

Repeated breaches often indicate that the site has outgrown the original ASC. The remedy is to apply for an ASC increase, which involves a capital contribution if network reinforcement is needed but ends the excess charges.

In extreme cases where demand routinely exceeds the network connection capability, the DNO can require a connection upgrade as a condition of continued supply. This is rare but it does happen on sites that have expanded significantly without reviewing their connection.

maximum demand FAQs