Maximum demand: the charge that surprises factories, and how solar and batteries help

For medium-voltage customers, a large part of the bill depends on a single peak. Here is how it is charged and what reduces it.

Many factory and commercial building owners focus on how many units of electricity they use. For medium-voltage customers, a large share of the bill is driven by something else: how high their demand peaks.

How a medium-voltage bill is built

Under the tariff structure in force since 1 July 2025, a medium-voltage customer pays for energy by the unit, and pays capacity and network charges on demand, measured in kilowatts.

Peak hours for time-of-use tariffs are 2pm to 10pm on weekdays. Weekends and public holidays are off-peak all day.

What solar does, and does not do

Solar reduces the units you buy during the day, which lowers your energy charge. It often lowers daytime demand too. It does not guarantee a lower maximum demand, because your peak may fall on a cloudy afternoon or after sunset. On time-of-use tariffs the peak window runs to 10pm, well after solar output has stopped.

Where batteries come in

A Battery Energy Storage System (BESS) can discharge during your highest-demand periods so that less power is drawn from the grid at that moment. This is called peak shaving. Paired with solar, the battery charges from surplus daytime generation and covers the evening part of the peak window.

What we look at before recommending anything

• Your last 12 months of bills, to see energy use and maximum demand month by month.
• Your half-hourly load profile where available, to see when the peaks happen and how long they last.
• Whether simple operational changes, such as staggering machine start-ups, can cut the peak before any equipment is added.