What are DUoS charges?

DUoS stands for distribution use of system. DUoS charges are the part of an electricity bill that covers the cost of the local distribution network, the cables and substations that carry power from the high-voltage transmission grid to a site. They are set by the distribution network operator for the region and collected through the electricity supplier, so they reach the bill as a line the supplier passes on rather than one it sets itself.

For an energy manager reading a bill for the first time, DUoS is often the line that is hardest to place, because it sits apart from the wholesale cost of the energy and changes with the time of day.

What do the red, amber and green bands mean?

For sites settled on a half-hourly basis, the DUoS unit charge varies through the day. It is divided into bands that the industry labels red, amber and green.

The red band applies during the periods of highest demand on the local network, typically weekday late afternoons and early evenings, and it carries the highest rate. The amber band covers the shoulder periods around it at a lower rate. The green band applies at all other times, including nights and weekends, at the lowest rate.

The exact hours of each band, and the rate attached to it, are set by each distribution network operator and vary by region and by the voltage at which a site connects. They are published in the operator's use of system charging statement, under the Distribution Connection and Use of System Agreement that governs them.

Who sets DUoS charges, and how do they reach the bill?

DUoS charges are set by the distribution network operator, the company that runs the local network in a given region. There are separate operators across the country, each with its own charging statement and its own band timings. The charges are governed by the Distribution Connection and Use of System Agreement and regulated by Ofgem, and they reach a site through its electricity supplier, which collects them alongside the cost of the energy itself.

DUoS sits next to a second network charge, TNUoS, the transmission network use of system charge. DUoS covers the local distribution network; TNUoS covers the national high-voltage transmission network that moves power between regions. Both appear on a half-hourly bill, and both are separate from the wholesale cost of the electricity.

Why the bands matter for load shifting

Because the red band is priced well above the green band, the size of the DUoS charge depends on when a site draws power, as well as on how much it draws. A site that can move consumption out of the red band, or avoid drawing from the grid during it, lowers this part of its bill without using any less electricity overall.

This is where on-site solar generation and battery storage change the figure. A battery charged during green-band hours and discharged through the red band shifts demand off the most expensive periods, and solar reduces the grid import that would otherwise fall in the red band on a summer afternoon. Reducing red-band demand often lowers a site's peak draw as well, which is what sets its maximum import capacity.

Lupa models that effect against a site's own half-hourly data, and the platform reports how much each combination of solar and storage saves on DUoS across the year.