Maintaining our national electrical infrastructure is a costly business. Charges over and above energy consumption costs, are known as DUoS and TNUoS and apply to business energy users to cover infrastructure maintenance.


DUoS (Distribution Use of System)
The distribution network is responsible for delivering energy from the National Grid to homes and businesses. These networks are locally provided by 14 licensed distribution operators (DNOs). DUoS charges are added to businesses electricity bills to cover the costs of the distribution network – updating equipment, maintaining cables and poles, substations, transformers etc.

Time bands are set depending on how much electricity is in demand at different times of the day. This is designed to discourage energy use during high demand periods, such as 4pm-7pm and to encourage use when the network is under less pressure.

DUoS charges are based on the amount of electricity a business consumes and varies by region. DNOs impose charges within the price restrictions regulated by Ofgem.

TNUoS (Transmission Network Use of System)?
TNUoS is a charge for the electricity transmission network (The National Grid) and pays for the cost of maintaining and updating the network, including the cables, pylons, transformers, and other electricity infrastructure that transports electricity at a high voltage between the generators and the local distribution networks.

The TNUoS charges are levied on the electricity a customer uses during the three busiest half-hour periods of the winter. This charge represents a customer’s share of the costs of providing a transmission system strong enough to handle the peak load.



What is a Triad period?
Triads periods occur between 1 November and 28 February when demand on the transmission network is at its highest. Charges can range from £20-£60 per kilowatt depending on geographical location. The Triads refer to the three half-hour periods with highest demand, coupled with some additional rules about how close together these three periods can fall.

National Grid uses triads to determine TNUoS charges for customers with meters that measure their demand on a half-hourly basis. The annual charge is based on the amount of electricity consumed during the three triad periods.

Although the exact times of the these periods cannot be known until after the winter is over, various organisations attempt to forecast when a triad might occur. These forecasts are issued in the form of a “triad warning”. Typically 20-30 Triad warnings are issued each winter. They alert customers to the likelihood of demand being high and occur on the coldest days.


How to Reduce the DUoS/TNUoS charges
DUoS charges are rated per time band. If consumption is adjusted according to these bands, it assists the network in reducing peak time demand and therefore reduces energy costs.

DuoS charges vary by time of day, with the most expensive band corresponding with the time at which the distribution network has its heaviest demand. Reducing consumption at these times relieves demand on the network and results in a reduction in energy charges.

TNUoS charges will be lower if less electricity is used during the three triad periods (between November and February). The 3 half-hour Triad periods of maximum demand are calculated in March, if warnings are heeded, considerable savings are made.


DUoS and TNUoS in practice
For universities with large student accommodation blocks, being able to adjust their consumption can make massive savings. Simply adjusting the heating control to a 1000 room facility can save around £8000 in DUoS charges annually. However, if Triad warnings are acted upon, for the same facility, a saving in the region of £18,000 for EACH of the three half-hour periods could be made by adjusting water heating and room settings.

Prefect Irus – the central control system designed specifically for student accommodation, ensures energy is not used unnecessarily – for example, when rooms are empty, or windows are opened. Irus also receives Triad warnings by email, then; Automatically boosts water temperature prior to the Triad, and reduces energy use during it; Restricts output power in rooms; Cancels upward adjustment; and alters temperature levels/time periods. All of these actions combine to maximise cost savings during Triad periods.