Triad Warning Service

Help to reduce your charges

Each year, National Grid and its Scottish equivalents are paid a Transmission Network Use of System (TNUoS) fee in order to finance the cost of maintaining and updating the UK’s electricity grid. This fee is split between generators and consumers of electricity. Customers receiving pass-through charges pay their share based on consumption during Triads. These are the three highest half-hour periods of system demand between November and February each year, typically occurring during cold weather around 5-6pm, when industrial demand coincides with the domestic tea-time period. However, with prior warning, you can reduce this charge – which often runs to tens of thousands of pounds – by reducing consumption when you know a Triad is going to occur.

Be prepared with advance warning

npower offers customers receiving pass-through charges a free Triad Warning Service. Using experienced forecasting skills we have a very low call-out rate since 2005, issuing an average of just 17 warnings per season. Warnings are also given a day ahead, rather than just a few hours, allowing you more time to prepare. And you can choose to receive daily updates via email, text or fax – or all three if preferred.

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See how much you can save

This online calculator tool can help you estimate your potential savings if you lower your consumption during the three triads. If you have sites in a number of different regions then input your annual consumption per region for a more accurate estimate.

Triad warning savings calculator

Your estimated TNUos savings:

Please note that this is an estimated value based on an assumed Half Hourly consumption using the annual consumption figure given and an assumed distribution loss of 8%. Your regional charge is based on the 2014/15 zonal tariff set by national grid. Actual values may vary. Npower Limited has no liability for the accuracy of this information and it should not be relied upon. Npower Limited does not accept liability for any direct, indirect and consequential loss or damage arising or resulting from any actions or decisions you make on the basis of the information.

* This would be your estimated average reduction in consumption across the 3 half hourly triad periods within a year.

How is TNUoS calculated?

Each year, the total Transmission Network Use of System (TNUoS) fee paid to National Grid and its Scottish equivalents is translated into a £/kW tariff for each region. Tariffs are set by National Grid and are Zonal in nature – that is, the country is divide up into different zones, each with a different tariff for generation and consumption. For flexible purchasing customers receiving pass through charges, your share is calculated by multiplying your average kW consumption in the three annual Triad half hours by your average distribution losses and your regional TNUoS tariff charge.

Specialist help to manage consumption

To maximise the savings you could achieve during a Triad period, the SmartSTOR service from npower can provide expertise to carefully manage consumption on your behalf. This could include reducing power demand, but also tapping into any existing on-site generation from standby or renewable sources. As well as helping you reduce costs, SmartSTOR could generate income for your business by exploiting these resources during periods of high national demand on the grid. To find out more, visit or speak to your Business Development Manager.