Nobody Panic However the Triads are Coming

Triads all 99 since 1990 to 2023

The clock change at the end of October, then we come to November, winter, and Triads.Triads and how they are calculated are all related to electricity transmission and the costs associated with maintaining the high-voltage electricity network in the United Kingdom.

It is important to understand Triads and how they directly impact your business electricity bill. Although in recent years as the base cost of energy has increased, the percentage of electricity cost related to Triads has decreased, it can still make a significant pound and pence difference to your business.

Triads (Transmission-Related Peak Demand):

Triads for winter of 2022 into 2023
Triads for winter of 2022 into 2023

Triads refer to the three highest half-hourly demand periods during the winter months in the UK. These periods are used to calculate the Transmission Network Use of System (TNUoS) charges. The purpose of Triads is to incentivize large electricity consumers to reduce their demand during these peak times, which helps in managing the overall demand on the transmission network and reduces the need for costly infrastructure investments.

TNUoS (Transmission Network Use of System):

TNUoS charges are a component of the costs associated with using the electricity transmission network in the UK. They are levied on electricity suppliers and passed on to consumers. These charges cover the cost of maintaining and upgrading the high-voltage electricity transmission infrastructure. The charges vary depending on the level of demand placed on the network and the location of the customer. Triads are a significant factor in determining TNUoS charges because they are used to calculate the capacity charges.

How Triads are Calculated:

Triads are determined based on the half-hourly demand on the transmission network during the winter period, typically from November to February. The three highest half-hourly demand periods are selected as the Triads for that year. The key points to understand about the calculation of Triads are:

The probable dates and times of Triads are not publicly disclosed in advance by National Grid. This is to prevent consumers from gaming the system by reducing demand during known times. If there is a particularly cold snap, between November and February, between 4pm and 6pm, on a weekday, then highly likely, one of the days will result in a Triad charging period.

The National Grid, which operates the UK’s electricity transmission network, calculates the Triads after the winter season has ended, based on the 3 peak demands separated by 10 days.

Triads are used to set the capacity charges in TNUoS bills, and they can significantly impact the costs for large electricity consumers. Of the order of £45 per kWh for the average electricity used during the of all three Triad periods.

The Pie Chart of Days and Times

The pie chart above shows the frequency of the last 99 Triads in the UK, from the winter period of 1990 to 1991, up to 2022 to 2023. 33 years, 3 triads each year, 99 total. The data describes that the most likely time for a Triad event is a Monday 35%, at 5.30pm 67%. The reason this period is peak demand on the network is that this time is the overlap between people at work and home.

Note that Fridays are the least likely at 2% as the spread of times of people leaving work and going home is greater. People take half days on Fridays or leave earlier than Mondays through Thursdays. There are no Triad events on a Saturday or Sunday. The periods of Triads are always in the Red period for Distribution Network Charging periods, being the late afternoon, into the early evening.

Electricity consumers can work with their electricity suppliers or energy consultants to monitor demand and potentially reduce electricity consumption during peak periods to manage TNUoS costs. The best advice is to minimise all electricity use from 4.30pm till 6pm. Don’t charge EVs, switch electrical heating off, tell staff to go home, and switch off the lights!


Link to National Grid Triad Site –


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