Business Energy Glossary
What is Triad in UK electricity?
Triad refers to the three specific half-hour settlement periods in each winter (1 November to 28 February) at which electricity demand across Great Britain peaked. Under the old TNUoS charging system, demand TNUoS was billed to half-hourly metered customers based on their demand during these three Triad periods. The mechanism was abolished under the Targeted Charging Review (TCR), effective April 2023, but historical Triad periods are still referenced in legacy procurement decisions and energy management analysis.
For decades, Triad management was a major focus for UK industrial and commercial energy management. Reducing demand during the three Triad half-hours could save thousands of pounds per year for larger sites. The TCR change removed this lever overnight, with substantial impact on the demand response industry that had grown around Triad prediction.
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What Triad periods were
The Triad system designated the three half-hour settlement periods with the highest electricity demand across each Triad season (1 November to end of February). The three periods had to be at least 10 days apart, ensuring they captured genuinely separate peak events rather than three consecutive half-hours.
Each Triad period was identified after the winter ended, based on actual demand data. Customers and energy managers had to predict the likely Triad periods in advance and reduce demand during candidate periods to avoid being charged on them.
How Triad periods were identified
The process:
- Throughout the November to February Triad season, National Grid recorded total GB demand in every half-hour.
- At the end of the season, the three half-hours with the highest demand (subject to the 10-day separation rule) were designated as the Triads for that year.
- Demand TNUoS for the following financial year was then charged to each customer based on their average demand during those three half-hours.
Triad periods typically fell on cold winter weekday evenings between 16:30 and 18:00, when heating, lighting, and end-of-day commercial demand combined to drive peak system load.
How Triad demand was charged
The TNUoS charge per kW of Triad demand depended on the customer DNO region. Triad charges across the 27 demand zones could range from around £20 per kW per year (in low-cost southern zones) up to over £60 per kW per year (in northern Scotland).
A site with average demand of 500 kW across the three Triad half-hours, in a mid-priced zone at £40/kW, would face an annual TNUoS demand charge of £20,000. Reducing the Triad demand from 500 to 300 kW (through demand management during the actual Triad periods) would save £8,000 per year.
Triad reduction strategies
An industry grew around predicting and managing Triad periods:
- Forecasting services. Specialist providers predicted Triad timing based on weather, demand forecasts, and historical patterns.
- Demand reduction. Customers reduced consumption during likely Triad half-hours by shedding flexible loads (HVAC, refrigeration, process equipment).
- On-site generation. Standby generators, CHP, and battery storage discharged during Triad periods to offset grid imports.
- Demand response aggregation. Aggregators bundled multiple customers and managed Triad response collectively.
Effective Triad management could save 30 to 50 per cent of TNUoS demand charges for engaged customers. Less engaged customers paid the full charge.
Abolition under the TCR
The Targeted Charging Review (TCR), implemented by Ofgem in April 2023, abolished Triad-based TNUoS charging. The reasons:
- Distributive concerns. Customers with Triad-reduction capability paid less; those without paid more. Ofgem viewed the resulting cross-subsidy as unfair.
- Behavioural distortion. Triad reduction incentivised sometimes-economically-questionable demand response (operating standby generation, etc.).
- Network cost recovery. Triad charges did not closely reflect the actual network cost imposed by each customer.
The TCR replaced demand-based TNUoS with a fixed daily banded charge based on site size and voltage level. The new structure is simpler, more predictable, and not avoidable through behavioural change.
Legacy and ongoing relevance
Triad management is no longer a viable energy cost reduction strategy. The TCR change ended the industry overnight.
Triad still appears in:
- Historical pricing analysis (comparing 2022 and earlier bills to 2023 and later).
- Legacy procurement contracts signed before the TCR change, where Triad assumptions may still influence rates for the remaining term.
- Industry forecasting and analysis tools that still track GB peak demand patterns.
- Specialised demand response markets where flexibility from former Triad-trained sites can serve other purposes (Capacity Market, frequency response).
For most business customers, Triad is now historical context rather than active strategy.
Triad in UK electricity FAQs
What is Triad in UK electricity?
The three half-hour periods of highest electricity demand in Great Britain across each winter (November to February), historically used by National Grid to charge demand TNUoS to half-hourly customers. The mechanism was abolished in April 2023.
When were the Triad periods?
Determined after each winter ended based on actual demand data. The three highest-demand half-hours, at least 10 days apart, were the Triads. They typically fell on cold winter weekday evenings between 16:30 and 18:00.
When was Triad charging abolished?
April 2023, as part of the Targeted Charging Review (TCR) implementation. From 1 April 2023, demand TNUoS is charged through a fixed daily banded charge rather than Triad demand.
How did Triad reduction work?
Customers reduced electricity consumption during likely Triad periods by shedding flexible loads, running on-site generation, or using battery storage. Effective Triad management could save 30 to 50 per cent of TNUoS demand charges.
Why was Triad replaced?
Ofgem identified concerns about cross-subsidy (engaged customers paid less; others paid more), behavioural distortion (demand response that did not always make economic sense), and the loose relationship between Triad demand and actual network cost.
Is Triad still relevant to my business?
No, not for ongoing energy cost management. Triad has been replaced by fixed daily banded TNUoS charges that are not avoidable through behavioural change. Triad is historical context only.
What replaced Triad charging?
A fixed daily banded charge based on site size, voltage level, and DNO region. The new structure applies to all HH and NHH customers and does not vary with consumption timing.
Should I still try to reduce peak demand?
Yes for other reasons: lower kVA peaks reduce capacity charges, and demand flexibility can earn revenue through Capacity Market participation, frequency response, and other balancing services. But Triad-specific reduction is no longer relevant.