Triad

Triads were the three half-hour periods of highest national electricity demand each winter, used to calculate TNUoS transmission charges for half-hourly metered customers. This system was replaced by fixed TDR bands in April 2023 following the Targeted Charging Review.

How Triads worked:

• Three highest demand half-hours between November and February
• Each Triad had to be at least 10 days apart
• Your TNUoS charge was based on your demand during these three periods
• Final Triads only known after winter ended

The Triad avoidance industry: Because charges were based on just three half-hours, businesses could dramatically reduce costs by:

• Subscribing to Triad warning services
• Reducing demand when warned of potential Triad periods
• Installing on-site generation or storage
• Demand response agreements

Why Triads were replaced: Ofgem concluded the system was:

• Unfair - avoided costs shifted to other customers
• Inefficient - created artificial demand patterns
• Unpredictable - costs only known after the fact

Post-TCR (April 2023):

• Fixed Transmission Demand Residual (TDR) bands replaced Triad-based charging
• Charges based on agreed capacity, not peak demand
• ~88-100% of TNUoS now recovered through fixed charges

Legacy relevance: While Triads no longer drive charges for most customers, understanding them helps explain historical bills and why TCR was implemented.