Ofgem Typical Domestic Consumption Values (TDCV) Solar Sizing Report

Key Takeaways

• Ofgem's statutory TDCV decision establishes 2,700 kWh per year as the national medium benchmark for Profile Class 1 single-rate electricity households.
• Profile Class 2 multi-rate meters are benchmarked at 3,900 kWh per year, retaining a statutory split of 58% peak daytime usage and 42% off-peak nighttime usage.
• Around 90% of Profile Class 2 installations represent Economy 7 meters, where pairing solar PV with battery storage shifts peak daytime generation into night heating offsets.
• Designing a domestic solar PV array against official TDCVs ensures accurate sizing, preventing costly over-inverter specification and optimizing self-consumption economics.

What Are Ofgem Typical Domestic Consumption Values?

In the regulation of retail energy markets across Great Britain, Typical Domestic Consumption Values (TDCVs) serve as the authoritative national standard. Under Ofgem's official definition, the TDCVs are industry standard values for the annual gas and electricity usage of a typical domestic consumer. These values provide the vital baseline used across the energy ecosystem: they allow Ofgem to calculate and publish the Energy Price Cap (communicating cap levels like the Period 17a Direct Debit figure of £1,723 per annum), and they are utilized by licensed suppliers and price comparison websites to present indicative quotes to consumers.

Published on 25 May 2023 following an extensive public Call for Input, Ofgem's decision updated TDCV figures across all major fuel types and meter classifications to reflect long-term improvements in domestic energy efficiency:

• Profile Class 1 (Single-Rate Electricity):
• • Low Consumption: 1,800 kWh per year (maintained at 1,800 kWh).
  • Medium Consumption: 2,700 kWh per year (revised downward from 2,900 kWh).
  • High Consumption: 4,100 kWh per year (revised downward from 4,300 kWh).
• Profile Class 2 (Multi-Rate Electricity / Economy 7):
• • Low Consumption: 2,200 kWh per year (revised downward from 2,400 kWh).
  • Medium Consumption: 3,900 kWh per year (revised downward from 4,200 kWh).
  • High Consumption: 6,700 kWh per year (revised downward from 7,100 kWh).
• Gas Consumption:
• • Low Consumption: 7,500 kWh per year (revised from 8,000 kWh).
  • Medium Consumption: 11,500 kWh per year (revised from 12,000 kWh).
  • High Consumption: 17,000 kWh per year (maintained at 17,000 kWh).

How Does the Economy 7 Consumption Split Impact Solar Battery Sizing?

Profile Class 2 accounts for homes with restricted meter arrangements, including night-storage heating systems and heat pumps. Ofgem notes that around 90% of Profile Class 2 meters are Economy 7 meters, which have two rates, peak and off-peak.

During the 2023 review, Ofgem formally evaluated whether to adjust the historical day/night consumption proportion. The regulator concluded that in deciding not to proceed with updating the peak and off-peak consumption split, the current split remains appropriate. Specifically, the national consumption split is codified as:

1. Peak (day time usage): 58% of annual volume.
2. Off-peak (night time usage): 42% of annual volume.

For a medium Profile Class 2 household consuming 3,900 kWh per year, this baseline applies directly across peak and off-peak periods. This specific split has profound implications for solar system design:

• Daytime Solar Alignment: A domestic solar PV array generates power exclusively during daylight hours, directly coinciding with the 58% peak consumption window. Because peak electricity carries the highest retail unit rates under dual-rate tariffs, every kilowatt-hour of solar self-consumption delivers maximum financial avoidance.
• Battery Arbitrage Sizing: Sizing a battery storage system in an Economy 7 home requires balancing overnight grid charging against midday solar storage. During winter months with low solar irradiance, the battery can charge during the 42% off-peak window at discounted overnight rates. During spring and summer, the battery absorbs excess daytime solar generation, preventing spill into low-rate export tariffs.

Engineering Sizing Rules Based on TDCV Baselines

When designing a domestic solar installation in the UK, installers should utilize Ofgem's TDCV medium benchmark (2,700 kWh for single-rate homes) as a disciplined sizing anchor:

1. Generation-to-Demand Matching: Sizing rooftop solar requires establishing whether a home's baseline matches the low (1,800 kWh), medium (2,700 kWh), or high (4,100 kWh) Profile Class 1 benchmark. System capacity should align with the household's documented annual consumption rather than theoretical maximum roof capacity.
2. Self-Consumption and Storage Optimization: Without battery storage or intelligent hot water diversion, a typical household on the 2,700 kWh medium benchmark cannot absorb daytime peak solar generation concurrently, exporting surplus generation under the Smart Export Guarantee. Pairing PV with energy storage allows households to store daytime surplus and avoid drawing grid electricity during peak tariff periods.
3. Decarbonisation and Heat Transition: When a household replaces gas heating (benchmarked at 11,500 kWh medium TDCV) with a heat pump, domestic electricity demand shifts from Profile Class 1 single-rate baselines toward multi-rate structures. Assessing current TDCVs against future electrified heating loads prevents under-sizing the initial electrical infrastructure.