The wires and pipes: physical infrastructure to data
By the end of this module you will be able to:
- Trace the voltage cascade from 400kV transmission to 230V consumer supply
- Map physical infrastructure components to the data types they generate
- Explain the LV visibility gap and why it matters for EVs, heat pumps, and solar
Think about it - Every data point has a physical origin
Every piece of energy data comes from somewhere physical.
Module 2 introduced the organisations that handle energy data. But where does that data actually come from? The answer is the physical infrastructure itself. Every transformer, every cable, every meter, and every substation generates data as a byproduct of doing its job.
Understanding the physical network is essential because it determines what data exists, where it is generated, and - critically - where the gaps are. The biggest data gap in the GB system today sits at the lowest voltage level, exactly where the energy transition is creating the most change.
The electricity reaching your home has been stepped down through six voltage levels, each monitored by different systems generating different data types. Where does the data begin, and where does visibility end?
With the learning outcomes established, this module begins by examining the voltage cascade in depth.
3.1 The voltage cascade
Electricity in GB follows a voltage cascade from generation to consumption. At each level, transformers step the voltage down and monitoring equipment generates specific data types. Understanding this cascade is the key to understanding where energy data comes from.
Level 1: Generation (11-25 kV)
Power stations and large renewable installations generate electricity at 11-25 kV. Generators produce output data (MW, MWh, availability), fuel data, and emissions data. This feeds into settlement as generation metering data and into NESO's balancing mechanism as real-time availability declarations.
Level 2: Supergrid (400/275 kV)
Three transmission owners operate the supergrid: NGET (England and Wales), SPT (southern Scotland), and SHET (northern Scotland). At this level, SCADA systems sample voltage, current, power flow, and circuit breaker status every 2-10 seconds. This produces E-category data types (E1 transmission telemetry, E3 power quality, E5 fault records) that flow over air-gapped Operational Technology networks, physically separated from the internet for security.
Level 3: Grid and primary substations (132/33 kV)
Voltage is stepped down at grid supply points (132 kV) and primary substations (33 kV), operated by the six DNO groups across their 14 licence areas. D1-category data (distribution network telemetry) is generated here, including transformer loading, tap changer positions, and fault indicators. This is where distribution-level SCADA begins.
Level 4: High voltage (11 kV)
The 11 kV network connects primary substations to secondary (distribution) substations. D6-category SCADA data is generated here, monitoring feeder currents and voltages. Many 11 kV circuits now have automated switching (self-healing networks) that generates event logs and switching data used for reliability analysis.
Level 5: Low voltage (400/230 V)
The LV network runs from secondary substations to consumer premises. Historically, this was a data desert - DNOs had zero visibility of conditions on the 230 V cables between secondary substations and homes. D5-category LV monitoring data is now being generated by sensors deployed under RIIO-ED2 investment plans, but coverage remains patchy. This is the LV visibility gap - the single biggest data challenge in the GB distribution system.
Level 6: Your home (230 V, smart meter)
At the consumer end, smart meters generate A-category and B-category data: A1 (half-hourly consumption), B1 (export data from solar panels), and register reads for billing. This data flows through DCC's communications network to suppliers and settlement systems. With 40 million smart meters, this is the highest-volume data source in the entire system - 1.92 billion readings per day.
At which voltage level does the 'LV visibility gap' exist?
“Distribution Network Operators shall publish a Long Term Development Statement describing the current and future development of the distribution system, including available generation capacity and connection costs.”
Ofgem, Distribution Licence Condition 25
Licence Condition 25 mandates that DNOs publish planning data that reveals the physical infrastructure discussed in this module. The LTDS requirement means the topology, capacity, and investment plans for the network in Section 3.1 are not internal documents but public obligations.
The electricity voltage cascade explains the physical origin of most energy data. But gas generates a fundamentally different type of data through a different measurement process that most people never see.
3.2 The gas network
The gas network is fundamentally different from the electricity network in how it generates data. Electricity is measured in watts and watt-hours with instantaneous readings. Gas is measured in volume (cubic metres) at the meter, then converted to energy (kWh) using the calorific value of the gas - which varies depending on its composition.
The National Transmission System (NTS), operated by National Gas Transmission, carries gas at approximately 70 bar pressure from coastal terminals, storage facilities, and interconnectors to offtake points. Four Gas Distribution Networks (GDNs) then distribute gas at progressively lower pressures to consumers. The data generated is different from electricity: flow rates, pressures, linepack (the amount of gas stored in the pipeline system itself, which acts as a buffer), and composition data.
The most critical gas data comes from approximately 20 gas chromatographs positioned at NTS entry points. These instruments continuously measure the exact chemical composition and calorific value (CV) of gas entering the national system. Every gas bill in Great Britain depends on these CV measurements - the volume recorded at your meter is multiplied by the applicable calorific value to determine the energy you actually consumed. A 1% error in CV measurement across the entire network would affect billions of pounds in billing.
“The volume of gas recorded at a consumer's meter shall be converted to a calorific value-adjusted energy figure using the applicable Calorific Value data published by the Gas Transporter for the relevant Local Distribution Zone.”
Uniform Network Code
This UNC provision is why the ~20 gas chromatographs at NTS entry points described in Section 3.2 are so critical. The CV data they produce is legally required for every gas bill calculation in Great Britain. An error in CV measurement ripples through every gas settlement transaction in the affected Local Distribution Zone.
Common misconception
“Electricity and gas data work the same way - you just read a meter.”
Electricity is measured directly in kWh at the meter. Gas is measured in cubic metres at the meter, then converted to kWh using calorific value data from gas chromatographs at NTS entry points. This two-step process means gas billing depends on a completely separate measurement infrastructure that most people never see. A volume reading alone is meaningless without the corresponding CV data.
The static infrastructure described in Sections 3.1 and 3.2 was designed for one-way energy flow. The energy transition is fundamentally changing both the physics and the data requirements at every level.
3.3 The changing grid
The physical infrastructure described above was designed for one-way power flow: large power stations generate, the grid transmits, distribution networks deliver, consumers consume. The energy transition is breaking this model in three ways, and each creates a data challenge.
Electric vehicles
As of early 2025, there are approximately 473,348 battery electric vehicles (BEVs) on GB roads. Each draws 7-22 kW when charging (depending on the charger type), and clusters of EVs on the same street can push LV feeders to their thermal limits. Without LV monitoring data, DNOs cannot see where these clusters are forming until a cable or transformer fails. This is not a future problem - it is happening now in streets where multiple early adopters charge simultaneously.
Heat pumps
Approximately 51,886 heat pumps were installed in 2025, each drawing 3-12 kW of electrical power. Unlike gas boilers (which use the gas network), heat pumps add load to the electricity network. The critical concern is coincident winter demand: on cold mornings, every heat pump on a street starts drawing maximum power simultaneously, creating peak loads that the LV network was never designed to handle.
Rooftop solar
Great Britain now has over 18 GW of rooftop solar capacity. Unlike EVs and heat pumps (which add demand), solar creates reverse power flow - electricity generated on rooftops flows back into the LV network, through the secondary transformer, and potentially up into the 11 kV system. This reversal was never part of the original network design, and it can cause voltage rise issues on LV feeders. Without monitoring, DNOs discover these problems only when customers complain about appliance damage from overvoltage.
Why this is a data problem
The common thread across EVs, heat pumps, and solar is the LV visibility gap. All three technologies connect at the lowest voltage level - exactly where DNOs historically had no monitoring. Without LV data, DNOs cannot see where reinforcement is needed until something fails. They cannot plan proactively for EV clusters, cannot assess whether a feeder can accept more heat pumps, and cannot detect solar-driven voltage rise. The RIIO-ED2 price control (2023-2028) includes investment in LV monitoring, but closing the gap across millions of LV circuits will take years. This is why the LV visibility gap is the single most important infrastructure data challenge in GB energy today.
Why does rooftop solar create a data challenge for DNOs?
Key takeaways
- Electricity follows a six-level voltage cascade from generation (11-25 kV) through the supergrid (400/275 kV) down to your home (230 V), with each level generating distinct data types monitored by different systems.
- The LV visibility gap - zero historical monitoring on the 230V cables between substations and homes - is the single biggest data challenge in GB distribution, exactly where EVs, heat pumps, and solar connect.
- Gas data works fundamentally differently: volume is measured at the meter but must be converted to energy using calorific value data from ~20 gas chromatographs at NTS entry points.
- The energy transition (473K EVs, 52K heat pumps/year, 18+ GW solar) is breaking the one-way power flow model, creating data needs at the LV level that RIIO-ED2 investment is only beginning to address.
Standards and sources cited in this module
Ofgem, 'RIIO-ED2 Final Determinations' (2022)
Annex 5: Digitalisation and Data
Sets out the investment allowances for LV monitoring and digitalisation across the six DNO groups, directly addressing the visibility gap discussed in this module.
Energy Networks Association, 'Engineering Report 130: Low Voltage Network Monitoring' (2024)
Section 3: LV Monitoring Technologies and Deployment
Provides the technical detail on LV monitoring sensor types, deployment strategies, and data volumes that underpin the visibility gap analysis.