Why Ofgem reformed network charging in the first place
For most of the deregulated era of UK electricity, network charges — the cost of using the high-voltage transmission system and the regional distribution networks — were recovered from large customers in two ways: a forward-looking signal that reflected real-time use of the system, and a residual element that recovered the fixed costs of building and maintaining the network. The forward-looking signal made sense: it incentivised customers to manage demand at the times when the network was under strain. The residual element, however, was also recovered through volumetric charges — pence per kWh, plus the Triad mechanism on transmission — and this is where the problem developed.
Volumetric residual recovery had three structural issues. First, customers who reduced their consumption — through energy efficiency, on-site solar, batteries, or genuine demand reduction — paid a smaller share of fixed network costs, even though they continued to rely on the network being there. Second, customers with on-site generation behind the meter (CHP, rooftop solar, biomass) saw their measured net demand fall and could legally avoid most of their residual contribution, despite still using the network for backup and export. Third, the Triad mechanism encouraged a substantial industry of peak-prediction services and demand-shaving battery investment whose social value was much smaller than the private benefit the avoided charges represented.
Ofgem opened the Targeted Charging Review in 2017, published its decision in 2019, and began phased implementation in April 2022 (transmission) and April 2023 (distribution residual). The core change was simple: residual network costs are now recovered through fixed bands, set by historic data, rather than through volumetric or peak-period charges. Forward-looking signals — DUoS Red/Amber/Green and TNUoS locational — remain, because they continue to do useful work. The residual is gone.
How Triad used to work
Before the TCR, the Triad mechanism was the principal route by which large UK electricity customers paid their share of transmission residual costs. Each year, the system operator (then National Grid ESO, now NESO) identified the three half-hour settlement periods between November and February that carried the highest national demand, separated by at least ten clear days. Each customer's share of TNUoS for the following year was calculated based on their measured consumption during those three half-hour periods, multiplied by the relevant Grid Supply Point unit charge.
The economic effect was extraordinary. A customer who happened to be drawing high demand during one of the three Triad periods could face TNUoS charges in the tens of thousands of pounds; a customer who managed demand carefully and avoided drawing significant load during the suspected windows could reduce their TNUoS bill by 70–90%. An entire industry grew up around Triad warnings — services that issued day-ahead alerts predicting likely Triad periods, with which customers triggered battery discharge, generator dispatch and shed loads to minimise their measured demand.
The system worked, in the sense that it reduced peak demand at the times Triad was forecast. But the cost was significant: large amounts of investment in battery and standby-generator capacity whose primary use case was avoiding a charge rather than providing system services that the network operator would have valued. And smaller customers without the capability to manage demand against unpredictable warnings were paying the full uncapped charge.
How residual recovery works now
Under the TCR, the residual element of TNUoS and DUoS is recovered through fixed bands. Each customer is allocated to a band based on their historic agreed capacity and historic net consumption volume, with the band allocation reassessed periodically. The band is essentially a fixed pound-amount per year, recovered through a daily standing charge on the bill, and is independent of what the customer does in real time.
For most non-domestic customers, the bands run from a residual charge of a few hundred pounds a year for the smallest profile-class supplies up to tens or hundreds of thousands of pounds for the largest connections. Domestic customers sit in a single residual band recovered through the supplier's standing charge.
The forward-looking signal is unchanged in principle:
- DUoS Red/Amber/Green time-of-day bands remain on the forward-looking distribution element. Shifting load from Red to Amber or Green still saves money on this element.
- TNUoS retains a forward-looking locational signal, reflecting the cost of moving power across the transmission system to your Grid Supply Point. This element is volumetric and time-banded, but smaller than the residual it replaced.
The combined effect: a much larger fraction of network charging is now fixed and predictable than was the case under the old regime. Demand-side response and on-site generation continue to pay back where they reduce energy unit cost or provide system services, but the residual-avoidance business case has been substantially eroded.
The TCR bands in practice
For half-hourly customers, the TCR bands sit in the metered-demand customer category and are allocated based on maximum import capacity in kVA, with a secondary check on actual net volume. The bands are typically set as:
- Band 1: smallest HH connections, up to roughly 100 kVA agreed capacity.
- Band 2: 100–250 kVA.
- Band 3: 250–1,000 kVA.
- Band 4: 1,000+ kVA.
Each band carries a fixed annual residual charge per meter, set per DNO area for distribution residual and on a national basis for transmission residual. The actual band thresholds and pound-amounts are published annually by Ofgem and the DNOs and shift modestly year on year.
For non-half-hourly profile-class customers, allocation runs against the customer's peak-period unit consumption rather than agreed capacity, with bands calibrated for typical profile-class load factors.
The most consequential point for procurement: the band you sit in is set by historic data, and changes are slow. Reducing your agreed capacity today does not move you down a band tomorrow; it feeds into the next reassessment, typically annual. Conversely, an agreed-capacity increase today does feed into the next band reassessment and can push you into a higher band even if measured demand never reaches the new capacity.
DCP161 and excess capacity
Running alongside the TCR is the older Distribution Code change DCP161, which took effect in April 2018 and remains live. DCP161 introduced a multiplied excess-capacity penalty for HH customers whose maximum demand exceeds their Available Capacity. Before DCP161, exceeding Available Capacity simply meant paying the standard kVA rate on the excess; after DCP161, the excess rate is a multiple of the standard rate, with the multiple varying by DNO.
The TCR did not change DCP161, but the two interact. Increasing Available Capacity to avoid DCP161 penalties can push you into a higher TCR band, paying a permanent fixed residual on capacity you may not need every day. Reducing Available Capacity to drop into a lower TCR band exposes you to DCP161 penalties on any peak that exceeds the lower allocation. The right answer is to size Available Capacity to genuine peak with a sensible margin, then revisit annually.
For sites that have been through a project — refurbishment, EV charger installation, kitchen retrofit, plant upgrade — the right time to revisit Available Capacity is twelve months after commissioning, when real demand data is in. Most over-allocations we find date back to a project where the consultant specified the connection for project-day worst case and nobody trimmed back once the actual operating profile became clear.
BSUoS reform alongside the TCR
While the TCR was being implemented on residual transmission and distribution, Ofgem ran a parallel reform of BSUoS — the Balancing Services Use of System charge that recovers the cost of balancing the system in real time. From April 2023, the demand-side share of BSUoS moved from a half-hourly volumetric charge to a fixed daily charge, calibrated annually.
The combined effect of the TCR and the BSUoS reform is that three of the four pass-through cost components on a UK electricity bill — TNUoS residual, DUoS residual, and BSUoS — are now fixed rather than half-hourly. The volatility that used to characterise the network and balancing components of a flexible contract has been substantially removed. This makes flexible and pass-through contracts somewhat easier to compare against fixed alternatives, because there is less hidden upside or downside in the pass-through line items.
For demand-side flexibility — batteries, on-site generation, interruptible loads — the implication is that the value proposition has shifted. Real-time demand reduction continues to save money on energy unit cost (wholesale-linked), on the small forward-looking elements of DUoS and TNUoS, and through participation in the Capacity Market and balancing services. It does not save money on the residual elements that used to carry most of the value.
What the TCR means for procurement
The TCR has produced four practical changes to how we think about procurement for half-hourly customers.
One. Capacity sizing is now a multi-year decision rather than an annual one. Reducing Available Capacity to drop into a lower TCR band only pays back if the reduction is genuinely sustainable; over-running and triggering DCP161 penalties (or worse, requiring an emergency capacity uplift that pushes the band back up) costs more than it saves. We model capacity reductions against twelve to twenty-four months of half-hourly data before recommending them.
Two. Fixed-price comparison is more meaningful. Where suppliers are pricing fixed contracts that include all pass-throughs, the residual-band element is now genuinely fixed within the term — the customer is not exposed to volumetric drift in the residuals as they were under the old regime. This makes it easier to compare two fixed quotes line by line.
Three. Time-of-day demand management still pays back, but on the forward-looking elements only. Shifting load from DUoS Red to DUoS Amber or Green still saves money. Avoiding TNUoS Triad-equivalent windows on the small forward-looking element saves a small amount. Neither produces the headline numbers that pre-TCR Triad management did.
Four. Behind-the-meter generation business cases need rebuilding. Where a CHP, solar or battery investment was justified primarily on residual-charge avoidance, the case has weakened. Where it was justified on energy unit cost, system-services revenue or carbon-reporting value, it is largely unaffected.
What it means for behind-the-meter assets
For sites with existing on-site generation, batteries or significant flexibility, the TCR has reshaped the economics in three ways. First, residual-charge avoidance — historically a major component of the business case — is no longer available, because residuals are fixed and decoupled from net measured demand. Second, the value of energy arbitrage on flexible tariffs and pass-through contracts is unchanged. Third, the value of participating in the Capacity Market, frequency response, and other balancing services is unchanged in principle, though the prices in those markets shift independently.
The strategic implication for asset owners is that the optimisation horizon has shifted from "minimise net demand at residual-charge windows" to "maximise revenue across multiple stacked services". This is a more demanding optimisation, and it favours sites that can run an active flexibility platform — usually via a third-party aggregator — over sites that rely on simple peak-shaving rules. We do not act as an aggregator; where we identify a site whose flexibility justifies it, we refer to specialist providers and ensure the supply contract is structured to permit dual revenue streams without disadvantage.
The 2027/28 transition
The TCR is not a one-off reform. It sits within a longer pipeline of network-charging changes that will continue through the late 2020s. Three movements to watch:
- Annual band reassessments. Each year, the band thresholds and the pound-amounts attached to each band are recalibrated by Ofgem in consultation with the DNOs and the Charging Futures Forum. Customers near a band boundary can move between bands as their historic data shifts; the change in the bill is then a fixed step-change rather than a gradual drift.
- Locational signal review. Ofgem has signalled that the forward-looking element of TNUoS and DUoS may itself be reformed before 2030 to better reflect the cost of new generation connection in different parts of the country, particularly in light of the offshore wind build-out. Any reform here would shift the volumetric portion of network charging.
- Connection regime changes. The connection-queue reform that NESO is implementing in 2026 onwards changes how new generation and demand connections are processed. The customer-facing implications are largely on new-build and significant-upgrade sites rather than on existing supplies.
The 2027/28 horizon is therefore one of continued recalibration rather than another structural overhaul. Customers who set their procurement strategy now around the TCR fixed bands are not doing so against a target that will be moved within the contract term; they are doing so against a regime that is now structurally stable.
A six-line action checklist for large UK businesses
- Identify the TCR band for every half-hourly meter in your portfolio. Your supplier holds the figure; ask them to confirm in writing.
- Review Available Capacity against measured peak demand on twelve to twenty-four months of half-hourly data. Renegotiate downwards where headroom is consistently unused, taking care not to drop into DCP161 penalty territory.
- Reassess any behind-the-meter generation or battery business case that was originally justified on residual-charge avoidance. Where the case rebuilds on Capacity Market, balancing services or energy arbitrage value, continue; where it does not, factor that into capital reinvestment decisions.
- If you have multiple HH sites in different DNO areas, confirm that the residual fixed bands across the portfolio reflect each site's actual TCR allocation rather than a notional supplier-wide assumption.
- For new-build or significant upgrade projects, model the capacity allocation and the resulting TCR band before signing the connection agreement, not after.
- Where the contract is placed by a third-party intermediary, confirm in writing that the residual TCR fixed bands have been reflected accurately in the priced quote — they are a meaningful component of total cost and should not be treated as a generic adder.
Manufacturing, distribution and large multi-site groups are where these decisions bite hardest. If you operate at scale and your network-charge stack is no longer producing the savings it used to, that is exactly the territory of our manufacturing utility consultancy. Send through a recent half-hourly bill and a meter list and we will return a written audit inside 48 working hours.