TNUoS and DUoS charges are the network components of UK commercial electricity bills — together typically 25 to 40 percent of total cost on a standard commercial tariff. They fund the maintenance, expansion, and operation of the National Grid transmission system (TNUoS) and your local DNO distribution network (DUoS). For commercial sites with solar PV, network charges create both an opportunity and a complication: solar self-consumption directly avoids both charges on every kWh self-consumed, and battery storage paired with solar can deliver substantial additional DUoS savings by time-shifting load away from peak-priced periods. This page explains how TNUoS and DUoS work in 2026 (post-Triad reform), how they appear on commercial bills, the red/amber/green time-of-use structure, and the strategies that maximise solar plus battery savings against network charges.
TNUoS — Transmission Network Use of System
TNUoS is the charge you pay for using the National Grid Electricity System Operator (NGESO) transmission network — the high-voltage 275 kV and 400 kV lines that connect generators (large power stations, offshore wind farms, interconnectors) to the regional distribution network operator (DNO) connection points. The charge is levied on energy suppliers, who pass it through to commercial customers either as a separate line item on half-hourly metered bills or bundled into the unit rate on standard non-half-hourly bills.
Historically (pre-2023), TNUoS for half-hourly metered customers was calculated using the Triad system: your average demand during the three highest grid-demand half-hours each winter (typically 16:30-18:00 on cold weekday evenings in Nov-Feb) determined your annual TNUoS bill. Avoiding Triads was a major savings opportunity — businesses with sophisticated load management could trim hundreds of thousands of pounds off annual TNUoS by load-shedding or onsite generation during predicted Triad half-hours.
From April 2023 onwards, the Targeted Charging Review (TCR) reformed TNUoS by replacing the variable Triad component with a fixed annual residual charge banded by your supply line band (a categorisation reflecting your supply capacity and connection level). Most commercial customers now pay a flat annual TNUoS amount with much smaller variable component. Net result: TNUoS exposure is now mostly fixed cost; the variable component that solar and battery can flex against is much smaller than pre-2023.
DUoS — Distribution Use of System
DUoS is the charge for using your local DNO\'s medium-voltage and low-voltage distribution network — the cables, substations, and switchgear that take power from the transmission system to your meter. There are six DNOs in Great Britain (UK Power Networks, National Grid Electricity Distribution, Northern Powergrid, SP Energy Networks, Electricity North West, SSEN) and each publishes its own DUoS charging schedule.
For half-hourly metered customers (typically above 70-100 kVA peak demand), DUoS is charged on a time-of-use basis with three bands per the DNO\'s schedule:
Red band. Peak network demand period, typically 16:00-19:00 weekdays Nov-Feb (some regions Oct-Mar). Highest DUoS rate, typically 12-25p per kWh on top of energy cost.
Amber band. Moderate demand period — weekday daytime outside red band, weekend peak hours. Typically 5-12p per kWh.
Green band. Low demand period — overnights, weekends outside amber, summer daytime. Typically 1-5p per kWh.
The differential between red and green is where solar plus battery savings live. A 1 kWh battery discharge during red band that displaces a red-band import saves the customer the red-band rate (say 18p) instead of paying it. Recharge that battery overnight during green band at say 3p, and the net DUoS saving per cycle is 15p.
How solar reduces network charges
Two mechanisms:
Self-consumption directly avoids both TNUoS and DUoS. Every kWh you generate and self-consume is a kWh you do not import. No import means no network charge on that kWh. Pure unit cost saving — you save the energy cost, the supplier margin, plus the TNUoS and DUoS components, totalling 21-28p per kWh on most UK commercial standard tariffs.
Time-shifting via battery captures DUoS time-of-use spread. Solar generation peaks at midday (DUoS green or amber band on most schedules), but red-band imports happen 16:00-19:00 when generation has dropped substantially. Battery storage bridges the gap: charge battery from midday surplus, discharge during evening red band, replacing 18p red-band imports with 3p green-band recharge cost. Net DUoS saving per cycle: 15p per kWh.
Real numbers — DUoS savings worked example
250 kW commercial warehouse site, half-hourly metered, on a standard pass-through DUoS tariff:
Without solar or battery. Average winter weekday red-band import: 200 kWh per day across 16:00-19:00. At 18p DUoS red-band rate, that is £36 per day in DUoS charges alone, or £540 per month of red-band DUoS, or £6,500 per year of red-band DUoS exposure.
With 250 kW solar. Solar generation is essentially zero by 17:00 in winter. No direct red-band offset. But solar shifts midday self-consumption, indirectly reducing the building\'s reliance on grid imports across the day, and reducing peak demand readings. DUoS saving: marginal, maybe £500-1,500 per year.
With 250 kW solar + 100 kWh battery on time-of-use scheduling. Battery charges from solar surplus during midday (green band, ~3p effective recharge cost). Battery discharges 100 kWh into evening red band, replacing 100 kWh of would-be 18p imports with 0 import cost (battery provides). Net daily DUoS saving: 100 kWh × (18p - 3p) = £15 per weekday. Over 80 winter weekdays per year (Nov-Feb): £1,200 annual DUoS saving. Plus the energy cost saving from solar self-consumption: another £8,000-£12,000. Total annual benefit: £9,500-£14,000.
Triad reform 2024+ — what changed
The Triad system that drove TNUoS charges for half-hourly metered customers was retired in April 2023 under the Targeted Charging Review. Replacement: a fixed annual residual TNUoS charge banded by line band. The variable component of TNUoS is now substantially reduced.
Practical implications for commercial solar customers:
Pre-2023. Battery + solar payback economics included Triad avoidance — typically £20-50 per kW of contracted capacity per year of TNUoS savings on top of energy savings. Triad avoidance was a meaningful driver of battery business cases.
Post-2023. Triad savings gone; TNUoS is mostly fixed. DUoS red-band avoidance becomes the primary flex savings driver. Battery payback shifted from 7-10 years (pre-reform) to 8-12 years on DUoS-only (post-reform) for medium-sized commercial sites.
Note: TNUoS still has some volumetric component for very large customers (line band 7+ on the TCR table) but for most commercial sites under £1m annual energy spend, it is effectively fixed.
Half-hourly vs non-half-hourly metering
Half-hourly metering is mandatory for sites above 100 kVA peak demand and optional below — most sites above 70 kVA are half-hourly metered by default. Half-hourly metering exposes you directly to time-of-use DUoS bands, which is what makes battery savings possible.
Non-half-hourly metered sites (typically below 70-100 kVA, much of small-to-medium commercial) get a single blended unit rate that bundles DUoS into the per-kWh price. No direct time-of-use signal, no battery time-shift opportunity within DUoS pricing. Battery payback for these sites depends on supply tariff differentiation (e.g. economy 7-style day/night rates on commercial supply contracts) which is much weaker than DUoS time-of-use.
Practical advice: if your commercial site has annual energy spend above £100,000 and you are on non-half-hourly metering, ask your supplier to install a half-hourly meter (typically free, 4-6 week lead time). The time-of-use DUoS exposure unlocks battery storage economics that are otherwise marginal.
How to know your DUoS exposure
Three steps to assess your DUoS exposure:
Step 1: Check your bill format. Half-hourly metered bills show DUoS as a separate line item, broken out by red/amber/green band kWh and rates. Non-half-hourly bills bundle DUoS into the unit rate. If your bill shows separate DUoS lines, you have time-of-use exposure.
Step 2: Request half-hourly billing data. Ask your supplier (or check your portal) for the most recent 12 months of half-hourly consumption data — typically a CSV with each row being a half-hour, columns showing kWh consumed, kWh charges, and DUoS charges. From this you can calculate your red-band kWh per month and your DUoS red-band exposure.
Step 3: Run a battery sizing analysis. Take your typical winter weekday red-band consumption (16:00-19:00, summed) and size a battery to displace that. We do this analysis as part of feasibility — see /half-hourly-meter-data-analysis/.
Capacity Market and Balancing Services — beyond TNUoS and DUoS
Commercial customers above £1m annual energy spend often have additional network charge categories worth understanding:
Capacity Market charges. The Capacity Market is the UK\'s scheme for ensuring sufficient generation capacity is available to meet peak demand. Suppliers pass through Capacity Market levies to commercial customers based on contracted demand or peak-period consumption. Solar plus battery storage that reduces peak-period imports also reduces Capacity Market exposure. Annual savings for a 250 kW commercial site with battery: typically £500-£1,500.
Balancing Services Use of System (BSUoS). The charge for using National Grid ESO balancing services that keep grid frequency and voltage within tolerance. BSUoS is volumetric (per kWh imported) and varies by half-hour. Solar self-consumption directly reduces BSUoS exposure proportional to imports avoided. Annual savings on a 250 kW site: typically £400-£1,200.
Climate Change Levy (CCL). A volumetric levy on commercial electricity imports, currently 0.775p per kWh. Solar self-consumption avoids CCL. For a 250 kW site self-consuming 144,000 kWh/year, CCL savings alone are £1,116/year — material on top of the energy and DUoS savings.
Total network and levy savings on a properly sized 250 kW solar plus battery installation typically run £4,000-£8,000 per year over and above the headline energy cost savings, materially improving project payback.
Practical action steps for commercial customers
Step 1: Get half-hourly metering if you don\'t have it. Annual energy spend above £100,000 justifies the conversion — typically free with a 4-6 week supplier lead time. Without half-hourly metering, time-of-use battery savings are not visible in your tariff structure.
Step 2: Request 12 months of half-hourly consumption data. Most suppliers provide this via online portal. Analyse winter weekday red-band consumption (16:00-19:00) — this is your battery target.
Step 3: Model solar plus battery against the data. See /half-hourly-meter-data-analysis/. We typically run this analysis as part of feasibility. Outputs: kWh shifted per cycle, annual DUoS saving, battery payback.
Step 4: Specify time-of-use-capable inverter and battery. Most modern commercial inverter platforms (SolarEdge, Fronius, Huawei) support time-of-use battery scheduling natively. See /best-commercial-solar-inverters/.
Step 5: Configure scheduling at commissioning. Battery dispatch logic configured to charge during DUoS green/amber bands and discharge during red. Most platforms have this as built-in setting; some need third-party software (Predbat, PowerDog) for advanced day-ahead optimisation.
Authority resources
Ofgem on TNUoS and DUoS reform: Ofgem. National Grid Electricity System Operator: National Grid ESO. Energy Networks Association DNO charging schedules: Energy Networks Association. Targeted Charging Review documentation: Ofgem TCR.
Related decision pages
Battery storage for the time-shift strategy. Commercial solar PV for the broader business case. Half-hourly meter data analysis for the data work. SEG tariff comparison for export-side optimisation. G99 application for grid connection. G100 export limitation. Best commercial solar inverters for time-of-use-capable inverter platforms. Cost guide. Are commercial solar panels worth it. Grants and funding. Capital allowances. Maintenance.
TNUoS and DUoS — common questions
What are TNUoS and DUoS charges on my electricity bill?
TNUoS (Transmission Network Use of System) is the fee you pay for using the National Grid transmission system — the high-voltage transmission lines that move power from generators to local distribution networks. DUoS (Distribution Use of System) is the fee for using your local distribution network — the medium and low voltage cables and substations that bring power from the grid to your meter. Together they typically account for 25 to 40 percent of a commercial energy bill. Both charges appear separately on half-hourly metered bills (most sites above 70-100 kVA peak demand) but are bundled into the unit rate on standard non-half-hourly bills. The charges fund the maintenance, expansion, and operation of the UK’s electricity transmission and distribution networks.
How do solar panels reduce my TNUoS and DUoS charges?
Solar reduces TNUoS and DUoS charges by reducing your grid imports — when you self-consume solar generation, you draw less from the grid, and the network charges (which are levied per kWh imported plus capacity-based components) drop proportionally. The biggest savings come from offsetting imports during DUoS red band periods (typically 16:00-19:00 weekdays Nov-Feb in most regions), when distribution charges run 15-25p per kWh. Solar generation peaks at midday, which doesn’t directly offset red-band import, but battery storage paired with solar shifts midday surplus to early-evening discharge, replacing peak DUoS-priced imports. Real numbers: a 250 kW commercial site with battery typically saves £1,500-£3,500 per year on DUoS alone, on top of the energy savings from generation.
What is the difference between red, amber and green DUoS bands?
DUoS charges are time-of-use — the per-kWh distribution charge varies by half-hour according to the local DNO’s charging structure. Red band is the most expensive period, typically 16:00-19:00 on weekdays during winter months (Nov-Feb in most regions, Oct-Mar in some) when network demand peaks. Amber band is moderate, typically the rest of weekday daytime hours plus weekend peak hours, charged at 30-50 percent of red rate. Green band is cheapest, covering nights, weekends, and summer daytime — typically charged at 5-15 percent of red rate. The exact bands and rates vary by DNO region (UK Power Networks publishes different rates from National Grid Electricity Distribution from Northern Powergrid from SP Energy Networks from Electricity North West from SSEN). Your supplier passes these charges through directly on half-hourly metered tariffs.
Do small businesses have time-of-use DUoS exposure?
Smaller commercial customers (under 70-100 kVA peak demand, typically below 100 kW) are usually on non-half-hourly metered tariffs where DUoS is bundled into the unit rate as a flat blended charge. They have indirect exposure — the supplier prices the unit rate to recover average DUoS costs — but no direct time-of-use signal that rewards load-shifting. Larger commercial customers (above 70-100 kVA, half-hourly metered) get the full time-of-use signal and can capture savings by avoiding peak imports. Many larger businesses request voluntary half-hourly metering to access time-of-use tariffs — usually free with a 4-6 week lead time from the supplier. Worth asking your supplier if your annual energy spend is above £100,000.
How does battery storage save on DUoS charges?
Battery storage paired with solar enables time-shift: charge the battery during cheap midday periods (DUoS green band, with surplus solar generation), discharge during expensive early-evening periods (DUoS red band) when imports would otherwise be at peak rates. For a 250 kW site with 100 kWh battery and a 18p/kWh red-band rate, avoiding 1,000 kWh per month of red-band import via battery discharge saves £180/month or £2,160 annually on DUoS alone. Combined with the solar self-consumption savings, total annual benefit can run £6,000-£15,000 on a 250 kW site. The DUoS savings are pure additional return on top of the standard solar economics — they materially improve battery payback. See /services/battery-storage/.
What is the Triad and is it still relevant in 2026?
Triad was the historic mechanism for calculating TNUoS for half-hourly metered customers — TNUoS charges were based on your average demand during the three highest grid-demand half-hours each winter, called Triad periods. Avoiding the Triads (by load-shedding or solar+battery use) was a major savings opportunity for large commercial customers. The Triad system was reformed under the Targeted Charging Review (TCR) and replaced from April 2023 onwards with a fixed annual residual TNUoS charge banded by line band, removing the variable Triad component. Most TNUoS exposure is now fixed annual cost rather than peak-demand variable. DUoS time-of-use charges remain active and are now the main flex savings opportunity. The shift means battery storage payback economics changed materially — DUoS red-band avoidance is now the primary flex driver rather than Triad avoidance.