G100 export limitation is the technical compliance condition that around 30 percent of UK commercial solar installations above 100 kW will face during DNO connection approval. It is a regulatory mechanism that lets the network operator give you a connection without paying for expensive grid reinforcement, on the condition that your inverter electronically caps export to a safe level the local network can handle. For a generator owner it can save £20,000 to £200,000 in network reinforcement costs at the trade-off of some lost export income — and battery storage typically recovers most of that loss. This page explains what G100 is, when DNOs mandate it, how the export limitation hardware works, what it costs, the income impact, the compliance testing requirements, and how G100 differs from G98 and G99 grid connection standards.
What G100 actually is
Engineering Recommendation G100 is the UK Energy Networks Association (ENA) technical specification for export limitation devices fitted to embedded generators connecting to the GB distribution network. The current revision is G100 Issue 2, published 2018 and amended in 2022. It applies to:
Any generator above 17 kW per phase (or 50 kW total on three-phase) that needs to limit export to grid for either DNO connection approval or to avoid network reinforcement costs. The vast majority of G100 cases in commercial solar are 50 kW to 1 MW systems on rural networks, agricultural sites, or industrial estates with weak network spurs.
G100 specifies the performance requirements the export limitation device must meet: response time under 100ms for the export cap to take effect, fail-safe behaviour (if metering fails, export must default to zero — not to the cap), redundant communications between meter and inverter, and a documented testing regime to validate the function.
When G100 applies and when it does not
The default flow for any commercial solar above 17 kW per phase is: installer submits G99 application to your DNO. The DNO assesses local network capacity at the proposed point of connection. Three outcomes:
Outcome 1: Full export approved. Most common outcome on urban networks, on industrial estates with strong network presence, and on sites where solar capacity is well below local consumption. No G100 needed; standard G99 commissioning.
Outcome 2: Network reinforcement quoted. If the local network cannot accept full export at peak generation times, the DNO quotes a reinforcement cost — typically £20,000 to £200,000+ for transformer upgrade, switchgear replacement, or feeder reinforcement. Customer pays this to enable the connection. Common in rural areas.
Outcome 3: G100 export limitation offered as alternative. Instead of the reinforcement cost, the DNO offers a connection at a reduced export cap — say 100 kW export limit on a 250 kW solar system, with G100 export limitation enforcing the cap. No reinforcement payment required from the customer, but the trade-off is permanent capping of export.
Most commercial customers presented with Outcome 3 take it — paying £30k+ for reinforcement to recover ~£3-7k of additional annual SEG income makes no financial sense. G100 is the pragmatic answer.
How G100 export limitation works
The technical architecture is straightforward. A smart meter or current-transformer-based metering device sits at the Point of Common Coupling — the location where your private wiring meets the DNO network, typically at the incoming switch panel after the supply meter. This meter measures grid import and grid export every few seconds.
The meter communicates over Modbus RTU, Modbus TCP, or analogue 4-20mA signal to the inverter or to a central controller. The inverter receives the export reading, compares it to the configured G100 cap, and adjusts DC-side output (by ramping panels' MPPT operating point) to maintain export below the cap. Control loop runs at sub-second intervals — modern implementations have full response in under 100 ms.
Smart load tracking: the meter measures both import and export, so as building load rises during the day (offices switching on aircon, factories ramping up production) the inverter automatically increases generation to take advantage of the headroom — only capping when actual export to grid would exceed the limit. This means the financial impact of G100 is much lower than a fixed-output cap; on most sites, peak generation hours coincide with peak load hours, and load absorbs most of the would-be-curtailed generation as self-consumption.
Hardware options
Most commercial inverter platforms include G100-compliant export limitation natively:
SolarEdge. Three Phase commercial inverters integrate with the SolarEdge Smart Meter (Carlo Gavazzi EM340 or EM530) for native G100 compliance. Configuration is via the SolarEdge SetApp during commissioning. See /solaredge-monitoring/ for the broader SolarEdge platform.
Fronius. Symo and Tauro commercial inverters integrate with the Fronius Smart Meter (50A, 63A, or 65A 3-Phase) for G100. Configuration via the Fronius DataManager. See /fronius-solarweb-monitoring/.
Huawei. SUN2000 commercial inverters integrate with the Huawei Smart Power Sensor for G100. Configuration via the FusionSolar app. See /huawei-fusionsolar/.
SMA. Sunny Tripower commercial integrates with the SMA Energy Meter for G100. Mature and stable platform.
ABB / FIMER. TRIO and PVS-100 commercial ranges integrate with ABB's own metering for G100.
Standalone EVR (Energy Volume Restrictor). For retrofit cases where existing inverters do not support native G100, standalone EVR units from Carlo Gavazzi (EM340 + relay), Solar-Log (Solar-Log 1200 or 2000 PM+), or PowerOne (Lumel) sit at the meter point and signal cap state to the inverter via dry contacts or Modbus. Cost: £600-£1,800 retrofit.
Why DNOs sometimes mandate G100
The UK distribution network was designed in the 1950s-1970s for one-way power flow from large central power stations down through transmission and distribution to customers. Embedded generation reverses that flow on rural and weakly-connected feeders — a 250 kW solar system on a remote farm shed can put more power into the local 11kV feeder than the feeder is rated to carry safely.
Three specific network constraints that trigger G100 requirements:
Voltage rise on distribution feeders. When solar exports back through the local feeder, voltage at the point of connection rises. Above 11kV +6 percent or 400V LV +10 percent the network breaches statutory voltage limits. G100 caps export so the voltage rise stays within limits.
Reverse power on transformers. Older distribution transformers may not be specified to safely accept reverse power from embedded generation. G100 cap keeps total reverse flow within the transformer's rated capability.
Switchgear fault rating. Adding generation increases the fault current available on the local network. If existing switchgear is not rated for the new fault level, network reinforcement is needed unless G100 limits the contribution.
Network reinforcement to address any of these constraints typically costs £20k to £200k+ and takes 12-30 months. G100 limitation costs ~£200-£800 of additional install hardware and zero months. The math is overwhelming for most customers.
Income impact and recovery
The income impact of G100 limitation depends on the cap level relative to your nominal generation:
Cap at 80 percent of nominal output. Typically 3 to 6 percent of annual generation curtailed. Minimal financial impact, especially on sites with substantial midday load.
Cap at 60 percent of nominal output. 8 to 14 percent of annual generation curtailed. Material but recoverable with battery.
Cap at 40 percent of nominal output. 18 to 28 percent of annual generation curtailed. Substantial impact — battery storage is essentially mandatory to make the project economic.
Battery recovery: a battery sized at 1.5 to 2 hours of the cap-vs-nominal gap absorbs most of the would-be-curtailed energy. Example: 250 kW system, 100 kW G100 cap, gap is 150 kW, battery sized at 200 kWh (1.3 hours) recovers around 75-85 percent of curtailed kWh. The recovered kWh is high-value because it is genuine additional generation that would otherwise be lost. Battery payback on G100-curtailed sites is typically 6-9 years versus 12-15 years on uncurtailed sites — G100 is one of the strongest cases for battery storage in UK commercial solar. See /services/battery-storage/.
Compliance testing and documentation
G100 commissioning requires:
Initial witnessed test. At commissioning, the installer demonstrates the export limit is enforced. Test method: simulate high generation (panels uncovered on a sunny day, or simulated DC input from test equipment) and confirm the inverter ramps down to keep export at or below the cap. The DNO may witness this test directly or accept the installer's MCS witnessing.
Documentation pack. G100 declaration of conformity (signed by the installer's qualified engineer), inverter equipment compliance certificate, single-line diagram of the metering and control circuit, RTU/relay protection schedule. All filed with the DNO at G99 commissioning.
Periodic re-test. Some DNOs require annual or 3-yearly compliance verification. UK Power Networks and National Grid Electricity Distribution (formerly Western Power Distribution) typically require periodic re-test. Other DNOs rely on the initial commissioning certificate.
Continuous monitoring. The inverter's monitoring platform records export readings continuously and the data must be available for DNO inspection on request.
G98 vs G99 vs G100 — how they fit together
G98. Engineering Recommendation G98 covers single-phase generators up to 16A per phase (sub-3.68 kW). Notification only — no DNO approval needed. No export limitation involved. See /g98-application/.
G99. Engineering Recommendation G99 covers all generators above G98 thresholds — three-phase or single-phase above 16A per phase. Full DNO connection application required. Approval timeline 6 to 18 months depending on capacity and network constraints. The vast majority of UK commercial solar uses G99. See /g99-application/.
G100. Engineering Recommendation G100 is the export limitation specification, used as a condition within a G99 connection where export needs to be capped. Not a separate connection process — part of G99. Required when DNO offers a capped connection as an alternative to network reinforcement.
So the sequence: G99 application submitted → DNO assessment → either full export, or network reinforcement quoted, or capped connection offered with G100 requirement → if G100 path taken, installer specifies and commissions G100 hardware as part of the G99 commissioning.
Authority resources
Energy Networks Association G100 Issue 2 specification: Energy Networks Association. National Grid ESO connection guide: National Grid ESO. Ofgem distribution connections guidance: Ofgem. MCS-listed installer database: MCS Certified.
Related decision pages
G98 application for sub-3.68 kW. G99 application for the broader connection process. Best commercial solar inverters for G100-compliant inverter selection. Battery storage for G100 income recovery. Maintenance for periodic compliance testing. SolarEdge monitoring, Fronius Solar.web, Huawei FusionSolar for the platform-specific G100 implementation. SEG tariff comparison for the export tariff context. Commercial solar PV. Are commercial solar panels worth it.
G100 export limitation — common questions
Do I always need G100 export limitation on a commercial solar install?
No — G100 only applies when the DNO mandates it as part of your G99 connection approval. The default position for a commercial install above 17 kW per phase is to apply for G99 with a full export agreement; the DNO assesses local network capacity and either approves the full export, or comes back saying network reinforcement is needed (often £20,000 to £200,000+) which you fund, or offers G99 with a G100 export limitation cap as a no-cost alternative. Roughly 30 percent of UK commercial G99 applications in 2026 receive an export limitation requirement, concentrated in rural areas and on weak network spurs. Check at desk-based feasibility before committing to capex — see /g99-application/.
How much income will G100 export limitation reduce by?
Typically 5 to 30 percent of nominal generation, depending on the cap level and your site load profile. A 250 kW system with a 100 kW export cap will see ~12-18 percent of annual generation curtailed in summer when output exceeds 100 kW for several hours daily. The income impact is smaller than the curtailment percentage suggests because high-output hours generate the cheapest electricity from a SEG perspective (oversupply pushes wholesale prices down), and many sites have substantial daytime load that absorbs much of the would-be curtailed generation as self-consumption. We model G100 income impact at the feasibility stage with site-specific load profile data — typical summary: 200kW system with 50kW G100 cap on a 9-5 office: roughly 6-9 percent total income reduction.
Can I add battery storage to recover income lost to G100 limitation?
Yes — battery storage is the canonical answer. When the inverter would otherwise curtail output to stay below the G100 cap, the battery absorbs the surplus, then discharges later in the day when generation has dropped below the cap (or overnight to support next-morning load). Real-world example: 250 kW system with 100 kW G100 cap, paired with 200 kWh battery, recovers around 80 percent of would-be-curtailed kWh. Payback on the battery is typically 7-9 years on a G100-curtailed system because the recovered kWh is high-value (would have been curtailed entirely otherwise). See /services/battery-storage/.
Is G100 the same as G99?
No — G99 and G100 are separate Engineering Recommendations covering different aspects of grid connection. G99 is the ENA standard for connecting any embedded generator above 17 kW per phase to the GB distribution network — it covers the technical commissioning, anti-islanding protection, and grid synchronisation requirements. G100 is the technical specification for export limitation devices, used when the G99 connection includes an export cap. Most commercial installs need G99 commissioning. Some additionally need G100 if the DNO requires export limitation. Both are mandatory where applicable and both have specific testing and documentation requirements.
Who installs and certifies the G100 export limitation system?
Your MCS-certified installer specifies, installs, and commissions the G100 system as part of the overall solar PV installation. The export limitation device is typically integrated into the inverter platform (SolarEdge, Fronius, Huawei, ABB and SMA all have G100-compliant export limitation built into their commercial inverter ranges) so no standalone hardware is needed. For retrofit installs (where solar is added to an existing site and G100 is required late in the process) standalone EVR (Energy Volume Restrictor) units from Carlo Gavazzi or Solar-Log are added separately at the meter point. Commissioning includes a witnessed test where the installer demonstrates the export limit is enforced — typically by simulating high generation and confirming the inverter ramps down. Certification documents are filed with the DNO at G99 commissioning.
How does the G100 limit work technically?
A smart meter or current transformer at the point of common coupling (where your supply cable meets the DNO network) measures grid import and export every few seconds. When export approaches the G100 cap, the metering device sends a Modbus or analogue signal to the inverter, which ramps down DC-side output to keep export below the limit. The control loop runs at sub-second cycles — so even when a cloud passes and load drops simultaneously, the system maintains the cap continuously. Modern integrated G100 implementations have response times below 100ms which means very little energy is technically curtailed at all (the inverter operates just below max output during cap-binding periods rather than oscillating).
Do I need annual G100 compliance testing?
Yes for some DNO areas — UK Power Networks and Western Power Distribution (now National Grid Electricity Distribution) both require periodic G100 compliance verification, typically every 1 to 3 years depending on system size. The test is a witnessed demonstration that the export limitation function still works correctly. Cost is usually £200-450 for the witnessing visit plus your installer’s time. Other DNOs (Northern Powergrid, SP Energy Networks, Electricity North West, SSEN) currently rely on the original commissioning certificate without annual re-test in most cases. Build the periodic test cost into your O&M budget where applicable. See /services/maintenance/.