G98/G99 DNO Solar Export Limitation or Refusal: UK Appeal and G100 Guide

Key Takeaways

• Under Energy Networks Association standards, systems Connecting generation, including energy storage at 16 amps or less per phase, for a single or multiple premises qualify for G98 simple connection.
• Where generation exceeds 16A per phase or local networks are saturated, DNOs may reject export or impose strict export limitation caps to protect local grid stability.
• Homeowners can resolve export refusals by commissioning an ENA G100-compliant failsafe limiter to Set the Backflow Power Limit, enabling full generation for self-consumption.
• Flexible connections allow us to manage the demand of electricity across the network and can result in a quicker 'power on' date and potentially cheap grid energization without expensive infrastructure reinforcement.
• Safety warning: Setting export limiters and connecting external boundary CT coils involves working near unmetered mains voltage service cutouts; all electrical work must be performed by certified installers.

1. The UK grid connection framework: G98 versus G99

Every solar photovoltaic array and battery storage system connected to the British electricity network must comply with Energy Networks Association (ENA) engineering recommendations. Across Great Britain, six licensed Distribution Network Operators (UK Power Networks, National Grid Electricity Distribution, Electricity North West, Northern Powergrid, SSEN, and SP Energy Networks) manage regional infrastructure.

Under standard industry procedures, We provide a range of generation connections for solar panels and wind turbines, including energy storage. The regulatory boundary between small and large installations is defined by current carrying capacity:

• Engineering Recommendation G98: Applies when Connecting generation, including energy storage at 16 amps or less per phase, for a single or multiple premises. In single-phase homes, 16 amps corresponds to approximately single-phase capacity. Under G98, installers can connect the system and notify the DNO within 28 days (for example, Please email your G98 form to g98notifications@enwl.co.uk).
• Engineering Recommendation G99: Mandatory whenever total generation or battery inverter capacity exceeds 16 amps per phase. Under G99, the installer cannot connect the system until the DNO completes a network study and issues a formal connection offer.

When homeowners apply for larger arrays (such as 6 kW solar with a 5 kW battery on a single-phase supply), DNO engineering studies frequently return with a refusal letter or an offer capping export to zero or a fraction of requested capacity.

2. Why DNOs refuse or limit solar export

DNO export restrictions are driven by localized physical constraints on the low-voltage distribution network:

Cause 1: Substation Thermal Overload

Local medium-voltage to low-voltage ground-mounted or pole-mounted distribution transformers have fixed thermal capacity limits. If dozens of homes on your rural or suburban feeder install rooftop solar, the cumulative midday reverse power flow can exceed the transformer rating, creating catastrophic overheating.

Cause 2: Statutory Voltage Rise Limits

Under the Electricity Safety, Quality and Continuity Regulations (national electricity safety standards), UK mains voltage must remain within statutory supply voltage tolerances. When an inverter exports power, it must elevate its output voltage above the local grid to push current into the street main. On long rural cable runs, exporting high solar currents pushes street voltage above the statutory voltage ceiling, forcing inverters to trip on overvoltage alarms.

Cause 3: High Voltage Network Upstream Constraints

In many areas, the regional high-voltage transmission grid has reached capacity. Where upstream constraints exist, DNOs utilize active monitoring where the Capacity of distributed energy resources actively managed within zone to maintain stability.

3. The G100 export limitation solution

Receiving an export limitation letter does not mean you must cancel your solar and battery project. The standard UK engineering remedy is to install an ENA EREC G100-compliant Export Limitation Scheme (ELS).

Under an approved G100 scheme, the solar array and battery inverter are sized to match your household energy consumption. A high-speed current transformer (CT) clamp or meter monitors the boundary between your home and the grid. Inverter firmware features an Internal EPM Set menu. As technical guidance explains, The CT solution is only suitable for systems with one inverter. For multi-inverter systems, use the EPM solution instead.

Within the menu, the installer will Set the Backflow Power Limit. You can Choose how much power your system is allowed to export to the grid, setting the parameter to match the DNO letter (whether that is 0 kW, partial kilowatt limit, or single-phase capacity). The system will Control export power dynamically, adjusting inverter output to prevent unwanted export. These schemes Improve system stability and comply with local export-limit rules.

Under ENA G100 rules, the export limiter must respond within five seconds of detecting excess export, and must possess failsafe redundancy: if the CT sensor wire is cut or communication drops, the inverter must automatically drop to the safe backflow limit within seconds.

4. Flexible connections and formal appeal routes

If your DNO refuses connection outright or quotes exorbitant grid reinforcement fees (often tens of thousands of pounds for transformer upgrades), explore these alternative resolution pathways:

Pathway 1: Request a Flexible Connection

Ask your DNO: What is a Flexible Connection? DNOs offer managed agreements where Flexible connections allow us to manage the demand of electricity across the network and can result in a quicker 'power on' date and potentially cheap network access. Under these agreements, you may accept an automated timed flexible connection because you only needed power overnight when demand across the network was lower.

Pathway 2: Three-Phase Supply Upgrade

If your single-phase service is capped at single-phase capacity, request a quotation from your DNO to upgrade your domestic service to three-phase supply. A three-phase connection allows balanced G98 connection of up to expanded three-phase capacity (16 amps per phase across all three phases) without triggering single-phase voltage rise issues.

Pathway 3: Dispute Escalation and Section 23 Determination

If you believe the DNO's technical refusal or reinforcement quote is unreasonable or discriminatory, you have the statutory right under Section 23 of the Electricity Act 1989 to refer the dispute to the energy regulator, Ofgem, for a legally binding determination.