A G99 application is the request you send to your Distribution Network Operator (DNO) for permission to connect generation above 16 A per phase, which means 3.68 kW on a single-phase supply (ENA EREC G99 Issue 2, 2025). Unlike G98, approval must arrive before installation starts.
That makes it the one piece of paperwork that can stall a sold job for weeks. And the volume is rising fast. UK installers completed a record 267,032 certified solar installations and more than 40,000 battery installations in 2025 (MCS, 2026). Every battery retrofit that pushes a site past the threshold turns a notify-after job into an apply-first one. This guide covers the whole process: which route applies, what goes in the pack, where to submit, what it costs, and why applications bounce.
Key Takeaways
- Above 16 A per phase (3.68 kW single-phase), you must apply under G99 and wait for DNO approval before installing. At or below it, G98 lets you connect first and notify within 28 days (ENA, 2025).
- DNOs must return an LV generation quotation within 45 working days under Ofgem's guaranteed standards; fast-track routes can cut this to days.
- Existing generation counts toward the limit, so adding an AC-coupled battery to a G98 solar site frequently triggers G99.
- Most domestic applications cost nothing. Published DNO assessment fees start around £187 and mainly apply above 50 kVA or at HV.
- The most common rejections: incomplete single line diagrams, blank protection settings, and inverters missing from the ENA Type Test Register.
Do You Need G98, G99 or G100?
The dividing line is 16 A per phase: 3.68 kW at 230 V single-phase, roughly 11.04 kW across three phases (ENA EREC G98/G99 Issue 2, 2025). At or below it, G98 applies: install, then notify. Above it, G99 applies: submit, wait for approval, then install.
Two details decide more jobs than the headline threshold. First, the limit is set by inverter AC export capacity, not panel kWp. A 5 kWp array on a 3.68 kW inverter stays inside G98. Second, capacity is counted per connection point, combining everything on site. Bolt an AC-coupled battery with its own inverter onto an existing G98 solar system and the combined rating usually crosses the line. With battery installations almost doubling to 40,000+ in 2025 (MCS, 2026), this is now the most common way installers meet G99. Our guide to the IET Code of Practice for electrical energy storage covers the design side of those retrofits.
G100 is the pressure valve. Where the network cannot take full output, an export limitation scheme under EREC G100 caps what leaves the site. A compliant scheme must pull output back to the agreed limit within five seconds and fail safe if the control link drops (National Grid, 2025). NGED, for example, accepts single-phase installed capacity up to 17 kW where export is limited. One version note: G98 and G99 Issue 2 took effect on 10 March 2025. New requirements for storage-based generating modules apply from 1 March 2026, so check your BESS models are certified against the current issue.
Step 1: Confirm the Connection Route Before You Quote
By the end of this step, you can state the connection route and a realistic energisation timeline on the customer quote. That matters commercially: a job priced as "no paperwork" that turns out to need G99 inherits a 45-working-day dependency you never planned for. Work through four checks:
- Record the MPAN and confirm single or three-phase supply.
- Identify existing generation at the connection point, including anything a previous installer fitted. Undeclared existing kit is a classic rejection trigger.
- Sum the inverter AC ratings for everything that will exist after your work, per phase.
- Map the result to a route: 16 A or below is G98. Above 16 A with export limitable to 16 A or 32 A may qualify for a fast-track small generation route with a G100 scheme. Everything else is a full G99.
We have seen battery retrofits sold on a two-week promise die in the diary because check 2 was skipped and the DNO spotted the original solar system. Verification is simple: if you cannot name the route and the wait, the survey is not finished.
Step 2: Assemble the Application Pack
A complete G99 pack contains the application form (A1-1), an accurate single line diagram, protection settings, a site plan, inverter details with their ENA Type Test Register references, the MPAN and a letter of authority (NGED G99 procedures, 2026). Most delays trace back to this pack, not to the network.
The single line diagram carries the most weight. It needs the array capacity and string count, DC isolators, each inverter with make, model and rated AC output, the AC isolator, protection, metering, and any export limitation device. Draw the connection to the DNO network with standard symbols. If SLDs are not part of your standard design output, our single line diagram guide shows what assessors expect to see.
The quiet shortcut is the ENA Type Test Verification Report Register. For fully type-tested inverters listed on the register, the compliance verification forms (A2 series) do not need to be submitted at all. The installation document simply references the type test number (NGED, 2026). Choosing registered kit at design stage shrinks the pack now and avoids witness testing later.
Step 3: Submit Through the Right Portal
Small applications increasingly go through one front door. ENA Connect Direct, the industry-wide portal launched in May 2024, has passed 405,000 completed applications (ENA, 2026). It auto-approves routine domestic solar, battery and heat pump connections, and escalated cases average around 1.5 days.
Coverage is being expanded from G98-limit work toward full G99 scope, so check whether your job qualifies before defaulting to the DNO's own forms. Larger or non-standard schemes still go direct to the DNO portal for your region.
Fast-track routes are worth knowing by name. SSEN runs a dedicated G99 Fast Track service aiming to respond within 10 working days. Several DNOs, including NGED and Northern Powergrid, operate small generation installation (SGI) processes. These accept type-tested equipment with export capped at 16 A or 32 A per phase using a G100 scheme. Where they fit, these routes return answers in days rather than the statutory window.
How Long Does a G99 Application Take?
Ofgem's guaranteed standards give the DNO 45 working days to issue an LV generation quotation and 65 working days for HV (Ofgem). Budget estimates are quicker: 10 working days for schemes under 1 MVA, with an £80 payment due if missed.
Those are ceilings, not typical outcomes. Simple domestic G99s commonly come back within 4 to 12 weeks, fast-track and SGI routes within days, and Connect Direct auto-approvals instantly. The tail risk sits on constrained networks: if the assessment finds reinforcement is needed, the timeline shifts from weeks to months and the offer will carry costs. That is usually the moment to pivot to a G100 export-limited design rather than fund network works.
The practical rule for pipeline planning: submit at survey stage, not install stage. A G99 lodged the day the deposit lands is a background process. One lodged the week before scaffolding is a bottleneck.
What Does a G99 Application Cost?
For most domestic and small commercial jobs, nothing. SPEN and SSEN charge no connection offer expense for generation below 50 kVA. NGED's minimum assessment and design fee for a single small-scale embedded generator is £187 (NGED, 2024). Fees concentrate above 50 kVA and at HV. The published schedules compare like this:
- SPEN: fees start above 50 kVA. £500 at LV, £2,000 at HV, £6,000 at 33 kV (SPEN, 2022 schedule).
- NGED: assessment and design charges scale with size. £187 for a single SSEG; £620 to £1,674 at LV; £2,003 to £3,184 at HV (NGED, 2024).
- SSEN: micro generation under 50 kVA is free; £1,163 for HV up to 250 kVA and £3,169 above 1 MVA (SSEN, 2023 guide).
- UKPN: upfront assessment fees apply only above 1 MVA, so small and domestic G99s carry no upfront charge.
Two cautions. NGED extends upfront charging to HV quotations up to 250 kVA from 1 February 2026. And the SPEN and SSEN figures date from their 2022 and 2023 published schedules, so confirm against the current charging methodology statement before quoting a client. Fee schedules move; the pattern of "small is free, HV costs" has held.
Step 4: Handle the Offer, Then Commission and Notify
The offer arrives in one of three shapes: an unconditional connection offer, an offer with conditions such as an export limit, or a requirement for network reinforcement with costs attached. Accept in writing before the cooling-off period lapses, then install to the approved design. Any change to inverter make, model or protection settings after acceptance means telling the DNO, not improvising on site.
Commissioning triggers the second stage. You submit the actual commissioning date, test results, the electrical installation certificate reference, inverter serial numbers, and confirmation that the protection settings match what was approved. For larger schemes the DNO may require a witnessed commissioning test, which is a chargeable visit. Fully type-tested, register-listed equipment is exempt: the second payoff from Step 2's inverter choice.
Close the file properly. The installation document, the offer, the SLD and the test results belong in the project record alongside the MCS installation certificate. A future battery retrofit or an export tariff application will ask for them. Our renewable installation paperwork guide covers the full document set.
Why Do G99 Applications Get Rejected?
Industry application guides consistently name four causes: an incomplete or non-standard single line diagram, protection settings left blank or outside permitted ranges, an inverter without a valid ENA type test reference, and undeclared existing generation at the connection point (SurgePV, 2026). All four are process failures rather than engineering ones.
The fifth cause is the network itself. Where local capacity is insufficient, the DNO does not reject so much as attach reinforcement costs and delay. The productive response is rarely to fund the works on a domestic job. Redesign around a G100 export limitation scheme, resubmit, and keep the system size the customer paid for while capping what the grid sees. A pre-submission checklist that catches nearly everything:
- SLD complete, standard symbols, every inverter with make, model and AC rating
- Protection settings filled in and inside G99 ranges
- Type test register reference recorded for each inverter
- Existing on-site generation declared, even historic kit
- MPAN checked character by character
Conclusion
G99 stops being a bottleneck when it becomes a workflow. Decide the route at survey, generate the pack from the design file, submit early, track the clock against the 45-working-day standard, and close out stage two the week you commission. Firms that run it this way quote accurate timelines and keep install teams moving. Design platforms like Reonic help by producing the SLD and holding inverter and project records in one place, alongside the rest of the design toolkit. For the wider compliance picture, see our UK PV and heat pump compliance guide.
FAQ
Q1: What is the difference between a G98 and a G99 application?
G98 covers type-tested generation up to 16 A per phase (3.68 kW single-phase): you install first and notify the DNO within 28 days. G99 covers everything larger and works the other way round: the DNO must assess and approve the connection before installation begins (ENA, 2025).
Q2: How long does a G99 application take?
The DNO has 45 working days to issue an LV generation quotation and 65 for HV under Ofgem's guaranteed standards. Straightforward domestic applications often return in 4 to 12 weeks, while fast-track and SGI routes, such as SSEN's 10-working-day service, come back in days.
Q3: How much does a G99 application cost?
Usually nothing for domestic work. SPEN and SSEN charge no offer expense below 50 kVA, and NGED's minimum assessment fee for a single small generator is £187. Published fees rise with scale: roughly £500 to £2,000 at LV and HV for larger schemes, and more at 33 kV.
Q4: Does adding a battery trigger a G99 application?
Often, yes. Capacity is combined per connection point, so an AC-coupled battery inverter added to an existing 3.68 kW solar system typically pushes the site over 16 A per phase. With over 40,000 battery installations in 2025 (MCS, 2026), this retrofit scenario is now the most common G99 trigger.
Q5: Can export limitation avoid a full G99 assessment?
It can simplify one. A G100-compliant scheme that caps export within five seconds and fails safe lets larger inverters connect on constrained networks, and NGED accepts single-phase installed capacity up to 17 kW with limited export. Fast-track SGI routes rely on exactly this arrangement (National Grid, 2025).
