A G99 application is the formal request you lodge with your distribution network operator (DNO) for permission to connect generation above 16 A per phase to their network, and it must be approved before you energise. G99 itself is Engineering Recommendation G99 — the Energy Networks Association standard governing how distributed generation connects to the low-voltage and 11 kV distribution network. The 16 A per phase trigger (~3.68 kW single-phase, ~11 kW three-phase) captures almost every commercial solar PV installation. Fully type-tested systems up to 17 kW per phase (~50 kW three-phase) qualify for a streamlined fast-track on ENA Form A1-2, usually decided inside 15-20 working days; larger arrays follow the full application process, which can take anywhere from 6 months on an unconstrained rural network to 24 months on a severely constrained urban grid. This page lays out exactly which form to lodge, what the DNO checks, what it costs, where projects get stuck, and how a competent installer compresses the timeline.
What G99 actually is — and where it differs from G98
G99 is one of two Engineering Recommendations published by the Energy Networks Association governing connection of distributed generation in the UK. Its smaller sibling, G98, covers connect-and-notify installations of fully type-tested micro-generation up to and including 16 A per phase (~3.68 kW single-phase, ~11 kW three-phase) — straightforward, fast, no pre-approval required. G99 covers everything above that threshold, and unlike G98 the DNO must approve the connection before any energisation. Within G99 itself, fully type-tested systems up to 17 kW per phase (~50 kW three-phase) follow a streamlined fast-track application — simpler forms, much quicker DNO turnaround, but still apply-before-connect. Above the fast-track ceiling, the application is a formal study by the DNO of how your proposed generation will affect their network: voltage rise, fault levels, thermal capacity of cables and transformers, and protection coordination. It is also where the DNO charges any required network reinforcement back to you.
Trigger points for G99 are unambiguous: anything above 16 A per phase on any phase. A balanced 10 kW install on a three-phase 400 V supply (~3.3 kW per phase) sits inside G98. A 45 kW type-tested install (15 kW per phase, balanced) is G99 but qualifies for the fast-track. A 110 kW install (37 kW per phase) is firmly full G99. A 10 kW install on a single-phase 230 V supply is also G99 because it exceeds the per-phase limit — most small commercial sites with single-phase supplies hit this constraint and have to choose between a three-phase upgrade or a heavily capped array. We size every quote against these thresholds deliberately, not by accident.
G98 or G99 — which applies to my system?
Everything turns on current per phase, not headline kW, and on whether every piece of generating equipment is fully type-tested. Read the table left to right: find your band, and it tells you the route, the form and the timing. If the answer is G98, the G98 application page covers the connect-and-notify process in full.
| System and supply | Route | What you lodge | Timing |
|---|---|---|---|
| Up to and including 16 A per phase, fully type-tested (~3.68 kW single-phase, ~11 kW three-phase) | G98 connect and notify | G98 notification | No pre-approval and no application fee. Notify the DNO within 28 days of commissioning |
| Above 16 A per phase, fully type-tested, up to 17 kW per phase (~50 kW three-phase) | G99 fast-track (Small Generation Installation) | ENA Form A1-2 | Apply before connect. Most DNOs decide in ~15-20 working days |
| Same band, but equipment not fully type-tested or only part type-tested | G99 small generation, standard | ENA Form A1-1 plus Compliance Verification Report A2-1 (or A2-2 / A2-3) | Apply before connect. Slower than fast-track — the DNO has to assess the uncertified equipment itself |
| Same band, output shared between two or more customers (landlord and tenant, multi-MPAN) | G99 small generation, shared output | ENA Form A1-3 | Apply before connect. Expect extra questions on metering and ownership |
| Above 17 kW per phase (above ~50 kW three-phase) | Full G99 application | DNO connection application with the full technical pack | Acknowledgement within 5 working days, formal connection offer within 65 working days |
| Any system above ~3.68 kW on a single-phase 230 V supply | G99 — the single phase is the binding constraint | Whichever band above applies, capped at 17 kW on that one phase | Usually forces a three-phase upgrade decision before the array can be sized properly |
The trap worth naming: a 50 kW three-phase array is G99 fast-track, not G98. It sits at roughly 17 kW per phase, comfortably above the 16 A per phase G98 ceiling, so it needs approval before it is energised. Installers who treat 50 kW as connect-and-notify get the system switched on illegally, and the DNO can and does require disconnection.
Fast-track versus full G99 application side by side
Which side of this table you land on decides the timeline, the cost and how much of your project is exposed to network risk. It is the single most useful thing to establish before you design the array.
| Aspect | G99 fast-track (SGI) | Full G99 application |
|---|---|---|
| Capacity band | Fully type-tested, up to 17 kW per phase (~50 kW three-phase) | Above ~50 kW three-phase, or any size where full type-testing is absent |
| Form lodged | ENA Form A1-2 | DNO connection application, plus A2-x Compliance Verification Report where equipment is not fully type-tested |
| Approval needed before energising | Yes | Yes |
| Depth of DNO assessment | Screening review against the local network record | Full study — voltage rise, fault level, thermal capacity, protection coordination |
| Typical decision time | ~15-20 working days | Acknowledge in 5 working days, offer within 65 working days |
| DNO application fee | Normally none | Indicative only, check your DNO's published charges: ~£350-£500 up to 200 kW, £750-£3,000 for 200 kW to 1 MW, £3,000-£15,000+ above 1 MW |
| Reinforcement contribution | Rare — the band exists because these sizes usually fit the existing network | Possible: £0 on a healthy network up to £250,000+ for transformer or HV cable works |
| Formal connection offer | No offer — you receive an approval to proceed | Yes, and it lapses if not accepted within 90 days |
| ANM / flexible connection terms | Rarely applied | Commonly offered as the alternative to reinforcement on constrained networks |
| Witness test | Not normally attended for fully type-tested equipment — the installer returns the commissioning confirmation | Yes, a DNO engineer attends before energisation |
| Commissioning date rule | On Form A1-2 the planned commissioning date must fall between 10 working days and 3 months from the application date | Set by the accepted offer and the DNO works programme |
| Realistic end to end | 4-8 weeks | 6-24 months depending on DNO and network constraint |
Because the fast-track band is generous — 17 kW per phase, so a balanced ~50 kW three-phase array — a large share of SME commercial projects can be designed to stay inside it deliberately. On a constrained feeder, a 48 kW array approved in three weeks beats a 90 kW array that waits a year and carries a reinforcement bill.
Which G99 form do I need?
Most delays we see start here: the right technical pack lodged on the wrong form. The Energy Networks Association publishes a set of G99 forms and each has a defined scope. Confirm the current version on your DNO connections pages before submitting, because form revisions track the EREC G99 issue and amendment in force.
| Form | What it is | Use it when |
|---|---|---|
| A1-2 | Application for connection of fully type-tested generation under the Small Generation Installation procedures — the fast-track form | Every inverter fully type-tested and registered on the ENA Type Test Verification Report Register, and capacity within 17 kW per phase (~50 kW three-phase) |
| A1-1 | Application for connection of power generating module(s) with total aggregate capacity up to 50 kW three-phase or 17 kW single-phase | Same capacity band, but the installation is not going down the fully type-tested fast-track |
| A1-3 | As A1-1, where the output is shared between two or more customers | Landlord and tenant arrangements, multi-MPAN sites, shared rooftop arrays across units |
| A2-1, A2-2, A2-3 | Compliance Verification Reports for Type A power generating modules | Submitted alongside the application whenever a module is not fully type-tested, or is only part type-tested |
| G100 declaration | Export limitation scheme declaration (a separate Engineering Recommendation, submitted with the G99 pack) | Where the design holds export inside an agreed capacity using an export limitation device |
| Above the SGI band | The DNO connection application on its own portal, leading to a formal connection offer | Anything above ~50 kW three-phase — the full G99 route described in the seven stages below |
What people actually mean by a "G99 certificate"
Three separate documents get called a G99 certificate, and confusing them causes real problems on site. The inverter type-test certificate is issued by the manufacturer or test house and registered on the ENA Type Test Verification Report Register — it proves the model meets EREC G99, exists before you apply, and gets submitted with the application. The DNO approval is the portal confirmation or letter accepting your G99 application on the fast-track route, or your accepted connection offer on the full route; that is what most customers mean and it must be in hand before install completes. The commissioning confirmation is what the installer returns after the work, recording that the system was built to the approved design, set to the agreed protection settings, and witness tested where required. Ask which one is being referred to before assuming a project is cleared to energise.
The seven stages of a G99 application
The stages below describe the full G99 application — the route above roughly 50 kW three-phase. A fast-track application on Form A1-2 collapses stages 2 to 4 into a single submission and a DNO approval, typically inside 15-20 working days, and normally skips stage 5 entirely. Every full G99 application moves through the same sequence regardless of DNO. Knowing the stages lets you see where the project is and what is realistically the next bottleneck.
Stage 1: Eligibility and pre-application check
Before lodging anything, we run a desk-based check of your supply: import capacity (Available Supply Capacity on the MPAN), phasing, distance to the nearest substation, and known network constraints in the postcode. The DNO publishes a heat map (UK Power Networks' Network Capacity Map, NGED's Network Capacity Map, SSEN's Distribution Future Energy Scenarios) showing where the 11 kV network is constrained. Sites in red zones face longer timelines and higher reinforcement costs and we factor this into the quote upfront. This stage takes 2-5 working days and costs nothing — the data is open.
Stage 2: Application submission
The formal application is lodged on the DNO's connection portal with: customer details and MPAN, single line diagram showing the existing supply, proposed PV array configuration, inverter type-test certificates (PDF), protection settings, generator data sheet, expected energisation date, and — on the full route only — a non-refundable application fee (typically £350-£500 for under-200 kW, £750-£3,000 for 200 kW to 1 MW, and £3,000-£15,000+ above 1 MW; a fast-track submission on Form A1-2 normally attracts no DNO fee). The DNO has 5 working days to acknowledge and 65 working days to issue the connection offer — those clocks come from the connection standards of performance set under the DNO's distribution licence and enforced by Ofgem, not from DNO goodwill.
Stage 3: DNO study and connection offer
This is the longest stage at this point in the process and what you are paying for. The DNO models the proposed generation against their power-flow analysis of the local network, looking at voltage rise, thermal capacity of the upstream transformer and 11 kV cables, fault levels, and protection coordination. They issue a written connection offer that says either "you can connect at the proposed capacity with no network reinforcement" (best case), or "you can connect with limited capacity / curtailment under ANM" (good case), or "you can connect but the network needs reinforcement at a cost of £X" (variable case). Expect 8-13 weeks for a routine study, longer where the network is constrained or where the application has gone into queue management.
Stage 4: Offer review and acceptance
You have 90 days from the date of offer to accept it or it lapses. Accepting is a binding commitment to pay the connection charges and proceed with the project. Before accepting we model the financial impact of any curtailment terms or reinforcement costs in the project DCF — sometimes a higher capacity offer with reinforcement is worse for IRR than a lower curtailed offer with no reinforcement. We share that comparison with the customer alongside the offer review.
Stage 5: Connection works and reinforcement
If the offer requires DNO works (cable reinforcement, transformer upgrade, new substation tie-in), they happen at this stage. The DNO programmes the work into their delivery calendar — this is where 6-month delays creep in on constrained networks because the queue of customer connection works runs deep. We chase weekly and escalate where DNO programme dates slip materially against the offer.
Stage 6: Physical install
Panel mounting, DC cabling, inverter installation, AC cabling and switchgear all run in this stage and largely run in parallel with Stages 4 and 5 — we don't wait for the DNO to be ready. The only thing we don't do until the DNO has finished is the final tie-in to the network and energisation.
Stage 7: Witness test and energisation
A DNO engineer attends site to verify protection relay settings, anti-islanding response, earthing, and as-installed configuration against the application. A clean witness test is signed off same-day and the system is formally energised onto the network. Generation begins immediately. SEG (Smart Export Guarantee) registration follows within 14 days post-energisation.
Typical timescales by DNO
Great Britain's distribution network is run by six DNO groups across 14 licence areas, with NIE Networks operating separately in Northern Ireland. Performance varies materially between them. Below are realistic 2026 ranges for a 200-500 kW PV connection assuming a routine application without major reinforcement.
- UK Power Networks (London, East, South East): 9-15 months. Heavy queue, urban constraints in central London and parts of Hertfordshire. Strong portal and clear documentation. ANM available on most constrained feeders.
- Northern Powergrid (Yorkshire, North East): 6-10 months. Lower queue, more rural network with capacity headroom. Generally the fastest of the major DNOs for routine PV connections.
- Electricity North West (Greater Manchester, Lancashire, Cumbria): broadly comparable with Northern Powergrid on routine PV connections, with the constrained pockets concentrated around Manchester and the M60 corridor rather than the network as a whole.
- SP Energy Networks (central and southern Scotland, Merseyside, Cheshire, North Wales): 9-13 months. Some constrained networks around Liverpool and Glasgow. ANM and flexible connections widely offered.
- SSEN (Southern, Scottish Hydro): 8-14 months. Wide variance — Scottish Highlands often 6 months, southern coast and Hampshire/Berkshire run 12+ months due to congestion.
- National Grid Electricity Distribution (formerly Western Power, covering South West, Midlands, South Wales): 9-16 months. Cornwall and Somerset are particularly constrained for solar export.
- NIE Networks (Northern Ireland): 7-12 months. Smaller network, separate regulatory framework but similar G99 process.
Above 1 MW the project may also need to cross into the National Energy System Operator (NESO, formerly National Grid ESO) approval process for transmission-level impact assessment — that adds another layer and another 6-12 months. Most SME and mid-market commercial PV projects stay inside the DNO process exclusively.
What the application costs
The single biggest cost question is which route you are on, because the G99 fast-track normally carries no DNO application fee at all — the only cost is the installer time to assemble and chase the pack, which sits inside our quote. Fees start on the full route.
| Cost line | Fast-track (Form A1-2) | Full G99 application |
|---|---|---|
| DNO application or assessment fee | Normally £0 | Indicative only, check your DNO's published charges: ~£350-£500 up to 200 kW, £750-£3,000 for 200 kW to 1 MW, £3,000-£15,000+ above 1 MW |
| Network reinforcement contribution | Rare at this capacity | £0 on a healthy network, £30,000-£250,000+ where transformer or HV cable works are triggered |
| DNO connection works | Usually none | Quoted line by line inside the connection offer |
| Three-phase supply upgrade where the site is single-phase | £3,000-£15,000 | £3,000-£15,000 |
| Our project administration | Included in the install quote | Included in the install quote |
Three cost categories matter on the full route. Application study fee is the desk fee paid to the DNO when the application is lodged. Currently £350-£500 for sub-200 kW connections, £750-£3,000 for 200-1,000 kW, and £3,000-£15,000+ for over 1 MW. Network reinforcement charges are project-specific and can range from £0 (healthy network) to £250,000+ (full transformer upgrade). On constrained networks the DNO is required to offer a flexible connection (ANM curtailment) as an alternative to reinforcement — flexible connections almost always have lower upfront cost and we usually recommend them unless modelling shows curtailment >8% of annual generation. Our project administration fee covers the time to manage the entire process — included in the install quote, never a separate line item.
For comparable cost ranges across project sizes, see our full cost guide. Asset finance covers all of this — see finance options.
What the DNO needs from you
A complete G99 application bundle includes: customer details and active MPAN, current Available Supply Capacity, single line diagram showing the existing connection arrangement, proposed PV array drawing showing inverter location, generator data sheet, type test certificates for every inverter model on the system, protection coordination study, expected energisation date. Missing information sends the application back to "incomplete" status and stops the 65-day clock — a single missed protection setting can add 4-8 weeks to your timeline. We assemble everything in-house against a checklist before lodging.
Here is that checklist in the order the DNO assessor works through it, with the failure mode we see most often against each line. Every one of these applies to a G99 application on either route.
| Document or data item | What the DNO checks | Most common failure |
|---|---|---|
| MPAN and site details | Live supply, correct DNO for the postcode, current Available Supply Capacity, number of phases | Application sent to the wrong DNO, or ASC left blank |
| Single line diagram | Existing supply arrangement, array and inverter positions, isolators, metering, earthing, and the demarcation between DNO and customer equipment | Informally drawn or incomplete SLD — the single biggest cause of an application bouncing back |
| Inverter type-test certificate | A valid EREC G99 certificate for every inverter model, listed on the ENA Type Test Verification Report Register | Expired or superseded certificate, wrong firmware variant, or a grey-import model never registered |
| Protection settings schedule | Voltage and frequency trip envelopes, time delays, anti-islanding, ROCOF or vector shift where required | Left blank, or values outside the range that DNO publishes for the network |
| Existing generation declaration | Any PV, CHP, standby generator or battery storage already present at the connection point | Not declaring an existing array — this invalidates the whole network assessment |
| G100 export limitation declaration | Scheme design, limiting device, setpoint and how the limit was verified | Omitted on a design that only fits the network because export is limited |
| Generator data sheet and array layout | Panel count, DC and AC ratings, string design, structural layout | AC rating on the form not matching the inverter data sheet |
| Planned commissioning date | On Form A1-2 it must sit between 10 working days and 3 months from the application date | A date set by hope rather than the install programme, so the form is rejected on submission |
Why G99 applications get rejected or delayed
Refusal on genuine network grounds is far rarer than people expect. The overwhelming majority of rejected or stalled applications fail on paperwork, and every one of these is preventable at design stage.
| Reason | What it costs you | How we prevent it |
|---|---|---|
| Type-test certificate missing, expired, or for a different model | Refusal and a re-specification of the inverter mid-project | Only specify models currently on the ENA register; certificate pulled and filed at design stage |
| Single line diagram incomplete or non-standard | 2-4 weeks lost, application returned as incomplete | Drawn to the DNO template and reconciled against the physical site survey |
| Protection settings schedule blank or out of range | 2-4 weeks now, or a failed witness test and a return visit later | Settings taken from that DNO guidance and cross-checked against the inverter menu before submission |
| Existing generation at the connection point not declared | Assessment invalidated and the application restarted from zero | MPAN and site generation history checked before anything is lodged |
| Export limitation relied on with no G100 declaration | Returned incomplete, clock restarts | G100 pack assembled and submitted with the application, not after it |
| Capacity above the fast-track band lodged on Form A1-2 | Rejected, then weeks lost resubmitting on the full route | Capacity checked against 17 kW per phase before the form is even chosen |
| Planned commissioning date outside the allowed window | Rejected on submission | Dates set from the live install programme, inside the 10 working day to 3 month window |
| The network genuinely is constrained | A reinforcement quote, or ANM curtailment terms attached to the offer | Capacity heat map checked at quote stage so the array is sized to the network you actually have |
Common pitfalls and how to avoid them
Capacity-constrained networks. If your site sits on a feeder already carrying multiple PV connections, you may face reinforcement charges even on a modest install. Check the DNO's network capacity heat map before designing the array — it sometimes pays to size a type-tested system to 17 kW per phase (~50 kW) and take the G99 fast-track rather than push to a larger array that triggers a full study and £40k of reinforcement.
Fault level limits. Older 11 kV substations can hit fault current limits when too much rotating or inverter generation is added — limits the DNO will protect by quoting reinforcement or by refusing capacity. Modern type-tested inverters with low-fault-contribution settings sometimes resolve this without reinforcement.
Single-phase site assumed three-phase. A small office on a single-phase 230 V supply can only host ~3.68 kW of PV under G98, and even the G99 fast-track caps a single phase at 17 kW. Anything bigger forces a three-phase upgrade — typically £3,000-£15,000 — that should be costed into the proposal upfront, not bolted on as a change order.
ANM curtailment misunderstood. Some installers either ignore curtailment in DCF (overstating IRR) or panic about it (recommending against ANM offers that are actually fine). 1-5% curtailment is normal and acceptable; above 8% it is material. Always model.
Inverter type-test mismatch. Specifying inverters not on the current G99 type-test register fails the application instantly. We only specify currently certified inverters from established brands.
How we manage the process for clients
Every commercial solar quote we issue that needs G99 — fast-track or full — includes complete G99 management as part of the headline price, no separate line item, no surprise admin fee. That covers: pre-application desk study including DNO heat map check; full application bundle assembly to DNO checklist; submission via the DNO portal and acknowledgement chase; ongoing liaison with the DNO connection engineer including weekly status during the study period; offer review with financial modelling of any curtailment or reinforcement terms; acceptance recommendation against the project DCF; scheduling of network works in coordination with our install programme; witness test attendance; energisation paperwork and SEG registration. Customers see fortnightly progress updates with explicit DNO milestone tracking. If the DNO programme slips materially we escalate through the DNO connection manager and, where warranted, to the regulator (Ofgem). See our about page for the team and accreditations we hold.
How to compress the timeline
Five tactics consistently shave weeks or months off the felt timeline. Lodge early. The 65-day study clock starts when the application is complete. Lodging while the customer is still finalising contract pushes the clock forward by weeks. Run physical install in parallel. Panel mounting, DC cabling and inverter install can run during the DNO study — only AC tie-in waits for the connection works. Accept ANM offers where curtailment is modelled below 5%. Waiting another 6 months for full reinforcement to win 4% of annual generation is rarely the right call. Specify DNO-friendly inverters. Some inverter models have lower fault current contributions and clear higher G99 thresholds without triggering reinforcement — the right model selection at design stage avoids the wrong conversation at study stage. Pre-empt single-phase / three-phase issues. A site that needs a three-phase upgrade is best identified at quote stage so the upgrade and the PV install run on coordinated programmes.
Useful authority links
The Energy Networks Association publishes the canonical G99 standard and updates: Energy Networks Association — Distributed Generation. Each DNO's connection portal and capacity heat map is the source of truth for your specific site. Ofgem regulates connection charging and timeline performance: Ofgem. The MCS certification framework governs installer competency for sub-50 kW domestic and small commercial PV: MCS. For broader UK government net zero policy context, see gov.uk Net Zero Strategy.
Related decision pages
If your project is genuinely micro scale — up to 16 A per phase — see the G98 application process. To understand why solar still pays back even with a 12-month G99 process, read are commercial solar panels worth it. For larger industrial sites, the industrial solar panels hub covers HV and 11 kV connection. To compare solar against alternatives at the same capex, see solar vs alternatives. For sector-specific quotes see factories, warehouses, or cold storage. To pull funding into the project, our grants and funding page covers all current schemes.
G99 application — common questions
When does my commercial solar project need a G99 application instead of G98?
G99 applies whenever the proposed generation exceeds 16 A per phase — around 3.68 kW on a single-phase 230 V supply or 11 kW on a three-phase 400 V supply — which captures almost every genuinely commercial array. Within G99, fully type-tested systems up to 17 kW per phase (~50 kW three-phase) qualify for a streamlined fast-track application with much quicker DNO turnaround; larger systems follow the full application process. A single-phase site is forced into G99 territory above ~3.68 kW — which is why most genuine commercial sites with single-phase supplies need a three-phase upgrade before the PV install can proceed.
How long does a G99 application take in 2026?
It depends on the route. Fully type-tested systems up to 17 kW per phase (~50 kW three-phase) qualify for the G99 fast-track — a simplified application with turnaround typically measured in weeks, though still apply-before-connect. For the full G99 application above that band: acknowledgement is statutorily within 5 working days, the DNO connection offer must follow within 65 working days for a standard application (3 months), and acceptance and physical works then run another 3-12 months depending on whether network reinforcement is required. Realistic end-to-end timeline is 6-10 months for unconstrained networks (Northern Powergrid, Electricity North West, SSEN rural, parts of NIE), 9-16 months for moderately constrained networks (UK Power Networks, SP Energy Networks, NGED), and 15-24+ months for severely constrained urban or southern networks. Plan accordingly.
How much does a G99 application cost?
The G99 fast-track route (ENA Form A1-2, type-tested systems up to 17 kW per phase / ~50 kW three-phase) normally carries no DNO application fee at all — the cost is your installer’s admin time, which we build into the quote. On the full G99 route above that band the DNO charges an assessment fee: indicatively £350-£500 up to 200 kW, £750-£3,000 for 200 kW to 1 MW, and £3,000-£15,000+ above 1 MW. UK Power Networks runs higher than Northern Powergrid for comparable studies. Network reinforcement charges are the wild card: a connection on a healthy substation costs £0 in reinforcement; a constrained network might quote £30,000-£250,000+ to upgrade transformers, reinforce HV cables, or extend the local network. Curtailment-based connections (ANM and flexible connections) usually waive reinforcement at the cost of accepting export limits during peak network stress.
What is a G99 form and which one do I need?
There is no single G99 form — the Energy Networks Association publishes a set, and picking the wrong one gets the application bounced. Form A1-2 is the fast-track application for fully type-tested generation under the Small Generation Installation procedures, used for systems up to 17 kW per phase (~50 kW three-phase). Form A1-1 is the standard application for the same capacity band where the equipment is not going down the fully type-tested route. Form A1-3 covers the same band where the output is shared between two or more customers. Forms A2-1, A2-2 and A2-3 are Compliance Verification Reports submitted alongside the application when a generating module is not fully type-tested or is only part type-tested. A G100 declaration is added where the design relies on an export limitation scheme. Above roughly 50 kW three-phase you leave the standard forms behind and lodge a full connection application on the DNO’s own portal.
What is a G99 certificate and when do I get it?
Three different documents get called a "G99 certificate". First, the inverter type-test certificate — issued by the manufacturer or test house and registered on the ENA Type Test Verification Report Register, proving the inverter model meets EREC G99. That one exists before you apply and you submit it with the application. Second, the DNO approval — the portal confirmation or letter accepting your G99 application on the fast-track route, or your accepted connection offer on the full route. That is what most customers mean and it arrives before installation. Third, the commissioning confirmation returned to the DNO after install, confirming the system was built to the approved design and set to the agreed protection settings, together with the witness test record where one was required.
Can I submit the G99 application myself or does the installer do it?
Legally the DNO will accept an application from the customer, but in practice the installer submits it because the form demands data only the installer holds: the single line diagram, the inverter type-test certificate reference, the protection settings schedule, the earthing arrangement and the planned commissioning date. A self-submitted G99 application missing any one of those is returned as incomplete and the clock restarts. We submit on your behalf on every commercial quote and stay named as the technical contact through to energisation.
What is the G100 declaration and do I need one?
G100 is the Engineering Recommendation covering export limitation. If your design holds export inside an agreed capacity using an export limitation device — common where the DNO will only offer a small export capacity, or where you want to stay inside the fast-track band on a constrained network — you submit a G100 declaration alongside the G99 application describing the scheme, the device, the setpoint and how it was verified. If your system exports freely up to its full rating you do not need one. Applications that rely on export limitation but omit the G100 pack are returned incomplete.
What is Active Network Management (ANM) and how does it affect my project?
ANM is a real-time control system DNOs use to throttle generators when the local network would otherwise hit thermal or fault-level limits. If your connection offer comes with ANM constraint, your inverter will be remotely curtailed (output capped) during peak network stress hours. In practice ANM curtailment averages 1-5% of annual generation on UK PV connections — far less than the cost and time of full network reinforcement. We always model curtailment impact in PVSyst before signing acceptance.
Can I install panels on the roof while waiting for the G99 connection offer?
Yes — the physical install can run in parallel with the DNO process up to (but not including) energisation and witness testing. We typically schedule structural work, panel mounting, DC cabling and inverter installation before the connection offer is finalised, then complete AC tie-in and DNO witness test once the offer is accepted and connection works are complete. This compresses the felt timeline for the customer by 8-16 weeks.
What inverters and protection settings do DNOs accept under G99?
Inverters must hold valid type-test certification under the issue of EREC G99 your DNO is working to — most applications in 2026 are assessed against Issue 1 Amendment 9, with Issue 2 (published March 2025) being adopted across the networks, so check which version the DNO states in its current connection guidance before you lock the specification. The certificate must be registered on the ENA Type Test Verification Report Register. Protection settings must include voltage and frequency relays meeting the specified trip envelopes, anti-islanding, ROCOF and vector shift detection where required. Any inverter brand we specify (SolarEdge, SMA, Fronius, Huawei, Sungrow, Solis) holds current G99 type certificates. Protection settings are configured per the connection offer — wrong settings fail witness testing and force a return visit.
What happens at the witness test?
A DNO engineer attends site to verify protection relay settings, anti-islanding behaviour, and overall installation compliance. They will trip the inverter, verify it disconnects within the required milliseconds, check earthing, and review the as-installed single line diagram against the design submitted at application. A clean witness test is signed off the same day and the system is energised onto the network. A failure means re-work, a return visit (usually 4-8 weeks later), and rescheduled commissioning — material delay we work hard to avoid.
Do you handle the G99 process or do I need to manage it?
We handle the entire process end-to-end as part of every commercial solar quote that needs G99 — fast-track or full, which in practice is almost every commercial install. That covers eligibility check, single line diagram, type test certificates, protection settings, application submission, DNO liaison, offer review and acceptance recommendation, scheduling of network works, witness test attendance, and energisation paperwork. You see status updates at each stage but the process administration sits with us. The customer cost is built into the install quote — no surprise add-ons.