The DNO Guide. UK solar DNO applications, explained.

A DNO is a Distribution Network Operator. It owns and runs the local electricity distribution network in a set region, the underground cables, the overhead lines, the substations, the service connections and all the network kit that goes with it.

The DNO's job is to keep that local network running and to manage anything new connecting to it. So for solar PV, battery storage and any other generation, they want to know what's being connected, where, how much it can generate or export, and whether it needs approval before it's energised.

A DNO is not the customer's electricity supplier. That's the bit people mix up. Suppliers like Octopus, British Gas or EDF sell the electricity and handle the billing. The DNO owns the physical network that actually delivers it to the property. A customer can switch supplier whenever they like, but they can't pick their DNO. That's fixed by where the property sits and which network region it's in.

Some properties, new build developments especially, or private networks, connect through an IDNO instead, an Independent Distribution Network Operator. The same connection standards apply, but the application goes to the IDNO rather than the regional DNO, so it's worth checking which one you're dealing with before you submit.

There are six DNOs covering Great Britain, each with a fixed patch:

• UK Power Networks (UKPN), London, the South East and the East of England.
• National Grid Electricity Distribution (NGED), the Midlands, South West England and South Wales.
• SSEN, central southern England and the north of Scotland.
• SP Energy Networks (SPEN), central and southern Scotland, Merseyside, Cheshire and North Wales.
• Northern Powergrid (NPg), the North East, Yorkshire and northern Lincolnshire.
• Electricity North West (ENWL), the North West of England.

The reliable way to identify yours is the MPAN on the electricity bill, the first two digits of the bottom row identify the network region. A postcode search on the ENA website does the same job.

The Energy Networks Association, the ENA, is the industry body for the UK energy networks. They're the ones who write the rule book, the engineering recommendations that govern how generation equipment connects to the distribution network. G98, G99 and G100 all come from them. Every DNO works to those same standards, even if each one has its own portal and its own admin quirks on top.

The ENA also holds the type test register, the list of inverters that have been type tested against those connection requirements. The type test reference is a key part of the submission pack, because it tells the network operator exactly which certified inverter is going in.

Where a job needs export limitation, it has to be declared, either inverter integrated or external. If it's inverter integrated, it shows on the SLD and the chosen export limit has to be set at installation. That's the whole reason type tested inverters matter here. They're the ones proven to hold that export setting the way the declaration says they will.

This is where a lot of jobs get held up. A wrong or mismatched type test reference is one of the most common reasons a DNO comes back. The inverter make, model and ENA reference all have to match the form, the SLD and the actual kit on site, and where there's an export limit, the declared limit has to match what's set on the inverter. Get one out of step and you're into back and forth.

Solar doesn't just feed the house it's bolted to. Whatever that house doesn't use flows back out onto the street, and the local network was built for power running the other way, from the substation to the homes, not from the homes back up.

Push enough export into one area and you start loading cables and transformers that were sized decades ago, long before anyone on that street had panels. Street voltage has to stay inside legal limits, and every exporting system nudges it up a bit. Kit that misbehaves during a fault can turn a small problem into a big one. And when an engineer's about to put hands on live wires in an emergency, they need to know what's connected where before they start.

That's the whole reason the DNO wants to know. Not to make your life hard, to keep the network they're responsible for inside its limits.

Honest answer: nobody turns up the next morning. That's exactly why unregistered systems are out there. But the problems don't arrive on install day, they arrive later, and they cost more when they do.

An unregistered system has no record with the network, and that gap shows up at the worst possible moments. Selling the house, the buyer's solicitor asks for the DNO paperwork. Claiming on insurance after an electrical fault, the insurer wants it too. Signing up for export payments, the supplier wants evidence the connection's legitimate. And if the DNO finds an unnotified system causing a network problem, they can make you disconnect it until the paperwork's put right.

The notification itself is free, and for small systems it's quick. There's no good reason to skip it.

If a system's already in and was never registered, it can still be regularised. You contact the DNO and submit the paperwork retrospectively. They deal with it more often than you'd think, and a late notification beats none every time.

A DNO application tells the network operator exactly what is being connected at a property: where it is, what equipment, how big, and how it's wired in. The single most useful distinction in this whole subject is between the two kinds:

A notification is after the fact. You install, you connect, then you tell the DNO what you did. That's mostly the G98 world.

An application for approval is before the fact. You describe what you intend to install, the DNO assesses whether the local network can take it, and you wait for a yes before energising. That's mostly the G99 world.

People say "DNO application" or "DNO pack" for both, which is fine, but knowing which side of the line a job sits on tells you if you're allowed to connect yet. Get that wrong and you've either sat on your hands waiting for an approval you never needed, or energised something you weren't cleared to.

G98 covers generation at or under 16A per phase, about 3.68kW on a normal single phase supply. That's most standard domestic solar with a modest inverter.

The deal is connect first, notify after. Install it, switch it on, then send the DNO the completed G98 form within 28 days of commissioning. They don't approve or reject it, they just need the record.

One catch worth knowing: the 16A limit is per phase and per property, and it includes what's already there. Add a second system, or a battery, to a property that already has G98 solar, and the total can tip over the line into G99.

A few other things take a small system out of G98 even under the line. A battery arranged to keep the house running in a power cut, whether backed up circuits or a whole home gateway, puts the job on G99 SGI-1, which is still install then notify, on a different form. So does an inverter type tested to G99 but not G98, or one software limited down from a bigger design of up to 32A. Any export limitation scheme, whatever the size, makes it a G99 SGI-2 application, because a scheme is applied for and accepted rather than notified. And where several neighbouring properties are installed as one programme, a shared G98 application has to be approved before any of them connect, with each property still notifying after its own install.

Rather hand it over? The CLRD team files the G98 notification for you, with the single line diagram and the commissioning paperwork included. See how it works →

Anything above the G98 limit needs a G99 application, approved before the system's energised. In practice that's bigger domestic systems, most systems with a decent battery, larger three phase installs, and effectively all commercial work.

The DNO's engineers check whether the local network can take the export: cable ratings, transformer capacity, voltage headroom. For a standard low voltage connection you're usually looking at around two weeks for an initial response on a smaller type tested system, stretching to around ten where a full design study is needed. It varies by DNO and by how loaded the local team is. If the network needs reinforcing to take your connection, they tell you, along with what it costs and how long it takes.

Bigger commercial systems have a form of their own. Above 50kW on a three phase supply, and below 1MW, the job is still Type A but applies on the ENA's Standard Application Form rather than Form A1-1. The DNO then has 45 working days from a complete application to make its connection offer, or 65 where its own works reach high voltage. From 1MW it's Type B, a different process again, and outside what CLRD covers. Single phase has a lower ceiling: G99 caps generation on a single phase supply at 17kW.

Kit that's only partially type tested can still connect, but never on the lighter procedures. It takes a full Type A application with the manufacturer's Compliance Verification Report attached, and the rest of its protection is tested on site at commissioning and recorded on G99 Form A2-4.

The discipline that matters: do not energise before the approval lands. Connecting a G99 scale system without consent is a breach of the connection agreement, and the DNO can make you disconnect.

Rather hand it over? The CLRD team runs the G99 application end to end in your name: the pack, the DNO's replies, amendments and the connection offer. See how it works →

G100 is the standard for limitation schemes, and for export limitation it's the most useful tool most people have never heard of. It lets you install a system bigger than the network could normally accept by capping how much it exports.

Say the local network can only take 5kW of export but the customer wants a 10kW system with a battery. With a G100 compliant limitation scheme, the system generates its full 10kW, the house and the battery use what they can, and the export to the grid is held at the agreed limit. The DNO gets certainty, the customer gets their system.

The evidence has to line up though. Where a job needs export limitation it gets declared, either inverter integrated or external. If it's inverter integrated, it shows on the SLD and the chosen limit has to be set at install. The configured limit, the application and the SLD all have to agree. If those three don't match, expect questions.

The same standard covers import limits, a scheme holding what the property draws from the network, and those add the G100 forms to whatever route the job is on, G98 included.

Choosing between an inverter integrated scheme and a stand alone device, and what the DNO sees on Forms A and C, is covered in depth in CLRD's export limitation guide.

The short version, in plain terms:

• Total generation at or under 16A per phase, about 3.68kW single phase, no export limitation, no backup power? G98, notify within 28 days of commissioning.
• Same size, but a unit software limited from a bigger design capacity of up to 32A, a unit type tested to G99 but not G98, or a battery set up to keep the house running in a power cut? G99 SGI-1, still install then notify, on Form A3-3. The ENA register doesn't publish design capacity, so CLRD fills it in from the manufacturer's datasheet where it holds one.
• Over that limit, adding to a property that crosses the limit in total, or kit that's only partially type tested? G99, apply and wait for approval first.
• Any export limitation scheme, whatever the size? A G99 application, SGI-2 at the least, with the G100 forms attached. A scheme is applied for, so it never rides a G98 notification.
• Several neighbouring properties installed as one programme? A shared G98 Form A, approved before any of them connect, then each property notifies after its own install.

For the arithmetic, kW to amps per phase, what aggregates and the full procedure ladder with worked examples, see CLRD's registered capacity guide.

Watch the edge cases. A battery usually changes the answer, because its inverter counts. Three phase properties measure the limit per phase, not in total. And an existing system at the property counts toward the threshold, even if someone else installed it years ago.

Rather hand it over? Hand the job to CLRD and the route is worked out and filed for you, whichever form it needs. See how it works →

Some G99 jobs don't really need a full network study. A small, fully type tested system a little over the G98 line looks the same to the network almost everywhere it lands. For those, G99 has two lighter procedures, SGI-2 and SGI-3, filed on the shorter Form A1-2 and usually called Fast Track.

The criteria are national, written into G99 rather than set by each DNO: every unit fully type tested, each unit and the total under set limits per phase, and an export limit once the total goes above 32A per phase. That makes an export limitation scheme the usual way a bigger system gets onto Fast Track: holding export to 16A per phase or less opens SGI-2, and to 32A per phase or less opens SGI-3. The DNO's first answer is due within 10 working days, but at SGI-3 that answer can be that a design study is needed first, and approval then waits on the study. What does vary by DNO is how they check an SGI-3, so ask yours before you promise a customer a date.

Two operators trade a fast track for a loop impedance reading taken at the premises on an SGI-3 application whose export isn't already limited to 16A per phase: SSEN on their own form, with a published 180 mΩ threshold, and UK Power Networks with no form and no published figure. The ways round the test are to limit export to 16A per phase, or to file a standard Type A application instead, which at UK Power Networks can take up to 45 working days. The method is in CLRD's impedance test guide.

Every electricity supply point in the country has an MPAN, a Meter Point Administration Number. It's a 13 digit number printed on the customer's electricity bill — and found on the meter too, where it's the second line of the 21 digit supply number block, preceded by a big S.

The DNO uses it to pin the application to an exact supply: which property, which substation feeds it, what capacity is already there. A wrong MPAN sends your paperwork to the wrong place, or nowhere. Copy it from the bill, not from memory, and if the property has more than one supply, make sure you're quoting the one the solar connects to.

A complete pack for a typical solar job contains:

• The application form for the route, G98 or G99, with the G100 forms where a limitation scheme is declared.
• A single line diagram showing how the system wires into the property.
• The inverter details: make, model and its ENA type test reference.
• The property's MPAN and address.
• A letter of authority if anyone other than the owner is applying.
• A site plan showing the property boundary with the meter marked, on a full Type A application and wherever else the DNO asks for one, and the main fuse rating where the DNO asks for it.
• Any supporting documents the job needs: export limitation evidence on G100 jobs, commissioning confirmations after the install.

The theme running through every rejection story is agreement. The form, the diagram and the equipment references all describe the same system, or the application bounces. It doesn't matter that the engineering's sound. If the form says one inverter and the SLD shows another, that's a query, and a query is weeks.

One that catches people out. A full Type A application should carry a site plan: the property with its boundary marked and the meter position shown. DNOs have put applications on hold for want of one, and some ask for it on Fast Track applications too.

Some DNOs also want the main fuse details as part of the pack. That's the cut out fuse, at the point where their network ends and the customer's installation begins, and it's the DNO's own equipment, not yours. You can't always read it off site, and guessing it is how a submission gets queried. Where a DNO asks for it, it has to be right, because it feeds into how they assess the capacity that's already on the supply.

Since G98/G99 Issue 2 in March 2025, the standards ask for a clear photograph of the cut out with a connect and notify submission through Connect Direct, and DNOs ask for it more widely, so always get a clear shot while you are at the property for the survey. Chasing it later means a second trip.

An SLD is a simplified wiring drawing. One line stands in for each electrical path, and standard symbols stand in for the kit: the incoming supply and meter, the consumer unit, the inverter, the isolators either side of it, the array, the battery if there is one, and the export limiter on a G100 job.

The DNO engineer isn't marking your draughtsmanship. They're checking, at a glance, that the system's connected safely and matches the form: where generation ties into the installation, that isolation sits in the right places, DC isolation on the array side, AC isolation between the inverter and the consumer unit, and that what's drawn is what's declared on the form.

Here's a real generated one, so you can see what good looks like:

SLD · Generated

Enlarge

Reading it top to bottom: the PV strings feed the inverter, isolators sit on both the DC and AC sides, the AC side lands in the consumer unit, and the supply runs through the meter to the DNO's cutout, where their network ends and the customer's installation begins. A battery comes off as its own branch with its own protection. On a G100 job the export limiter and the CT position show too, because the engineer wants to see where the system's being measured and held. Every pack needs a drawing that tells this story for the actual system going in, not a generic one lifted off the last job.

An LOA is a short signed statement from the property owner confirming the installer, or any agent, is allowed to deal with the DNO on their behalf. Without it the DNO won't discuss the connection with anyone but the owner, and a submission without one just sits in limbo.

It's the least technical document in the pack and one of the most commonly forgotten. Get it signed early, at survey or contract stage, not on the morning you're trying to submit.

Every mainstream inverter sold in the UK has been type tested against the ENA's connection requirements, and each tested model carries a reference in the ENA register. Quoting that reference on the form is how you prove the kit behaves properly on the network during a fault, that's what spares a small job from a full engineering study. The test is per standard: the register records whether a model is fully type tested to G98, to G99 or to both, and one tested to G99 alone can't go on a G98 notification.

To find one by hand you search the ENA register by manufacturer and model and copy the reference exactly. The classic mistakes: quoting the reference for a different model variant, or using a superseded entry for kit that's been re registered. Either one gets the submission queried, and the frustrating part is the inverter's usually fine, it's the reference that's wrong.

This is also where export limitation ties back in. If the job's export limited inverter integrated, the inverter doing the limiting has to be one that's type tested to hold that setting, and the declared limit has to match what's set at install and what's drawn on the SLD.

Picking the right register entry, and the right variant of it, is its own skill. CLRD's device chooser guide covers the filters, the G98, SGI, Type A and CLS badges, and what it means when a device isn't offered.

Ten minutes of gathering saves the resubmission later. You need:

• The MPAN, from the electricity bill.
• The full site address, exactly as the supply is registered.
• The inverter make and model, and its type test reference from the ENA register.
• The panel layout and rating: how many panels, their kWp, string arrangement.
• Battery details if fitted: make, model and storage size, plus the inverter rating and type test reference if it has its own inverter (an AC or smart battery).
• The supply details: single or three phase, main fuse rating if known.
• A signed letter of authority if applying for someone else.

Every field on these forms is learnable, and most are the details you just gathered. But this is exactly where the industry loses its evenings: one wrong entry and the whole application comes back weeks later. The parts that catch people out:

Capacity figures. The DNO cares about the inverter's rated AC output, not the panel kWp. A 5kWp array on a 3.68kW inverter is a G98 job, as long as the inverter is tested to G98 and isn't a limited version of a bigger model. Quote the inverter rating in the capacity field, and be consistent everywhere it appears.

Per phase, not total. On three phase supplies, limits and declarations are per phase. Split the figures correctly, and say which phase a single phase inverter lands on.

Equipment references. Copy the type test reference character for character. The engineer will look it up, and a mismatch triggers a query even when the kit is fine.

The diagram agrees with the form. Same inverter, same battery, same limiter, same everything. Most rejections are disagreement between documents, not wrong engineering.

Rather hand it over? Hand the job to CLRD and the forms are filled, checked and submitted for you, in your name. See how it works →

Applications reach the DNO through their online channels: the ENA's shared submission portal, which carries your G98 or G99 application form to the network, individual DNO portals, and in some regions still by email to the connections team. The route matters less than people think, because the channel is just transport.

Here is the part that matters: none of those channels make your application right. Some run automatic checks, but the portal is free and the form is free, and being right first time is not. A submission channel will happily accept the wrong form with mismatched references and pass it to a DNO engineer, who bounces it weeks later. Where the time and money go is never the submitting, it's the correcting. Whatever channel you use, the quality of the submission is decided before you press send.

For a G98 notification, nothing needs to come back. The DNO records it, and may acknowledge it. Keep the submission confirmation with the job file and you're done.

For a G99 application, the DNO first acknowledges receipt, then assesses. Smaller type tested jobs on the Fast Track usually come back in around two weeks, with larger ones needing a design study taking up to around ten, and above 50kW the DNO has 45 working days to make its offer, 65 where its own works reach high voltage. The answer is usually one of these: an approval, often called a connection offer; an approval with an export limit, lower than you applied for or where you asked for none, sometimes zero; word that a design study is needed first, which takes a Fast Track job onto the longer timetable; a request for more information; or a refusal with reasons, which at domestic scale is rare and usually really means "not without export limitation or reinforcement".

If the stated window passes with silence, chase with your application reference. Politely and in writing, so the trail exists.

A query or rejection isn't a disaster, it's a list of what to fix. Read exactly what the engineer flagged, fix precisely that, and resubmit quoting the original reference so it stays with the same case rather than joining the back of the queue as a new one.

The industry's most common bounce reasons, in rough order: a type test reference that doesn't match the declared inverter, an SLD that disagrees with the form, a missing or unsigned letter of authority, a wrong MPAN, capacity declared as panel kWp instead of inverter output, and jobs submitted on G98 that should have been G99 because of what was already on site.

Every one of those is avoidable at desk stage, which is why the checklist at the start of this part earns its keep.

Rather hand it over? When a job goes through CLRD, amendments are part of the job: the team answers the DNO and resubmits on the same thread. See how it works →

A G99 approval isn't the end. Install the system, commission it, and send the DNO the commissioning confirmation the offer asks for, that's what moves the connection from "approved" to "connected" in their records. It's due within 28 days of commissioning, or on the day where the DNO witnesses the tests, as some do on larger jobs.

Then keep everything: the application, the approval, the commissioning evidence, the final SLD. The next section explains why that folder matters years after everyone's forgotten the install.

Rather hand it over? When CLRD runs the job, the commissioning paperwork is part of it, filed after the install without a second fee. See how it works →

A battery is generation as far as the network's concerned. Its inverter can export just like solar can, so adding one is never paperwork free. On a new combined install, the battery's inverter counts toward the total that decides G98 or G99. Retrofit one to existing solar and it's a fresh notification or application, and because the property's total usually crosses the 16A line at that point, it's very often the moment a household meets G99 for the first time.

A retrofit battery can still go Fast Track, but check the numbers first. If the property's total stays at or under 32A per phase it can go SGI-3 as it is. Past that, and 3.68kW of solar plus a 5kW battery already is, it needs an export limitation scheme holding export to 32A per phase or less to stay on Fast Track. Without one it's a standard Type A application, with a design study.

Which box counts as the generating unit, a smart battery with its inverter built in or a DC battery behind a hybrid, is a question of its own. See batteries and inverters.

Three phase changes the arithmetic, not the principle. The 16A limit applies per phase, so a three phase property can host roughly 11kW of evenly spread generation and still sit inside G98. The catch is "evenly spread": a single phase inverter dumping 8kW onto one phase of a three phase supply is over the limit on that phase, and that's a G99 job even though the total looks modest.

Declare which phase each inverter sits on, and where possible balance across all three. The imbalance is what network engineers actually worry about, and G99 sets a hard line: no more than 32A between the most and least loaded phase.

New build developments add two wrinkles. First, the network is often owned by an IDNO rather than the regional DNO, so the paperwork goes to a different desk, same standards, different letterhead. Second, solar across a whole development is assessed as a cluster: fifty houses each under the G98 limit still add up to serious export on one bit of network, so developers and housing programmes get one approval from the operator at scheme level before the first plot connects, then each plot still notifies after its own install.

And this is about to be a much bigger part of the industry's workload. Under the Future Homes Standard, published as the Part L 2026 update, every new home in England built to the new regs needs solar PV equivalent to 40% of the dwelling's ground floor area, or a reasonable amount where that's not achievable. It comes into force on 24 March 2027, with a transition window running to 24 March 2028 for plots already under way. Batteries weren't mandated in the end, but solar effectively was. More on that in the changes section below.

The rule that decides when a shared G98 Form A is mandatory, the Close Geographic Region conditions and the 28 day window either side of an install, is set out in CLRD's close geographic regions guide.

Solar work gets audited from more directions than most trades: MCS audits installers, DNOs audit connections, insurers and buyers audit properties. Years after an install, someone may ask for the original application, the approval, the as built SLD and proof of submission.

The industry's default filing system is a mix of inboxes, shared drives and a folder in the van, and that's exactly where audits go wrong. Whatever your system, make it one place per job, kept for the long term: application, correspondence, approval, commissioning evidence, final diagram.

If this guide compresses to one list, it's this one. The mistakes behind most delayed connections:

• Treating the battery as an afterthought and blowing through the G98 limit.
• Quoting panel kWp where the form wants inverter output.
• Copying a type test reference for the wrong model variant.
• An SLD that doesn't match the form, usually after a late kit substitution.
• Forgetting what's already installed at the property counts toward the threshold.
• No letter of authority when applying on the owner's behalf.
• Energising a G99 job before the approval arrives.
• Not closing the loop with commissioning confirmation after approval.

This corner of the industry doesn't stand still, and a guide that pretends the rules are finished would age badly. The changes worth watching as of 18 September 2026:

Solar as standard on new homes. The Future Homes Standard makes solar effectively standard on new homes in England, in force from 24 March 2027 with a transition window to 24 March 2028. That turns DNO applications from a retrofit trade into part of volume housebuilding, with scheme level network conversations and IDNO involvement becoming the norm rather than the exception.

The G98 forms were renamed, and plug-in solar arrived. G98 Issue 2 Amendment 1 landed on 27 August 2026, the day plug-in solar became legal to self-install in Great Britain. Form B became Form B1 and Form D became Form D1, making room for B2 and D2, the householder's own plug-in documents. If you have a blank G98 form saved on a drive, check which issue it is before you fill it in.

The 16A line itself may move. Ofgem's Connections End-to-end Review (8 December 2025) committed, at Decision 6.5, to requiring every DNO to review its G98 limit with a view to raising it above the national 3.68kW recommendation, and expects the review to be a one-off. The near-term risk is not a national change but divergence: operators raising the limit at different times, so the same system is G98 in one licence area and G99 in the next.

Two way EV charging is already here. Vehicle to grid puts car batteries on the network as exporters, and the paperwork exists: a V2G charger is filed as electricity storage on the generation side, routing on its declared export capacity like any battery, while the ENA EVCP and HP Connections Form carries the charging demand and has a section for V2G applications specifically. What is still settling is how much of the network's flexible future runs through it.

A more flexible network. The wider direction of travel is toward flexible connections: arrangements where the network manages exports dynamically instead of sizing everything for the worst case. Export limitation under G100 was the first mainstream taste of this, expect more of the same thinking at domestic scale.

We update this page when the standards move, the date at the top is the promise. If something here has been overtaken by events, tell us and we'll fix it.

Straight answers to the questions people actually ask. For questions about CLRD itself, the CLRD FAQ is the place.