A DNO can refuse a G99 application, but its options are wider than a straight yes or no. Under the Electricity Act 1989 the network has a duty to connect you, and the grounds to decline the exact arrangement you asked for are narrow. So instead of an outright refusal, a constrained network can offer a lower export capacity, attach a condition such as an export-limiting device, or quote for works before you connect. Knowing which of those you are holding decides your next move, and none of them means the project is dead.
This page is for the homeowner staring at a G99 decision that is not the clean approval they expected. It explains what the network can and cannot refuse, which lines of the offer to read, and your rights if you think the decision is wrong. If you are unsure which network even covers you, find your DNO from your postcode with the Energy Networks Association lookup before you apply or dispute.
Can a DNO refuse a G99 application?
Yes, within narrow limits. The Electricity Act 1989 puts a duty on your DNO to make a connection offer, but that offer can carry conditions, and the network can decline the exact capacity or design you asked for where connecting it would be unsafe, outside its control, or not reasonable to require. Declining your requested arrangement is not the same as refusing you any connection, and on a constrained network the answer is far more often a lower export limit than a closed door.
What outcomes can a G99 decision bring?
A G99 decision usually reaches you as a connection offer with terms, not a simple pass or fail. It helps to sort what lands in your inbox into a few practical outcomes. This is a homeowner’s way to read the decision, not an official list of regulatory categories, and the wording of your letter tells you which one you are holding.
| Outcome | What the DNO is telling you | Your realistic first move |
|---|---|---|
| Returned, not yet validated | Documents are missing or inconsistent, so the arrangement has not been assessed yet | Fix and resubmit; this is not a decision on your capacity |
| Offered as applied | The network can accept the export capacity you declared | Commission, notify, then arrange a supplier export tariff |
| Offered with a lower export limit | Capacity is tight; you may connect but must cap what you push to the grid | Accept the cap and self-consume more, or export-limit and keep a larger inverter |
| Offered subject to works or a quote | A study or reinforcement is needed before the declared capacity can connect | Ask for the indicative cost and timescale, then weigh it against a lower limit |
| Requested arrangement declined | The exact capacity or design cannot be accepted on this network | Ask what can be accepted: a lower limit, a flexible connection, or a revised design |
When I took my own system past the 3.68kW single-phase limit and applied under G99, the answer was a clean yes, and the DNO responses were fast, sometimes the same day. That is worth saying plainly: a G99 is not a hostile process by default. But the offer is where the network’s real answer to your capacity lives, so read it before you assume you have simple approval.
Which parts of the offer do you actually read?
Before you accept anything or buy more kit, find these fields in the offer letter or portal decision. They decide whether you have the system you designed or a different one.
- The export figure, in kW and amps. An offer that says 3.68kW (16A) or 5kW is capping export, not generation. Check it against your inverter’s AC nameplate.
- Any export limitation condition. If the offer requires a limitation scheme, it will reference EREC G100 and a device that holds export at or below the agreed figure.
- Reinforcement or works. Wording about network studies, a quotation, or works before connection means the plain export capacity is not available yet.
- Flexible or managed-connection terms. Some offers connect you sooner in exchange for the network being able to curtail export at rare peak times.
- The acceptance and validity dates. Offers expire. If you let one lapse the network position may have changed by the time you re-apply.
- The device reference it expects. The form is built around the ENA type-test reference for your inverter and any external limitation device, so a mismatch here reads as an incomplete application.
If any of those lines is unclear, ask the DNO connections team to confirm it in writing before you accept. An export limit you did not notice is far more expensive to unpick after commissioning than a clarifying email is now.
What are your realistic choices after a restricted offer?
Order these by cost, cheapest first. An export cap bites less than it first appears, because it only limits the surplus you send back, not what your own house uses. Each route has its own trade-off, so match the effort to how much export you genuinely need.
- Accept the export limit and use more of your own generation. If the cap is at or near your likely export anyway, the practical loss can be small. Shifting loads into the middle of the day, charging a battery or an EV, and heating water on solar all raise self-consumption so less hits the capped export point.
- Fit an export limitation scheme. A G100-compliant scheme lets you keep a larger inverter while holding export to the agreed figure. It measures current near the meter and reduces output typically within 15 seconds. You cannot alter the protected setting yourself; any change needs the DNO’s written agreement and recommissioning, so it is a decision to make carefully at commissioning, not a dial you tweak later.
- Lower the arrangement the DNO assesses. Two honest routes exist. You can set a certified Registered Capacity limit that the manufacturer’s conformity paperwork backs, or genuinely redesign to a smaller aggregate capacity. A software zero-export mode does not remove the assessment on its own: the DNO assesses maximum physical capacity, so it must approve the revised arrangement before you connect.
- Add or grow a battery. Storage can soak the midday surplus a constrained network objects to, then release it in the evening for your own use. But an export-capable battery inverter is itself treated as generation, and its capacity is normally added to the aggregate the DNO assesses, so it can make the application harder rather than easier. It protects an export limit only inside a DNO-approved coordinated control or G100 scheme, so tell the DNO and expect a reassessment.
- Move to a three-phase supply. Three phase raises the connect-and-notify ceiling to 11.04kW, at 3.68kW per phase. It is a real job with its own cost and lead time, so it only makes sense when you genuinely need the extra export headroom.
- Fund network reinforcement. This is the last resort for a home system, and since 2023 it is far less likely to land on you than older guides suggest (see below).
Accepting a limited offer now does not bar you from asking for more capacity later. If the network is reinforced or you change the design, you can submit a fresh application, which the DNO assesses against the network’s condition at that time rather than treating your earlier acceptance as a ceiling.
Do you have to pay for network reinforcement?
For an ordinary home, usually not. Ofgem classifies a house that both draws power and generates as a final demand site, meaning a site that consumes the electricity it imports, and its connection follows the demand charging boundary. Under Ofgem’s Access and Forward-Looking Charges Significant Code Review, effective April 2023, the cost of reinforcing the wider existing network to accommodate new demand connections shifted onto the DNOs and is recovered through use-of-system charges spread across all users, rather than billed to the customer whose connection triggered it.
You can still be charged for the assets that serve only you, such as a new service cable or metering position, for any service upgrade you request, and for reinforcement above the scheme’s high-cost cap, which Ofgem set at £1,720 per kVA at your voltage level and one level above it. The move that protects you is to ask the DNO for an itemised quotation that separates the sole-use connection assets, any reinforcement, and any high-cost-cap contribution, so you can see exactly what, if anything, is yours to pay.
How long does a G99 take, and what if it stalls?
Plan in weeks, not days, and take the timescale from your own DNO’s published procedure rather than a rule of thumb. The streamlined fast-track route is the quick one, and it is only for eligible small installations: SSEN, for example, aims to respond within 10 working days, then gives you up to three months to install and commission before you return the A3-2 commissioning form within 28 days. A full G99 assessment on a constrained network can run considerably longer, so check the published target for your connection type and postcode.
If the clock runs past the published window, chase in writing and quote your application reference. A stalled application can be waiting on any of several things: a single-line diagram the network asked for, an ENA type-test reference it could not match, a query about your aggregate capacity, or a step sitting in the DNO’s own queue. Ask the connections team directly what is outstanding rather than assuming a capacity problem.
What if you think the DNO got the decision wrong?
You have a route. The Electricity Act 1989 places a duty on the DNO to offer a connection, and the grounds to decline the arrangement you asked for are narrow: safety, a matter outside the network’s control, or a connection it would not be reasonable to require. Start by raising it as a formal complaint with the DNO, in writing, and ask it to set out the constraint behind the decision and the options to lift it.
If the complaint does not resolve it, two escalation routes exist, and they are different things. As a domestic customer you can take a connection complaint to the free Energy Ombudsman once you hold a deadlock letter or the DNO has had eight weeks to resolve it; the ombudsman can review a problem with a connection and direct a remedy. Separately, where the dispute falls within Ofgem’s jurisdiction, a person requiring a connection can refer it to Ofgem for a statutory determination under sections 16 to 23 of the Electricity Act 1989, which is enforceable much like a court judgment. Ofgem expects you to have exhausted the DNO’s own process first, and it generally assumes the offered terms are reasonable unless you can show the network did not follow its procedures.
Both routes are slower than fixing the application, so weigh them against the practical options. A corrected submission, an export limit you can live with, or a revised design usually gets you connected faster than a formal dispute, and none of that stops you registering a complaint in parallel if you still believe the decision is wrong.
The next move
Read the offer line by line and settle which outcome you are actually holding. Before you accept anything, confirm the maximum export capacity in kW and amps, any equipment or export-limiting condition, any works required before connection, the acceptance deadline, and the commissioning steps the network expects. If an export figure sits below your inverter rating, work out how much you would export anyway before you treat the cap as a loss.
A restricted G99 offer sets the terms of your connection; it is not a verdict on your solar. Confirm the figures, take the cheapest route that meets your real export need, and keep the formal complaint and determination routes in reserve if you believe the network got the decision wrong.
Sources
- Energy Networks Association, Engineering Recommendation G99 (requirements for connecting generation above 3.68kW per phase).
- Legislation.gov.uk, Electricity Act 1989 section 16 and section 23 (duty to connect and determination of disputes).
- Ofgem, Guidance on the determination of disputes for use of system or connection to energy networks.
- Energy Ombudsman, Disputes with network operators (free for domestic customers; eight-week or deadlock trigger).
- National Grid Electricity Distribution, Customer Export Limitation Schemes (G100 limitation, reaction times, protected settings).
- SSEN, G99 Fast Track Process (10 working-day response aim, three-month install window, A3-2 within 28 days).
- Ofgem, Access and Forward-Looking Charges Significant Code Review decision (final demand sites, shallow demand connection boundary, and the high-cost cap from April 2023).
- Energy Networks Association, Who is my network operator? (postcode lookup) and ENA Generator Type Test Register.
