Most people planning a solar system worry about the roof, the panels and the price. Very few realise there is a third party with a say in the job: the company that owns the electricity cables in your street. Getting a system connected to the grid needs their agreement, and on larger installations that agreement has to be in place before anyone climbs a ladder.
It sounds like red tape, and occasionally it is. But it is also the single most common reason a solar installation gets delayed, and it is worth understanding before you accept anyone’s quote.
Who your DNO is, and what they actually do
Your Distribution Network Operator (DNO) owns and maintains the local electricity network — the poles, cables and substations between the national grid and your meter. They are not your energy supplier, and you do not choose them. Which one you get depends entirely on where you live.
Across the area we cover, that is usually Scottish and Southern Electricity Networks (SSEN) in Hampshire, Wiltshire, Berkshire, Oxfordshire and much of east Dorset, or National Grid Electricity Distribution across Devon, Somerset, Gloucestershire and parts of west Dorset. The boundary does not follow county lines neatly, so if you want to know for certain, the Energy Networks Association runs a free postcode lookup.
Their interest in your solar panels is straightforward. The local network was built to deliver power to homes, not receive it from them. When enough properties in one street start exporting at midday, voltage on that section can rise beyond safe limits. The DNO’s job is to make sure that does not happen.
G98: the small-system route
If your system’s inverter output is 16 amps per phase or less — roughly 3.68kW on a standard single-phase domestic supply — it falls under a standard called G98. This is a “connect and notify” arrangement. Your installer fits the system, commissions it, and then tells the DNO within 28 days. No waiting, no application beforehand.
This covers a good number of modest domestic solar arrays, and it is why smaller systems tend to move from order to switch-on quickly.
G99: the one that needs permission first
Go above 3.68kW per phase and you are into G99 territory, which works the other way round. The application goes in first, and the work waits for the answer. The DNO has up to 45 working days to assess it and come back with a connection offer.
In practice, straightforward domestic applications are often turned around well inside that. But 45 working days is around nine weeks, and if your local network is already carrying a lot of generation, it can take longer or come back with conditions attached. Anyone who tells you a large system will be installed next week, before an application has been submitted, is either not planning to do it properly or has not thought it through.
The point that catches people out most often is batteries count too. The figure the DNO cares about is the total inverter capacity at your property, not the panels. A 3.68kW solar system sitting happily under G98 can be pushed straight into G99 by adding an AC-coupled battery with its own inverter. If you are considering battery storage now or later, it is far better to declare the whole plan up front than to make two separate applications.
What happens if they say no
Outright refusals are rare. What is more common is an offer with a lower export limit than you hoped for, or an offer that comes with a network reinforcement cost attached.
Neither necessarily kills the job. There is a third standard, G100, which allows a larger system to be installed on the condition that its export is automatically capped at whatever figure the DNO has agreed. A device at your connection point monitors what is flowing out and throttles the inverter, or pushes the surplus into the battery, the moment export approaches the limit.
That is genuinely useful — it means a constrained network does not force you into a smaller array. But be clear-eyed about what it changes. If your export is capped, the electricity you would have sold under the Smart Export Guarantee is worth less to you than it would have been. For a household that uses a lot of power during the day, or that is storing the surplus anyway, this barely registers. For a household that is out all day and was relying on export income, it matters, and it is a conversation worth having honestly before you commit rather than afterwards.
Who handles all this?
Your installer should, entirely. You should not be filling in G99 forms yourself, and you should not be chasing the DNO. When we quote a system, the application route is part of the design conversation, and we submit and track it on your behalf.
It is also worth knowing that MCS certification and grid paperwork are linked. Your MCS certificate is what allows you to claim Smart Export Guarantee payments, and the commissioning documentation that supports it sits alongside the DNO notification. Both need doing properly. As an MCS-certified installer using our own employed teams rather than subcontractors, the people who design the system are the ones who commission it and complete the paperwork — which removes a lot of the gaps where this sort of thing normally goes missing.
If you are at the earlier stage of working out whether solar suits your property at all, our free suitability checker and system size estimator will give you a sensible starting point in a couple of minutes, with no sign-up. And if you want to know what the installation itself involves once approval is in place, we have written that up in how long a solar panel installation takes.
Talk to a local installer
We are based in Wimborne and install across Dorset, Hampshire and Wiltshire, so we deal with these applications week in, week out and know how the local networks tend to respond. If you would like a straight answer on what your property would need, request a free, no-obligation quote and we will talk it through properly — including the timescales, before you commit to anything.