Somewhere in your solar quote, or in your installer's emails, you'll come across the letters DNO. It sounds bureaucratic and it is, but the process behind it is simple, your installer deals with it, and understanding it explains a lot about how your system gets sized.
The thirty-second version
A DNO is a Distribution Network Operator: the company that owns and runs the local cables, substations and transformers that carry electricity to your house. It is not your energy supplier. You pay Octopus or EDF for your electricity, but the wires it travels down belong to a regional DNO such as UK Power Networks, National Grid Electricity Distribution, Northern Powergrid or SP Energy Networks.
When you put solar panels or a battery on your house, you're no longer just taking power from that network. You can push power back into it. The DNO needs to know about anything that exports onto their wires, because too much generation in one street can push the local voltage out of its legal range. So every solar and battery installation must either be notified to the DNO or approved by them in advance.
G98 and G99: the two routes
The rules come in two flavours, named after the engineering standards that define them. G98 covers small systems: anything that exports up to 3.68kW per phase (a normal house has one phase). For these, your installer simply notifies the DNO within 28 days of switching the system on. No waiting, no permission needed. Fit first, tell them after.
G99 covers anything bigger. If your inverter can export more than 3.68kW, the DNO has to approve the connection before installation. Your installer submits an application, the DNO studies whether the local network can take the extra export, and comes back with an approval, sometimes with conditions. This typically takes anywhere from a couple of weeks to a couple of months depending on the DNO and how busy your local network is.
Why 3.68kW shapes so many quotes
That 3.68kW threshold explains a pattern you'll see in quotes: a 5kW or 6kW array of panels paired with a 3.68kW inverter. By capping the export at the G98 limit, the installer avoids the G99 application entirely. The job can go ahead next week instead of waiting for DNO approval.
Whether that's the right call for you depends on the system. Panels rarely produce their full rated output in the UK, so a modest inverter wastes less than you'd think. But on a large array it does cost you generation on the best days. A good installer will explain the trade-off rather than quietly defaulting to the smaller inverter. Some will apply for G99 and fit an export limiter in the meantime, which caps what flows to the grid without limiting what you can use in the house.
Who handles it and what it costs
Your MCS-certified installer handles all of it. G98 notification is part of the standard commissioning paperwork and shouldn't appear as an extra charge. A G99 application involves more admin, and some DNOs charge an assessment fee for larger or more complex connections, so you may see a line for it on a quote for a bigger system. If it's there, ask what it covers.
You should never need to phone the DNO yourself. The one document worth keeping is the DNO's notification confirmation or approval letter, because some Smart Export Guarantee suppliers ask for it when you sign up to be paid for your exports.
What can slow things down
Most G99 applications sail through. The ones that don't are usually in areas where lots of homes already have solar, where the local transformer is near its limit, or on long rural lines where voltage rise is a real constraint. In those cases the DNO may approve a lower export limit than requested, ask for an export limitation device, or occasionally quote for network reinforcement.
If you're told your connection needs reinforcement, get a second opinion on the system design before paying for anything. Often a slightly smaller inverter or an export limit makes the problem disappear at no cost. This is exactly the kind of thing a competent installer sorts out as a matter of routine.