G98 and G99: telling the network operator about solar in Wales

Your solar panels do not run alone. They connect to the local electricity network, so the company that runs it must know about them. In Britain this works through two engineering rules called G98 and G99.

Most homeowners never see the forms, because the installer handles them. Still, it pays to know which route applies, since one route lets you switch on first and the other makes you wait.

Who runs the network in Wales?

Two network operators serve Wales. National Grid Electricity Distribution covers South Wales, from Pembrokeshire to Monmouth and up to Aberaeron and Rhayader, while SP Energy Networks covers North Wales through SP Manweb. SP Manweb also serves Merseyside, Cheshire and North Shropshire.

Mid Wales is less clear. No primary source we could read confirms how Powys and Ceredigion split between the two. Therefore you should check your address with the operator finder run by the Energy Networks Association before you rely on either name.

The operator matters for the paperwork and for any network upgrade. National Grid Electricity Distribution lists Cardiff, Swansea, Newport and Haverfordwest in its South Wales report, for example. SP Manweb’s development statement covers North Wales, where Wrexham and Rhyl lie.

The G98 route for small systems

G98 applies to small generators with a combined rating of 16 amps per phase or less. On a single-phase supply that is 3.68 kW. On three phases it is about 11 kW, because the limit applies to each phase. That is our own arithmetic.

However, for solar the rating is the inverter’s continuous AC output, not the panel size in kWp. National Grid Electricity Distribution gives worked examples. For example, a 3 kW single-phase inverter draws 13.04 amps, so it follows G98. A 4 kW inverter draws 17.39 amps, so it follows G99.

Under G98, the installer can fit and switch on the system first. They must then send the G98 installation document and an operation diagram to the operator within 28 days. Ask for a copy, because you may need it later for export payments.

What the timeline looks like

With G98, the system can run on the day it is fitted, and the paperwork follows within 28 days. With G99, the order reverses. The application comes first, the operator agrees second and commissioning comes last.

Therefore a G99 job can start later than a G98 job, even when the roof work takes the same time. Ask for the expected wait in writing, because it can shape your plans.

The G99 route for larger systems

G99 applies above 16 amps per phase. It also covers generation and energy storage together, so a battery counts towards the rating. Under G99, the installer applies first and agrees the connection with the network operator before commissioning.

As a result, G99 takes longer. You cannot switch on until the operator agrees. Sometimes the operator must strengthen the local network before a system can connect, and the customer can be asked to contribute to the cost.

National Grid Electricity Distribution has its own policy here. It fully funds reinforcement for qualifying small G98 sites at existing premises up to 100 amps per phase. However, that policy belongs to that operator alone, so do not assume SP Energy Networks does the same.

Multiple installs in one area

There is one exception to the G98 shortcut. If several premises within 500 metres install within 28 days, the operator treats them as a group. This is the “multiple premises” route, and it needs agreement before work starts.

That can matter, for instance, on a new estate or a street where neighbours order together. Tell your installer if friends nearby plan to fit solar at the same time.

Why the paperwork matters for your money

Meanwhile, the Smart Export Guarantee pays you for exported power. You need an export meter and an export MPAN, and for solar of 50 kW or less you need an MCS certificate or an equivalent. Our post on the Smart Export Guarantee for Welsh homes explains the rates and how to choose a supplier.

MCS certification and grid approval are separate checks. Read about MCS certification and your quote to see what the installer must show you. The paperwork file should include the grid document next to the MCS certificate, since both matter.

Batteries and the grid

A battery changes your rating under G99. Therefore even a small solar system with a large battery can cross the limit. Our post asking whether a solar battery is worth it explains the other side of that choice.

Heat pumps add demand rather than generation. Still, they often come into the same design talks. See our post on solar panels and heat pumps before you plan both together.

Businesses and farms

Larger roofs on shops, workshops and farms usually pass the 16 amp per phase line quickly. They therefore follow G99, and the lead time can shape the whole project. Our page on commercial solar covers the wider picture for businesses.

Start the grid conversation early because delays can build up. Ask your installer when they will apply, what the operator is likely to ask for and whether an upgrade could change the price.

Local pages for your network area

North Wales sits in the SP Manweb area, since SP Energy Networks runs it. If you live near Wrexham, read about solar installers around Wrexham. The same applies to solar panels in Rhyl, where the planning and grid notes sit on one page.

South Wales homes use National Grid Electricity Distribution, while the page for solar panels in Cardiff shows the operator for that area. Each local page names the operator for that town.

What to ask your installer

Ask these questions before you sign:

• Which route does my design follow, G98 or G99?
• Who applies, and when?
• Will you give me a copy of the paperwork?
• Could my inverter size or battery change the route?

Our grid and export guide for Wales explains each step in more detail, because the route shapes your timetable. When you are ready to compare designs, ask for solar panel installation quotes from MCS-certified installers through the Solar Cymru enquiry form.