Grid connection: what your installer does, and when

The two routes

The limit is about how much the inverters can send out, not the panels' combined rating. Many Runcorn pitched-roof systems fall within the first route. A larger flat-roof array, or a system with a battery, may not; the installer can sometimes choose an inverter size, or an export limit, that keeps a system on the simpler route at little cost in output.

Five Runcorn systems and their route

Flat roofs are where the question comes up most in Runcorn. Low east-west pairs fit many panels, here 12, and an inverter close to their 5.28 kW rating, such as a 5 kW one, needs approval. A 3.68 kW inverter keeps the same array on the simpler route at the cost of some output on the brightest middays, and because east-west panels never all face the sun at once, they reach their full rating less often than a south roof does. Ask the installer to show both options with their predicted output.

Three-phase supplies

Some homes have a three-phase supply. The connect-then-notify limit then applies to each phase, 16 amps or 3.68 kW on each, so up to 11.04 kW of inverters can connect first as long as the output is spread across the phases. A single-phase inverter larger than 3.68 kW on one phase of such a supply is still over that phase's limit; a three-phase inverter shares its output and is judged against the combined figure.

Changing a system later

The route belongs to the finished system. A battery added with its own inverter, a larger replacement inverter, or a second array on a garage or extension with an inverter of its own each raises the total, and each needs either a fresh notification or, once the total passes the limit, an application. Lifting an export limit that was a condition of approval counts as a change as well.

Export limits

When approval is given for a larger system, the network sometimes asks for a cap on what the house may send back. A sensor on the incoming supply lets the inverter hold exports at the cap, while anything used in the house is unaffected. The cost is the output that would have gone over the cap at moments when nothing was using it, which a battery charging at midday can largely absorb. Ask what limit, if any, is expected before you sign.

Time and money

An application adds weeks more often than it adds pounds, though some firms charge for preparing it or for an export-limiting device. A quote should say whether approval is needed, who applies, and what happens to the price if the answer comes with conditions. Weigh that alongside the totals on costs, and if a battery is part of the plan, read batteries and storage before choosing the inverter.

The network operator

SP Energy Networks runs the local network in Runcorn through its SP Manweb licence. Halton Borough Council's infrastructure plan records the whole borough as on its network, and the council's own recent grid connections have been offered by it. Your installer's notification or application goes there.

What the installer sends

A notification after switch-on, or an application before it, tells the network where the system is, what equipment it uses, including the make, model and rating of each inverter and battery, and who installed it. For an application the network also needs the design and any export limit. You may be asked to sign the application as the customer, and you should be sent a copy of whatever goes in. Halton Borough Council's own grid offer for its planned solar farm by Ditton Road in Widnes came from SP Energy Networks in June 2021: on a far larger scale, the same company and the same principle.

Being paid for exports

You need an MCS certificate for the installation and a meter that records exports, usually a smart meter. Then apply to a supplier for an export tariff; it need not be the company that sells you electricity.

What to keep

• The G98 notification, or the G99 approval and any export limit.
• The inverter settings.
• The MCS certificate and the electrical installation certificate.
• Datasheets and warranties for the panels, inverter, mounting system and any battery.

Keep reading

• Batteries
• Finding an installer
• Caring for your panels
• Costs

Where the figures come from

1. SP Energy Networks: getting connected
2. Halton Borough Council: infrastructure plan (network operators)
3. Find a Tender: Halton Microgrid notice, including the council's 2021 grid offer from SP Energy Networks
4. Ofgem-hosted SP Energy Networks submission (2020): the SP Manweb area
5. MCS: The Solar PV Standard (Installation), MIS 3002 v6.0
6. Ofgem: Smart Export Guarantee for households
7. EU JRC PVGIS 5.3: solar output by location, tilt and direction