Export payments for Liverpool homes: how the rules work

The export rules in brief

Ofgem runs the scheme that requires larger electricity suppliers to offer a tariff for power that small generators send to the grid. Its formal name is the Smart Export Guarantee; from here on this guide calls it the export rules (Ofgem). The main points, as Ofgem and GOV.UK set them out:

• Larger suppliers must offer an export tariff, and its rate must always be above zero. Smaller suppliers can choose to offer one.
• Each supplier sets its own rate, contract length and other terms, and tariffs can be fixed or variable (GOV.UK).
• Solar panels qualify, up to a capacity of 5 MW, far beyond any home roof (Ofgem). A home system needs MCS certification, of the installation and of the installer, or an equivalent scheme.
• You need a meter able to provide half-hourly export readings, which usually means a smart meter.
• The export supplier does not have to be the company that sells you electricity, although an individual tariff's terms may restrict it to its own customers.
• Only the units you send out are credited. Electricity the house uses from its own panels is not credited; it simply means less is bought from the grid.

That last point shapes everything else on this page. Because exported and self-used electricity are treated so differently, the useful question for a Liverpool household is how much of a roof's output is likely to leave the house at all.

Note, too, what "above zero" means. It is a floor, not a promise of a good rate: a tariff paying a small fraction of a penny per kWh would still meet it. Nor are you obliged to sign up at all. That is why the comparison further down matters more than the rules themselves.

What a supplier will ask for

Before an export tariff starts, the supplier will want proof that the system qualifies. The central document is the MCS certificate, which the installer issues once the system is registered; keep the certificate number to hand, because the application asks for it. If the certificate has not arrived within a few weeks of the system going live, chase the installer, as the export side cannot start without it. Check before signing a contract that the firm is on the MCS register (MCS), because a system without certification will not qualify however well it works.

The meter comes next. A smart meter that records exports in half-hour blocks is the usual route; if yours is an older meter, or a smart meter that has stopped talking to its supplier, raise it with the export supplier early so readings start from the first sunny day.

The grid side runs separately. For a system under 16 amps per phase (3.68 kW on a single-phase supply), the installer tells SP Energy Networks under the G98 process and sends it the commissioning confirmation afterwards. That notification is not an export tariff and does not start any credit; the guide to SP Energy Networks and your panels explains it, including when a larger system or a battery moves into the G99 route.

Comparing export tariffs

This guide prints no export rates. They change too often to stay accurate on a page like this, and a figure quoted without the date it was set is worse than none. Instead, put the same questions to every tariff you look at:

1. The rate per kWh, and the date it applies from. Is it fixed for a period, or can the supplier change it?
2. Any link to your import supply. Does the tariff require you to buy electricity from the same company, and on which import tariffs?
3. The contract. How long it runs, how you leave, and whether leaving the import side ends the export side too.
4. Readings and credit. Whether exports are read from the smart meter every half hour, and how often the credit reaches your account.
5. Equipment conditions. Whether the tariff asks for a particular battery, inverter or other kit.

GOV.UK advises checking regularly that you remain on a competitive tariff, because rates move over time (GOV.UK). Diary a yearly check against the market, as you might for home insurance. When two tariffs look close, the terms behind points 2 and 3 usually decide it. If you are still weighing up the panels themselves, the cost page sets out what North West homes paid per kW, which is a separate decision from the export tariff.

The same caution applies to quotes for the panels themselves. If a proposal includes an export rate in its forecast, check the date of that rate and whether the forecast assumes it never changes; a rate that moves is the norm, not the exception.

A worked example in kWh

Take 3 kW of panels on a south-facing roof at 35° in central Liverpool. PVGIS gives month-by-month output for that roof (PVGIS 5.3), and the twelve months add up to about 2,892 kWh. Set beside it Ofgem's typical household use of 2,500 kWh a year (Ofgem), spread evenly at about 208 kWh a month. Spreading it evenly is a simplification, as most homes use more in winter, but it makes the arithmetic clear.

The right-hand column is a floor, not a forecast. In any month, the house cannot use more of the panels' output than it uses in total, so whatever the roof makes above the month's consumption has to go somewhere. From March to September the roof outruns the household's entire monthly use, by as much as 170 kWh in May. Over the year that floor comes to 812 kWh, 28% of the roof's output (our arithmetic).

Household size moves the floor a long way. Run the same sums for a home using half Ofgem's typical figure and the floor rises to about 1,672 kWh, with surplus in ten months of the year rather than seven. A large household using well above the typical figure may see almost none.

Real exports will be higher. Panels only generate in daylight, and a household's use is spread across mornings, evenings and nights, so even in December, when the roof makes just 84 kWh, some of a bright lunchtime's output will slip out while nobody is using it. Your smart meter will show the true figure after the first year; this table shows the least you should expect.

Direction changes the picture. The same 3 kW facing west at 35° makes about 2,295 kWh a year, and its floor drops to 541 kWh, because less of its output exceeds the month's use. Its generation also arrives later in the day. The rooftop estimator runs the same monthly shape for any direction and pitch.

Using more of it at home

Because self-used electricity displaces bought electricity, most households try to use more of their own output before worrying about the export rate. The ordinary tools are timing and storage.

Timing means running the washing machine, dishwasher or hot water in the middle of a bright day. Storage means a battery, which holds spare midday power for the evening. A battery is good at the daily mismatch, and it will cut exports through spring and summer. It cannot touch the floor in the table above: no battery makes a house use more electricity than it uses, and a battery shifts power by hours, not by months. The battery page covers sizes and what North West households paid, and a battery's inverter counts towards the G98 limit.

A heat pump raises household use, but mostly in the months when the roof makes least, so it does less to soak up summer surplus than people expect; the guide to solar with a heat pump sets the seasons side by side.

Renters, flats and plug-in kits

Who holds the export tariff is a matter for the agreement with the supplier, and in a rented home it is something landlord and tenant should settle in writing before the panels go up. The guide to renting and solar lists the other points to agree. In a block, panels on a shared roof often serve the building's own supply, and any export arrangement sits with whoever runs it; see flats and apartments.

Plug-in kits are a different case. Export tariffs need the installation and the installer to be MCS-certified (GOV.UK), which a kit you plug in yourself is unlikely to be, so plan on using its output at home; the plug-in solar guide has the figures.

If you sell the house, expect the buyer to need the MCS certificate to set up an export tariff of their own, so pass it on with the rest of the sale papers.