Solar PV Export Tariff Options

When the solar panels on the House were commissioned in 2017, the UK’s Feed-In-Tariff (FIT) arrangement was still available so currently (2024-25 pricing) that system generates payments based on:

  • 5.87p per kWh of Generation, as reported by the dedicated generation meter
  • 7.14 p per kWh of Export, based on 50% of generation being treated as “deemed export”

When the new solar panels on the Outbuildings get commissioned later in 2025, those will not be eligible for any sort of FIT payments – but they will be able to generate revenue based on the actual exported energy, as reported by the SMETS2 Smart Meter.

Since the Smart Meter won’t be able to distinguish an export originating from the ‘new’ solar panels from one originating from the ‘old’ ones, it’s not possible to continue on the 50% “deemed export” basis for the older installation; the whole site needs to be switched to a tariff which makes payments based on actual, measured export.

The question then is whether it’s worth swapping over now, or waiting until the new panels are commissioned in about 6 months time – which depends on:

  • The relative rates per kWh for a metered-export tariff versus the deemed-export tariff
  • Whether the site is actually exporting (more than) 50% of generation or not

The electricity supplier is currently Octopus Energy, and the import tariff is Intelligent Octopus Go, which is very good for overnight EV charging. Octopus offer quite a wide range of export tariffs. The ‘best’ ones being:

  • Octopus Outgoing, which pays a flat rate of 15p per kWh exported
    • This is generally the best option for sites with no battery
  • Octopus Outgoing Agile, which pays a variable rate based on half-hourly electricity prices
    • This is generally preferred when there is a battery which can store a significant proportion of the solar PV generation during the middle of the day then export that in the early evening, when export prices are often (but not always) higher than 15p

On the face of it, 15p per kWh is significantly better than 7.14p per kWh, and spring-into-summer is generally very good for solar generation so a greater proportion of generated power is likely to be exported – which implies it would be beneficial to switch sooner rather than later, as long as Octopus Outgoing is compatible with Intelligent Octopus Go.

Good Day for Solar PV Generation

It’s only reasonable to expect the generation from solar panels to be less impressive in winter than in summer but today was a good illustration that some days in winter can still deliver good results. The almost complete absence of cloud today meant some level of generation right from sunrise (07:44) to sunset (16:00) and peak generation of 3.143 kW around noon (from a nominal 5.4 kWp installation). The daily total of 17.52 kWh is half that of the best days in May (the best month so far) but much better than the worst days in May. The graph from the SolarEdge dashboard is a very pleasing shape, without the usual ups and downs as clouds pass over.

Near perfect solar generation profile

The generation was more than sufficient to re-heat the hot water via the immerSUN automatic solar PV diverter (as still happens most days) and managed to supply the 2 kW required for the ground source heat pump when it ran for 20 minutes to heat the house around noon. At other times it was exporting to the grid, managing 6.8 kW of export in total.

Overall: not a bad result for a month before the shortest day of the year.