When you think of solar your first thought is often of the electricity you will generate on your roof and how it will reduce the amount of electricity you will import from the grid. Any electricity produced that you can consume is a saving of your previous import rate. For many that would be the current Price Cap day rate thats currently circa 26p/kWh.
But what about the solar generation you can't use? Thats currently the great bit because you can export your excess solar generation to your local grid and get paid for it! That sounds fantastic, as not only can you use your own generation but get paid for any solar generation you can't use.
It's one of the reasons why many will fill their roof with as many solar panels as they can get on their roof. Why wouldn't you install more solar panels than you need to meet your normal daytime consumption if you can get paid for an excess generated electricity you can't use. All of this currently helps reduce the pay back of the solar system.
Export to Import Ratio
Over the last few years we've also seen the ratio of export rates to off peak import rates being 2:1 or even 3:1, which have been a huge bonus for those with higher consumption due to EV's, heat pumps etc.
Export to Off Peak Import ratios such as these cause reduced self consumption of solar generation in order to export as much as possible. This is because those with home batteries will recharge them overnight in the off peak period at the lower rate in order for the home batteries to be fuller and reduce solar generation stored. Those with electrical cars will minimise charging them during the day off their excess solar generation because it will result in lost export payments.
Why would you charge an EV with excess solar at 12/kWh when you can charge it at 3.5p/kWh overnight? It also means you can double or triple your imported electricity during the off peak period for the same cost of export solar generation. If you were to export 2000kWh @ 12p/kWh (i.e. £240) you could import 6857kWh @ 3.5p/kWh during the off peak period for no additional cost. Thats the difference between 7,000 miles direct solar charging compared to 24,000 miles by using the grid as an Export-Import multiplier. Why wouldn't you do that if you could just double/triple at no additional cost?
Why will the Export to Off Peak Import ratio likely change in the future?
When we look at the generation sources on the National Grid on a sunny day in the summer months we can see there is a clear correlation in peak solar production and low price per kWh.
Recent changes such as Octopus officially retiring the 'Greener Nights initiative' on 31st July 2026 is due to this very reason as Octopus say the cheapest and greenest energy periods are changing from overnight to the middle of the day due to the rapid expansion of solar power.
Promoting plugging in EV's when parked at home rather than only overnight means Octopus can still charge them when the energy is cheapest and greenest.
We are also seeing new solar export tariffs such as 'Prime Outgoing Octopus' that offer a higher export rate in the evening prime and a lower export rate during the day to promote storing and export solar generation during the evening peak.
Changing to two rate export tariff makes sense when you notice the 9p daytime export rate is quite close the 8p/kWh Intelligent Octopus Go EV low charging rate on their newer fixed tariffs. When the daytime export and EV charging rates are similar this promotes charging your EV during the peak solar periods during the day as you're not losing out on a higher export rate. The only thing you need to ensure is your EV Charger is 'blinded' from your home battery to prevent draining the home battery when the EV is charging. Thats something I will need to sort out when my very lower 3.5p/kWh Intelligent Octopus Go fixed tariff ends in October 2026.
How do other countries do export rates?
We only have to look at other countries where solar export rates are quite different. Two years ago The Guardian reported that in Australia when there is a huge surplus of solar generation at midday export rates can go negative. This means solar owners can end up paying to export their surplus solar generation to the grid if they can consume it themselves.
This has the potential to increase self consumption it can also have the knock effect of reducing solar uptake or causing a reduction in the size of solar arrays that are installed (smaller solar arrays reduce the likelihood/need to export excess solar generation to the grid).
Hopefully we don't yet go this way, but if plug in solar is a huge success and daytime EV charging doesn't see a huge increase in self consumption of solar sadly we could see similar lower export rates in the UK.
Whatever happens we should know that home solar and EV charging will evolve as the UK's grid changes over the coming years.