Not quite as easy as it sounds – a common theme in the electric future – but it can be done.

We used solar charging from Apr – Sept this year, it provided 82% of all the charge put into the car and gave us more than 2,500 miles of free motoring (if you ignore the capital costs of solar and battery). As all that electricity came from the sun it was genuinely CO2 emission free – unlike charging from the grid. Read on for how.

You could just plug in the ‘granny lead’ to a 13A socket but that means the car is going to charge at 2.2 kW no matter what the solar is doing. Say the solar produces 1.1 kW on average on a cloudy day – half your charge will come from free solar the other half from the grid. Cost of the charge will be 34p (October price cap figure) divided by 2 – so 17p per kWh. That’s around twice the price of charging using cheap overnight electricity!

There are charge points that divert excess solar energy into your EV automatically. If there’s plenty of excess solar around – a clear sunny day – then great. On cloudy days when the excess solar is less consistent the charger will keep charging at a minimum of around 1.4 kW even if there’s less excess solar than that being produced because EV batteries need a steady minimum charge. So your EV can end up being charged from the grid at 34p per kWh for some of the time.

Of course for both of the above you could only charge when it’s clear and bright but that is going to limit how many hours and days you can use solar charging. Charging at 2.2kW takes nearly 13 hours to get the same charge as you can in 4 hours overnight from a 7kW home chargepoint.

To get plenty of miles from solar charging you need to be able to plug in on most days in the summer without worrying too much about the what the weather is going to do. Our car was solar charging for a total of 273 hours from Apr-Sept. Our home battery made it possible and practical.

Connect up the ‘granny lead’ and start charging. The 2.2kW will flow from the solar and if there isn’t enough around then the battery will automatically make up the difference. No risk of importing costly power from the grid…

…until your battery runs out! So make sure it doesn’t. A smart plug timer is an easy solution but it does require a bit of thought – How sunny is it? How much power is in the battery? You can put it on for two or three hours and see what charge is left in the home battery – it’s easy to turn it on again. All a bit manual though – you want free solar charging not a new hobby!

We think a better way is to automatically monitor the home battery charge level and turn off solar charging when the home battery discharges to a preset level you choose. You can make sure you have enough charge to get you through the evening and pour everything else into the car. It requires no more thought than plugging in the car and turning on the smart plug. Using a smart plug with power sensing allows you to keep track of how much energy has come from solar. We use the excellent and free Home Assistant software running on a Raspberry Pi to monitor the home battery and turn off the smart plug when required – it even sends an email when the charge has turned off with the number of miles added. All the details are here>

Charging overnight on Octopus Go is so cheap you won’t save a fortune – we saved just over £50 using solar charging this summer – full details here: ev-running-costs-what-can-you-save