Enter your annual mileage and your car’s efficiency rating (miles per kWh — you can find this in your EV’s trip computer or spec sheet). Add your solar system size and any home battery storage. Select when you typically charge — this significantly affects how much solar you can capture. Finally, enter your electricity rates including any off-peak tariff and your typical public charging cost. The calculator shows how much of your driving can be solar-powered and compares the annual cost against alternatives.
Solar-Powered Driving
This percentage shows how much of your annual driving can be powered by solar electricity — essentially free fuel. The actual miles are shown below. This depends heavily on when you charge: if you work from home and can charge during the day, you’ll capture far more solar than if you only charge overnight.
Cost Comparison
The three cards compare annual charging costs for public charging only, home charging at your standard rate, and your solar setup. The “best value” badge shows which option is cheapest. For most people with solar, the savings vs public charging are substantial — often £500-1,000+ per year.
Charging Mix Chart
The coloured bar shows your recommended charging split: gold for free solar, blue for off-peak/battery, and red for peak grid. This represents the optimal mix based on your setup and charging pattern. Aim to maximise the gold section for the lowest running costs.
Petrol Comparison
The cost breakdown shows how much you save compared to running an equivalent petrol car (assuming 45mpg and current fuel prices). Even charging entirely from the grid, EVs are cheaper to run than petrol — with solar, the savings are dramatic.
Charge During Solar Hours
Typically 10am-4pm when generation peaks. Even partial charging during this window helps.
Use a Smart Charger
Devices like Zappi, Ohme, or Wallbox Pulsar can automatically use excess solar, pausing when clouds pass and resuming when the sun returns.
Add a Home Battery
Captures daytime solar for evening charging if you’re not home during the day.
Pre-Condition While Plugged In
Heat or cool your car before departure while connected, using solar instead of battery power.
Size Your Solar for EV
If you’re installing new panels, consider a larger system to cover your EV needs. An extra 2-3 kWp dedicated to EV charging often pays back quickly.
Combine with Off-Peak Tariffs
Octopus Go or Intelligent Octopus give you cheap overnight rates (7-12p/kWh) for winter months when solar is limited.
Can solar panels really charge an electric car?
Yes, absolutely. A typical UK solar system generates 3,000-4,000 kWh per year. A typical EV doing 8,000 miles needs around 2,500 kWh. So a reasonably sized solar array can theoretically cover all your driving — the challenge is matching when you charge with when the sun shines.
What size solar system do I need to charge my EV?
As a rough guide, 1 kWp of solar generates enough electricity for about 3,000 miles of EV driving per year. So a 4 kWp system could theoretically cover 12,000 miles. However, you won’t capture 100% for your EV — some powers your home, some is exported. A 4-6 kWp system with smart charging typically covers 40-60% of average UK driving.
Do I need a special charger to use solar?
You don’t need one, but a smart charger with solar diversion makes a huge difference. Chargers like Zappi, Ohme, or Wallbox can monitor your solar generation and adjust charging power in real-time. They’ll automatically use excess solar when available and pause when it’s not, maximising free charging without any effort from you.
What about winter when there’s less solar?
Winter solar generation in the UK drops to about 25-30% of summer levels. This is where off-peak tariffs shine — Octopus Go gives you 7p/kWh electricity overnight, so you can charge cheaply even when solar is limited. Many EV owners use solar in summer and off-peak in winter for the best of both worlds.
Is it worth getting a home battery for EV charging?
If you’re out during the day and can only charge evenings/overnight, a home battery captures daytime solar for later use. However, your EV battery itself is huge (typically 40-80 kWh vs 5-10 kWh home batteries). Some people use vehicle-to-home (V2H) systems to use their EV as the battery, though this requires compatible hardware.
Combining solar panels with an electric vehicle creates a powerful synergy — free, clean fuel for your car. While you won’t capture 100% of your solar for EV charging, even 40-60% solar coverage can save £500-1,000 per year compared to public charging. With smart chargers and off-peak tariffs filling the gaps, you can drive thousands of miles annually on sunshine while dramatically reducing your carbon footprint and running costs.
