EV + Solar Matchmaker

The number of panels depends on three factors: your EV's real-world efficiency (kWh/mile), your annual mileage, and how much solar energy your roof receives. A typical UK driver covering 8,000 miles/year in a Tesla Model 3 needs around 8–10 x 400W panels (3.2–4 kWp). A Ford Mustang Mach-E covering the same mileage needs closer to 12–14 panels due to its higher consumption. The calculator above uses verified real-world efficiency data — not optimistic manufacturer WLTP figures.

Effectively, yes — with an important nuance. When your solar panels generate electricity during the day and your EV charges at home, you avoid paying the grid rate (24.67p/kWh in Q2 2026). The true "cost" of solar charging is the export opportunity cost — the 12p/kWh you could earn from Octopus Outgoing if you exported instead. So solar EV charging costs around 3p/mile for most models, compared to 5–6p/mile on grid electricity and 17p/mile for petrol.

Solar output peaks between 10am and 3pm on sunny days. Using a smart EV charger (such as an Ohme, Zappi, or Indra) that is integrated with your solar inverter, you can configure the car to only charge when surplus solar power is available — preventing any grid draw. This is called "solar divert" mode and is the most cost-effective way to charge. Without this feature, scheduling a charge for midday (11am–2pm) is a reasonable approximation during British summer.

Yes, in two ways. First, UK solar generation drops significantly in winter — a South East system might produce 400+ kWh in July but only 80–120 kWh in December. Second, your EV itself uses 25–29% more energy per mile in cold weather because the battery is less efficient and cabin heating draws power. The calculator accounts for both effects by applying seasonal weighting: 75% of your mileage in milder months and 25% in cold months when winter degradation applies.

A home battery is highly complementary to EV solar charging. Without a battery, any surplus solar generated while your EV is not plugged in (e.g., when you're at work) is exported to the grid at 12p/kWh. A battery stores that surplus so it can charge your car overnight. For drivers who commute during the day and need to charge in the evening, a battery dramatically increases the self-consumption of solar generation. For home workers who can charge midday, the benefit is lower.

Toggle the "I already have solar" switch in the calculator and enter your system size to find out instantly. A 4 kWp system in the South East generates approximately 3,400 kWh/year. A Nissan Leaf driving 8,000 miles/year needs roughly 2,400 kWh. In this scenario, the existing system fully covers EV charging with surplus left over for household use. However, larger or less efficient EVs at higher mileages may require additional panels.

The payback period shown is how long it takes to recover the solar installation cost purely from the fuel savings on your electric car — comparing solar EV charging costs (opportunity cost at 12p/kWh) against charging from the grid (24.67p/kWh). This is a conservative, EV-specific view. In reality, solar panels also save money on your household electricity bill, which accelerates the true payback considerably.