Saving money charging your electric car with solar panels. What an absolute false economy that is. Or is it? That’s what our solar panel EV charging savings calculator helps you find out.
Before you dive into the numbers, let’s be clear about what we’re measuring. When you charge your EV with solar power, you’re not exactly saving money – you’re avoiding spending it in the first place. But there’s also an opportunity cost to consider ↓
Every kilowatt-hour you put into your car is a kilowatt-hour you could have exported back to the grid through the Smart Export Guarantee (SEG). Most suppliers pay you somewhere between 4p and 15p per kWh for exported electricity. Meanwhile, you’re avoiding buying grid electricity at around 26p per kWh (or 7p if you’re on a clever overnight tariff).
So the actual saving per kWh is the grid rate you’re avoiding, minus what you would have earned by exporting. If you’re paying 26p per kWh and missing out on 15p export payments, your net saving is only 11p per kWh. Still decent, but not the 26p headline figure the solar salespeople bang on about.
So, without further ado, the calculator. Input your information below and it’ll provide accurate cost savings for charging your electric vehicle.
Solar Panel EV Charging Savings Calculator (UK)
What Solar Actually Generates in the UK
A 4kW solar system generates different amounts depending on where you live in the UK:
- Scotland/Northern Ireland: 4,000 kWh/year
- North England: 4,200 kWh/year
- Midlands/Wales: 4,400 kWh/year
- South England: 4,600 kWh/year
- South West: 4,800 kWh/year
That’s your total generation. How much actually goes into your EV depends entirely on when you charge.
The Timing Problem
Your solar panels generate most power between 10am-3pm. Your EV probably needs charging in the evening. This mismatch means most people only charge their EV with solar for 30-40% of their annual consumption. Work from home and charge during the day? You might hit 50-60%.
Use the calculator above to model your charging pattern and see realistic solar usage percentages.
Working Out Your EV’s Annual Energy Need
Take your annual mileage and divide by your EV’s efficiency. A typical EV does 3.5 miles per kWh.
- 7,400 miles (UK average): 2,114 kWh
- 10,000 miles: 2,857 kWh
- 15,000 miles: 4,286 kWh
Add 10% for charging losses. That 10,000 miles actually needs 3,143 kWh from the grid.
What You Actually Save Per kWh
This is where people get confused. If you’re paying 26.35p per kWh on a standard tariff, you’re not saving 26.35p every time you charge from solar.
You’re missing out on the export payment. Most Smart Export Guarantee (SEG) tariffs pay 4-15p per kWh. Let’s use 15p as a decent rate.
Real saving per kWh = 26.35p (grid rate) – 15p (lost export) = 11.35p
That’s your actual net saving. Not 26.35p. 11.35p.
Some quick calculations:
- 10,000 miles needing 3,143 kWh
- 40% charged from solar = 1,257 kWh
- Net saving at 11.35p = £142.67/year
Input your actual grid and export rates in the calculator to see your real savings.
The Overnight Tariff Complication
On Octopus Go or Intelligent Go, you pay 7p per kWh overnight. Now your calculation flips:
Solar “saving” = 7p (cheap rate) – 15p (export) = -8p
You lose 8p per kWh by charging from solar instead of exporting it and buying overnight. If you’re on a cheap overnight tariff, solar EV charging costs you money.
The workaround: charge from solar when convenient during the day, use cheap overnight electricity when you need a full charge. You’re not locked into one method.
System Costs and Payback
Current UK prices for solar installations:
- 3kW system: £4,500-£6,000
- 4kW system: £5,500-£8,000
- 5kW system: £6,500-£9,500
Using our 4kW system at £6,500 and annual savings of £142.67 from EV charging alone:
Payback period = £6,500 ÷ £142.67 = 45.6 years
That’s awful. But you’re not installing solar just for EV charging. A typical household uses 2,700-4,100 kWh annually. If your solar offsets 50% of household consumption plus 40% of EV charging, your combined annual saving is £400-£600.
New payback period = 11-16 years
Much more realistic.
Home Battery Addition
A 9.5kWh home battery costs £4,500-£7,000. It stores daytime solar for evening EV charging, potentially boosting your solar EV charging from 40% to 70%.
Additional annual saving on EV charging: roughly £100-£150.
Battery payback from EV charging alone: 30-70 years
Home batteries make financial sense for time-of-use tariff arbitrage and household consumption shifting, not primarily for EV charging.
Regional Variations
Your location matters. Compare two identical setups:
Scotland (4kW system, 10,000 miles/year, 40% solar charging):
- Annual generation: 4,000 kWh
- Solar EV charging: 1,257 kWh
- Annual saving: £142.67
South West England (same setup):
- Annual generation: 4,800 kWh
- Solar EV charging: 1,257 kWh (same)
- Annual saving: £142.67 (same)
Wait, the same? Yes. Because you’re limited by when you can charge, not total generation. Extra generation gets exported. The financial benefit is identical unless you can use more of that excess generation elsewhere.
Comparing to Petrol Costs
A petrol car doing 45 MPG at £1.45/litre:
- 10,000 miles = 1,010 litres = £1,464.50/year
EV charging costs for the same mileage:
- 100% grid at 26.35p/kWh: £828.18/year
- 40% solar, 60% grid: £638.86/year
- 100% overnight at 7p/kWh: £220.01/year
Annual petrol saving with solar-charged EV: £825.64 Annual petrol saving with cheapest EV tariff: £1,244.49
Use the calculator’s petrol comparison to see your vehicle’s costs.
High Mileage Changes Everything
Do 20,000 miles annually and the numbers shift:
- Energy needed: 6,286 kWh/year
- 40% from solar: 2,514 kWh
- Annual net saving at 11.35p: £285.34
- Petrol equivalent cost at 45 MPG: £2,929/year
- Total annual saving vs petrol: £2,643.66
Higher mileage makes both EVs and solar more financially attractive. The percentage payback from solar EV charging doubles, though absolute payback periods remain similar because you’re still limited by when you can charge.
When Solar EV Charging Makes Financial Sense
Solar panels for EV charging work financially when:
- You’re on a standard tariff (not cheap overnight rates)
- You work from home or charge during the day regularly
- You do high annual mileage (15,000+ miles)
- You’re already installing solar for household consumption
- Energy prices increase (likely)
Solar panels don’t make sense for EV charging when:
- You’re on Octopus Go or similar (7p/kWh overnight)
- You can only charge evenings/weekends
- You do low mileage (<5,000 miles/year)
- You’d install them purely for EV savings
What About Energy Price Increases?
Every 1p increase in the grid electricity rate adds £31.43 to your annual saving (10,000 miles, 40% solar charging). If rates hit 35p/kWh:
New saving per kWh = 35p – 15p = 20p Annual saving = £251.40 Payback on £6,500 system: 25.9 years (EV only)
Still long, but improving. Combined with household savings, payback drops to 8-12 years.
The Bottom Line
Solar panels will not pay for themselves through EV charging alone unless you’re doing serious mileage and charging primarily during daylight hours. A typical driver doing 10,000 miles will save £140-£180 annually from solar EV charging.
The financial case for solar relies on combined benefits:
- Household electricity savings: £300-£500/year
- EV charging savings: £140-£180/year
- SEG export payments: £50-£150/year
- Total: £490-£830/year
That gives you a realistic 8-15 year payback on a typical system.
Use the calculator to input your exact situation: system size, location, mileage, efficiency, tariffs, and charging patterns. It’ll give you the numbers that matter for your setup, not generic estimates.
The calculator accounts for all the variables: grid rates, export rates, charging efficiency losses, opportunity costs, and regional generation differences. Run your numbers, see your actual payback period, and decide if it makes financial sense for you.
Check out our other calculators:
- EV Charging Cost Calculator
- EV vs Petrol Cost Calculator UK
- EV Pay Per Mile Calculator
- EV Charging Time Calculator
- Electric Car Depreciation Calculator UK
Additional reading and sources: