Solar Panel Calculator for Your Home & Tesla
How many panels does it take to run your house and your Tesla on sunshine? Size the system from your usage and your state'sregion's sun, see what it costs and when it pays back — and how much of it is really there for the car.
System size
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Annual production
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Roof area
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≈ 21 sq ft per panel≈ 2 m² per panel
Net system cost
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Savings, year 1
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Payback
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How much of the system is for your car
* The car's share of the net system cost spread over 25 years of its share of production. Grid cost uses today's rateunit rate, which is likely to rise.
Monthly production vs use
Typical seasonal shape — summer surplus banks credit for winterTypical UK seasonal shape — summer surplus is exported, winter leans on the gridCumulative savings over 25 years
After paying for the systemCompare system sizes
Bigger isn't always better when exports earn lessYear by year
How this is calculated
- EV energy = miles × Wh/mi ÷ 1000 × the share charged at home × (1 + charging losses). Supercharged miles aren't counted — your panels don't help there.
- Yield = peak sun hours × 365 × (1 − system losses) kWh per kW of panels. Sun hours are rounded stateregional averages for a south-facing, unshaded roof; your installer's site survey will be more precise.
- System size = (home + EV kWh × offset target) ÷ yield, rounded up to whole panels. Roof area assumes ≈21 sq ft≈2 m² per panel before setbacks.
- Savings: solar used directly saves your full unit rate. Everything else is exported and earns your SEG rate (kept flat, since export tariffs don't track prices). Unit rates rise and panels degrade by the percentages you set. Standing charges aren't affected by solar.
- Savings: solar used directly saves the full retail rate. Exported solar earns the export percentage of retail. Production beyond your yearly use earns the lower of that or 5¢/kWh (typical annual true-up / surplus rate). Rates rise and panels degrade by the percentages you set.
- The car's share of the system is proportional to its share of the energy you're offsetting.
Why does the monthly chart show winter shortfalls?
UK panels produce around four times as much in June as in December. Summer surplus is exported at your SEG rate rather than banked for winter, so in December and January most of your power still comes from the grid. Raising the "used directly" share — daytime EV charging in summer, a hot-water diverter or a battery — gets more value from each kWh.
Do I need permission to install panels?
Most roof-mounted panels on houses count as permitted development in England, though listed buildings and conservation areas have extra rules. Your installer notifies the local network operator; systems with more than about 3.68 kW of inverter output per phase need approval before connection. You'll need an MCS-certified installation to claim SEG export payments.
Why does the monthly chart show winter shortfalls?
Panels produce roughly twice as much in June as in December. Under net metering, summer surplus credits carry over to cover winter; on net-billing plans the credits are worth less, which is why a battery or daytime EV charging (raising the "used directly" share) helps.
Should I size for a future EV?
Adding panels later usually costs more per watt than including them up front, and many utilities cap system size at your historical usage, as scaffolding is a big part of the cost. If an EV is coming, ask your installer whether you can size for it now.
What about storage?
A home battery stores midday surplus for the evening, which matters most when exports are credited at a low rate. Run the numbers with the Powerwall Payback calculator.