Solar PV Calculator
System size, annual yield, savings, SEG earnings, payback & CO2
Size from roof area
Enter available roof space - calculator works out how many panels fit and the system output
Enter panel count
Know how many panels you want or have been quoted - enter the number directly
🇬🇧 UK & Ireland
🇺🇸 USA & Canada
🇪🇺 Europe
🇦🇺 Aus & NZ
🌍 Other
Flat (0°)
15°
25°
35°
45°
60°
400 W
450 W
500 W
550 W
Measure the usable roof plane - exclude ridges, hips, verges, and Velux windows.
Chimney stacks, roof lights, vents. Leave blank if none.
■ Approx. 0 panels fit
Tariffs & Usage
Unit rate from your energy bill in pence, cents, or eurocents per kWh
UK: Smart Export Guarantee (SEG). US: net metering credit. AUS: feed-in tariff.
Typical household: 30-40%. Higher with battery storage.
Full installed cost in local currency. Used to calculate payback period.
Solar PV Results
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Frequently Asked Questions
How many solar panels do I need for a typical home?
A typical 3-4 bed home uses 3,000-4,500 kWh/year. A 4 kWp system on a south-facing roof generates approximately 3,400-3,800 kWh/year and needs around 20-24 m² of unshaded roof space. The number of panels depends on individual panel wattage - a 400W panel occupies roughly 2 m².
How much electricity does a solar panel generate per year in the UK?
South-facing roof at 30-35°: approximately 850-950 kWh per kWp per year. A single 400W panel generates around 340-380 kWh/year. East/west-facing: 15-20% less. North-facing: not recommended (40-50% reduction). Shading from chimneys or trees can significantly reduce output - always assess before installing.
Do I need planning permission for solar panels?
Generally no planning permission needed for domestic roof panels under permitted development: panels must not protrude more than 200 mm beyond the roof plane or exceed the roof's highest point. Listed buildings need listed building consent. Conservation Areas: panels must not be visible from a highway. Check with your Local Planning Authority if unsure.
What is the payback period for solar panels in the UK?
A typical 4 kWp system costs £6,000-£9,000 installed. At current rates: approximately £600-£900/year savings (50% self-consumption + SEG export income). Payback: roughly 8-12 years. Adding battery storage increases self-consumption from ~50% to 70-85%, improving payback - especially with time-of-use tariffs.
What is the Smart Export Guarantee (SEG) and how does it work?
The Smart Export Guarantee (SEG) requires large electricity suppliers to pay for surplus solar exported to the grid. Rates: typically 4-20p per kWh, varying by supplier. You need a smart meter to receive payments. Apply through your electricity supplier after installation. The SEG replaced the Feed-in Tariff (FiT), which closed to new applicants in 2019.
Do solar panels work in cloudy weather?
Yes - panels generate from daylight, not just direct sunlight. Output in overcast conditions is typically 50-80% lower than in bright sunshine, but panels still produce useful power. UK yield estimates (850-950 kWh/kWp/year) already account for the UK's cloudy climate. Modern monocrystalline panels perform better in low light than older polycrystalline technology.