Solar Panel Calculator
Size your PV system in minutes — panels, kW, battery and savings. Free results, optional installer PDF.
Solar sizing setup
Usage → location → roof → battery → tariff
How much electricity do you use?
Use your bill total. Monthly or annual — whichever is easier.
Typical EU home: 3,500–5,500 kWh/year
Live solar size
LiveSystem size
9 × 450 W · 19.3 m²
Production
0kWh
Coverage
0%
CO₂ cut
0.00t/yr
Savings
€0
Annual bill
Est. payback ~8.3 years
Your solar system estimate
Updates live as you change inputs — free, no sign-up
System size
0.00kW
Panels
0× 450 W
Annual production
0kWh
Savings
€0/year
Before
€0
/year
After
€0
/year
Savings
€0
Payback ~8.3 years
Annual bill impact (€)
Usage vs solar production (kWh/yr)
Solar coverage of your usage
Where solar kWh go
CO₂ reduction
0.73 t/year
Roof needed
19.3 m²
Battery
None
How we estimate your solar potential
Your estimate is based on the inputs you entered — written for planning, not jargon.
1. Solar system size
We recommend PV size from your annual electricity use, desired solar coverage, available roof space, and panel wattage.
2. Solar production
Estimated yearly production uses system size, local sunlight availability for your region, roof orientation, and typical system efficiency.
- Local climate conditions
- Roof direction
- Typical system losses (inverter, wiring, temperature)
3. Number of panels
Required system power ÷ panel wattage, rounded up to whole panels.
4.05 kW ÷ 450 W ≈ 9 panels
4. Battery recommendation
Battery size depends on backup needs, evening electricity use, and how independent you want to be from the grid.
Your roof direction: South-facing · Expected impact: Excellent
This is an engineering estimate for planning and comparison. Final system design should be verified by a qualified solar installer.
Technical details
Annual production ≈ system kW × specific yield (kWh/kWp/year) × orientation factor × performance ratio.
Your climate preset uses ~1050 kWh per kWp per year (before orientation and efficiency).
Performance ratio ≈ 0.82 — covers typical inverter, wiring, temperature and conversion losses.
Orientation factor for this roof: 1×.
Panel count = ceil(required kW × 1000 ÷ panel wattage). Roof area ≈ panels × footprint including spacing.
Battery usable capacity from your backup preset: 0 kWh. Savings assume higher self-consumption with storage.
Does not include site shading, detailed temperature curves, year-by-year degradation, or string/MPPT design — those belong in a full installer survey (and in the optional PDF).
Installer checklist preview
- Confirm roof orientation and shading on site
- Verify structural capacity for panel weight
- Full 3-page Solar Installation Report unlocks below →
Solar Installation Report
3-page PDF: system recommendation, financial analysis, and installer checklist.
Report preview
- System size & panel count
- Annual production estimate
- Bill savings preview
- 25-year benefit & investment estimate
- Full installer checklist & next steps
$9.99
One-time payment · instant PDF + email
- Secure Stripe checkout
- Delivered in under 2 minutes
Need multiple projects? Thermopy Premium ($29.99/month) unlocks unlimited calculators & PDF reports.
How to Use This Calculator
How to Use This Calculator
- 1
Enter your electricity use
Use monthly or annual kWh from your utility bill — whichever is easier.
- 2
Pick your climate region
Choose a location preset and how much of your usage solar should cover. Specific yield stays in the engine — not in the form.
- 3
Describe your roof
Select orientation, panel wattage, and roof area — or tick “I don’t know my roof size”.
- 4
Choose battery backup
No battery, evening, overnight or full backup — we map that to usable kWh.
- 5
Set your tariff and view results
Enter your electricity price to see before/after bills, savings, CO₂ and an optional installer PDF.
Pro Tip: Use Ctrl+Enter to calculate quickly, or Ctrl+R to reset the form.
Frequently Asked Questions
How many solar panels do I need?
Panel count depends on annual electricity use, how much of that usage you want solar to cover, your climate, roof orientation, and panel wattage. This calculator converts those inputs into a rounded panel count and system kW.
How much electricity can solar panels produce?
Annual production is estimated as system kW × specific yield (kWh/kWp/year) × orientation factor × performance ratio. Sunnier climates and south-facing roofs produce more per installed kW.
Is solar worth it for my home?
Compare your current annual bill with the estimated bill after solar self-consumption. Payback depends on electricity price, system cost, and how much production you use on-site. Free results show before/after savings and a payback preview.
What size battery do I need?
Choose a backup intent: none, evening usage (~5 kWh), overnight (~10 kWh), or full backup (~15 kWh). These presets map to usable storage without asking for technical DoD settings.
How long does solar take to pay back?
Payback is estimated investment ÷ annual bill savings. Typical residential ranges are often 6–12 years depending on incentives, tariffs and self-consumption. The optional PDF includes a fuller 25-year benefit view.
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