Solar planning
Solar Panel Size Calculator
Estimate the solar array size and number of panels needed to match an annual energy target using location-based PVWatts yield or a known manual specific yield.
Size a solar array
How many solar panels do I need?
Enter the energy target and panel wattage, then use a location-based PVWatts model or provide a known annual yield. The calculator separates the base array requirement, the recommended design target and the installed size after whole-panel rounding.
Solar system size formula
Annual target energy is divided by modeled specific yield to find the base array requirement. A design margin creates the recommended target, then the panel count is rounded up to a whole number:
Base kW = annual target kWh ÷ specific yield
Recommended kW = base kW × (1 + design margin)
Solar panel system sizing guide by household energy consumption
Typical solar array sizes and panel counts needed to offset 100% of household electricity (assuming 400W modern monocrystalline panels and average 1,450 kWh/kW-yr specific solar yield):
| Monthly Electricity Use | Annual Energy Target | System Size (kW) | 400W Panel Count | Est. Roof Area Needed |
|---|---|---|---|---|
| 300 kWh/mo (Apartment / Small Home) | 3,600 kWh/yr | ~2.8 kW | 7 panels | ~140 sq ft (13 m²) |
| 600 kWh/mo (Medium Energy Efficient Home) | 7,200 kWh/yr | ~5.2 kW | 13 panels | ~260 sq ft (24 m²) |
| 900 kWh/mo (Average US Household) | 10,800 kWh/yr | ~8.0 kW | 20 panels | ~400 sq ft (37 m²) |
| 1,200 kWh/mo (Large Home + Central AC) | 14,400 kWh/yr | ~10.4 kW | 26 panels | ~520 sq ft (48 m²) |
| 1,500 kWh/mo+ (Large Home + EV + Heat Pump) | 18,000 kWh/yr | ~13.2 kW | 33 panels | ~660 sq ft (61 m²) |
Annual energy coverage
Annual energy coverage compares modeled annual production with the annual target. It may exceed 100%, but it is not self-sufficiency or self-consumption. Seasonal production, nighttime use, exports, imports and battery behavior are not modeled.
Location and solar yield
Location mode requests an exact 1 kW PVWatts model and scales its authoritative annual and monthly AC outputs to the installed panel array. Manual specific yield is an explicit user-provided fallback and does not invent a monthly production pattern.
Solar Array Sizing & Panel Count Formulas
Calculates the total photovoltaic DC nameplate system capacity and whole-number panel count required to generate your target annual electrical energy.
System_kW = (Annual_kWh_Target × (1 + Margin)) / Specific_Yield | Panels = ⌈(System_kW × 1,000) / Panel_Watts⌉Variable Definitions
Annual_kWh_TargetTarget Annual Consumption(kWh/yr)- Total electricity energy requirement for the year.
MarginDesign Buffer(fraction)- Safety margin for degradation and inverter clipping (typically 10%–20%).
Specific_YieldAnnual Solar Yield(kWh/kW-yr)- Location-specific AC kWh generated per installed DC kWp per year (typically 1,100 to 1,750 kWh/kWp).
Panel_WattsSingle Module Wattage(W)- Rated peak DC power of individual panel (e.g. 400W).
Engineering Notes & Standards
- Total roof area footprint ≈ Panel Count × 20 sq ft (1.85 m²).
- Installed array size = Panel Count × Panel Watts ÷ 1,000.
Frequently Asked Questions (FAQ)
How many solar panels do I need for an average home?
How much roof space does a solar panel system require?
Why does required solar system size vary based on location?
What design margin should I add when sizing a solar panel system?
Related solar calculators
Use the Solar Panel Output Calculator for detailed monthly yield modeling, or the Solar Battery Bank Size Calculator to size off-grid storage.