liminfoSolar Panel Output Calculator
Free web tool: Solar Panel Output Calculator
Panels Needed
19
System Size
7.60 kW
Est. Annual Production
11096 kWh
Est. Roof Area
32.3 m²
Daily Consumption
30.0 kWh
Annual Consumption
10800 kWh
Min. System Size
7.50 kW
Each panel assumed ~1.7 m². System efficiency accounts for inverter losses, wiring, shading, and temperature derating.
About Solar Panel Output Calculator
The Solar Panel Calculator helps homeowners, electricians, and solar installers estimate the number of photovoltaic (PV) panels needed to cover a household's electricity consumption. Enter the monthly electricity usage in kWh, the peak sun hours per day for your location, the wattage of the panels you plan to install, and the overall system efficiency, and the calculator returns the minimum system size in kW, the actual system size after rounding up to whole panels, the number of panels required, the estimated annual energy production, and the approximate roof area needed.
The core formula divides the daily energy demand (monthly kWh ÷ 30) by the product of peak sun hours and system efficiency to yield the minimum system size in kW. This is then divided by the panel wattage to determine the panel count, always rounding up to ensure full coverage. System efficiency (default 80%) accounts for real-world losses including inverter conversion losses (typically 3–5%), DC and AC wiring resistance, module mismatch, soiling and shading, and temperature derating — a monocrystalline silicon panel rated at 25°C loses roughly 0.3–0.5% power for each degree above that. Annual production is then calculated as: actual system kW × peak sun hours × 365 days × efficiency.
Each panel is modelled at a standard footprint of approximately 1.7 m² (roughly 1.0 m × 1.7 m), which matches typical 400 W residential monocrystalline modules. The roof area estimate helps confirm that the available roof space is sufficient before commissioning a full site survey. All calculations are performed client-side in the browser and no data is transmitted to external servers.
Key Features
- Calculates minimum and actual system size in kW from monthly energy consumption
- Panel count computed by dividing system watts by panel wattage, always rounded up
- Annual production estimate: actual system kW × peak sun hours × 365 × efficiency
- Estimated roof area based on standard 1.7 m² per panel footprint
- System efficiency input (1–100%) models inverter losses, wiring, shading, and temperature derating
- Separate display of daily consumption, annual consumption, and minimum system size
- Real-time recalculation on every input change
- 100% client-side computation — no data sent to server, completely free
Frequently Asked Questions
How does the solar panel calculator determine the number of panels?
The calculator first converts monthly kWh usage to a daily figure (monthly ÷ 30), then divides by (peak sun hours × system efficiency) to get the minimum system size in kW. Converting to watts and dividing by panel wattage gives the raw panel count, which is always rounded up to the next whole number to ensure the system covers 100% of consumption.
What are peak sun hours and how do I find mine?
Peak sun hours (PSH) represent the number of equivalent hours per day when solar irradiance averages 1,000 W/m². A location with 5 PSH receives the same daily solar energy as 5 hours of full midday sun. Values range from about 2.5 PSH in cloudy northern regions to over 6.5 PSH in sunny desert areas. You can find your location's PSH from NASA's PVGIS database or the NREL PVWatts calculator.
What does system efficiency include?
System efficiency (also called the performance ratio or derate factor) accounts for all real-world losses between the panel's rated output and the actual AC power delivered. Main sources of loss include: inverter conversion (3–7%), DC wiring resistance (1–3%), module mismatch (1–2%), soiling and shading (2–5%), and temperature derating (1–10% depending on climate). A value of 75–85% is typical for well-designed rooftop systems.
How accurate is the roof area estimate?
The tool estimates roof area as number of panels × 1.7 m² per panel. This matches the typical footprint of a 400 W monocrystalline panel (approximately 1.0 m wide × 1.7 m tall). Actual installation requires additional spacing for mounting hardware, maintenance access, fire setback requirements, and avoiding structural obstructions. A professional site survey is needed for final design.
Does the calculator account for battery storage?
No, the calculator is designed for grid-tied solar systems where surplus power is fed back to the grid and deficit power is drawn from the grid. Battery storage sizing involves additional factors including depth of discharge, round-trip efficiency, desired days of autonomy, and load priority. A separate battery sizing tool or professional energy audit is recommended for off-grid or hybrid systems.
How do I use the annual production figure?
Annual production (kWh/year) can be compared to your annual electricity bill to estimate the percentage of consumption offset by solar. For financial analysis, multiply annual production by the local electricity rate ($/kWh) to estimate annual savings. For example, a 6 kW system producing 8,000 kWh/year at $0.15/kWh saves approximately $1,200 per year before accounting for feed-in tariff income.
What panel wattage should I enter?
Common residential panel wattages in 2024–2025 range from 350 W to 500 W. Mainstream 60-cell and 72-cell monocrystalline PERC and TOPCon panels are typically 400–430 W. Higher-wattage panels (450–500 W) are available in N-type heterojunction (HJT) and bifacial formats. Using higher-wattage panels reduces the panel count and required roof area for the same system size.
Should I oversize the solar system?
Mild oversizing (10–20% above calculated minimum) is common practice because: (1) real-world production is often lower than modelled due to unforeseen shading or soiling, (2) electricity consumption typically grows over time, and (3) inverters operate more efficiently when not running at 100% capacity. However, in grid-tied systems without batteries, excessive oversizing produces surplus power that may be curtailed or sold at reduced feed-in tariff rates.