Sustainability
Instant, private, and free
Solar Panel Calculator.
Estimate solar array power and panel count from daily energy use and explicit sun-hour, panel-power, and system-loss assumptions.
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Results update as you type.
How to Use
Required array power = daily energy use ÷ (peak sun hours × (1 − system-loss fraction)).
Use locally measured or sourced assumptions for sun hours and losses; no location data or tariff is included.
FAQs
Does this use location data?
No. Peak sun hours and system losses are explicit user inputs, so no live resource or tariff assumptions are applied.
Related Calculators
Cite this calculator
Canonical URL: https://mathify.one/en/sustainability/solar-panel
Cite as: Mathify. (n.d.). Solar Panel Calculator. https://mathify.one/en/sustainability/solar-panel
Use Cases
Residential rooftop solar sizing
Homeowners can estimate how many panels they need to cover their daily electricity consumption, helping them plan a rooftop installation.
Example: If you use 30 kWh/day, have 5 sun hours, and use 400W panels with 14% losses, you'd need about 18 panels.
Small business or community project planning
Small businesses or community solar projects can quickly estimate the required array size and panel count for their energy needs.
Example: A workshop using 50 kWh/day with 4.5 sun hours and 350W panels would need around 37 panels.
Frequently Asked Questions
- How does the solar panel calculator estimate the number of panels?
- It uses your daily energy use (in kWh), the average peak sun hours for your location, the wattage of each panel, and a system loss percentage. It calculates the required array size in kW, then divides by the panel wattage to get the number of panels.
- What is a typical system loss percentage?
- System losses account for inefficiencies like inverter losses, wiring, shading, and temperature. A common default is 14% (or 0.86 efficiency). You can adjust this based on your specific setup.
- Can I use this calculator for off-grid systems?
- Yes, it works for any solar array sizing. For off-grid, you'll need to account for battery storage separately, but the panel count and array power estimate remains valid.
Tips & Common Mistakes
Tips
- Use your average daily energy use from your electricity bill (kWh/day) for the most accurate estimate.
- Find your location's average peak sun hours from a reliable solar resource map or database.
- Adjust the system loss percentage based on your specific conditions; 14% is a good starting point.
- Consider future energy needs (e.g., EV charging) when sizing your array.
Common Mistakes to Avoid
- Using monthly energy use instead of daily – divide by 30 to get daily kWh.
- Ignoring system losses, which can lead to undersizing the array.
- Using panel wattage that doesn't match the actual panels you plan to install.
Last updated: August 13, 2026