Solar Panel Calculator
Size a solar array from daily kWh usage (or your electric bill), peak sun hours, panel wattage, and losses.
Processed locally in your browser — nothing is uploaded.
Solar Panel Calculator
Typically 3–4 in northern/cloudy regions, 5–6 in sunny ones.
Inverter, wiring, soiling, temperature — ~14% is a common default.
Results
- Required array size
- 6.98 kW
- Number of panels
- 18
- Estimated production of that array
- 31 kWh/day
Peak sun hours vary by season and latitude; check a solar irradiance map for your location. Shading, roof orientation, and tilt can change output substantially.
About Solar Panel Calculator
Start from your daily kWh (or let the tool derive it from a monthly bill and rate), enter your region's peak sun hours and a panel wattage, and get the array size in kW and the panel count. A default 14% system loss covers inverter, wiring, soiling, and temperature derating.
Peak sun hours are the daily solar energy expressed as hours of full-strength sun: typically around 3–4 in cloudy or northern regions and 5–6 in sunny ones.
Common uses
- Rough-size a rooftop system before talking to installers
- Plan an off-grid cabin or van array around real consumption
- See how panel wattage choices change the panel count
Example
Input
30 kWh/day · 5 sun hours · 400 W panels · 14% losses
Output
≈ 6.98 kW array · 18 panels
Limitations
- Roof orientation, tilt, and shading are not modeled; check an irradiance map for your location's real sun hours.
Frequently asked questions
How many solar panels do I need for 30 kWh a day?
With 5 peak sun hours, 400 W panels, and 14% system losses, about 18 panels — a 6.98 kW array. The count scales directly with your sun hours, so a cloudier region at 3.5 hours would need about 25 of the same panels.
What are peak sun hours?
Peak sun hours express your location's total daily solar energy as equivalent hours of full-strength (1000 W/m²) sunshine. Cloudy or northern regions typically get 3 to 4, sunny regions 5 to 6 — check an irradiance map for your actual figure.
How do I work out my daily kWh usage for solar sizing?
Divide your monthly electric bill by your rate per kWh and then by 30 days — the calculator's bill mode does this for you. Reading actual kWh off the bill is even better, since it avoids errors from fixed fees folded into the total.
Is my electric bill information kept private?
Yes. The bill amount, rate, and usage figures are processed entirely in your browser, so your energy consumption and cost data never leave your device.
What does the 14% system loss figure cover?
It bundles inverter conversion losses, wiring resistance, panel soiling, and hot-weather temperature derating into one derate factor. It is a reasonable default for grid-tie systems, and you can edit it if you have better data.