Solar Panel Size Calculator

Estimate solar panel wattage, panel count, daily output, and charge controller size based on energy use, peak sun hours, losses, and panel wattage.

Enter Your Solar Setup


Presets are rough examples. Use your actual daily energy use and local peak sun hours when possible.


Use known daily watt-hours if you already estimated your load. Otherwise use watts and hours per day.


Example: a 60W load running 10 hours uses 600Wh per day.


This is not daylight hours. It is usable full-sun equivalent hours.


Accounts for wiring, charge controller, temperature, angle, dirt, and real-world losses.


Adds headroom for cloudy days, seasonal changes, and imperfect conditions.


Use the rated wattage of one solar panel.


Used for a rough charge controller output-current estimate.


Adds current headroom for charge controller planning.


Optional. Enter 0 if you do not want a panel cost estimate.


Your Results

Suggested array size

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Enter values and calculate.

Panels needed

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Rounded up to whole panels.

Daily output estimate

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Based on panel count and sun hours.

Controller current

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Rough MPPT output-current estimate.

This calculator gives a planning estimate only. Real solar output can vary because of weather, shade, season, panel angle, temperature, wiring losses, controller limits, and battery condition.

How to Use This Solar Panel Size Calculator

Enter your daily energy use, local peak sun hours, estimated system efficiency, planning buffer, and the wattage of one solar panel. The calculator estimates the solar array size and number of panels needed.

This calculator is best for early planning on small solar, battery, shed, workshop, camping, and backup-power projects. It does not replace a full solar design.

Formula Used

Daily energy use = load watts × hours per day
Base solar array watts = daily watt-hours ÷ peak sun hours ÷ system efficiency
Suggested array watts = base array watts × (1 + planning buffer %)
Panels needed = suggested array watts ÷ panel wattage, rounded up
Estimated controller current = installed panel watts ÷ battery voltage × controller buffer

Example Calculation

A setup using 600Wh per day with 4 peak sun hours, 75% system efficiency, and a 25% buffer needs about:

600Wh ÷ 4 sun hours ÷ 0.75 = 200W base array
200W × 1.25 = 250W suggested array

If each panel is rated at 200W, that means the project would likely use 2 panels for a rated array size of 400W.

Common Solar Sizing Mistakes

  • Using daylight hours instead of peak sun hours.
  • Ignoring cloudy days, winter sun, shade, panel angle, and temperature losses.
  • Assuming a 200W panel produces 200W all day.
  • Sizing panels without checking battery capacity and charge controller limits.
  • Forgetting that inverters, chargers, and wiring all have losses.
  • Building a system with no fuse, disconnect, weather protection, or safe wiring plan.

Important Safety Note

Use this calculator as a planning tool only. Solar panel wiring, batteries, charge controllers, inverters, fuses, breakers, disconnects, grounding, waterproofing, and code requirements can all matter.

For roof-mounted solar, permanent wiring, grid-tied solar, high-voltage strings, lithium battery banks, permits, inspection, fire risk, or code-sensitive work, get qualified professional guidance.