Solar Panel Calculator

Estimate how much energy your solar panels can generate each day and each year. This page also keeps the formula, examples, FAQs, and references close by so you can check the result with confidence.

What This Solar Panel Calculator Helps You Do

More panels, more sun hours, and higher efficiency all increase output. Review the formula and examples below if you want to see how the result is derived.

This page is meant to give you a fast answer, but it also helps you double-check the math before you make a decision. Start with the inputs that you already know, run the calculation, and then compare the output with the formula, examples, and FAQs below so you can see whether the answer fits the situation you are modeling.

If the result looks off, the usual causes are a unit mismatch, a missing decimal, the wrong scenario, or a value that needs to be entered as a rate instead of a total. The notes on this page are designed to make those checks easy without forcing you to leave the calculator and search for context elsewhere.

  • Use the calculator first for a quick estimate.
  • Use the formula to understand how the result is built.
  • Use the examples to compare common use cases.
  • Use the references when the answer depends on a standard or assumption.

Common Checks

A quick result is useful, but the best result is one that still makes sense when you look at it a second time. If you are comparing scenarios, try changing one input at a time so you can see which variable has the biggest impact on the final answer. That makes it much easier to spot whether the calculation matches your expectations.

It also helps to keep the context of the problem in mind. A calculator can tell you the math, but you still need to decide whether the input represents a total, a rate, an average, or a category-specific assumption. When in doubt, start with a simple example from the page and scale up from there.

  • Check that every unit matches the rest of the problem.
  • Keep rates, totals, and averages separate.
  • Adjust one variable at a time when testing scenarios.
  • Use the smallest realistic input first, then scale upward.

Scenario Planning

This calculator is especially useful when you want a quick answer before you commit time, money, or effort. Try one baseline input set, then change a single number and compare the result so you can see how sensitive the answer is to that variable.

That makes the page useful for more than just arithmetic. It becomes a small decision aid that helps you compare options, test assumptions, and explain the final number with confidence when you need to share it with someone else.

W
h/day
%
%
$/kWh
kg CO2/kWh

Solar output

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Quick Answer: More panels, more sun hours, and higher efficiency all increase output. Review the formula and examples below if you want to see how the result is derived.

How to Calculate Solar Panel Calculator

  1. Set your panel size: Enter the rated wattage per panel and how many panels you have.
  2. Add sunlight and efficiency: Use your local sun hours and a realistic performance factor.
  3. Review energy and savings: The calculator shows daily and annual output plus estimated savings.

Solar Panel Calculator Formula

Daily output = panel wattage × panel count × sun hours × efficiency
Variable Meaning Unit
panel wattage Rated wattage of one panel W
panel count Number of panels installed count
sun hours Average direct sunlight per day h/day
efficiency System efficiency after losses %

Worked Examples

USA - Small rooftop array
  • Panel wattage: 400
  • Panel count: 10
  • Sun hours per day: 5

Result: 17.0 kWh/day

A 4 kW system in a sunny location can produce a useful amount of daily power.

UK - Compact system
  • Panel wattage: 350
  • Panel count: 8
  • Sun hours per day: 3.5

Result: 8.33 kWh/day

Lower sun hours still produce meaningful yearly energy.

How to Interpret Your Results

Range Meaning Action
Under 5 kWh/day Small system Best for partial household coverage or small loads.
5 to 20 kWh/day Typical home system Can offset a good share of household electricity use.
Over 20 kWh/day Large array Check roof space, inverter size, and grid export rules.

Frequently Asked Questions

It represents real-world losses from heat, dust, wiring, and shading.

Yes, but you should also account for battery storage and inverter losses.

Yes. The savings estimate uses your electricity price.
Planning note: This is a planning calculator. Actual solar output varies by weather, orientation, shading, and inverter losses.

References

Last reviewed: March 28, 2026