Solar Panel Output Estimator — Free & Instant

What this calculator does

Estimated daily and yearly generation from system size and local peak sun hours, and the share of your usage it covers. Fill in the fields in the calculator above and the results update as you type — nothing is sent anywhere, and there is no sign-up or paywall.

Most people reach for this after a quick mental estimate has already gone wrong: the numbers are close enough to feel right, but the decision behind them is worth real money or real time. Working it out properly takes seconds here.

How to use the tool above

1. Enter your own numbers in these fields: system size, peak sun hours per day, system losses, daily household use.
2. Read Daily generation first — that is the figure most people came for.
3. Change one field at a time to see how sensitive the outcome is. That single habit is what turns a calculator into a decision tool.
4. Note the result somewhere before you compare options, so you are comparing like with like.

The method, in plain words

• Daily generation = system size × peak sun hours per day × (1 - system losses ÷ 100)
• Yearly generation = system size × peak sun hours per day × (1 - system losses ÷ 100) × 365
• Share of usage covered = system size × peak sun hours per day × (1 - system losses ÷ 100) ÷ the larger of (daily household use, 0.000001) × 100

Nothing here is hidden: the same arithmetic runs in the tool above, so you can reproduce any number by hand if you want to check it.

Worked example 1

What you enter

• System size: 5.00 kW
• Peak sun hours per day: 4.50
• System losses: 15 %
• Daily household use: 22 kWh

What you get

• Daily generation: 19.13 kWh
• Yearly generation: 6,981 kWh
• Share of usage covered: 86.9 %

Worked example 2 — one input doubled

The fastest way to understand any calculation is to move a single input and watch what happens.

What you enter

• System size: 10.00 kW
• Peak sun hours per day: 4.50
• System losses: 15 %
• Daily household use: 22 kWh

What you get

• Daily generation: 38.25 kWh
• Yearly generation: 13,961 kWh
• Share of usage covered: 173.9 %

Comparing the two runs tells you which input actually drives the outcome — and therefore which one is worth negotiating, adjusting or planning around.

Common mistakes to avoid

• Mixing time periods. Monthly, weekly and annual figures cannot be compared until they are converted to the same basis.
• Rounding too early. Round only the final answer; rounding an input first quietly shifts everything after it.
• Forgetting what the number excludes. A clean calculation still leaves out fees, taxes or extras that are specific to your situation — add them separately.
• Treating a single run as the answer. Run a slightly pessimistic version too, then plan against that.

Every figure here is an estimate for planning purposes, not professional financial, tax or legal advice. Confirm anything that affects a contract, a filing or a loan with a qualified professional.

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