How are payback and 25-year savings calculated?

From your bill the calculator finds annual usage and the system size needed, estimates cost and production, then models 25 years with rising tariffs and panel degradation. Self-consumed energy is valued at your price, exported surplus at the feed-in price. Payback is the year cumulative savings cover the cost.

What is the 0.8 factor?

The performance ratio — a correction for real-world losses: inverter, panel heat, dirt and wiring. Actual output is usually 75–85% of the ideal.

What sun hours should I enter?

“Peak sun hours” is the equivalent of full-sun hours per day. It averages 3–5 by region — closer to 5 in sunny latitudes, nearer 3 further north.

Does it include rebates?

Yes — “more parameters” has a rebate field: it's subtracted from the cost, and payback is calculated with the incentive included.

What currency does it use?

Any — it works with numbers. Enter the bill, price and install cost in the same currency and the result is in that currency.

Solar panel payback calculator

Solar panel payback calculator: enter your electricity bill to see the payback period, 25-year savings, the system size you need and the CO₂ you cut. Open “more parameters” for a detailed projection.

Runs in your browser — nothing is uploaded to a server

Monthly electricity bill

Price per kWh

Peak sun hours per day

Around 3–5 depending on your region.

How to use it

1

Enter your electricity bill

What you pay for electricity in an average month — that alone is enough for an estimate.

2

Refine price and sun

Your price per kWh from the bill and the peak sun hours per day for your region (3–5 on average).

3

Open “more parameters”

Install price, rebate, rate rise and degradation — for a detailed 25-year projection with a chart and CO₂ saved.

Why it's useful

The real question before going solar isn't “how much do panels cost” but “when do they pay off and what do they earn over their life.” That depends on your usage, install price and tariff — hard to hold in your head, and a rough guess can be years off.

This calculator starts from what you know — your electricity bill — and derives the system size, cost and production for you. Then it models not one point but 25 years, with rising tariffs and panel degradation, showing payback, total savings and CO₂ cut.

FAQ

Just your electricity bill and price per kWh — both on your statement. Everything else (install price, rebate, rate rise) can be set in “more parameters” or left at sensible defaults.

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