Solar Geometry
Solar Annual Yield Estimate Calculator
Estimate annual and monthly generation from a system
Updated July 12, 2026 · Live
What this tool does
Estimates annual and monthly solar generation from system size, local sun hours, losses and a tilt derate.
Enter system size, peak sun hours, losses and a tilt derate; the calculator returns estimated annual generation and the monthly average.
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Formula Used
How the solar annual yield estimate works
Annual generation is the system size multiplied by peak sun hours and 365 days, then reduced by the system losses and the tilt-and-orientation derate. The monthly figure is the annual total divided by twelve, and the specific yield — kWh per kWp per year — lets you compare this site with published figures for your region.
What you enter
Enter system size, peak sun hours, losses and a tilt derate; the calculator returns estimated annual generation and the monthly average. Every field is editable, and the result recalculates the moment you change a value.
Reading the result
The annual kWh is what feeds a payback or cost-per-kWh calculation. Because it depends on your own sun-hours figure, it is only as good as that input — use a local value, not a national average.
Safe by design
This calculator does the arithmetic of sizing — quantities, geometry and cost. It deliberately stops at the line a certified installer must sign off. It will never tell you a cable or fuse size, an earthing arrangement, a battery charge voltage, or a roof structural load: those are regulated calculations where a wrong number causes fire, electrocution or collapse. All electrical work must be carried out by a qualified, certified installer, and this page is not an installation guide.
Assumptions and limits
Nothing time-sensitive is baked in. Electricity prices, export tariffs and local peak sun hours all change and differ by location, so the calculator asks you to enter your own figures rather than embedding a database that would silently go stale. Real output varies month to month with weather and sun height; this is a flat annual average. Panel output also degrades slowly over decades, which a single-year estimate does not show.
Using it with the rest of BuildMetricLab
This calculator is one step in planning a system. Pair it with the other solar sizing, geometry and cost tools to go from an energy figure to a panel count, a layout and a costed bill of materials. Every BuildMetricLab tool runs entirely in your browser — no sign-up, nothing sent to a server, and the formula is shown on the page so the maths can be audited.
Sources & methodology
Estimates annual and monthly solar generation from system size, local sun hours, losses and a tilt derate. Every result is calculated from the values you enter, all inputs are editable, and no time-sensitive prices or tariffs are embedded.
Frequently asked questions
What is specific yield?
Specific yield is annual generation divided by system size, in kWh per kWp per year. It lets you compare your estimate against published figures for your region.
Where do I get peak sun hours?
From a local solar resource map or a neighbour’s monitored system. Peak sun hours vary by location — typical daily figures are 2–3 in northern Europe, 4–5 in southern Europe and much of the US, and 5–6 in India and the Middle East. Use your own local value.
Why apply a tilt derate?
A roof that is not at the ideal angle or facing generates a little less than a perfectly oriented array. The derate captures that shortfall.
Is annual output steady month to month?
No. Generation is far higher in summer than winter. This tool gives an annual total and a flat monthly average, not a seasonal profile.
Spotted something off?
Calculations or display — let us know.