Solar Output Calculator
Solar Output: Output = kWp × peak sun hours × performance ratio × days. Methodology stated, your own inputs only.
In short
Solar Output: Output = kWp × peak sun hours × performance ratio × days. Methodology stated, your own inputs only.
Formula: Output = kWp × peak sun hours × performance ratio × days.
What this calculator does
Solar Output: Output = kWp × peak sun hours × performance ratio × days. Methodology stated, your own inputs only. Worked example, questions and limitations included.
Use it to turn Array size (DC rating), Peak sun hours per day at your site (from a solar resource map), Performance ratio / derate (your estimate or design tool), Days in the period into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this energy calculation.
Inputs and what they mean
- Array size (DC rating)
- — number value.
- Peak sun hours per day at your site (from a solar resource map)
- — number value.
- Performance ratio / derate (your estimate or design tool)
- — number value.
- Days in the period
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Methodology: simplified PVWatts-style estimate (NREL PVWatts v5 manual) — irradiance in peak sun hours times system size times a combined loss factor.
Peak sun hours and the performance ratio are site- and system-specific; none is assumed.
Use a full simulation tool for design decisions.
Output = kWp × peak sun hours × performance ratio × days.
Inputs used: Array size (DC rating), Peak sun hours per day at your site (from a solar resource map), Performance ratio / derate (your estimate or design tool), Days in the period.
Worked example
A rooftop system
- 6 × 4.5 × 0.80 = 21.6 kWh per day.
- 21.6 × 365 = 7,884 kWh.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Average day — no hour-by-hour weather or shading.
- Degradation over years is not included.
- Results are estimates built only from the figures you enter. No electricity, fuel or gas price, equipment efficiency or benchmark is built in — tariffs vary by supplier, region and time, and equipment data must come from the manufacturer. Designs and installations must be checked by a qualified professional.
- The result depends on the values you enter for this solar output calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: NREL
Last reviewed:
Common questions
Where do I get peak sun hours?
From a solar resource map or tool for your location, tilt and orientation. It varies by season.
What goes into the performance ratio?
Inverter, wiring, temperature, soiling, shading and mismatch losses. Your installer or design tool should provide it.
Is this a design guarantee?
No. It is a quick estimate; weather and shading make real output vary.
How do I use the Solar Output Calculator?
Enter the required values for Array size (DC rating), Peak sun hours per day at your site (from a solar resource map), Performance ratio / derate (your estimate or design tool), Days in the period. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Solar Output Calculator use?
Output = kWp × peak sun hours × performance ratio × days. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Solar Output Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Sources
Method based on NREL.
Cite this page
Free Calculator. (2026, October 20). Solar Output Calculator. https://freecalculator.tech/tools/solar-output-calculator
"Solar Output Calculator." Free Calculator, 20 Oct. 2026, https://freecalculator.tech/tools/solar-output-calculator.
Solar Output Calculator — Free Calculator, https://freecalculator.tech/tools/solar-output-calculator
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