# Solar Output Calculator

> Solar Output: Output = kWp × peak sun hours × performance ratio × days. Methodology stated, your own inputs only.

Page: https://freecalculator.tech/tools/solar-output-calculator
Last reviewed: 2026-10-20

## Formula

Output = kWp × peak sun hours × performance ratio × days.

- 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.

## Inputs

- 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 kWp, 4.5 peak sun hours, 80% performance ratio, a year.
1. 6 × 4.5 × 0.80 = 21.6 kWh per day.
2. 21.6 × 365 = 7,884 kWh.

## 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.

## 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.

## Sources

- NREL — https://www.nrel.gov/docs/fy14osti/62641.pdf

## Cite this page

- APA: Free Calculator. (2026, October 20). Solar Output Calculator. https://freecalculator.tech/tools/solar-output-calculator
- MLA: "Solar Output Calculator." Free Calculator, 20 Oct. 2026, https://freecalculator.tech/tools/solar-output-calculator.
- Link: Solar Output Calculator — Free Calculator, https://freecalculator.tech/tools/solar-output-calculator