How much Solar will I produce on a Cloudy Day?

Published: April 10, 2025

Overview

Solar panel performance during overcast conditions depends on geographic location and seasonal variations rather than constant peak efficiency.

Average Sunlight Hours

For each region, the amount of sunlight hitting the ground varies, particularly during winter months. The example provided notes that Queenstown experiences approximately 1.7 kWh per square meter of sunlight on its shortest day -- a metric essential for estimating cloudy-day performance.

Practical Example

A 100-watt flat-mounted solar panel can generate approximately 170 watt-hours daily in Queenstown even under cloud cover, according to average sunlight hours for that location.

Recommended Tools

The article recommends the NIWA Solar View tool, which estimates the solar energy that can be collected by solar at a given address, panel direction and slope within New Zealand. The tool combines local landscape imagery with hourly irradiance data from climate stations with at least 10 years of measurements.

Conclusion

LUX Solar's calculator provides rough winter capacity estimates, while the NIWA Solar View tool offers greater precision for detailed planning needs.

Key Takeaway: Solar output fluctuates based on cloud cover, temperature, season, and location -- making regional sunlight data crucial for realistic performance expectations.