During these last few weeks of hot sun, which are a welcome change from the rain of previous  few years, we have been getting calls from customers asking why the output from their solar PV panels is down, even though there is bright sun beaming down onto it.

The simple answer is solar heating!... Unlike solar thermal systems which rely on the sun's heat to do their work, solar PV works on light, and would like to stay as cool as possible. You'll notice your solar PV panels will produce as much output on a clear sunny winter's day as in the summer, even though the sun is lower in winter.

In winter your solar PV panels will be far colder, maybe almost zero degrees, which will improve their efficiency. In the summer sun, the solar PV module temperature will soar far over the Standard Test Condition (STC), rating of 25 degrees C, causing output to slump a little.

A recent example showed our office solar PV system drop off by 10% in the recent 30 degree plus days. So dont worry that a module is failing. Your system will perk up when the weather is cooler.

Photo: Wichita Renewable Energy Group

About the author: Chris Rudge is a qualified electrician who specialises in renewable energy.

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