October 5, 2021

How to measure solar panel output

There’s a quick, non-technical way to see if your solar panels are producing maximum energy.

Solar panels on the rooftop of an Australian suburban home producing optimal energy.

Higher efficiency panels generate more energy.

Given your solar panels’ efficiency and production directly impacts your access to clean electricity, it’s smart to measure your solar panel output from time to time.

With minimal monitoring and maintenance, you can rest assured that your home’s solar system output is always optimised for efficiency.

Electricians use amp meters to measure the amp output of solar panels. A quicker method is to use your current electricity bill and a calculator.

Key measurement

The number of watts a solar panel is designed to produce might be anywhere between 250 and 370 watts – this number gives an approximation of how many watts a solar panel is able to produce in optimal conditions. So a 300-watt solar panel should produce 300 watts of electricity per hour that it’s exposed to sunlight.

Of course, conditions are rarely ideal. There are variables to take into account

  • Shading from nearby trees and other buildings.
  • Drifting cloud cover throughout the day.
  • Build-up of dirt, dust and grime.
  • Amount of seasonal sunshine.
  • Quality of solar panels.
  • Direction of solar panels.


These factors can drastically affect your solar panels’ efficiency.

Wattage determines how much power each solar panel is capable of generating under ideal conditions. Efficiency refers to how much solar radiation the solar panel is actually capable of converting into useable electricity.

If your solar panels have an efficiency rating of 34 percent, this means that 34 percent of the sunlight that’s reaching your solar panels is actually absorbed and transformed into electricity that you can use to power your home.

How to measure your solar panels’ efficiency

There is a straightforward formula that allows you to quickly measure what sort of output you should be getting from your solar panels.

Multiply the combined wattage of your solar panels by the average hours of sunlight where you live, and then remove 25 percent from this total sum. The resulting figure is your estimated daily watt-hours.

For example, if your solar panels are 330 watts and they’re exposed to four hours of direct sunlight each day. 330 x 4 = 1,320. The 25 percent deduction is for all those variables that disrupt some of the solar radiation from being absorbed, so the answer is 990 daily watt-hours (or 0.99 kilowatt-hours).

Refer to your last electricity bill and compare the two figures to determine how efficient your solar panels’ actual output is versus what they’re capable of.

If the real output is considerably lower than what it should be, consider the variables listed above to improve efficiency and output.

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