Testing the Output Voltage of your Solar Panel

Tips & Articles | January 5, 2017

How do I know it is working?

A lot of neophyte solar enthusiasts wonder how they can verify if their solar panel is working. While checking if your 12V battery can run devices or vehicles is a pretty good sign that everything is well, this doesn’t always tell you how the panel is doing. The fact is that solar panels are passive energy gatherers and we can’t tell much just looking at or touching them. The best way to check for signs of life is to measure a solar panel’s voltage.

If you’d like to learn more about what voltage is, we’ll let you look up Ohm’s law in order to keep things short and sweet in this article.

Voltage is pretty easy to measure and it’s the best indicator we have to see if a panel has output. We can do this with the help of an instrument called a voltmeter. A voltmeter can often be part of a multi-meter, a tool that allows to read other things like current and resistance.

Dreaded by some and misunderstood by others, the voltmeter can actually be your best friend when entering the world of 12V living and solar power. You can always check if your solar panels are healthy, as well as getting more detailed information about the status of your battery.

Setting the voltmeter

We’ll be using a multi-meter, which is the tool most people would own or have access to through their local electrical shop.
To test a 12V panel, meters should always be set to the DC voltage area, which usually identified by the symbol below.
Voltmeter symbol
You want to choose a voltage range capable of displaying the maximum possible voltage of the panel in open circuit, that is, when not connected to the battery or charge controller.

A range of 3 digits is usually the best, such as 100 V or 200 V. Don’t choose 20 Volts or less as you may fail to see correctly your panel’s output.

Make sure your multi-meter probes are connected in the right location. The negative (black) probe connects to the port labeled COM and the red (positive) probe connects to the port usually labelled V/Ω/mA, etc.

Open-circuit voltage is to be measured directly from the solar panel’s lead wires. This means that the panel is not connected to either a battery or a charge controller. If you have added extra wire or an extension to your lead wires, you can measure the voltage at the end of these.

Depending on your solar panel size and type, your lead wires can end on either bare wires or a Quick-Connect Plug as the ones as the ones shown below.

Bare wire

On bare wires (A), red identifies the positive lead and black the negative lead. On a Quick-Connect plug(B) coming from the solar panel, the covered (female) part is the positive lead and the exposed (male) prong is the negative.

Testing the Voltage

Simply touch the solar panel leads with the multi-meter probes, matching their corresponding polarity (red to red, black to black).

Open-circuit voltage can vary depending on your solar panel, but the readings we are usually looking for are in the range of 15 to 23V. Some exceptions may apply based on panel type. Consult your solar panel’s documentation for information or contact our technical support desk.

Voltmeter testing to solar panel