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How To Test Solar Panels | A Comprehensive Guide

A comprehensive guide on how to test solar panels

Switching to solar can save money. Lots of it. But they cost a lot, too, so it only makes sense that you know how to make sure they’re working properly. Well, look no further because I’m here to teach you how to test solar panels.

More details are below but, before anything else, you’ll need a multimeter and a clamp meter. You’ll find these at your local hardware store. They’re also pretty cheap, so don’t worry about taking a mortgage out of your home.

That being said, listed below are the topics I’m covering. Feel free to tap on any of the bullets if you want to skip sections. Otherwise, let’s get to testing solar panels!

Method #1: Using a multimeter

What does it measure and why is it important?

You can use a multimeter to measure your solar panel’s output of open circuit voltage (Voc) and short circuit current (Isc).

It’s important to check your Voc because it tells you how many solar panels you can connect to your inverter without damaging it.

Your Isc, on the other hand, is somewhat the opposite. It tells you the maximum current your module can handle when paired with your inverter. Knowing this allows you to integrate fuses or circuit breakers where necessary to protect your system.

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How to test solar panels with a multimeter

How To Test Solar Panels With A Multimeter
An informative visual guide demonstrating the procedure for testing solar panels using a multimeter.

Step 1: Check the spec of your solar panel.

Specifically, look for open circuit voltage and short circuit current (or Voc and Isc). You can find this at the back of your module or the manufacturer’s website.

Step 2: Whip out your multimeter and plug the black probe into the COM terminal

“COM” here stands for common. The black color is just to signify that it’s meant to connect to your module’s ground or negative cable.

Step 3: Set your dial and red probe, depending on what you want to measure.

  • For your multimeter to measure Voc, set your dial to the amp setting – the setting with a V and a solid line over a dotted line. Plug in your red probe to the voltage terminal – it’s the terminal with the VΩ symbol.
  • For your multimeter to measure Isc, set your dial to the amp setting – it’s the setting with an A and a solid line over a dotted line. Plug in your red probe to the amperage terminal – it’s the terminal that says 10A or 10ADC.

Step 4: Locate your solar panel’s positive and negative cables.

Differentiating between the two should be easy. The positive cable will generally be the one with the red band around it. The negative cable will almost always be pure black.

That being said, make sure these cables aren’t connected to your system.

Step 5: Solar panel testing.

  • Insert your multimeter’s red probe into your solar panel’s positive cable. Likewise, insert the black probe into the negative cable.
  • Check the number shown on your multimeter. If it’s close to your solar panels’ specs, you’re good to go. They don’t have to be exactly the same so if you’re off a few decimals, it doesn’t mean your solar panel is broken.
  • P.S.: There might be a small spark when you test for Isc. That’s perfectly normal.

Method #2: Using a clamp meter

What does it measure and why is it important?

A clamp meter measures the current (or amperes, “amps”) of electricity flowing through your circuit.

This is important to test particularly after you’ve had your solar panels installed because the number you’ll see on this test is what you should expect to see on your solar charge controller.

How to test solar panels with a clamp meter

Step 1: Check your solar panels’ Imp

Imp stands for optimum operating current, maximum operating current, current at maximum output, or some other phrase that means the same thing. Manufacturers word these things differently but Imp is the common ground.

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Step 2: Make sure your clamp meter tests DC

Some amp meters will only test AC, so make sure yours is capable of testing DC current as well.

After that, just switch your clamp meter to the DC current mode that’s within (or closer to) the range of your solar panels’ rated Imp. A bit confusing? Here are a couple of examples.

  • Scene #1: Your clamp meter has modes that measure 60A or 600A. The spec sheet of your solar panel says your Imp should be at 9A.
  • What mode you should choose: The 60A mode is the one you choose because it’s the closest option, and 9A is well within 60A.
  • Scene #2: Your clamp meter has modes that measure 60A or 600A. The spec sheet of your solar panel says your Imp should be at 65A (or any number higher than 60, really).
  • What mode you should choose: 600A now becomes the correct option because 65A is outside the range of your clamp meter’s 60A mode.

Just a couple of notes before moving on to the next step:

  • Most clamp meters will only give you 2 DC modes: A lower current and a higher current (e.g. 60A and 600A, or 20A and 400A).
  • Most household solar panels have Imps well below 60A. So, you might not ever have to choose the higher DC mode.

Step 3: Measure the Imp of your solar panels

Simply press the trigger that opens the clamps, put one of the cables of your solar panel inside, and then release the trigger to close the clamp.

Compare the number shown on your clamp meter’s screen to your solar panel’s rated Imp. If it’s close, everything should be fine. Again, the numbers don’t have to be perfectly the same. A few decimals off doesn’t mean your solar panels are broken.

Also, you might also read a negative number on your clamp meter’s screen. That’s perfectly normal, too. Just turn your clamp meter the other way then measure again.

What if my solar panels are faulty?

Good question. After testing your solar panels and you find the number just don’t add up, there may be a couple of reasons for it:

  • Maybe your solar panels aren’t receiving direct sunlight. Shade, even if it’s just a thin line, can cause significant reductions in solar panel power output. The same can be said for dirty modules. Either way, try testing your solar panels again on a sunny day.
  • Maybe your solar panels are physically damaged.  Check for cracks, discolorations, or anything else that’s out of the ordinary . If you find any, that could be why your solar panel output isn’t where it should be.
  • Maybe it’s your cables. Are they loose, frayed, or anything else that indicates damage? If so, then yes, it could be your cables that need fixing; not your solar panels.
  • Maybe it’s your inverter. Inverters generally have shorter lifespans than solar panels. So, in most cases, it’s the inverter that’s causing problems; not the modules.

In any case, the best way to handle faulty solar panels is to either contact your installer or manufacturer. Solar systems have product and performance warranties so if yours is still covered, you should be fine.

Not to mention, your home insurance covers your solar panels as well. If necessary, contact your provider as well.

For further reading: Our complete guide to insurance for solar panels

FAQs:

How do I know if my solar panels are working properly?

You’ll know if your solar panels are working correctly if they’re outputting what they’re supposed to. Or close to that, at least. So if you notice a change in power output, dust off your multimeter and get to testing. Or, better yet, leave that to a professional (for safety and accuracy purposes, of course).

How to read a smart meter with solar panels

The easy way to read a smart meter is to use the app that’s connected to your solar inverter. If you want readings from the actual meter, though, you’ll need to find the scroll button and scan through the displays until you find what you’re looking for.

For further reading: Our full guide to reading smart meters

Can you test a solar panel without sunlight?

Technically, yes, you can test solar panels without sunlight. Testing your solar panels with artificial light sources isn’t ideal, though, as they’re not nearly as powerful as the sun. This way of testing will only be enough to confirm that your solar panels are working but it won’t test performance.

Conclusion

Knowing how to check if solar panels are working is a crucial skill to have, especially considering that these things are hefty investments. It’s even more important if you installed, or are planning to install your solar panels yourself.

That being said, I do recommend having your solar system installed by a professional. This grants you access to thousands of dollars in rebates, as well as the security that comes with warranties.

Now, if you don’t have an installer yet, we have a network of pre-vetted ones that can help. We can get you 3 FREE quotes from them right away. All you need to do is ask.