Solar Panel Testing (3 Methods)

By the end of this article, you’ll know three different methods to test a solar panel and be able to choose the one that works best for you.

You need to know how to test your solar panels to guarantee you’re getting the appropriate wattage from them to avoid possible parasitic drains and connection issues. Working as a handyman and contractor, I have done a few installations where residents had their panels improperly installed and had half their panels working at only a portion of capacity; this is devastating considering the installation cost, another reason why it’s important to test them to make sure you get your money’s worth. 

In general, follow these three methods to test solar panels.

  1. Use a digital multimeter to test the solar panel.
  2. Test the solar panel with the solar charge controller.
  3. Use a watt meter to measure the solar panel output.

Get more details from my below article.

Before We Start

Before getting into the how-to guide, you should know a few things. First, you should know why is solar panel testing so important. Then, I’ll give you a brief introduction to three methods you will learn about.

When you test the solar panel, you can get a good idea of the power production and the efficiency of that panel. For instance, a solar panel that is rated as 100W should provide 100W in ideal conditions. But what are the ideal conditions?

Well, let’s find out.

Ideal Condition for Your Solar Panel

The following conditions should be ideal for a solar panel to produce its maximum output.

  • Peak sun hours in a day
  • Level of shading
  • Outside temperature
  • The direction of the solar panel
  • The geographical location of the panel
  • Weather condition

If the above factors are ideal for a solar panel, it will work at maximum capacity.

Why is my Solar Panel Not Working to its Full Capacity?

Assume your brand new 300W rated solar panel only produces 150W. You might get frustrated in such a situation. But don’t worry. This is an issue most people have while using a solar panel, and there are two reasons for this.

  • The solar panel is not exposed to its ideal conditions.
  • The panel might be malfunctioning due to mechanical error.

Whatever the reason, the only way to confirm the issue is through testing. That is why in this guide, I’m going to teach three methods that can help you with testing solar panels. Whether the panel is working properly or not, you should test it occasionally. It will give you a clear idea about the solar panel’s output.

Need to Know Things About These Three Tests

When testing a solar panel, you should check the panel’s output.

That means the panel’s wattage. Hence, you should measure the voltage and amperage of the solar panel. Sometimes, this voltage and amperage are more than enough to test the solar panel. In some cases, you might have to calculate the watt value. You’ll know better about that when the calculations are shown later in the article.

Method 1 – Testing Solar Panel with a Digital Multimeter

In this method. I’ll use the digital multimeter to measure open circuit voltage and short circuit current.

Step 1 – Find out the VOC and ISC

First and foremost, examine the solar panel and find the rated VOC and ISC value. I use a 100W solar panel with the following rated values for this demonstration.

Pmax= Max Power = 100W

Vmp = Operating Voltage = 17.2V

Imp = Operating Current = 5.81A

VOC = Open Circuit Voltage = 21.6V

ISC = Short Circuit Current = 6.46A

Most of the time, these values should be labeled on the solar panel, or you can find them in the instruction manual. Or get the model number and find it over the internet.

Step 2 – Set the Multimeter to Voltage Mode

Then, get the multimeter and set it to voltage mode. To set the voltage mode in the multimeter:

  1. First, connect the blackjack to the COM port.
  2. Then, connect the red jack to the voltage port.
  3. Finally, turn the dial to DC volts and turn ON the multimeter.

Step 3 – Measure the Voltage

Next, locate the negative and positive solar panel cables. Connect the multimeter’s black probe to the negative cable and the red probe to the positive cable. Then, check the reading.

Quick Tip: When the connection is completed, the multimeter probes might spark a little. This is entirely normal, and there is nothing to worry about.

As you can see, I got a 21V as open circuit voltage, and the rated value is 21.6V. So, it is safe to say that the solar panel’s voltage output is working properly.

Step 4 – Set the Multimeter to Amp Settings

Now, take the multimeter and set it to amp settings. Turn the dial to 10 amps. Also, move the red jack to the amp port.

Step 5 – Measure the Current

Then, connect the two multimeter probes to the positive and negative cables of the solar panel. Check the reading.

As you can see here, I’m getting a 5.09A reading. Even though this value is not close to the rated short circuit current value of 6.46V, it is a good result.

Solar panels only produce 70-80% of their rated power outputs. These panels only reach their maximum output in ideal conditions. So, try to take the reading under good sunlight. For instance, my second test under ideal conditions gave me a 6.01A reading.

Method 2 – Test the Solar Panel with Solar Charge Controller

solar charge controller

For this method, you’ll need a solar charge controller. If you aren’t familiar with this device, here is a simple explanation.

The solar charge controller’s main purpose is to prevent the battery from overcharging. For instance, when connecting the solar panel to the battery, you should connect it through the solar charge controller. It regulates the current and voltage.

You can use the same principle to measure the solar panel’s voltage and current. Here’s how you can do that.

Quick Tip: You’ll need a solar charge controller to measure PV current and voltage for this testing process.

Things You’ll Need

  • Solar charge controller
  • 12V battery
  • Few connector cables
  • Notebook and pen

Step 1 – Connect the Solar Charge Controller to the Battery

solar charge controller to battery

First, connect the battery to the solar charge controller.

Step 2 – Connect the Solar Panel to the Controller 

solar charge to controller

Then, connect the solar charge controller and the solar panel. Turn on the solar charge controller.

Quick Tip: The solar panel should be placed on the outside where the panel can receive direct sunlight.

Step 3 – Calculate the Amount of Watt

CITIZEN 12-digit calculator

Cycle the controller’s screen until you find the PV voltage. Note down that value. Then, follow the same process and note down the PV current. Here are the corresponding values I got from my test.

PV Voltage = 15.4V

PV Current = 5.2A

Now calculate the total watts value.

Watt = Voltage × Amperage


Output of the solar panel = 15.4 × 5.2 = 80.8 watts

As you already know, I used a 100W solar panel for this demonstration. With the second test, I got an 80.8-watt output. This value is an indication of a perfectly working solar panel.

Depending on the conditions, you might get a different final answer. For instance, you might get a 55W for a 100W rated solar panel. When that happens, do the same test in different conditions. Here are a few things you can try out.

  • Place the solar panel where sunlight can directly contact the panel.
  • If you previously initiated the test in the morning, try the second attempt at a different time (the sunlight might be more powerful than in the morning).

Method 3 – Test the Solar Panel Using a Watt Meter

A watt meter can measure the watt value directly when connected to the source. So, no calculation is needed. And you don’t have to measure the voltage and amperage separately. But you’ll need a solar charge controller for this test.

Quick Tip: Some recognized this device as the power meter.

Things You’ll Need

  • Solar charge controller
  • 12V battery
  • Watt meter
  • Few connector cables

Step 1 – Connect the Solar Charge Controller to the Battery

First, take the solar charge controller and connect it to the 12V battery. Use a connector cable for this.

Step 2 – Connect the Watt Meter to the Solar Charge Controller

Then, connect the watt meter to the solar charge controller’s adapter cables. After connecting, the watt meter should be in-line with the controller. In other words, two cables that connect with the solar panel should connect to the watt meter first. If you remember, the controller’s cables were directly connected to the solar panel in the previous test. But don’t do it here.

Step 3 – Connect the Solar Panel

Now, place the solar panel outside and connect it to the watt meter using connector cables.

Step 4 – Measure Solar Panel Output

Next, check the reading on the watt meter. For this test, I got a reading of 53.7 watts. Considering the sunlight, this is a pretty decent output.

What We Learned So Far

After checking your solar panel with one of the above methods, you’ll get a good idea of its performance. But remember, all three tests are different from each other.

In the first one, we measured the voltage and current of the solar panel. The second method is based on the solar charge controller. Lastly, the third one uses a solar charge controller and watt meter.

Which Method is Most Suitable?

Well, that depends on your situation. For some, finding a watt meter won’t be an easy task. For instance, some people might not have heard of a watt meter and have no idea how to use it.

On the other hand, finding a digital multimeter or solar charge controller is not that difficult. So, I would say 1st and 2nd methods are the best. So, you’ll be better off with 1st and 2nd methods.

Why is Solar Panel Testing So Important?

Even though I mentioned this topic at the beginning of the article, I’m hoping to discuss this matter in detail. So, here are a few reasons solar panel testing is so important.

To Recognize Physical Damage

Most of the time, the solar panel will be outside. Hence, it might get damaged without even you knowing it. For instance, Small animals such as rodents might chew the exposed cables. Or birds might drop things onto the panel.

Testing is the best way to check this. Whenever you bring a new solar panel, test it on the first run. That way, you’ll know the panel is working properly. If you detect any issues with the output, test the solar panel again. Then, compare the recent results with the first test results.

To Identify the Corroded Parts

Don’t be surprised; even solar panels can get corroded. It doesn’t matter if you brought the best anti-corrosive solar panel in the world. With time, it might get corroded. This process can impact the performance of the solar panel significantly. So, remember to check it at regular intervals.

To Identify Faulty Devices

In some instances, you might get a faulty solar panel. The above three tests can be handy for such a situation. As I mentioned earlier, it would be best if you could check the solar panel immediately after buying.

To Avoid Fire Dangers

man installing solar panel at the rooftop
Video | jwsolarusa

Most often, solar panels will be installed on the rooftops. Hence, they will absorb a large amount of sunlight during the day. Because of that, the solar panels might overheat and start a fire due to faults in electricity. So, to avoid such situations, test the solar panel regularly.

Warranty and Regular Maintenance

Due to high usage and performance, these solar panels need to be maintained regularly. Most manufacturers provide these services for free during the warranty period. However, to get these benefits, you’ll have to test the solar panel from time to time. Otherwise, the warranty might become null and void. (1)


Can I Test My Solar Panel on a Cloudy Day?

Yes, you can. But this is not a method I would recommend. Because of the clouds, the panel won’t get sunlight properly. So, the solar panel won’t be able to display its full performance. If you test a solar panel on a cloudy day, the results might mislead you to think the solar panel is malfunctioning. But in truth, the panel is working properly. The issue lies in the low sunlight. A clear and sunny day is the best day to test your solar panel. (2)

I Have a 150W Rated Solar Panel. But It shows Only 110W in My Watt Meter. Is My Solar Panel Working Properly?

Yes, there is nothing wrong with your solar panel. Most solar panels give an output of 70-80% of their rated output, so if we did the calculations.

(110 ÷ 150) × 100% = 73.3333%

Hence, your solar panel is just fine. If you need more output, position the solar panel in ideal conditions. For instance, a place with better sunlight might do the trick. Or try changing the angle of the solar panel. Then, measure the solar panel output.

Can I Use a Digital Multimeter to Test My Solar Panel?

Yes, you can. Using a multimeter is one of the easiest ways to test the solar panel. Check the voltage and the current and compare them with the rated values.

Take a look at some of our related articles below.

(1) warranty period –
(2) clouds –

Video References




The Campervan Builder

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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