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How to Test a Solar Panel with a Multimeter? (Voltage, Current)

Written by Eddie B. Robinson / Checked by Justin Tucker

how to test a solar panel with a multimeter

Have you ever wondered how much electricity your solar panels are generating for your home or vehicle? Determining your solar system’s actual power output is easy if you know how to test a solar panel with a multimeter.

Multimeters are versatile devices that help you determine the operational characteristics of any electronic device, including solar panels. Knowing your solar panel’s power output lets you determine how to optimize its yield.

If you want to learn how to check your solar panel’s output, I prepared this article for you.


Things You Will Need For This Tutorial


Aside from a good-quality multimeter, you will also need the following things to carry out the steps in this tutorial.

Understanding of Basic Electrical Terms

We are not going to discuss technical terms, except for three essential electrical concepts. Your understanding of these concepts will help you gain a better perspective on how to use a multimeter. It will help you assess different electrical items, not only your solar system.

The first concept you must learn is “voltage.” Your solar panel’s voltage reflects the pressure exerted by the electrons on a conducting material. You can think of it in terms of water pressure. The greater the water pressure, the more powerful and faster the water travels through the pipe.

It is the same thing in an electrical circuit. The voltage defines the strength of electrons’ passage through the system.

The second concept everyone must understand is “ampere.” Whereas voltage is the strength of electrons, amperes refer to the number of electrons passing through the system. We know this as a circuit’s electric current.

The third concept is the product of a solar panel’s voltage and amperes. Many of us refer to ”watts” as the power output of any given electronic device.

Knowledge of Multimeter Types

Multimeters can be digital or analog, which refers to how the device displays or presents the test readings.

Analog multimeters look like a conventional weighing scale with a needle pointing to markings on the unit’s measurement plate. While inexpensive, they are not suitable for people with diminished visual acuity because determining where the needle points can lead to inaccurate readings.

Digital multimeters offer an easy-to-read display. Even if the readings fluctuate, you should still be able to read the number on display. Digital multimeters can be fluke, clamp, or auto-ranging.

Fluke multimeters can test different parameters, including voltage, electrical resistance, duty circles, pressure, temperature, frequency, and humidity.

Auto-ranging multimeters are the easiest to use, making them suitable for absolute newbies. These devices feature few controls, keeping their user interface simple.

Clamp multimeters are specific for measuring amperes in a circuit. If you use the probes, they can measure the voltage.

Understanding of Factors Affecting Solar Panel Output

Manufacturers provide technical information about their solar panels, including wattage, amperes, and voltage.

However, these figures represent the ideal circumstances, such as a 25-degree Celsius environmental temperature and non-deteriorating solar panels.

Your solar panel’s ability to convert solar energy to electricity is a crucial factor. No solar cell can convert 100% of absorbed light energy, generating only 20% at most.

Different locations also have varying amounts of sunlight hitting the ground surface, affecting the solar panel’s power output. For example, solar panels in colder regions have a lower electrical yield than systems in warmer locations.

There is also the effect of wear on solar panel efficiency. Solar panels deteriorate over time, reducing their power output by as much as 0.8% annually. Some high-end products have an output reduction of only 0.3%.

Steps to Test a Solar Panel with a Multimeter (Voltage)


Step 1. Prepare your solar panel.

Testing solar panels for their voltage requires you to place the solar panels under the sun. It would also be best to conduct the testing on a bright, sunny day without clouds or an overcast sky.

Pro Tip: Clean your solar panel’s surface with a soft cloth or microfiber towel before testing. Dust can affect the solar cells’ ability to absorb light energy, giving you false readings.

Step 2. Set your multimeter.

Get your multimeter and turn the knob to “DC Volts.” Set the multimeter to its highest possible voltage setting to get a more accurate solar panel voltage reading.

For example, if your multimeter can read up to 200 volts, you must set it to this level even though your solar panel only has a 20-volt rating.

Step 3. Take a reading.

Connect the black probe to the multimeter’s COM port and the red probe to the V/Ω/mA port. Touch the black probe on the solar panel’s negative terminal and the red probe on the positive lead.

Read the number on display. It is wise to remember that old solar panels can show a slightly lower voltage reading than their rated value. You might also not get a whole-number reading.

Here is a short yet informative video from Tech2TechTelugu about using a multimeter to test solar panel voltage and amps.

Steps To Testing A Solar Panel’s Electric Current

Step 1. Prepare your solar panels.

Dirty solar panels can prevent your system from optimally collecting sunlight. That is why you should always clean the solar cells’ surface before you conduct solar panel testing. No one wants an inaccurate or unreliable reading.


Moreover, always perform the test under direct sunlight without an overcast sky. Testing in cloudy weather will still yield results, albeit inaccurate.

Step 2. Set up your multimeter.

Turn the multimeter’s knob to “DC Amps” to measure your solar panel’s electric current. Set the multimeter’s amperage sensitivity a little higher than your solar panel’s amperage rating.


If your solar panel has a rated electric current of 20 amperes, you may want to set the multimeter to 22 or 25 amperes to avoid blowing your fuse.

Step 3. Test your solar panel’s current.

Plug the black probe into the multimeter’s COM port and the red probe to the port named 10A.


Touch the black probe on the solar panel’s negative lead and the red probe on the positive terminal.

Read whatever is on the display.

You can observe the same steps to test a 12 volt solar panel; just ensure the right connection of the multimeter probes to the solar panel’s terminals.

Steps To Measuring A Solar Panel’s Power Output

Step 1. Determine your solar panel’s current and voltage.

You can use the steps outlined in the preceding sections to measure solar panel output with multimeter.

Your solar panel’s output is the product of the amperes and voltage. Thus, a 12-volt, 20-ampere solar panel will produce a theoretical power output of 240 watts (12×20).

However, we all know a solar panel’s actual output is often less than its ideal or rated power. That is why we are also going to determine its efficiency.

Step 2. Determine your solar panel’s ideal efficiency.

Find out the incident radiation flux (IRF) in your area, which is the amount of sunlight hitting the Earth’s surface. You can check this information from your local solar organization or the US Geological Survey.

Multiply the IRF value (in watts per square meter) by your solar panel’s total surface area (also in square meters).

For example, if your solar panel is 2 sqm and the local IRF is 1,000 watts/sqm, you will get 2,000 watts.

Check your solar panel’s power rating and divide it by the computed watts value.

For instance, if you have a 400-watt solar panel, the solar panel efficiency is 0.20 or 20% (400 watts divided by 2,000 watts).

Step 3. Determine your solar panel’s operating efficiency.

Measure your solar panel’s surface temperature (in Celsius). Subtract 25 degrees Celsius from your solar panel’s temperature reading.

For example, if your solar panel’s temperature is 35 degrees Celsius, you should get a final value of 10 degrees Celsius (35oC minus 25oC).

Next, multiply 10 degrees Celsius by the Pmax temperature coefficient. You can check the Pmax value from your solar panel manufacturer.

Let us say your solar panel has a Pmax value of minus 0.45% per degree Celsius. Our computed value will be minus 4.5%.

Subtract this value from your solar panel’s ideal efficiency (20%) to obtain an operating efficiency of 15.5%.

Step 4. Adjust for solar panel degradation.

Like other things, solar panels degrade over time. The National Renewable Energy Laboratory says that solar panels lose 0.8 percent of their output every year.

Suppose your solar panel produces 100% of its rated power output when brand new. After one year, this solar panel will only be able to yield 99.2% power. Within a decade, the figure will only be 92%.

In our example, let us say you already have a 4-year old solar panel. With our computed operating efficiency of 15.5%, we can subtract 3.2% (0.8 x 4 years) to get an efficiency rating of 12.3%.


Learning how to test a solar panel with a multimeter lets you evaluate your solar system’s actual operating performance. You can then take the necessary steps to optimize your solar energy-gathering device or replace it with a new system.

Did you find this tutorial meaningful and helpful? If so, you might want to share it with your colleagues, acquaintances, and friends. You can also shoot me any questions you may have or share your thoughts about this article.

Furthermore, if you learn more about other tips and tricks, I prepared these guides for you. Such as guide make a homemade solar panel with household items, guide mount solar panels on a roof, and ways to use solar panels during a power outage. Hope you will find helpful knowledge for yourself.

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