How to Test a Solar Panel Output

With the different type of Solar Panels on the market these days, performance and efficiency is the practical way of comparison between them. Like everything else, some types are better than others or get older faster. Solar Panels can be tested for performance and efficiency easily to check them one at a time and find which one is not working in an array of Solar Panels you use. How Do You Test a Solar Panel Output?

  • Check each Solar Panel
  • Use Volt Meter
  • Open Junction Box on the back of Panel
  • Find Pos. & Neg. terminals
  • Connect the Neg. & Pos. leads of the Volt Meter to terminals in the Junction Box
  • Use correct Dial Settings on Meter
  • Check Volts & Amps Output readings of the Solar Panel
  • Compare results to specs on label


There are numerous ways for a Solar Panel to lose efficiency and even stop working. UV Degradations, current leakage on the edges of the Solar Panel, Thermal Cycling are just a few and they can be deficiencies right out of the box that you can find by using this simple technique before you install it or find out the hard way.  


Solar Panel Efficiency 2020

What is important to understand when checking the efficiency of a Solar Panel is that the efficiency of an individual solar cell does not equate to the efficiency of solar panels modules as a system. While solar panel efficiency today is generally around 15-27%, solar cell efficiency can reach 42% in some cases. The best way to check for the efficiency of a panel is to do it on-site and midday with the panel as clean as possible.

Solar panels are normally able to process the average 15% to 22% of the Sun into usable energy, depending on factors like placement, orientation, weather conditions, and similar. The amount of sunlight that solar panel systems are able to convert into actual electricity is called Performance, and the outcome determines the solar panel Efficiency which will decrease over time. In a lab setting everything including temperature is controlled.

That is why credible manufactures will label and certified their Solar Panels because under normal conditions Solar Panels will experience these types of conditions in most parts of any country.

The Panels that reach 40% or higher are typically tested under laboratory conditions.


There are numerous types of solar panels. The most common types of solar panels are:

  • Monocrystalline solar panels- Monocrystalline used with the finest material mainly the purest type of silicon its process creates a long Rod. The Rod is then cut into wafers that make solar cells. Monocrystalline Solar Panels are known to deliver the highest rating and efficiency of other types of panels. Today’s monocrystalline solar panel efficiency stands at a solid  22-27%. You can recognize a monocrystalline type panel by its rounded edge and the dark color.
  • Polycrystalline solar panels-Solar panels made of polycrystalline solar panels, also called multi-crystalline cells are slightly less efficient than those made up of monocrystalline solar cells. In its production, the silicone used is not grown as a single cell but as a block of crystals. The blocks are then cut into wafers to produce individual cells. Today’s polycrystalline solar panel efficiency stands at 15-22%. You can recognize a polycrystalline solar panel by the square cut and blue speckled color.
  • Thin-film solar panels-Production of this kind of panels is less complex, using cheaper materials thus their output is 5% less than monocrystalline solar panel efficiency. Normally, thin-film cells deliver between 15-22% of solar panel efficiency. They are flexible panels used in large projects.

How to Calculate Solar Panel Output

Your Solar Panel is made to capture and harvest a certain amount of Watts from the sun, but in actuality in the environment and not in a test setting won’t be able to do that. That’s where those variables come in. But a solar panel efficiency number is a simple gauge of how many watts your solar panel is capable of producing in ideal conditions. The variable may take away from the efficiency or may even boost it. You may live in states in the US that get up to 7-8 hours per/day or in states that get 4-5 hours in Winter. 

The area around your rooftop solar panel system can also change your efficiency numbers. The most common environmental factors that can subdue efficiency are:

  • Shading from nearby trees or other buildings
  • Excessive cloud coverage
  • Excessive dirt, dust, and pollution
  • Thick layers of snow

Factors that take away from your Solar Panel’s Efficiency no matter if it’s on your Off-Grid Log Cabin or your Smart Tent at a Campsite are:

  • Your solar panels’ efficiency
  • Location how much sunlight shines on your solar panels
  • Which direction your solar panels are facing

There are other variables that can affect the output of the number as well, but the three above are the main contributors are the ones above. Just taking the Total output of your Solar System’s Panel and say a simple 300 Watt two Monocrystalline portable system and multiplying it by average efficiency.  300 x .27 x hrs/sunlight = 81 watts. Then factor in other variables like hours of direct sunlight rain or snow and you’ll get a ballpark measurement.

To narrow that down on bigger stationary systems like you would have on a roof for your home you can use 75% for variables that may come into play (not necessary on the small portable smaller systems) where you have complete access to cleaning and directing them by hand.

How To Test A Solar Panel


On the back, of each Solar Panel is a junction box below the junction box that will be a tag that contains the information for the panel. This will include the amps that the panel will put. With a standard Volt Meter, you can identify the negative and positive terminals inside the junction box or you can work with the wire terminals that plug into the panel. it’s very easy and I will go ahead and add a simple video below to show you. You will be looking to match up the Uoc and the Vmp that are located on the label on the flip side of the panel.

For Voltage reading:

  1. Lay the panel flat and faced down so that no sun is able to register on the Volt Meter
  2. Assuming you already hooked up to the panel positive and negative terminal leads turn on the meter
  3. Set the dial voltage (always set your meter higher than the voltage you are looking for) If you are looking for a voltage around 20 volts than set the dial on the meter higher than 20 volts
  4. Flip the Solar Panel over and you should see the Voltage start to move until you get a stable reading.

For Amperage reading:

  1. Set your Volt Meter to read Amps with the meter’s negative and positive terminal to the Amperage setting along with the Dial setting for amperage.
  2. Again set the Volt Meter above the expected or assumed reading that is on the label on the backside Solar Panel

When you determine the Amp and Voltage by reading you get you can verify that the panel is working and that it’s working and to what the specs that are advertised by the manufacturer.



Make sure that you measure the solar panel’s output and compare it with the panel’s specifications and nominal rating. To ensure an optimal reading, measure the output at noon on a bright, sunny day with the least cloudy sky. 



JimGalloway Author/Editor



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