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How To Test A Solar Panel

Testing your solar panels doesn't need to be a mystery. Learning how to test a solar panel is straightforward; just take it step by step.
Solar Panels
6 minutes
Written by:
Joey Cheek
Updated on:
November 10, 2022

Solar panels continue to rise in popularity as a means of producing clean energy. However, understanding solar energy, solar panel installation, and managing a solar power system can be daunting when starting out. However, testing your solar panels doesn't need to be a mystery. Learning how to test a solar panel is straightforward; just take it step by step.

A solar panel isn't Pandora's box—it's just a machine. Drawing an accurate reading is an uncomplicated process; with just a few tools and some patience, you can get an accurate reading of how much power each panel generates.

From the outset, it feels like there's a lot to know: how does solar panel testing work? How can you know if your solar power system has the correct power output? How can you measure a short circuit current or read an amp meter? Along with terms like “converter box,” “measure open circuit voltage,” and “DC voltage setting,” those unfamiliar with electricity lingo may feel intimidated by the process of testing solar panels.

What You Need to Test a Solar Panel 

  • DC Amp meter
  • Multimeter
  • Variable resistor box

Getting Started: How to Test Your Solar Panel

In the simplest terms, testing your solar panels is easy with a simple math equation: Volts x Amps = Watts. Before using this formula, you will need to know how much voltage and how much current you have. 

Find the Power Rating Before Testing Solar Panels

The first thing you will want to do when preparing to test a solar panel is to figure out your power rating. When under testing in manufacturing facilities, solar panels are exposed to a few hours of simulated full sunlight that measures about 1,000 watts per square meter. This simulates natural sunlight conditions to test if the unit is working correctly. There's also a temperature control on these tests, as the temperature can influence performance.

The result of a solar panel's performance under these conditions becomes its power rating; so, a panel that's rated at 300W produced 300 watts of electricity while being tested. But keep in mind that the way a solar panel works in perfect conditions might not be the same as how it works when you test it at home. Solar panels, like anything else, can only perform as well as their environment allows.

Measuring Solar Panel Amperage or Solar Panel Output

Once you know your power rating, move on to measuring your solar power system's DC amperage. Checking your DC amp output is critical for assessing function when testing a solar panel. Your voltage reading indicates the power of your system, which helps you know if the system's power output meets your power needs. Your solar panels will each have a different rating or level of contribution, too, so test each one.

You will need a DC amp meter to monitor your DC voltage and power output. You can purchase this device at any hardware store. With your amp meter in hand, check your solar panel terminals and identify each voltage terminal (your panels will have positive and negative terminals). 

Attach the meter to the positive terminal and negative terminal of the solar panels. Try to test solar panels under fairly normal conditioners, and don't move the unit from its usual placement to measure amps effectively and get the most accurate reading of your DC amps.

Measuring Solar Panel Operating Current

Once you've got the amp reading on your solar panels, it's time to measure the solar panel current. Knowing your panel's short circuit current (your true solar power) helps you understand how well the unit is functioning as you test solar panels.

To measure current correctly, you will need a multimeter and a variable resistor box. This device indicates the current flowing through the system while under resistance. This will help you measure the operating current of your solar panels.

Steps to Measure Short Circuit Current

  1. First, locate your junction or converter box. It's usually in the back of the panel. You will see a metal pin inside; the metal pin(s) are your panel connector points.
  2. Ensure your solar panels are under normal operating conditions (direct sunlight)
  3. Locate the positive lead and negative lead connectors (usually a metal pin inside)
  4. Set the multimeter to read DC power and measure a voltage level that suits your solar panel (i.e., a level higher than the panel's voltage rating). A switched multimeter set to a low voltage setting will interfere with your panel reading of the direct current
  5. Connect the solar panel to the multimeter, using the negative connections and positive connections. Make sure the multimeter can accept current, to ensure it is positioned correctly.
  6. Receive your panel voltage reading. This will indicate the current passing through the unit.

Making Sense of Your Energy Reading

If you're testing new solar panels, the reading should be similar to the voltage rating on the manufacturer's specs label. If your panels are older, the rating efficiency may vary beyond the auto range. Know that the listed open circuit voltage was calculated under ideal conditions and that your readings of direct current may be different.

Calculating Solar Panel Output After Solar Panel Testing

Now that you know your amperage and your current, you will want to calculate your solar panel output. You can use the simple equation we shared above: volts x amps = watts.

Next, you'll do another simple calculation: watts x average hours of sunlight. This will get you your daily watt-hours number.

You may want to then multiply your daily watt-hours by about 75% to account for times when your panels are not in direct sunlight. These calculations give you a pretty accurate depiction of your solar generator's power.

Joey Cheek

Making Sense of Your Readings After Testing Solar Panels

Now that you've learned to test your solar panels, you can make sense of what your specific calculation indicates about your panels. If you know your house's daily watt-hour needs, you can compare that to the reading you've gotten from your panels.

The positive and negative aspects of solar power and panel use bear out, here: you can't just make your solar panels produce more energy, and you also may not have the roof space or money to add more solar panels if the production level you've got is insufficient. If you're unhappy with the level of production your panels generate, you may need to investigate replacing your panels with more efficient models. A new solar panel model will surely cost more to install but may save money and provide peace of mind in the long term.

Solar panel care can seem really overwhelming, but the process of monitoring and testing your solar panel output is easier than you think. Solar panels work like any other machine—a positive cable here, a metal pin there, a charge controller here, etc. But you're armed with knowledge now, and a step-by-step process to figure out if your panels are working for you.

Take the SmartSolar.org quiz and learn more about the benefits of installing solar panels.

Meet the author:

Joey Cheek

Joey Cheek spent 10 years on the US National Speedskating Team where he competed in two Olympic Games, winning gold, silver, and bronze medals. He attended Princeton before diving into the startup and tech world. In 2011 he launched a livestreaming platform for sports before leading a team of engineers building next-gen news and content apps for Fortune 100 companies. He is the CEO and co-founder of SmartSolar.org, whose mission is to move the earth to cheap, abundant, carbon-free energy.

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