How to Test Solar Panels – Tools, Terms, and Instructions

Testing solar panels is a fairly straightforward process, requiring few tools and little to no expertise. But one single false step or wrong connection can turn this ostensibly simple task into a stressful ordeal. You can end up damaging your panels, testing devices, or even getting shocked. Therefore, you’ll want to know how to test solar panels correctly.

To lend you a helping hand, we’ve compiled this guide that will take you through a step-by-step process of testing your solar panels to make the panels last. By the end of this guide, you’ll be equipped with everything you need to know to test a solar panel.

The blog post includes:

• Instructions
• Required tools
• Key electrical terms: Current (amp), Voltage (volt), and Power (watt)
• Standard Testing Conditions (STC)
• Testing the Open Circuit Voltage (Voc)
• Testing the Short Circuit Current (Isc)
• Testing the Charge Controller
• Other considerations

Already overwhelmed? Fret not! You can always skip to your desired section by clicking the relevant heading in the table of contents.

Instructions on How to Test Your Solar Panel

Before you begin to test your solar panel, we advise you to take the necessary precautions and follow these instructions:

• Closely observe the positive and negative terminals/polarities when connecting any device to the solar panel.
• Cover the front of the solar panel with an opaque sheet to block sunlight and prevent heat build-up. Uncover the solar panel only when you’re taking the measurements
• Solar panels are large & heavy and demand safe lifting techniques.
• Short circuit the solar panel only for testing purposes
• Limit the short circuit testing to less than five minutes
• Use gloves to avoid burns and unexpected electric shocks.

These instructions and precautionary measures will allow you to safely and accurately test solar panels.

Tools Required to Test Solar Panels

To carry out solar panel tests, you will need these resources handy:

• A high-quality digital multimeter (DMM)
• Pair of wire to connect DMM with the solar panel’s terminals
• A small screwdriver (2.5mm)
• A spreadsheet or pen and paper to note down accurate reading
• A nice SUNNY day

Once you’ve gathered these tools, you’re all set to test a solar panel.

But before we lift the lid on the solar panel’s testing process, it’s necessary to understand the key electrical terms – current, voltage, and power – since these are the factors that we’ll evaluate during the test.

Key Electrical Terms

The performance of a solar panel depends on the current and voltage it produces. Once you understand these concepts, you can determine the solar panel amperage and voltage reading. Afterward, you can use the two values to calculate the solar power/efficiency of the solar power system. Efficiency is equivalent to the amount of full sunlight that the solar panels convert into electricity.

To understand the electrical terms, think of electricity as water in a tank. A higher water level would mean a higher voltage, i.e., there is more potential for water flow (current).

What Is Voltage?

Voltage (V) is defined as the difference in electric potential between two points in a circuit. The electric potential difference is measured in volts (V) and is responsible for the flow of current. For this test, we will calculate the open-circuit voltage (Voc) of the panel.

Voc of a solar panel is affected by several factors, including;

• Sunlight conditions: The more solar energy (irradiance) falls on the solar panels, the higher Voc will it produce
• Temperature: Higher temperatures have an adverse effect on the solar panel output wattage. Don’t be surprised to see maximum efficiency on a cold sunny day than on warmer days.
• Panel orientation: The pitch and azimuth of the solar panel also impact the voltage generated by the panel

What Is Current?

Electric current is the flow of charged particles (usually electrons) through an electrical conductor.

• DC stands for Direct Current
• AC stands for Alternative Current

In our previous analogy, the water flowing through a pipe out of the tank is analogous to the current flowing in the circuit. Electric current is denoted by “I” and is measured in amperes or simply amps.

What Is Electric Power?

Electric power (P) is the rate at which energy is transferred in an electric circuit per unit of time. It’s measured in Watts (W) and is equivalent to the product of Voltage and Current.

Power (P) = Volts (V) x Amps (I)

Now that you understand the key terms, you can measure their values and compare them to those calculated under standard testing conditions.

Standard Testing Conditions

Standard testing conditions, or shortly STC, are the industry standard conditions under which solar panels are tested. STC correspond to the following three conditions:

1. Temperature: 77oF or 25oC (this refers to the temperature of the cell, not the surroundings)
2. Solar irradiance: 1 kW/m2 (the power per unit area obtained from the sun)
3. Air mass: 1.5 spectra

Under these conditions, a 200-watt solar panel will generate 200 watts of electricity. The values of Voc and Isc under STC are usually mentioned on the back of the solar panel.

When we test solar panels in our own backyard, the conditions are nowhere near standard. It may be windy, the weather may be hot, and the direct sunlight may not fall optimally on the solar cell. However STC numbers provide a good standard against which we can assess a solar panel’s actual performance. As far as how well solar panels may perform in practical scenarios, you can find it out by conducting these tests.

Open Circuit Voltage Test (Voc) for a Solar Panel

To find Voc of a solar panel, here are the steps you need to follow:

1. Locate the converter box: To begin this test, first locate the converter box, which is mounted on the back of the solar panel. Remove the screws and detach the cover from the box.
2. Locate positive and negative connections: After removing the converter box, you’ll see connections with various energy setups. Locate the positive and negative connections and turn on your multimeter
3. Set up the multimeter: At this point, configure the multimeter so that it measures DC volts. You need to ensure that the multimeter’s energy level is set higher than what the solar panel is approved for. This will ensure that you take an accurate reading. You can find the approved Voc level in the converter box.
4. Connect the alligator clips: After setting up the multimeter, it’s time to attach the alligator clips to the solar panel. Connect the positive side of the multimeter to the red terminal and the negative lead to the panel’s black terminal. The digital multimeter should now measure the dc voltage that the solar panel produces. Note down the reading and check it against the one mentioned on the back of the solar panel.
5. Switch off the multimeter and disconnect the leads

Short Circuit Current Test (Isc)

The procedure to measure the current of the solar panel is similar to the volt test. However, there’s a slight difference in the preparation process. When testing solar panels for dc amp, it is a good idea to cover the solar panel temporarily. With solar energy striking the panel, the terminals and leads of the multimeter can produce sparks and damage the solar panel’s multimeter or panel.

Attach the positive lead to the red terminal and the negative lead to the black terminal, similar to the volts test. You’re now ready to measure DC amps by following these steps.

1. Set your multimeter to measure amp so that you can measure the solar panel output dc amps coming from the solar panel
2. Move the red lead on the multimeter to the 10ADC port and set the range to 10 amps or higher.
3. Connect the solar panel to the multimeter (red probe to the positive cable and black probe to the negative) and expose the solar panel to the sun

The multimeter will now show an accurate reading of Isc.

How to Test a Solar Output Wattage?

Unlike the previous tests, the wattage measurement doesn’t require a multimeter. There is a specific calculation that you need to use to test a solar panel output wattage:

Multiply the results of the Isc and Voc tests, and you’ll get the power output wattage.

P = Voc (volts) * Isc (amps)

Testing the Charge Controller

For the charge controller test, ensure the battery isn’t full. If it’s full, the charge controller will not pass any current to the battery, thus resulting in zero reading. Here are the steps you need to follow to test the efficiency of your charge controller.

• Connect the solar panel to the charge controller and the controller to the battery
• Disconnect the positive terminal between the battery and the charge controller
• Measure the current by connecting the multimeter’s positive lead to the controller’s positive port and the meter’s negative lead to the battery’s positive terminal.
• Remove the regulator now and connect the panel directly to the battery.
• Measure the amps by wiring the positive lead of the meter to the positive cable from the controller and the negative lead of the meter to the positive terminal of the battery

If there was no current in the presence of the regulator, but there is some now, then these possibilities may exist:

1. There is a loose cable connection. Go back and check all the connections.
2. The regulator is faulty and needs repair or replacement.

Additional Considerations

Apart from these tests, you should also regularly conduct strength tests to inspect any damage to the solar panels’ physical structure. When testing solar panels for mechanical strength, check the frame and see if it wobbles. If the panel feels unsteady, use a screwdriver and tighten the frame. All these tests, including the solar strength inspection, should be conducted after every extreme weather event.

We hope this guide provides a clear picture of the solar panel testing process. Armed with the knowledge in this article, you can test a solar panel on your own. If you still have questions, please ask us in the comments.