This tutorial contains everything you need to know about how to test solar panels.
You’ll learn:
- How to test a solar panel with a multimeter
- How to test solar panel amps with a clamp meter
- How to measure solar panel output in watts
Let’s get started.
1. How to Test a Solar Panel with a Multimeter
Your multimeter is your best friend when testing solar panels.
You can use it to check:
- Open circuit voltage (Voc)
- Short circuit current (Isc)
- Current at max power (Imp)
Here’s how.
What You Need
- Multimeter — I recommend getting one that is auto-ranging. Also, a simple voltmeter won’t work here. You need a multimeter that can measure both volts and amps.
Video Walkthrough
Here’s a short video I made of testing solar panels with a multimeter. Check it out and consider subscribing to my YouTube channel for more DIY solar tutorials!
Step 1: Measure Open Circuit Voltage (Voc)
Locate the open circuit voltage (Voc) on the specs label on the back of your solar panel. Remember this number for later.
For this method I’m using the Newpowa 100W 12V panel. It has a Voc of 19.83V.
Prep your multimeter to measure DC volts. To do so, plug the black probe into the COM terminal on your multimeter. Plug the red probe into the voltage terminal.
Set your multimeter to the DC voltage setting (and the correct voltage range if yours isn’t auto-ranging). It is indicated by a solid line above a dotted line next to the letter V.
Take your solar panel outside and place it in direct sunlight. For best results, angle it toward the sun.
Locate the positive and negative solar panel cables. The positive cable is typically the one with the male MC4 connector, which has a red band around it.
Touch the red probe of your multimeter to the metal pin inside the positive MC4 connector. Touch the black probe to the metal pin inside the negative MC4 connector.
Read the voltage on your multimeter and compare it to the open circuit voltage (Voc) listed on the back of your panel. (If your voltage reading is negative, reverse the probes and measure again.)
I measured a Voc of 19.85V on my panel. The claimed Voc for this panel is 19.83V, so we’re spot on.
The voltage you measure with your multimeter should be close to the open circuit voltage listed on the back of the panel. It doesn’t have to be identical, though.
If they’re similar, so far your panel seems to be in good condition. You can move on to the next step — measuring short circuit current.
If the voltage you measure is significantly less than the Voc, try the following then remeasure:
- Make sure it’s a sunny day, the panel is in direct sunlight and it’s angled toward the sun
- Make sure no part of the solar panel is shaded
- Clean the solar panel
If your measurement is still off, your solar panel may be damaged.
Step 2: Measure Short Circuit Current (Isc)
Locate the short circuit current (Isc) on the specs label on the back of the panel. Remember this number for later.
My panel’s Isc is 6.56A.
Prep your multimeter to measure amps. To do so, move the red probe to the amperage terminal. Set your multimeter to the amp setting (A), choosing the right limit if yours isn’t auto-ranging.
Warning: Make sure your multimeter’s fuse size is greater than your panel’s short circuit current. The fuse size is usually listed above the amperage terminal. For example, my multimeter has a fuse size of 10A and my panel’s Isc is 6.56A, so I’m okay.
Take your panel outside and put it in direct sunlight. Throw a towel over it to stop it from generating power.
Touch the red probe of your multimeter to the metal pin inside the positive MC4 connector. Touch the black probe to the metal pin inside the negative MC4 connector.
Warning: There may be a small spark when you complete the connection. This is normal.
Remove the towel, read the current on your multimeter, and compare it to the short circuit current (Isc) listed on the back of your panel.
The short circuit current you’re measuring should be close to the one listed on the back of the panel. It doesn’t have to be the same, though.
For instance, I only measured 6.08A but my panel’s claimed Isc is 6.56A. There was a little haze in the sky when I tested, though, plus it was 11AM on a November morning, so I’m fine with these results. On a clear summer day at noon I’d expect it to be nearly identical to the Isc.
If your measurement is similar to the Isc listed on the back of the panel, great! Your panel is working fine.
For most people, measuring open circuit voltage and short circuit current are all you need to do to test that your solar panel is in good working order. You can stop testing if you want.
However, if you want to keep at it, there are more ways to test a solar panel with and without a multimeter. Keep reading to find out how.
If your measurement is pretty far off the claimed Isc, try the following and measure again:
- Make sure it’s a sunny day and the panel is in direct sunlight
- Test the solar panel as close to noon as possible
- Angle the solar panel towards the sun
- Make sure no part of the solar panel is shaded
- Clean the solar panel
Time of year also effects solar panel output. If your measurement doesn’t quite reach the Isc, it may not be your solar panel. It might just be the winter sun.
Step 3: Measure Operating Current (aka PV Current)
Note: You can also measure PV current by connecting the solar panel to a charge controller, which I discuss below in method #2.
That’s right — you can use a multimeter to measure how much current your solar panel is outputting. You’ll need some extra equipment, though:
- Solar charge controller — e.g. this cheap PWM charge controller
- Battery — e.g. this cheap 12V 33Ah lead acid battery
Here’s how:
Connect the solar charge controller to the battery.
Tutorial: How to connect a charge controller to a battery
Connect adapter cables to the charge controller.
Tutorial: How to connect a solar panel to a charge controller
Connect the negative solar cable to the negative adapter cable. DON’T connect the positive solar cable.
Prep the multimeter to measure amps, like you did in step 2. Throw a towel over the solar panel or place it face down on the ground so that it’s not generating any power.
Touch the red multimeter probe to the metal pin on the male MC4 connector (the one connected to the solar panel). Touch the black multimeter probe to the metal pin on the female MC4 connector (the one connected to the charge controller), thereby completing the connection.
Remove the towel from your solar panel (or flip it face up) and read the amperage on your multimeter to see how much current your solar panel is producing. My panel output 4.46A.
Pretty cool!
You can experiment with the panel’s tilt angle and direction to see how these factors affect output.
You can compare this number to the current at max power (Imp) on the back of the panel to see how close to maximum output your solar panel currently is. For instance, my panel’s Imp is 6.26A, and I measured a current of 4.46A.
While this may seem far off, it’s actually not that bad. Solar panels typically produce 70-80% of their rated power output, only reaching close to 100% in the industry-standard set of test conditions. (Not to mention the haze in the sky at the time of testing, and it being later in the year.)
4.46A is 71% of 6.26A, so this measurement is in line with expectations.
So:
You’ve learned how to test solar panels with a multimeter.
Now it’s time to talk about how to test solar panel amps with a clamp meter. That’s right — you’ll learn how to check how much current your solar panel is producing.
2. How to Test Solar Panel Amps with a Clamp Meter
A clamp meter, sometimes called an ammeter, can measure the level of current flowing through a wire. You can use one to check whether or not your solar panels are outputting their expected number of amps.
A clamp meter makes solar panel testing incredibly quick and convenient because you don’t have to disconnect your panels in order to check them.
What You Need
- Clamp meter — Get one that can measure AC and DC current; many can only measure AC current.
- A working solar panel system — This testing method assumes your solar panel is already connected to your system and producing power. (If yours isn’t, first set it up.)
Step 1: Prep Your Clamp Meter to Measure DC Amps
Turn the clamp meter’s dial to the correct amps setting. For most people, that will be the lowest amperage setting. For instance, the solar panel I’m testing this time around — the Renogy 100W 12V solar panel — outputs only around 5-6 amps at max power, so I turned mine to the 60A setting.
Some clamp meters default to measuring AC current, so switch to the DC current mode if needed. You also might need to zero out the reading before measuring DC current.
Now your clamp meter is good to go.
Step 2: Measure the Solar Panel’s Current
Open the jaws of the clamp meter, place one of the solar panel’s wires inside, and close the jaws. The solar panel’s current reading will show on the display. Remember this number. I got 5.24 amps when I checked mine.
Sometimes, depending on which way the meter is oriented, you may get a negative current reading. That’s completely normal, just clamp the other wire or point the meter in the opposite direction and then re-clamp the wire.
Tip: When checking solar panel amps with a clamp meter, never clamp more than one wire at a time. If you do, because the current is flowing in opposite directions, it will cancel itself out and you’ll get a reading of zero amps.
Step 3: Compare Your Current Reading to the Panel’s Max Power Current
Look at the label on the back of your solar panel. Find the panel’s current at max power, abbreviated Imp. It may also be called the maximum operating current or something similar. In this example, my panel’s listed Imp is 4.91 amps.
Compare the panel’s Imp to your current reading. Your current reading should be in the ballpark of the panel’s current at max power, but by no means does it have to be identical. The current I measured was 5.24 amps and my panel’s Imp is 4.91 amps, so I know my panel is working properly!
If your current reading is significantly less than the panel’s Imp, try the following and recheck:
- Check that the the clamp meter is set to the DC current setting and the right amperage range. Also, make sure that, before measuring, you zero out the DC current reading, if needed.
- Make sure you’re only clamping one wire with your meter
- Make sure the solar panel is in direct sunlight with no clouds blocking the sun and no shade on the panel
- Check that the solar panel is angled towards the sun
- Clean the solar panel
- Make sure your battery isn’t full charged. If a battery is mostly or full charged, the charge controller will reduce the solar panel’s output. If it is, discharge the battery a bit and then retry.
If you’ve tried the above and your solar panel is still outputting much less current than expected, it may be damaged.
You can repeat these steps for all the solar panels in your system. If you find a panel that is outputting significantly less current than the listed Imp, it’s worth disconnecting and diagnosing that specific panel further.
3. How to Test Solar Panel Output with a Solar Charge Controller
You can also test solar panels by connecting them to a solar charge controller.
Once connected, you can measure:
- PV voltage
- PV current
- Power output in watts
Some charge controllers make this easier to do than others.
For instance, some have LCD displays that show system specs such as PV current and PV voltage, which you can use to calculate wattage. Others can be connected via Bluetooth to your phone where you can monitor your system and measure its output.
And some have neither feature — they can’t tell you how much power your solar panel is generating. Avoid these ones.
What You Need
- Solar charge controller — Get one that either displays PV voltage and PV current (e.g. Renogy Wanderer 10A), or has Bluetooth (e.g. Victron SmartSolar MPPT or Renogy Wanderer 30A with Renogy BT-1 Bluetooth Module)
- Battery — e.g. this 12V 33Ah lead acid battery
- Battery to charge controller cables
- Solar panel to charge controller cables
Step 1: Connect the Battery to the Charge Controller
Connect your battery and charge controller.
For my setup, I used the Renogy Wanderer 10A, this 12V 33Ah lead acid battery, and some connector cables.
Step 2: Connect the Solar Panel to the Charge Controller
Next, connect your solar panel to the charge controller.
Step 3: Calculate Power Output
Cycle through the display screens until you find PV voltage. Mine was 15.2V.
Next, find the PV current. Mine was 4.5A.
To calculate the solar panel wattage, simply multiply volts times amps to get watts:
15.2 volts * 4.5 amps = 68.4 watts
My solar panel was outputting 68.4 watts. Not bad for a 100 watt solar panel on a hazy November day.
If you have a charge controller with Bluetooth, you can also use the brand’s app to measure solar panel output from your phone.
For example, let’s say you’re using the Renogy Wanderer 30A. As you can see, it doesn’t have an LCD display, so there’s no way of calculating the solar panel output by looking at it.
To find out, we need to use Bluetooth. Some charge controllers, like the Victron SmartSolar MPPT, have Bluetooth built-in.
The Wanderer 30A, on the other hand, has a compatible Bluetooth module you can buy, called the Renogy BT-1. I plugged the BT-1 into my Wanderer 30A and connected the charge controller to my phone using the Renogy DC Home app.
Then I opened up the app and was able to see a slew of system specs, including wattage. The clouds rolled in as I was setting up this system, so my 100 watt solar panel was outputting just 28 watts. (That’s typical for a 100 watt solar panel on cloudy days.)
Using the charge controller’s app is my favorite way of measuring solar panel output. It’s just so convenient. Bluetooth is definitely a worthwhile upgrade in my opinion.
Plus, apps like these automatically track solar energy production over time. Now we’re talking!
But:
If you can’t measure solar panel power output with your charge controller, don’t fret.
There is another way.
4. How to Measure Solar Panel Output with a Watt Meter
This is a watt meter (aka power meter):
You can find them for cheap on Amazon. Connect one inline between your solar panel and charge controller and it’ll measure voltage, current, wattage, and more.
Here’s how to use one.
What You Need
- Solar charge controller — e.g. Renogy Wanderer 30A
- Battery — e.g. this 12V 33Ah lead acid battery
- Watt meter — Get one with MC4 connectors attached to it or be prepared to crimp them on yourself
- Battery to charge controller cables
- Solar panel to charge controller cables
Step 1: Connect Battery to Solar Charge Controller
Connect the battery and charge controller.
Step 2: Connect the Watt Meter to the Adapter Cables
Connect the watt meter inline to the charge controller adapter cables. You can see I crimped the MC4 connectors to one end and a length of wire to the other.
Tip: You can buy this watt meter with MC4 connectors if you don’t want to fuss with crimping wire connectors.
Connect the adapter cables (with watt meter) to the charge controller.
Step 3: Connect the Solar Panel
Connect the solar panel to the charge controller adapter cables.
Step 4: Measure Power Output
Place the solar panel outside in direct sunlight. Once you do, the watt meter will automatically turn on and start measuring your solar panel’s power output.
At this point in the day, the clouds were here to stay, so my watt meter measured an output of 24.4 watts from my 100 watt solar panel.
As you can in the photo, you can also use a power meter to measure solar panel amps (1.86A) and voltage (13.14V). The meter also measures total watt hours, a useful metric for seeing how much energy your solar panel generates in a day.
Note: A watt meter placed in this location automatically turns off when the solar panel stops generating power. When it turns back on, the totals will all be reset to zero. If you want to record your solar panel’s energy production over time, I recommend getting a charge controller with Bluetooth such as the Victron SmartSolar MPPT.
