3 Ways to Test Solar Panels: Output, Voltage & Current

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 measure solar panel output
  • And more

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 measure:

  • Open circuit voltage (Voc)
  • Short circuit current (Isc)
  • Operating current

Here’s how.

What You Need

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 tutorial 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.

Identify which cable on your solar panel is positive and which is negative. The positive cable is typically the one with the male MC4 connector.

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.

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 will likely be a spark when you complete the connection. This is normal.

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:

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.

Connect the negative solar cable to the charge controller, but leave the positive solar cable disconnected.

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.

Connect the multimeter inline to the positive solar panel cable.

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 ideal 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 measure solar panel output. That’s right — you’ll learn how to see exactly how many watts your panel is producing.

2. How to Measure Solar Panel Power 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.

The Renogy Wanderer 10A (left) has an LCD display that shows system specs which let you measure and calculate solar panel power output. The Renogy Wanderer 30A (right) only has LED indicators, but it can connect via Bluetooth to an app to tell you system specs on your phone.

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

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, have Bluetooth built-in.

The Wanderer 30A, on the other hand, has a compatible Bluetooth module you can buy, 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 power output in watts. The clouds rolled in as I was setting this system up, so my 100 watt solar panel was outputting just 28 watts.

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.

3. 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

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.

The meter also measures total watt-hours, a useful metric for seeing how much power your solar panel generates in a day.

Note: This watt meter 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.

Share This Article
Share on pinterest
Share on facebook
Share on twitter
Share on email
Share on print
Alex Beale
Alex Beale
Hi, I'm Alex. I started Footprint Hero to help people reduce their environmental impact. My current obsession is DIY solar power projects, which I've been building since 2020.
Alex Beale

Alex Beale

Hi, I'm Alex. I started Footprint Hero to help people reduce their environmental impact. My current obsession is DIY solar power projects, which I've been building since 2020.

Share This Article

Share on facebook
Share on twitter
Share on pinterest
Share on email

Contents

Leave a Comment

Your email address will not be published. Required fields are marked *