How To Test Solar Panels’ Power Output (Both With and Without a Multimeter)

Georgette Kilgore headshot, wearing 8 Billion Trees shirt with forest in the background.Written by Georgette Kilgore

Solar Panels | March 29, 2024

Man hold multimeter connected to a solar panel asks how to test a solar panel and what is the best power output of a solar panel testing methods and steps?

Knowing how to test a solar panel and the panel’s power output (both with and without a multimeter) can come in very handy if you feel that the electricity being provided by them is below what it should be.

Because solar panels have no moving parts, any faults or under-performance issues are very rare, but other factors can impact the output over time.

In fact, any decrease in output could have been years in the making, even originating during the initial manufacturing process, from transportation, from the supplier, or even when the panels were first installed.

So, the best course of action is to personally locate the problem on the solar panel.4

Knowing how to test solar panels power output can ensure that your power generation is working the way it’s supposed to. This guide explains how to do it.

Problems With the Power Output of a Solar Panel (Solar Panel Testing)

The effects of a reduction in the power output of up to 20% from a solar panel can be felt very quickly.

Ignoring it, or just living with it, can lead to further degradation and compound the problem until the panel’s performance is so bad that it is virtually useless.

Physical inspection should be the first course of action to locate the power problem, or the lack thereof.

Here are 5 potential issues that can be checked immediately and easily:

  1. Make sure that the panels are clean. If they become caked in dirt or debris, bird droppings or even leaves will result in a lack of exposure to the sun and they will become very inefficient at converting sunlight into electricity.8
  2. Check for any signs of damage. Solar panels are not indestructible and even a heavy torrential downpour, lightning, or a hailstorm can significantly damage the surfaces.
  3. Look for hot spots. This is where an electrical connection may have come loose or failed and emit undue heat in a part of the panel that will interfere with its operation.
  4. Carefully inspect the panels for micro cracks. These could have arisen during transportation and gone unnoticed for years, only affecting the efficiency of the solar panels as the cracks become more pronounced.
  5. Simple corrosion can be a problem. This can occur when the lamination covering the panels and glass has lifted imperceptibly (delamination) and water or moisture has penetrated beneath this protective covering.

Brown spots can appear in these areas, widening over time, corroding vital conduction cables, and worsening the solar panel’s performance gradually over months or years.

How to test a solar panel that isn’t giving its best should always start with a physical inspection. If any of the above have been identified, it may be time for a touch of maintenance.

If everything appears fine and there are no visible problems, then checking the output with a multimeter is the next step.

How To Test a Solar Panel With a Multimeter (How To Test a Solar Panel Output)

Despite the fact that solar panels have a tendency to degrade over the years from 0.5% to 3%, a sudden drop in performance is out of the ordinary and signifies a problem that needs to be resolved as soon as possible.

If the panels have passed the physical examination, the next option is to actually measure the dc (direct current)2 output to determine if they are experiencing a normal lack of energy conversion capability due to age, or if there is another cause for concern.

A solar panel technician using a Multimeter to check the solar panel output.

(Image: 85106709)

But how to test a solar panel with a multimeter and where do you start?

First, if you do not possess a multimeter that displays both amps and voltage, one can be purchased from any hardware store. The Auto Range multimeter switches automatically between amps and watts so is easier to use whereas the Switched multimeter needs to be manually changed between settings.

With a multimeter in hand, and making sure that it is a sunny day, follow these simple steps:

  • Remove the cover of the converter box which is located at the back of the solar panel.
  • Make a note of the manufacturer’s power rating on the solar panel label for comparison purposes.
  • Identify which connections are negative and positive.
  • Set the multimeter to DC volts.
  • Using the alligator clips, connect the red lead on the multimeter to the red positive cable connection and then the black lead to the black cable connection, and turn on the multimeter.
  • Make a note of the voltage reading, turn off the multimeter, and change the setting to DC amps. Turn the multimeter back on.
  • Write down the reading, turn off the multimeter, and disconnect the clips.
  • Multiplying the voltage readings by the amperage readings will give an accurate output in watts.
  • To have an understanding of what the daily output is, multiply the total watts by the hours of daily sunlight.
  • These figures can then be compared to the manufacturer’s recorded power rating to decipher at what level the solar panels are functioning.

The age of the panels will also reflect in these power output findings, but if a 3% yearly decline is factored into the equations, an accurate reading can be reached on whether the solar panels need to be replaced immediately, will last a few more years, or if any onsite repairs can be done to increase its performance.

A solar panel installer would be able to advise on the next course of action. Another piece of advice that they often recommended for new converts to solar panels,7 is to have an energy monitor installed alongside the panels.

An electric meter device with the needle pointing to 400 volts.

(Image: StockSnap13)

This monitor will send out an alert if there are any reductions in the power output and even indicate the site of the malfunction.

How To Test a Solar Panel Without a Multimeter

There are different types of solar panels with varying output capabilities. What they all have in common is a solar inverter which is needed to convert the dc (direct current) electricity from the solar panels into ac (alternating current) current for household and commercial usage.

A modern or hybrid inverter can be used to read the output of solar panels to gauge their performance. The main electricity from the power grid needs to be disconnected- and the reading displayed will be the output from the solar panels.

This is an alternative method of how to test a solar panel if a multimeter is not available.

How To Measure a Roof for Solar Panels

The size of standard solar panel in square feet is 17.5. Measure the roof to calculate the square footage and multiply that figure by .75.

Close up view of a man measuring a roof for solar panel installation.

(Image: sandid12)

To answer a commonly asked question of how many solar panels do I need, divide that figure by 17.5.

That figure will be the optimum amount of solar panels that will be able to fit onto your roof.

You can also use a calculator to determine your solar needs:

Charging Tesla With Solar Panels: How To Test a Solar Panel

Many homeowners are interested in finding out how to test a solar panel because they are interested in charging their brand-new Tesla vehicle in the comfort of their own homes.

Installing a charging point in your home to boost your EVs battery power overnight is a money and time-saving option that is more than worth the cost.3 However, EVs require quite a bit of energy to power up.

If the electricity from the grid is used it can work out to be an expensive endeavor to fully charge up your Tesla for the next day’s long-distance journey.

Using the stored electricity generated from solar panels is not only a climate-friendly solution but a much cheaper alternative than electricity provided to your home from the grid.

Charging Tesla using solar panels at an EV charging station, with other EVs parked and plugged into the charging hub.

(Image: Kindel Media10)

But is it just a matter of installing a solar panel on the roof and a charging point in the garage? Not exactly.

Like most EVs, a Tesla requires a significant amount of energy, consuming approximately 18.1 kWh every 62.13 miles that it travels. To meet that demand for charging Tesla with solar panels, 10-12 solar panels would have to be installed depending on the wattage output from each one.

Once the additional solar panels are installed, once the charging port is set up, whizzing around in your Tesla vehicle on virtually free energy couldn’t be more liberating.

Carbon Footprint Solar Panels (Solar Farm Income per Acre)

Not only are more and more Americans installing solar panels on the roofs of their properties for personal use, but solar farms are beginning to become more popular across the country as solar panel technology keeps improving.

Now the question that comes into mind is, how much carbon footprint solar panels produce?

Even though solar panels are hailed as clean energy, they do have an initial carbon footprint cost that is derived from the production, transportation, and installation process. Manufacturing the actual panels creates a carbon footprint from gathering all the individual components such as copper, silver, and lithium needed for the batteries as well other parts.

Further carbon emissions are created by trucking the finished panels to the installation site and if it is to a new solar farm site, then the land has to be prepared, generally by diesel-powered vehicles. It can take up to 3 years for a solar farm to offset these initial CO2 emissions and become carbon neutral.

After that, it can be producing clean energy to power hundreds of homes for up to 40 years, and that’s where the appeal comes in for landowners. As well as the income that can be derived from it, of course.

Depending on whether the land to be utilized for a solar farm is in a state that has more days of sunshine than clouds,1 will determine the potential profits that can be made. The size of the land will also factor into how much landowners can make per acre as well as if they shoulder the full cost of purchasing the solar panels and the actual installation costs themselves.

In this scenario, an annual profit per annum can be approximately $42,000 per acre.

Bird's-eye view of a solar farm situated on a plain with few greenery around it.

(Image: TheOtherKev11)

The profit for a landowner who wants to lease their land to a utility company or third party would be considerably less as profits would be based on a percentage of the kilowatts generated by the solar panels, not the entire load. Under this type of agreement, a profit of $21,000 per acre is possible annually.

Although not as profitable as actually setting up a solar farm business and receiving 100% of the profits, it is nevertheless a healthy yearly income, especially considering that start-up costs can run up to $1M. Despite this initial cost, however, many entrepreneurs are being attracted to this industry as the demand for clean energy increases.

Their investment may only be a desire to capture a share of an industry that is estimated to be worth billions in the United States alone, yet at the same time they are helping to reduce greenhouse gas emissions. With most solar farms being at least 10 acres in size and some of the larger farms covering hundreds of acres, the potential solar farm income per acre are significant.

Solar energy is part of a cleaner, greener future that climate activists have been championing for years to combat climate change.5 Fortunately, the solar panels themselves very rarely have any energy output issues, functioning properly for years without requiring any form of maintenance whatsoever.

If there are any performance problems at any stage, though, it is always handy to know how to test solar panels’ power output (both with and without a multimeter).

Frequently Asked Questions About How To Test a Solar Panel

What Are the Steps on How To Test a Solar Panel Charge Controller?

On a multimeter, there is a setting for the solar controller. A low or zero output reading indicates that the controller is not working properly.

What Are the Ways on How To Test Solar Panels Are Working?

A green light on the solar inverter basically indicates that the solar panels are working correctly.6 An orange light indicates a problem in the system.

What Are the Steps on How To Test a Solar Panel (Solar Cell Testing)?

A multimeter can be used to detect a faulty cell in a solar panel.

How Much Do Solar Panels Cost?

For those wondering, how much do solar panels cost, prices vary between models and sizes and can cost from $3,500 to $35,000.

What Are the Steps on How To Measure Solar Energy?

The installation of a kWh power meter between the inverter and the panels will monitor the amount of electrical energy produced.

What Will a 100-Watt Solar Panel Run?

Only small appliances and devices such as laptops ceiling fans, and lamps can be run from such a small solar panel. A considerably larger solar panel for ac unit would be needed to keep you really cool in the summer.

What Are the Steps on How To Test Second-Hand Solar Panels?

How to test a solar panel if it is second-hand, involves a thorough on-site physical inspection for signs of damage and any brown spots under the lamination, and also check the power output with a multimeter.

What Are the Ways on How To Check if Solar Panel Is Charging Battery?

If there is any doubt whether the solar panel is charging the battery, a before and after test with a multimeter will reveal if the battery voltage has changed after being attached all day.


References

1Department of Agriculture, Environment and Rural Affairs. (2023). Solar PV on the farm. Department of Agriculture, Environment and Rural Affairs. Retrieved March 10, 2023, from <https://www.daera-ni.gov.uk/articles/solar-pv-farm>

2Early, E. (2013, September 17). What’s the difference between AC and DC? School of Engineering. Retrieved March 10, 2023, from <https://engineering.mit.edu/engage/ask-an-engineer/whats-the-difference-between-ac-and-dc/>

3Minos, S. (2022, January 27). EV Charging at Home. Energy Saver. Retrieved March 10, 2023, from <https://www.energy.gov/energysaver/articles/ev-charging-home>

4National Renewable Energy Laboratory. (2023). Solar Energy Basics. National Renewable Energy Laboratory. Retrieved March 10, 2023, from <https://www.nrel.gov/research/re-solar.html>

5Smithsonian Institution. (2018, April). Climate Change. OCEAN Find Your Blue. Retrieved March 10, 2023, from <https://ocean.si.edu/conservation/climate-change/climate-change>

6Solar Energy Technologies Office. (2023). Solar Integration: Inverters and Grid Services Basics. Energy Efficiency & Renewable Energy. Retrieved March 10, 2023, from <https://www.energy.gov/eere/solar/solar-integration-inverters-and-grid-services-basics>

7U.S. Department of Energy. (2023). Homeowner’s Guide to Going Solar. Energy Efficiency & Renewable Energy. Retrieved March 10, 2023, from <https://www.energy.gov/eere/solar/homeowners-guide-going-solar>

8U.S. Energy Information Administration. (2017, March 17). Photovoltaics and electricity. Solar explained. Retrieved March 10, 2023, from <https://www.eia.gov/energyexplained/solar/photovoltaics-and-electricity.php>

9Photo by 8510670. Resized and changed format. Pixabay. Retrieved from <https://pixabay.com/photos/technician-solar-panel-renewable-3936982/>

10Photo by Kindel Media. Resized and changed format. Pexels. Retrieved from <https://www.pexels.com/photo/light-city-road-landscape-9800033/>

11Photo by TheOtherKev. Resized and changed format. Pixabay. Retrieved from <https://pixabay.com/photos/solar-farm-solar-panels-6619505/>

12Photo by sandid. Resized and changed format. Pixabay. Retrieved from <https://pixabay.com/photos/measure-tape-ruler-size-roof-645800/>

13Photo by StockSnap. Resized and changed format. Pixabay, retrieved from <https://pixabay.com/photos/electricity-meter-electrical-2595842/>