A Simple Guide on Solar Panel Output Checking

how to measure solar panel output with multimeter

If you would like or already have added solar panels to your home, testing solar panels for their output is an important thing to do. This will enable you to better understand how much solar power your panels can generate, what their solar output is during the day, and finally, what is the solar panel efficiency of your solar array. As these numbers change throughout the day, it is also important to understand that what the label of your solar panels says are measures taken in ideal conditions. Solar panels can indeed reduce your energy bill and provide you with power during a power outage, so installing them is a way to go. 

The labeled panel voltage and maximum power can be misleading sometimes, although they are presented in a true way. To help you avoid this kind of confusion, we’ve prepared instructions on calculating solar panel output and how much electrical power you can realistically create by means of your solar system. Let’s read on and learn how to measure your solar power output and see how to lower your energy bill with solar panels. 

What is a Solar Panel?

A solar panel is a device that can convert sunlight into renewable electrical power. A solar panel is composed of solar cells, which are made of different kinds of silicate materials. The maximum power and the output voltage depend on the type of the solar panel, the kind of materials used to create it, as well as its orientation, and the local weather conditions. 

Your solar panel does not immediately produce electrical power that you can use in your home. On the contrary, your solar panel produces DC power – Direct Current. To enable your devices and appliances to use that energy, you should use a solar inverter. Your solar inverter converts DC power to AC power – Alternating Current. This is the type of electricity that can then be used by your appliances and that you can then send to the power grid if your state enables net metering

Is Testing Solar Panels Important?

Whenever you purchase your solar panels, it is important to test them to understand how your solar system behaves on your property. As no two properties are exactly alike, your solar array may produce more or less power than your neighbors. This depends on a number of factors, such as: 

  • Solar panel orientation
  • The solar panel labeled maximum power, 
  • The solar panel labeled output voltage, 
  • Shading that is present on the terrain, 
  • The local weather conditions, and 
  • Many more. 

For these reasons, it is important to measure your solar panel wattage and voltage. After this, calculating solar panel output is relatively easy, and it will give you a better idea of how much solar output you can get out of your solar array. This is important to know when you want to make future changes, including: 

  • Optimizing your solar panels, 
  • Cleaning solar panels
  • Changing solar panel orientation, 
  • Expanding your existing solar array, and 
  • Purchasing solar power storage. 

Solar Panel Power Output

The actual output of your solar panel depends mostly on the electrical load that is connected to it. When there is no load that is connected, there is no energy flow, and the output or the solar electricity that is generated is equal to zero. However, connecting a load means that the panel can now generate electricity. This, in turn, powers your device or appliance or stores the energy generated in your solar battery. Let’s dive in and learn more about solar output. 

First things first, let’s understand the manufacturer’s label of your solar panels. If you take a close look, you will be able to see many fields explaining the technical characteristics of your solar panels. Let’s check out some of them: 

  • Max Power – this is the labeled power of your solar panel. In ideal conditions, this is how much output you can expect to get. A 100-Watt solar panel will produce 100 Watts of electricity in ideal conditions, 
  • Open-Circuit Voltage – Open-Circuit Voltage is the maximum voltage that your solar panel can produce when no electric load is attached to it, 
  • Short-Circuit Voltage – This is the current that you can expect to get when you introduce an electric load to the system, 
  • Optimum Operating Voltage,  
  • Optimum Operating Current, and 
  • Max System Voltage. 

Besides these, you can also see the information on the dimensions and the weight of your model. The STC or the Standard Testing Conditions that were applied when testing your solar panel can also be present, and they should give you a better idea of what the ideal conditions for your solar panels are. 

Factors That Affect the Output of Solar Panels

No solar panel can work at 100% of its rated output power all the time. This is because there are different factors that affect panel output. Besides the factors we’ve mentioned before, such as the orientation, the type, and the size of the panel, there are more factors that affect the output. These include temperature, the time (the age of the panel), and the panel type.


The temperature of the test solar cell or solar panel can play a big role in its efficiency. Generally speaking, the best temperature for your solar panel is the temperature it experiences in the autumn, winter, and spring. Any higher temperature and the efficiency of the solar cell drops. The ideal conditions for your solar panels include a temperature of 25°C. To calculate losses from a temperature that is too high, you should refer to the panel temperature and the Maximum Power Temperature Coefficient: 

( Current Panel Temperature – 25°C ) X Maximum Power Temperature Coefficient =

= Operating Efficiency of the Solar Panel


The time or the age of your solar array also plays a significant role in how well it will perform. Older systems perform worse than newer systems, especially as the technology progresses and makes new generations of solar panels more efficient in comparison to the older panels. Besides this, the age of your other solar equipment, such as your solar inverter and solar batteries, also has a big say in the overall system efficiency, as degradation appears over time. 


Degradation of the solar panel is the silent killer of your PV array. Generally, the older your system is, the higher the degradation of the solar cells. This means that you should test solar panels to see how much potential they have left in them. Your PV panel generally degrades over time: cheaper models lose around 0.8% of their output power every year, while expensive models lose around 0.3%. 

Solar Panel Type

Based on the price and the technology used to make them, there are standard and premium solar panels. Comparing the technology is not easy as the premium solar panels seem to outdo the standard models in all the metrics except the price. Let’s make a quick comparison. 

A premium PV panel offers much better efficiency in terms of how much sunlight it can convert into electricity. Furthermore, this decreases the average hours needed to generate enough electricity to power your home. It also means that less physical space is needed to reach the same wattage rating of the entire system

On the other hand, standard models come in larger panel sizes. Their lower efficiency tells that more preparation is needed to reach the same output level: they need more sunlight, so trimming trees is a good starting point to prepare for the solar installation. More sunlight means more power per square meter, and this means more power for your home. Nearby trees are known to affect standard solar panels to a higher degree than premium ones. 

Solar Panel Power Output Calculation

Whatever PV system you may want to purchase, testing it is important. If you want to test solar panels, there are a few things that you should know. Although it may seem a bit lengthy, this is a necessary but often overlooked procedure. The results can tell you more about the system you need and the actual performance of the system if you already have one and can make your entire investment more cost-effective. 

Prepare all of the Data & Resources 

To ensure you do all the calculations and measurements correctly, you should prepare beforehand. Calculating your solar panel power output is not difficult, and you will need to prepare your solar panel, have a good multimeter, a variable resistance box, proper wiring (pay attention to the specific resistance in Ohms), and somewhere to track all the readings. While some like an Excel Spreadsheet, others may find that a pen and paperwork equally as well. 

Prepare the Solar Panel System

The first step in calculating solar panel watts, solar panel amperage, maximum power point, and others is to connect the components. Ensure that the load is set to open and orient your solar panel towards the sun. This is necessary to ensure that the panel produces the maximum available power, so take time installing panels in bright sunlight (direct sunlight, no overcast sky) to get the most accurate reading. 

Test your Solar Panels using a Multimeter/Wattmeter/Solar Charge Controller

Your wattmeter and amp-meter can easily be substituted by a good multimeter. This type of device does the job of both meters, so ensure that you make an investment and avoid the cheapest product n the market. To test your panels, including your charge controller, you should first choose the type of multimeter that you would like to use. 

There are two kinds of multimeters: a Switched Multimeter and an Auto Range Multimeter. The difference between the two is whether they can set their own resistance settings and the ranges that they should measure. While a switched multimeter needs to be manually set, a good quality multimeter with an auto-range setting does not require any kind of manual input. Always choose quality products, even if for a single testing purpose only. 

When using a multimeter to measure your solar panel amperage output or to measure current, ensure you know how to properly use the meter. Having wrong settings on can give you improper readings and even damage your solar panel. Ensure you know how to use your specific device and avoid having hundreds in damage. 

Testing your Solar Panels for Volts 

When testing your panel for volts, you should set your multimeter to a higher volt setting than the maximum possible voltage of your panel in an open circuit (usually labeled as DC voltage or DC volts). This means you will be able to protect your solar panel and your multimeter, and it will give you a proper reading. If your solar panel rated maximum voltage in an open circuit is 22 V, you should set your multimeter range to 100 V or 200 V, depending on the model. 

Then, proceed to connect the black (negative) probe to the COM port, and the red (positive) probe to the port labeled V/mA/Ω. Then place the panel in full sunlight if you haven’t done so already and see the Volts X reading. If your panel is new, your volts should display the same amount that the panel is rated for. If they are used, you should receive a low voltage, depending on the degradation of your solar panels. 

Testing your Solar Panels for Amps 

To test your panel for amps, you should set the multimeter settings to DC amps or DC amperage. As before, you should set your amperage sensitivity to well above the maximum amperage of your device. This will enable accurate reading and prevent any damage to the panel. 

Measure the No-Load Voltage

When measuring the no-load voltage, you should know that this is the same as open-circuit voltage. With new solar panels, the reading on your multimeter with no load resistance should be equal to or very close to the labeled voltage value of your solar panel. You should avoid shading and be aware that your multi-meter reading also depends on the time of the year and your geographic location, as no two places receive the same amount of sunshine. 

Calculate the Solar Panel Output

Now that you know your voltage and amperage, it is time to calculate the wattage of your panel. To do this, simply multiply these two values and substitute the unit for Watts. Here is an example with this simple formula: 

Measured Voltage: 22.4 Volts 

Measured Amperage: 5 Amps 

Volts x Amps = Watts 

22.4 Volts x 5 Amps = 112 Watts 

Now that you know your solar panel Watt output let’s see how many daily watt-hours you can expect to get. To calculate this, simply multiply the Watts of your solar panel by the average number of sunlight you receive in your area for your time of the year. 

Watts X Hours of Direct Sunlight = Daily Watt Hours 

112 Watts X 6 Hours = 672 Watt-hours or Wh 

672 Wh / 1,000 = 0.672 kWh 

Furthermore, if you are doing solar panel testing to see how many solar panels you need for a large solar array, you can expand on this equation. This is usually done if you want to go off-grid or if you would like to offset 100% of your power consumption. The new equation is simple: 

Average Daily Watt Hours for your Region X 365 Days = Yearly Watt Hour Output

0.672 kWh X 365 Days = 245.28 kWh / year 

Now all you need to do is to divide your yearly power consumption (around 11,000 kWh for an average American home) by the yearly panel output in kWh, and you will get how many panels you need to produce 100% of your energy needs. Always purchase a solar array that is a bit higher (around 10%) to accommodate for system losses. 


How Many Watts Can a 12 Volt Battery Produce?

How many watts your 12-volt battery can produce depends on the Amp-hours. For example, a 12-volt, 100 AH battery can produce 12 volts X 100 AHs = 1,200 Watts or 1.2 kilowatts. Similarly, a 200 AH battery can produce 2,400 watts or 2.4 kilowatts. This is an ideal case, with new batteries and a 100% discharge rate. 

Do Solar Panels Charge with Moonlight?

Yes, your solar panels can charge your batteries with moonlight. However, since the moonlight is nothing else but reflected sunlight, the light hitting your solar panels is much weaker than the sunlight. Usually, during the full moon, you can only get around 0.3% of your solar panels’ output: a 1,000-watt solar system would only produce around 3 watts of power. 

How Many Watts Does a TV use?

Depending on the size, the model, and the technology used, a 50-inch flat-screen TV can use anywhere between 30 and 150 watts of power. Choosing LED, Energy-Star rated appliances keeps you at the lower end of the range. Choosing energy-efficient models saves energy and money for you. 

How Many Solar Panels do I need for 3 KW?

How many solar panels you need for 3 kW depends on the size, the technology, and the efficiency of your solar panels. As most solar panels come with a predefined output of 350-450 watts, you would need anywhere between 7 and 10 solar panels to get 3 kW of power. Note that it is always better to purchase more solar panels than risk not getting enough power to charge your batteries or run appliances. 


If you have recently purchased a solar panel and would like to check out its specs in your area and on your roof, you should follow our advice to get measurements that are as correct as they get. Understanding how Volts, Amps, and Watts interact to produce electricity for your home, camper van, or boat is necessary, as it can help you understand what devices you can power with your solar panel. Furthermore, you will be able to understand how many solar panels you need, which makes sense, especially if you would like to offset all your energy needs or go off-grid. 

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