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Solar panel output is usually measured in watts, but what if you are charging a battery, or your power load consumption is in amp hours? In these instances it is important to understand how many amps a solar panel can produce. This requires some math but it is nothing too difficult. In this guide you will learn how to do these calculations quickly.
A 100W solar panel generates about 5.5 amps, a 200W solar panel 11.1 amps and 2 x 150W solar panels 16.6 amps. Divide your solar panel’s VMPP by its rated watt output and you get the amps. A 100W 12V solar panel with an 18V VMPP can produce up to 5.5 amps (100 / 18 = 5.5).
How to Calculate Solar Panel Amps
To find out how many amps a solar panel can produce, divide its maximum power voltage by its watts. The maximum power point voltage (VMP or VMPP) can be found on the specifications sheet of the panel.
The formula is:
Watts / VMPP = amps
Watts / volts = amps
For example, take a solar panel like the Weize 100W 12V. These have a VMPP of 18V and you just have to divide the maximum power point voltage by its watts.
100 / 18 = 5.5
The amp output of a 12V 100W solar panel can reach 5.5 amps. If you have a 200W solar panel, the output is up to 11.1 amps.
200 / 18 = 11.1
However note the term, maximum power point voltage. Meaning, 18V is the maximum voltage, but it can go down anytime during the day.
Ideally the VMPP should hover between 17 to 18 volts throughout the day. If the solar panel is damaged, voltage can drop much lower. But if the VMPP ranges from 17-18V the difference is very small, but anything below 17V is significant.
If you have a 24V solar panel its VMPP will probably be around 36V, double that of a 12V system. However the calculations are still the same. If you have a 300W 24V solar panel with a 36V VMPP, its amp output is 8.3 amps.
300 / 36 = 8.3
Again these numbers assume the conditions are ideal. Having a quality solar panel like the HQST Solar 100 is important to ensure you get the highest possible output. It is normal for solar system voltages to fluctuate though, which affects both watt and amp output.
Nominal Voltage vs. Maximum Power Voltage
One of the things that bewilders people about solar panels is its voltage rating. Why is it that a solar panel is labeled as 12V, but is actually capable of generating 18V?
A 12V solar panel usually has a VMPP of 17-18V. 12V is a nominal voltage and is used only for classification.
For example, a 12V solar panel is designed for use with a 12V inverter, a 12V charge controller and a 12V battery. Even the 12V battery designation is nominal since they charge at 14.4V.
A 24V solar panel does not charge at 24 volts. It charges at up to 36V and the 24V is used to categorize its use with 24V batteries, 24V inverters and 24V charge controllers.
You can however, join two 12V solar panels in a series to turn it into 24V . You can do the same with 12V batteries as well.
60 cell solar panels are classified as 20V and have a VMPP of 31V. These solar panels are used in grid tied systems, whereas 12V and 24V solar panels are usually run with a battery bank. However you can use an MPPT charge controller to adjust the voltage of a 60 cell 20V system so it can work with deep cycle solar batteries.
Solar Panel Size and Amp Output Comparison
This table shows the average amp output of different solar panels. These figures are for general guidelines only. Solar panel power is affected by various factors including weather, environment, and efficiency and so on, so your mileage may vary.
|Solar Panel Size||Nominal Voltage||Maximum Power Voltage||Amps|
|200W (2 x 100W parallel connection)||12V||18V||11.1|
|300W (3 x 100W parallel connection)||12V||18V||16.6|
|400W (2 x 200W parallel connection)||12V||18V||22.2|
You can see the difference between 12V and 24V solar panel amp outputs here. Most solar panels for home and RVs are 12V while 24V panels are often used in commercial and industrial locations and buildings.
12V solar panels are available in 100W, 150W and 180W. Smaller solar panels from 10W-50W are 12V as well.
24V solar panels are sold in 300W, 330W and 350W.
You can of course use two or more solar panels to increase power. You can connect 2 x 100W 12V solar panels in parallel and get 200W.
With a parallel connection the amp output is combined but the voltage remains the same. Two 100W solar panels in a parallel configuration will remain at 18 VMPP.
With a series connection it is the opposite, the voltages are combined but the amps are not. If you configure 2 x 100W 12V solar panels in a series, third voltage is added up and turns into 24V. Its VMPP Is combined and becomes 36V.
So if you have 2 x 100W 12V solar panels with an 18V VMPP connected in parallel, the amp output is up to 11.1 amps.
If you have a 24V 330W solar panel its amp output is around 9.16 amps. Just like with their 12V counterparts, these are estimates based on ideal conditions. Due to changing weather, clouds, etc. the voltage will not always be at the maximum level.
A high voltage is not always a good thing. If you are charging a battery and its maximum capacity is only 15V, you have to use a charge controller to limit the solar panel voltage.
Factors That Affect Solar Panel Amp Production
So you have a 400 solar system and you notice that its power is less than you expected. This does not necessarily mean the solar panel is defective. There are many reasons why solar panels may not generate the expected power, and the following are the most likely reasons.
Solar panels are at their best in low temperature, around 77 F / 25 C. As the temperature climbs, voltage drops and solar output is reduced. Anything high than 111 F / 43 C and you could see a significant decrease in performance.
Solar panels do not necessarily need a lot of heat. What they require is energy from the sun. Even if the temperature is at the high 70s only, you can expect good results as long as the sun is out there. Too much heat and the voltage goes down. While this can lead to a slight increase in amps, the actual watt output will be lower.
It is important that solar panels are completely free from any shading, blocking or obstruction. Tree ranches, foliage etc. If there is anything blocking the cells, output will drop.
Before you install solar panels, make sure the location is free from any obstruction. If the power suddenly drops, check if there is anything shading the panels. Bear in mind that even if just one cell is affected, the entire solar system will see a downturn in power output.
How and where you position solar panels has a direct effect on its performance. In the northern hemisphere, the panels should face south. If you are in the southern hemisphere, the panels should be oriented north.
There are many factors to consider such as axis horizontal tracking, location and others. You may have to adjust the solar panel tilt to get the best production. If you have a solar powered home, the installer will ensure the panels are configured to get the maximum output possible.
I am an advocate of solar power. Through portablesolarexpert.com I want to share with all of you what I have learned and cotinue to learn about renewable energy.