A solar battery is the most expensive component of a solar system. Nonetheless, it is prone to damage due to undercharging and over-change. These causes can be prevented by getting a suitable charge controller for your panel.
A charge controller is a part of the panel that regulates the power going into the battery bank from the solar array.
It works by regulating the voltage, which prevents the batteries from overcharging during the day while also ensuring that the batteries do not drain their charge at night by controlling the backward flow of the current.
Further, there are several factors to consider when getting a solar controller. Alongside efficiency, lifespan, and reliability, you should be greatly concerned with the size of the charge controller.
The rule of thumb is that different solar panels use different charge controllers due to the difference in size. For instance, a solar charge controller for a 200w is smaller than a charge controller for a 400w solar panel.
Don’t worry about how you will know the right size for your panel. This guide will help you determine that without troubling your mind with several calculations.
What size charge controller for 200w solar panel?
To choose the right charge controller, you must first know the amount of current produced by the panel. Generally, the controller must be able to handle the maximum amount of electricity produced by the panel.
The amount of current generated by a 200 w solar panel highly depends on its voltage and current type. That is either direct or alternating current.
Thus, if you measure the current supplied at home, it will be in the form of alternating current because it has already passed through the inventors. However, if you measure it directly before passing through the inventors, it will be in the form of a direct current.
However, if you are not a hands-on person and are unwilling to take the measurements, let me save you. Generally, a 200-watt solar panel produces around 8 amperes.
Therefore the ideal size of charge controller for a 200-watt solar panel should be at least 8 amperes.
If you choose a smaller size than the recommended, you will be running the risk of damaging the battery and burning the entire equipment. So, choose wisely.
What size charge controller for 250w solar panel?
Purchasing a small-sized charge controller puts your solar battery at risk and may lead to a 50% power loss due to the backward flow of current, among other factors.
As we earlier said, the first thing to do before purchasing a charge controller is to calculate the amount of current produced by the solar panel.
Honestly, doing these calculations manually can be pretty tiresome. That is why we highly recommend that you use this solar current calculator.
Ideally, the charge controller’s sizes range from one to 60 amperes. As a rule, the ideal controller current rating should be higher than the panel’s current. Actually, most professionals recommend that the size of the controller be 20% higher due to environmental factors.
For instance, the current produced by a 250-watt panel usually ranges around 12 amps. Thus, the recommended charge controller size for a 250w solar panel is 14.4 amps.
One more thing to consider when looking for a charge controller is the system’s voltage. The charge controller has 12, 24, and 48 volts in most cases. Ideally, the nominal voltage of the panel should match the controller. Consequently, a 20-volt 250-watt solar panel should use a 20 volt 15 amps charge controller
What size charge controller for 300w solar panel?
Just like other solar panels, all you need to know to choose the suitable charge controller for a 300w solar panel is the voltage and the current.
Basically, the voltage should be directly proportional. That is, the charge controller voltage should be equal to the solar panel voltage. Nonetheless, there is no harm in getting a more powerful charge controller.
Additionally, instead of manually calculating the current flow in the system, you can apply physics formulas to simplify the work for you. However, you should first know the power and the voltage of the solar panel.
For instance, a 12v 300-watt solar panel current is given by dividing the power by the volts. That is, 300w divided by 12v, which offers 25 amps.
Hence, the current supplied by this panel is 25watts.
However, the charge controller should have a current flow of at least 120% of the solar panel. Hence, we add 20% of 25 apps to the size of the charge controller.
Consequently, a 12v 300-watt solar panel should use a 30amps charge controller.
What size charge controller for 400w solar panel?
A 400-watt solar panel has 80 inches in length and 40 inches in width. It weighs approximately 50 pounds and is usually mounted on rooftops.
You should never be tempted to think that because a 400 watt is slightly large than a 350-watt panel, its charge controller will be marginally higher. That might be true; it might not always give you the correct sizing.
Solar panels come in different voltage supplies. For example, some have 12v while others are 20 volts.
Let’s assume that the 400watt solar panel has a voltage rating of 40 volts. Thus, its current will be 10 amps, that is, power rating divided by volts.
Consequently, its charge controller sizing should be higher than 20 amps. Considering the environmental consideration, you should get a charge controller whose size is 20% more than the panel’s current rating.
Therefore, a 40 volt 400 watt supplying 10 amps needs a charge controller of 12 amps.
What size charge controller for 500w solar panel?
A 500-watt solar panel ideally supplies 1,500 to 2,500Wh of energy. However, this amount of power usually depends on the amount of sunshine.
Additionally, most 500-watt panels use 30 amps charge controllers.
However, there is no harm in purchasing a bigger-sized charge controller because it gives you room for expansion if you consider adding more solar panels to the system.
What size charge controller for 1000w solar panel?
To determine the size of a 1000 watt, take the total watts of the solar array and divide it by the battery bank’s voltage.
Let us assume that our battery bank is 24 volts. Then the current is 1000 watts divided by 24 volts, giving 41.7 amps.
Putting in the environmental factors, we find 120% of the current output.
Thus, we have 1.2 multiplied by 41.7, which gives approximately 50 amps.
As a result, a 1000watt solar panel with a 24-volt battery bank should use a charge controller of 50 amps.
What size charge controller for 1200w solar panel?
Lastly, we have a 1200-watt solar panel.
If you have been following along, this should be easy for you.
Assuming that the battery bank of the solar panel is 20 volts, then the current supplied by the solar panel is given by 1200 / 20, which is equal to 60 amps.
The recommended charge controller size should be 120% of the current output of the panel.
Thus, the charge controller size of a 100-watt solar panel using 20 volts battery bank is 72 amps. You can always get a higher charge controller sizing to allow room for expansion in the future.
How to calculate charge controller size for a solar panel?
As we come to an end, let me simplify things for you on how to determine tth right size of the solar panel charge controller.
First, look at the power and voltage of the solar panel. Fortunately, all these details are found in the user’s manual.
Next, divide the power labeled in amps with voltage labeled in amps to get the current.
Lastly, the correct charge controller sizing should be 20% more to count for the environmental conditions.
Take the current value obtained and multiply it by 120%, which can also be written as 1.2.
The value obtained above gives the least charge controller that can be used on your solar panel.
Below is a table showing the ideal charge controller of the commonly used solar panels.
| Solar panel power | Solar panel voltage | Current produced by the solar panel | Recommended charge controller size |
| 200 wats | 25 volts | 8 amps | 10 amps |
| 250 watts | 20 volts | 12.5 amps | 15 amps |
| 300 watts | 12 volts | 25 amps | 30 amps |
| 400 watts | 40 volts | 10 amps | 12 amps |
| 1000 watts | 24 volts | 41.7 amps | 50 amps |
| 1200 watts | 20 volts | 60 amps | 72 amps |
Final words
A charge controller is a solar panel component that controls the battery bank charge to prevent overcharging or underhanging. It also prevents the backward flow of current, preventing the battery from draining at night.
Different solar panels use different charge controller sizes.
The rule is that the charge controller size should be larger than the current supplied by the system. Typically, the size of the charge controller should be 20% more than the solar panels current.
However, the controller’s voltage should be equivalent to the nominal voltage of the solar panel.
Eng. Matthew Joseph Nandirio is the Founder of walkingsolar.
After graduating from the University of Houston in 2002, matt started working as a Solar Electrical Engineer for several multi-national solar energy companies.
He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research.
He now shares his 20 years of expertise through his articles on the walkingsolar website.
Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.
