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What Size Charge Controller Do I Need For A 100W Solar Panel

What Size Charge Controller Do I Need For A 100W Solar Panel

Short on Time? Here’s The Article Summary

The article discusses the importance of selecting the correct size charge controller for a 100-watt solar panel system. It highlights the risks of guessing the size and emphasizes the benefits of calculating the size accurately to prevent damage to batteries and ensure maximum efficiency. The article explains the role of a charge controller in preventing overcharging and outlines two types of charge controllers: PWM and MPPT. It suggests that PWM controllers are generally sufficient for 100-watt solar panels, but MPPT controllers may be needed for larger systems or configurations.

To determine the size of the charge controller needed, the article recommends calculating the amperage based on the power and voltage of the solar panel array. It provides a formula (power = voltage x current) and examples for single and multiple panel setups. Overall, the article emphasizes the importance of accurate calculation and suggests consulting a professional if unsure about the sizing process.


If you know how to install a 100-watt solar panel, then you know that a charge controller is a crucial part of your solar array, but just how big should it be, exactly?

When it comes to figuring out what size charge controller you need for a 100-watt solar panel, there are many rough estimates that people use to guess the size that will be needed. 

But, these estimates vary quite widely, and just guessing the size of the charge controller because it’s a 100-watt solar panel is a bit risky for your solar system. 

To make sure you are accurate, prevent any damage to your batteries, and make sure you are getting the most out of your solar array, it is best to calculate the size and type of the charge controller needed for a 100-watt solar panel specifically for the system you are planning to use.

By doing so, you will get a more accurate answer, and prevent damage and save money in the long run. 

What Size Charge Controller Do I Need For A 100-Watt Solar Panel

What Is A Charge Controller And Do You Always Need One?

First of all, for those of you who were told that you need to get a charge controller but actually have no idea what it is or does, let’s do a recap on what exactly the role of a charge controller is. 

To put it simply, a charge controller is a device that helps to prevent batteries that are connected to solar panels from overcharging. 

A solar charge controller regulates the voltage and current going to the batteries from the solar panels. It makes sure that the batteries are not overcharged during the day, and it also ensures that the power from the batteries doesn’t run back to the solar panels overnight and leave them drained in the morning. 

Batteries usually have a capacity of about 12 volts, and if the voltage coming from the solar panel is more than that, it will likely end up overcharging and causing damage to the battery. 

To answer the question of whether you always need one, the answer is not always, but in the majority of cases, you do. 

A simple way to tell if you need one is if your solar panel produces 2 or fewer watts for every 50 amp-hours, then it is not necessary. 

Even though it is something that you don’t always have to have, we would suggest investing in one anyway to rather be safer and save more electricity.

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Different Types Of Charge Controllers

There are two different types of charge controllers that you can get. The one that you end up choosing will depend on your 100-watt solar panel specifications, as well as the makeup of your solar system and the needs that it has. 

The two different types are a Pulse Width Modulation (PWM) charge controller and a Maximum Power Point Tracking (MPPT) charge controller.

The main difference between the two is that the PWM is a lot more simple than the MPPT, and can, unfortunately, lead to a substantial loss of solar energy.

MPPT charge controllers are usually used in larger solar systems. PWM controllers are normally sufficient for 100-watt solar panels, but if you know how to connect 2 100-watt solar panels in series, and choose to do so, then an MPPT controller will most probably be needed.


What Size Charge Controller Do I Need For A 100W Solar Panel

How To Determine What Charge Controller You Will Need

Now that you have come to terms with what exactly charge controllers are, and what type you will need, I’m sure you are still wondering “what size charge controller do I need for a 100-watt solar panel?

It is important to have a correctly sized charge controller. If your charge controller is too small, then the amount that the batteries can be charged, as well as their power output, will be limited and will result in loss of energy and won’t allow your solar system to work with peak performance.

For this reason, your charge controller either needs to be spot on with its size, or slightly bigger than what is required to get the maximum performance out of your system.

As much as the size is important, it is also crucial to make sure you don’t go for the cheapest, poorest quality charge controller. 

Although you may think it is something you can skimp on when you see the cheap ones that are available on the market, rather don’t.

If you do, it can end up damaging the batteries of your solar array and can lead to failure of the batteries, as well as the entire system as a result, leaving you in the dark. 

Estimates Of Charge Controller Sizes for 100-Watt Solar Panels

There are several suggestions given for the size of charge controllers needed according to the size of the solar panels they will be connected to. 

Some say for a 100-watt solar panel your charge controller should be 10 amps, others say 7.5 amps for every 100 watts, and some sources suggest that you should calculate the total watts of your solar panels, and divide that amount by 14.4 if your system is 12V, by 28.8 if it is 24V, and by 58.8 if your system is 48V.

With the huge discrepancies between these suggestions, it is not worth the risk of just randomly choosing one to follow and hoping for the best. 

Instead, we would recommend that you calculate the size of the charge controller needed specific to your 100-watt solar panel array. 

This way it will be much more accurate and beneficial to your system and can end up saving you money and frustration. 

Charge Controller Do I Need For A 100W Solar Panel

Factors To Consider Before Determining The Size Of The Charge Controller 

Before you can determine what size charge controller you will need, you will have to determine what the size and structure of your solar array are going to need to be.

This may also involve having to figure out things like “How many batteries do I need for a 100-watt solar panel, and what type?”, “What size inverter do I need for a 100-watt solar panel?” and “What gauge wire for a 100-watt solar panel?”. 

Although this may seem overwhelming, don’t panic just yet, we are going to break down the process of figuring out the sizing of your solar array step by step.

The Load Of Appliances That Need To Be Powered

First, you are going to need to estimate how much load and appliances you are going to be running, as well as for how long. 

This can be done by calculating the amperes or the watts that each appliance uses. These details should be stated at the back of each appliance. 

By using the above, and estimating how long you will need each appliance for, you can work out the amp hours required for each appliance.

Add the individual amp-hours together, and see how many amps you are going to require per hour, as well as for how many hours they need to be supplied. 

Battery Type And Size

You will also need to determine what type of battery you’d like to use - lithium or lead-acid - as this will affect the size of the battery that you will need to meet the demands of your load. 

After you have chosen the type, you will be able to determine the size, and the number of, batteries needed to keep your appliances running.

Amount Of Solar Panels Needed

You will need to figure out how many solar panels you need, especially if you are planning on using 100-watt solar panels. Ideally, your solar panels should be big enough to fully charge your chosen battery on a sunny day, but also provide enough energy if it is overcast.

For this reason, you might want to consider more than one 100-watt solar panel, depending on the size of the battery you have chosen.

Since there are so many changing and unpredictable variables to consider, nature being one of them,  it may be wise to get too many solar panels rather than too little. 

Charge Controller For 100 Watt Solar Panel

Calculating The Size Of The Charge Controller Needed For A 100-Watt Solar Panel

Since you have worked out all of the above, you can now figure out what size charge controller you will need for your specific 100-watt solar panel array.  

To do the calculation, we suggest using the formula power = voltage x current.

Since we know the power, and the voltage, we need to work out the current. This can be done by rearranging the formula to current = power/voltage.

In our case, 100/12 = 8.33 amps. So, if you have one 100-watt solar panel, a 10 amp charge controller would be necessary, as it is safer to round up.

If we had 3 100-watt solar panels, the equation would be 300/12 = 25 amp, so we would suggest getting a 30 amp charge controller.

Final Thoughts

So, even though the rough estimates of the size of the charge controller for a 100-watt solar panel may be close enough to our calculations, it is safer for you to work out the size as we did, and not just guess.

This may be more tedious to do but can possibly save you a lot of money and troubles in the long run. 

If you are still struggling with the process of figuring out exactly how big your solar array needs to be, before you can even attempt calculating the size of the charge controller, we would suggest consulting a professional.

They can guide you as to how big the solar array should be, which will allow you to then work out the size of the charge controller that you will need.

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Article by

Alex S

Alex is a co-founder of Shop Solar, a company that he established in 2018 to revolutionize the solar industry by simplifying the process and making it more simple and cost-effective. Under his strategic leadership, Shop Solar has grown into a comprehensive one-stop-shop, empowering over 40,000+ customers to access top-quality solar and storage solutions, comprehensive information, intuitive tools, and professional installation services.

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Lionel - February 9, 2024

I have a 100watt solar panel is it ok to use a 20amp controller? I will be charging a 12 volt lithium 100ah battery.

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