solar charge controller

What is a solar charge controller? Do you need one?

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If you’re considering installing an off-grid solar project with a battery attached, you’ll want to look into a solar charge controller for your system. Charge controllers act as a gateway to your battery, and ensure that you don’t overcharge and damage your energy storage system. In this piece, we’ll cover what a solar charge controller is, and how the two major types (PWM and MPPT) compare.

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Choosing the right solar charge controller: what you need to know

A solar charge controller is a regulator for your solar battery that prevents it from overcharging. Batteries are rated for voltage capacity, and exceeding that voltage can lead to permanent battery damage and loss of functionality over time. Solar charge controllers act as a gate to your battery storage system, making sure damage doesn’t occur from overloading it.

Charge controllers are only necessary in a few specific cases. Most commonly, you will want to look into charge controllers if you are trying to install an off-grid solar system, from rooftop systems to smaller setups on boats or RVs. If you are a homeowner looking to install a solar array with a battery that is connected to the electric grid, there is no need for a charge controller – once your battery is full, excess energy will be directed to the grid automatically instead, helping you avoid overloading your battery.

Types of solar charge controllers: PWM and MPPT

If you want to use solar to go completely off-grid, there are two types of charge controllers to consider: Pulse Width Modulation (PWM) controllers and Maximum Power Point Tracking (MPPT) controllers.

Pulse Width Modulation (PWM) solar charge controllers

PWM solar charge controllers are the standard type of charge controller available to solar shoppers. They are simpler than MPPT controllers, and thus generally less expensive. PWM controllers work by slowly reducing the amount of power going into your battery as it approaches capacity. When your battery is full, PWM controllers maintain a state of “trickle”, which means they supply a tiny amount of power constantly to keep the battery topped off.

With a PWM controller, your solar panel system and your home battery need to have matching voltages. In larger solar panel systems designed to power your whole home, panel and battery voltage aren’t typically the same.  As a result, PWM controllers are more suited for small DIY solar systems with a couple of low voltage panels and a small battery.

Maximum Power Point Tracking (MPPT) solar charge controllers

MPPT solar charge controllers are a more expensive and complex charge controller option. They provide the same switch-like protection that a PWM controller does, and will reduce the power flowing to your home battery as it nears capacity.

Unlike PWM controllers, MPPT charge controllers can pair non-matching voltages from panels and batteries. MPPT controllers adjust their input to bring in the maximum power possible from your solar array, and can also vary their output power to match the attached battery. This means that MPPT charge controllers are more efficient than PWM controllers, and more effectively utilize the full power of your solar panels to charge a home battery system.

How much do PWM and MPPT solar charge controllers cost?

Solar charge controllers usually cost a few hundred dollars, with variation depending on features and type.

In general, MPPT charge controllers are more expensive than PWM controllers due to their higher charging efficiency. MPPT controllers can reach up to 20% higher efficiency – this is due to its four-stage charging method that is generally healthier for your battery. PWM solar charge controllers are more versatile and more easily installed, but their lower efficiency usually means lower prices.

Is a solar charge controller right for you?

For the majority of solar shoppers, there’s no need to worry about charge controllers. Rooftop or ground-mount solar installations with a battery backup are almost always linked to the electric grid, and in the case that your battery completely fills up, your excess solar energy will automatically reroute there.

If you are interested in installing a small off-grid solar energy system with battery backup, you might need to look into a charge controller to ensure that your battery is safely charged. For relatively small batteries paired with low-output 5-10 Watt solar panels, a PWM charge controller should do the job. For more complex DIY solar projects with higher output panels, you may want to consider a MPPT charge controller.

PWM or MPPT: The pros and cons of each

If efficiency were the only concern in purchasing a controller, an MPPT controller would be the best choice every time. But it’s not always practical. Selecting the right solar charge controller involves several factors beyond just efficiency. To determine what controller is right for you, answer these questions:

  1. What type of panels do you have?

Most off-grid solar panels are 36-cell panels designed to charge a 12V battery. These systems work well with PWM controllers. 60-cell and 72-cell panels are typically used with a grid-tie solar panel system and have a higher voltage, thus requiring an MPPT controller.

  1. How big is your system?

A PWM controller works with any system size as long as the voltage between the solar system and home battery match—though typically they don’t match in larger systems, making a PWM ideal for smaller setups. MPPT controllers are less efficient unless your array is at least 170W.

  1. What temperatures can you expect?

MPPT controllers work better than PWM controllers when it gets colder. As the temperature drops, the voltage increases, and an MPPT controller can capture the excess voltage. In warm climates where the temperature doesn’t typically get very low, there isn’t extra voltage and an MPPT controller isn’t necessary.

  1. What is your budget for a controller?

While cost shouldn’t be the deciding factor, it should be considered. MPPT controllers are typically more expensive, and they may be less efficient in certain circumstances. It’s important to verify if an MPPT controller is needed and the best option before going to the expense of getting one.

 PWM ControllersMPPT Controllers
System SizeOff-Grid (12V)

Grid-Tie (variable volt)
System TypeVariable

170W or larger
ClimateWarm or HotAny

You don’t have to build your own solar setup to start saving money

On the EnergySage Marketplace, you can register your property to begin receiving quality quotes for solar installations. If you are interested in storage solutions to pair with your panels, you can simply indicate your interest on your profile for installers to see. Connecting your solar project to the grid (even with battery backup) is a smart move, as it provides a second backup for your system, and in the case that your battery storage capacity isn’t enough, you won’t simply run out of power to use.

While going completely off-grid with a DIY solar project may work in some cases, if your main concern is saving money, hiring a qualified installer to help you go solar is still a sound financial decision. What’s more, having a professional installer work on your solar project ensures that you are getting the expertise you need to have a functional and effective solar system. Installers also offer warranties and protections for their products that you can’t always get with a DIY project.

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About Jacob Marsh

Jacob is a researcher and content writer at EnergySage, where he focuses primarily on current issues–and new technology!–in the solar industry. With a background in environmental and geological science, Jacob brings an analytical perspective and passion for conservation to help solar shoppers make the right energy choices for their wallet and the environment. Outside of EnergySage, you can find him playing Ultimate Frisbee or learning a new, obscure board game.

9 thoughts on “What is a solar charge controller? Do you need one?

  1. Dalton Bourne

    Understanding what an MPPT or PWM solar charge controller does will help operate your RV appliances with clean, free, and efficient energy: An MPPT controller automatically adjusts the solar panels’ output voltage to recharge the deep cycle batteries. A PWM controller typically waits for the system voltage to stabilize and fall naturally before initiating the absorb charging state. I can say that the MPPT’s four-stage charging mechanism is better, safer, and healthier for your RV’s deep cycle batteries than a PWM’s three-stage design. A PWM charge controller is ideal for small-scale solar projects, generating less than 2,000 watts. The controller can accommodate up to 60 amperes and run on 12 and 24-volt systems. A MPPT is perfect for solar power systems that generate more than 2,000 watts. It can handle up to 100 amperes and operate on 36 and 48 volt systems.

  2. Rameshwar jadhav

    Need more information about solar charge controller and it’s working it will be increase voltage of solar panels like 12v input volts and output is 24v thank you wating for your reply

    1. victor Ejemerho

      Both charge controller work fine for any solar application.The statement made by the author that PWM is suitable for small solar arrays is incorrect..The basic advantadge an MPPT has over PWM is that it incooperate “voltage converter”. Stepdown converters are the main ingredient found in MPPTs in other words.And are very good in the winter season.If you are living in hot climate where the sun has long standing hours the pwm is the choice.

      1. Kent Evans

        Victor….. I’ve got a question. I have a new 60 amp PWM Controller. Specs say it will take up to 96 volts and 750 watts at 12 volts. I am charging 2/6 volt batteries combined into 12 volts. Shouldn’t I be able to us my 2 (60 cell) 38 volt 275 watt solar panels wired in series with this PWM??? Gives me 76 volts at 550 watts…… Or do I have to wire panels in parallel??

  3. Theresa Groff

    Do I need to sell energy back to power co if I have batteries.? $$$$cost of batteries.
    I think I want ground mounted solar panels with awesome open south facing aspect. Cost$$$ ???
    I live in CT.


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