How to Choose a Correctly Sized MPPT Charge Controller

Sizing is one of the most challenging aspects of choosing any solar power system components. There are many tools out there, such as oursolar panel calculator, that can provide an overview of how many and what type of panels you need. However, this can become more difficult to nail down for other components.

The charge controller is one of those components that aren’t always easy to size correctly. Many different factors are at play, including the capacity and voltage of both your solar array and your battery bank. There are also multiple types available, including the widely used maximum power point tracker (MPPT) charge controller.

What Is an MPPT Charge Controller?

Many individuals new to solar power systems might not be familiar with what exactly an MPPT charge controller is and what it does.Solar panel kits can make setting up your solar power system easy, but you should still have a thorough understanding of all of the components before you get started.

To make effective use of solar panels, you’re going to need a charge controller. They’re essential components that regulate the flow of electricity from your solar panels to your solar batteries, inverter, or direct DC loads.

Your solar array is certainly an impressive piece of technology, but the panels themselves operate on fairly simple principles. When light hits the panel, the panel generates electricity. That’s all well and good, but how much electricity is being generated and where is it going?

Without a charge controller, you can end up overcharging your batteries and seriously damaging them or even causing a fire or explosion. You would be at a similar risk of burning out your inverter or any DC loads connected to the panels as well.

There are multiple ways that voltage can be regulated when charging the battery. These include both PWM (pulse width modulation) and MPPT charge controllers. The MPPT charge controllers are generally considered to be the better of the two options, although both have their individual niches.

What Does an MPPT Charge Controller Do?

MPPT charge controllers implement the use of maximum power point tracking. This control method enables your solar powers to operate more effectively by having them output the optimal voltage at each moment. They’re widely used in high power systems where inefficiency is a major concern.

The MPPT controller accounts that your solar panels aren’t putting out constant voltage and current. Both are changing all of the time, which is bad news for your battery bank. The MPPT provides maximum charging by tracking the optimal voltage and current at any time to maximize total power output.

An MPPT charge controller is basically a DC to DC converter, an electronic circuit or electromechanical apparatus that transforms a direct current (DC) source from one voltage level to another.

MPPT charge controllers can shift voltages in order to optimize the output of yoursolar panels. The voltage from your solar panels varies all of the time as the intensity of the sun changes, although it does remain relatively consistent.

If you have a nominally 12-volt solar panel, its actual output will range from 16 to 18 volts. If you’re charging a 12v battery, that’s going to be too much. However, it doesn’t have to be reduced all of the way to 12 volts. Instead, these batteries require in the range of 13.2 to 14.4 volts.

The high-frequency DC to DC conversion carried out by your MPPT charge controller is a very precise process that requires carefully designed components to achieve. Because it operates at high frequencies, your charge controller can operate at higher efficiency. A charge controller makes this adjustment, and an MPPT charge controller ensures it’s done as efficiently as possible.

However, operating at such high frequencies means there’s the potential for your MPPT charge controller to lose power through broadcasting, effectively turning into a radio transmitter and potentially interfering with radio devices. Quality MPPT charge controllers are carefully designed for noise isolation to avoid this problem.

Is an MPPT Charge Controller Worth It?

In most situations, the primary thing to consider is weighing the benefits of MPPT charge controllers against their costs. They’re the best solution for almost any solar power system, so the only reason not to choose them is if you don’t believe that the increased efficiency justifies the increased price.

Anywhere with cold weather will see a significant benefit from having an MPPT charge controller. In fact, your solar panels work more efficiently at colder temperatures due to increased open-circuit voltage. There are many critical conditions in which MPPT charge controllers are particularly effective.

Making optimal use of each moment is well worth investing in an MPPT charge controller. However, you need the efficiency delivered by MPPT solar charge controllers to take advantage of that power. This is particularly important during the winter months when there are fewer sun hours each day.

In colder conditions, the voltage of your solar panels will increase beyond the nominal peak power output, generally tested at 25°C (77°F). Only an MPPT charge controller can effectively capture this higher voltage.

This will also depend on the layout of individual battery systems. If your solar power system is set up in a way that batteries are frequently reaching low battery charge, then you definitely want the maximum power point tracking MPPT charge controllers provide. They can deliver significantly faster charging for low batteries.

The increased speed at a low charge could make a significant difference in the viability of your solar power system. An MPPT charge controller can get a lithium battery from low to fully charged faster with deep cycle batteries.

You can also significantly increase efficiency for any solar power system that includes long wire runs. If your battery storage is far away from your solar panels, there could be a significant voltage drop across the wire. That means you’ll be dealing with a power loss as well.

The best way to get around this is to wire panels in series to get higher voltages. However, this means you’ll need to efficiently reduce that voltage for your batteries, even if you’re dealing with a 24v battery. MPPT charge controllers give you greater versatility for your solar power system design.

What Is Better: MPPT or PWM?

Your other option for a charge controller is PWM. This is a much simpler device that can protect your batteries from overcharging but won’t optimize power output for maximum charging.

In practice, the PWM charge controller is simply a switch that turns on and off. It connects the solar array to the batteries and will turn off as needed to regulate voltage.

Because the PWM charge controller only allows for on and off positions rather than varying voltage and current, there is an inevitable power loss. This power loss can be as much as 30% of the power put out by the solar panels.

The primary reason you would choose a PWM charge controller is the reduced cost. They are much simpler components that cost less than MPPT charge controllers. In many cases, the increased efficiency of the MPPT charge controllers makes them the clear winner due to energy savings over the years.

PWM charge controllers can still be effective for smaller solar power systems where efficiency isn’t a significant concern.Camping solar panels might only require a PWM charge controller due to the limited use and power output required.

MPPT charge controllers are generally your only choice when dealing with higher voltage systems. They’re basically only suited for portable use. You would never use a PWM charge controller for a home or cottage.

Any kind of portable solar system being used to charge devices on a trip likely isn’t worth the added expense of an MPPT charge controller. However, once you start looking into the kinds of solar power systems used for RVs, cottages, or even homes, an MPPT charge controller is likely the best way to go.

One scenario where PWM controllers are suitable is when the solar array has an output much larger than the power draw on the batteries. Basically, if you have far more solar panels than you actually need, then using a PWM charge controller won’t result in any serious losses.

Many modern grid-tie systems also require MPPT charge controllers to operate properly. These systems might create strange voltages that don’t correlate cleanly to common battery sizes. This means that MPPT charge controllers are the only effective method for charging battery banks from these grid-tie systems.

What Size MPPT Do I Need?

Your MPPT charge controller needs to be the right size to work effectively with your solar panel installation. Determining the right size isn’t always easy as individual solar power systems can vary widely, and there are so many factors to consider.

To obtain a rough estimate of the correct size for your MPPT charge controller, you can compare it to your total battery bank capacity. The amp rating charge controller should be rated for between 10 to 20% of the full bank capacity in amp-hours. However, a lot more goes into it than that.

Watt Capacity

Your solar panels have a capacity in watts being output to a battery at some voltage. Dividing the power in watts by the voltage will give you the current in amps, which is the sizing parameter for your MPPT charge controller. You can also determine this value based on the size of your solar panels.

For example, six 200 watt panels would provide 1,200 watts total, which could be divided by 12 volts to give 100 amps. That means you would need at least a 100 amp charge controller for your system. However, that isn’t the only thing to consider. Keep in mind that this will be different for different panels and other battery voltages.

To ensure that you’re really getting the highest efficiency from your system, you’ll have to include some room for deviation in these values. Almost every component of your solar power system will be designed a bit larger than required to account for this.

Charge Controller Capacity

Your charge controller should also have some excess capacity, and for an MPPT charge controller, you might expect to require 50% excess or more. However, this will vary based on individual factors among different solar power systems.

Choosing the best MPPT charge controller isn’t just about choosing the right size. There are plenty of different features that you can find from different MPPT charge controllers that can further influence your decision. You also want to ensure that you’re getting quality equipment from reputable manufacturers.

Many include Bluetooth compatibility for more convenient monitoring and control. These models provide easy access through a mobile app to provide users with more direct information about their solar power systems.

You also want to make sure the MPPT charge controller that you eventually settle on has several key safety features. Overload, over-discharge, reverse polarity, short-circuiting, and reverse current are all issues that can cause severe damage if a sub-par charge controller is used. Quality charge controllers have built-in protections against these potential dangers.

The actual maximum power point tracking methods employed by the charge controller can also vary. Improvements by some models can lead to even greater efficiencies, which means that you should also be comparing different MPPT charge controllers based on their efficiency, as well.

Renogy Solar Power Charge Controllers

You need to know that you’re making the right choice for your charge controller regarding capacity, safety, features, and quality. At Renogy, we have a wide range of solar power components available, including the latest MPPT charge controllers. Our selection ranges from 10 amps to 100 amps for any solar application.

In addition to our charge controllers, we have a variety of accessories like remote monitoring screens, Bluetooth modules, and battery temperature sensors to maintain complete control over your solar power system. Renogy is your source for quality solar power components of any kind.