Solar Charge Controller Selection

Before you consider which charge controller is best for your off-grid or hybrid solar system it is important to understand the basic function of a solar charge controller. A charge controller, regardless of which type or brand, takes the energy collected by your solar panels (or wind turbines) and sends the energy to a battery bank where the energy is stored.

Charge controllers do just that – control the charge. Your controller will make sure your batteries are receiving the most energy they can get from your panels while making sure to never over-charging them. You can use many online calculators which incorporate Ohms Law (Amps x Volts = Watts) to size your controller to your system and any reputable solar charge controller company will offer sizing tools and online or telephone support to help you make the best decision on what size and voltage is best for you.

Two Types of Charge Controllers: PWM and MPPT

There are two main types of solar charge controllers; PWM and MPPT. PWM (Pulse-width modulations) is a much more basic model of charge controller and can be found on the market for extremely low prices.

The second type of charge controller, which has become much more common in recent years, is an MPPT (maximum power point tracking) controller. MPPT controllers are much more advanced and typically offer a larger array of functions to help protect and prolong the life of your batteries. A maximum power point tracking solar charge controller will take the best possible amount of solar energy captured by your panels and deliver that to your battery bank.

MPPT controller offer efficiencies of up to 30% over traditional PWM charge controllers and have the ability to adapt much larger solar arrays and higher voltages to your system which reduces the amount of cable needed, the thickness (and therefore overall cost of the cable) and the amount of panels needed due to the higher efficiencies.

The plus side to the standard PWM controllers is most importantly the cost. If you have a small solar array on a cabin or an RV and have no shading and full sun, a cheaper – less advanced PWM charger will work just fine for your needs. If you are looking to take your summer home or business off-grid then MPPT is a must.

Besides being able to accept higher voltages and larger solar arrays, most high-end charge controllers have many functions that separate them from any other competition in the market. For example, both Outback Power and Midnite Solar make MPPT solar charge controllers that are packed with features. These two companies are powerhouses on the market and have been innovators in the solar industry for decades.

Both Outback Power’s Flexmax line of solar and wind charge controllers and the popular Midnite Solar Classic are user friendly and programmable to adapt to a 12, 24, 36, 48 or 60 volt battery banks. You can adjust charging currents, limits and all other combinations of voltages and amps to give your battery bank exactly what they need to give you a long service life.

One of the best features, which is rarely found in a standard PWM charge controller, is the “equalize” function. Whether you have sealed or flooded deep cycle batteries you will eventually need to “service” them.

The most common batteries on the market for renewable energy are lead-acid batteries. These types of batteries as well as many others have plates that separate individual cells filled with either gel or liquid. Sulfates and other minerals build up on these plates and greatly reduce your batteries performance and utility lifespan.

What Outback Power and Midnite Solar have incorporated into their top-tier charge controllers is the “equalize” function which allows you to regularly charge your batteries at a high voltage for a regulated amount of time. This controlled surge of electricity knocks the sulfates and other minerals off of the plates and greatly increases battery performance and life span. When it comes to charge controllers there is no other brand that can compete with either of these two companies.

Now that you have an idea of what to look for and what the solar market has to offer take time to consider your budget, your long term needs and remember to never sacrifice quality if you don’t have to and the golden rule of off-grid solar – leave room to grow!


Please continue reading to find out how to choose your other solar components and which type of system is best for your particular use.

Kyle Johnston
This post was written by: Kyle Johnston 

Originally from Easton PA, Kyle Johnston is a solar installer and owns and operates 
Lux Aeterna Solar Energy in Antigua, Guatemala. He provides system analytics, product comparisons, finance studies, energy audits and everything else to make the switch to renewable energy easy for his customers.

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1 comment

  • A solar charge controller is needed in virtually all solar power systems that utilise batteries. The job of the solar charge controller is to regulate the power going from the solar panels to the batteries. Overcharging batteries will at the least significantly reduce battery life and at worst damage the batteries to the point that they are unusable.
    The most basic charge controller simply monitors the battery voltage and opens the circuit, stopping the charging, when the battery voltage rises to a certain level. Older charge controllers used a mechanical relay to open or close the circuit, stopping or starting power going to the batteries.
    More modern charge controllers use Pulse Width Modulation (PWM) to slowly lower the amount of power applied to the batteries as the batteries get closer and closer to fully charged. This type of controller allows the batteries to be more fully charged with less stress on the battery, extending battery life. It can also keep batteries in a fully charged state (called “float”) indefinitely. PWM is more complex, but does not have any mechanical connections to break.
    The most recent and best type of solar charge controller is called Maximum Power Point Tracking or MPPT. MPPT controllers are basically able to convert excess voltage into amperage. This has advantages in a couple of different areas.
    Most solar power systems use 12 volt batteries, like you find in cars. (Some use other voltages and the same advantages apply to these systems as well.) Solar panels can deliver far more voltage than is required to charge the batteries. By, in essence, converting the excess voltage into amps, the charge voltage can be kept at an optimal level while the time required to fully charge the batteries is reduced. This allows the solar power system to operate optimally at all times.
    Another area that is enhanced by an MPPT charge controller is power loss. Lower voltage in the wires running from the solar panels to the charge controller results in higher energy loss in the wires than higher voltage. With a PWM charge controller used with 12v batteries, the voltage from the solar panel to the charge controller typically has to be 18v. Using an MPPT controller allows much higher voltages in the cables from the panels to the solar charge controller. The MPPT controller then converts the excess voltage into additional amps. By running higher voltage in the cables from the solar panels to the charge controller, power loss in the cable is reduced significantly.

    jay ranvir on

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