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M P P T   V S   P W M
S O L A R   C O N T R O L L E R S





 
Many of you may be wondering what the difference is between the old PWM type Solar Controllers,
and the new technology MPPT, and what makes MPPT so much better

MPPT = Maximum Power Point Tracking

We have compiled a small amount of information that will hopefully help you
to understand better what the difference is, and why you should choose
an MPPT or a PWM type Solar Controller for your system


MPPT vs PWM

Pros and Cons

MorningStar PDF





MPPT vs PWM


     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 wires 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 wires from the solar
     panels to the charge controller, power loss in the wires is reduced significantly.

     MPPT charge controllers are more expensive that PWM charge controllers, but the advantages are worth the cost. If you can afford it, you should definitely use an MPPT charge controller.

     The final function of modern solar charge controllers is preventing reverse-current flow. At night, when solar panels
     are not generating electricity, electricity can actually flow backwards from the batteries through the solar panels,
     draining the batteries. You’ve worked hard all day using solar power to charge the batteries, you don’t want to waste all
     that power! The charge controller can detect when no energy is coming from the solar panels and open the circuit,
     disconnecting the solar panels from the batteries and stopping reverse current flow.

Information from http://www.golandcentury.com/faqs/58-solar-controller/118-mppt-vs-pwm


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Pros and Cons


     When assessing which type of solar charge controller to purchase, you need to know about their functionality and features but
     it's also helpful to see a straightforward comparison of your options. To that end, we've put together a comprehensive look at
     the pros and cons of both PWM Type Solar Controllers and MPPT Solar Charge Controllers for your convenience!

 
PWM Type Solar Controllers
MPPT Solar Controllers
PROS
 
     - PWM controllers are built on a time tested
       technology
. They have been used for years in Solar
       systems, and are well established

     - These controllers are inexpensive, usually selling
       for less than $350

     - PWM controllers are available in sizes up to 60
       Amps

     -
PWM controllers are durable, most with passive
       heat sink style cooling

     - These controllers are available in many sizes for a
       variety of applications

     - MPPT controllers offer a potential increase in
       charging efficiency
up to 30%

     - These controllers also offer the potential ability to
       have an array with higher input voltage than the
       battery bank

     - You can get sizes up to 80 Amps

     - MPPT controller warranties are typically longer
       than PWM units

     - MPPT offer great flexibility for system growth

CONS
     - The Solar input nominal voltage must match the
       battery bank nominal voltage if you're going to use
       PWM

     - There is no single controller sized over 60 amps DC
       as of yet

     - Many smaller PWM controller units are not UL listed

     - Many smaller PWM controller units come without
       fittings for conduit

     - PWM controllers have limited capacity for system
       growth

     - MPPT controllers are more expensive, sometimes
       costing twice as much as a PWM controller

     - MPPT units are generally larger in physical size

     - Sizing an appropriate Solar array can be challenging
       without MPPT controller manufacturer guides

     - Using an MPPT controller forces the Solar array to
       be comprised of like photovoltaic modules in like
       strings

 

Information from http://www.altestore.com/howto/Solar-Power-Residential-Mobile-PV/Off-Grid-Solar-Systems/Comparing-PWM-and-MPPT-Charge-Controllers/a100/


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Updated September 2013