MPPT CHARGE CONTROLLERS VERSUS PWM
(Maximum Powerpoint Tracking Versus Pulse Width Modulation Controllers)
MPPT charge controllers’ benefits far outweigh those of PWM controllers.
Why:
A charge controller limits the voltage coming from the panels to that suitable for battery charging say around 14Volts for a 12Volts battery bank. A PWM charge controller effects this by simply cutting out the extra voltges. An MPPT will, simply put, convert the extra voltages to current.
Operation principle
PWM
PWM controllers were the pioneers in the industry. They simply monitor the panels’ output and lower it to required value (voltage) by simply shearing off the extra volts. Take for example a solar module designed to supply a current of 5A at 15V. The panel will almost never generate power at the stated values because the output is dependent on the weather conditions. Current and voltage will vary with vagaries of solar insolation. Say for example our panel at a certain time during the day delivers 3.5A at 18V. The controller will cut off the extra 3 volts and here are the ramifications.
Intended power output , 5*15= 75 Watts.
Modified output by the controller: 3.5*15= 52.5 Watts.
PWM will be responsible for up to 30% power loss
MPPT
MPPT controllers pick up all power generated by the module and convert it to AC. The power is then conditioned to values suitable for charging the battery bank by a special cylindrical transformer called a toroid transformer. Then the power is converted back to DC at the battery bank charging voltage. The extra volts are converted to amperes so that power remains constant (P=VI). This means all the power generated by the modules is delivered to the batteries.
What is maximum power point tracking?
An MPPT identifies the maximum point in the panel power curve(IV curve) and latches to this power point. Power from the module will be extracted at parameters defined at this point(V & I). This point is defined at the maximum voltage at which the current just starts dropping.
An MPPT IV curve, notice the maximum power point
The MPPT traces the point where the panel current just starts dropping (maximum power point).
Output from the panel is maximized with no power losses.
INVESTING in an MPPT is worthwhile because this will lower the number of panels required for a system saving on cost and spave.
Morningstar have the best charge controllers in the industry, PWM and MPPT.
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