MPPT and PWM Solar Charge Controller differences, advantage and disadvantages are discussed in detail in this article.
What is MPPT Controller?
Charge Controller an MPPT (Maximum Power Point Tracking) is a controller used to optimize the connection between solar panels and your battery, utility and grid supply. The maximum power point (MPP) is the optimal point on the I x V curve between current and voltage. These are fed into the system at the maximum current that can be generated in a given moment from the PV panel.
Difference between MPPT and PWM charge controller
PWM (pulse width modulation) and MPPT (maximum power point
tracking) charge controllers are DC to DC converters that convert the voltage
output voltage from the solar panels to a voltage more suitable for charging
the battery bank. PWM charge controllers are usually older and cheaper devices.
These are for small systems only. They have a charging efficiency of only 70%
to 75% of the current generated by the solar panel.
The main difference between MPPT and PWM charge controllers
is that the MPPT charge controllers allow the PV array output voltage to be
higher than the battery bank. It also converts the high voltage received from
the PV array output into high current and charges the battery. This means that
the battery is fully charged and the grid supply is cut off to operate other
electrical equipment and the output of the PV array output voltage is changed
directly.
A standard PWM charge controller can only control the
output voltage of the PV array. But it cannot convert the over-produced PV
array voltage into current. A PWM charge controller can only maintain the same
current as the PV array. This means that there are no systems in place to make
full use of the output power (current x voltage).
MPPT Controller
MPPT controllers are second generation solar controllers.
Compared to the PWM controller, it incorporates more control devices such as
power Transistors, Inductors and power Diodes. So, it shows more powerful
actions.
As an MPPT charge controller monitors the PV array for
maximum power point, it will track the output voltage of the PV array and try
to increase the maximum current. Normally, this increases the voltage coming
from the PV array to the current and maintains the majority of the total output
power.
The use of MPPT is essential for large PV systems, as it
greatly improves system design and performance. MPPTs are made in multiples of
the 12V range, which is a typical battery voltage. It is usually used in series
(12V, 24V, 36V, 48V, 60V, 72V) up to 72V. So far it has been said about the off
grid solar system because the batteries used for backup are off grid. There is
no need to use batteries for backup on-grid as it works by grid supply sense.
Advantages of MPPT
MPPT charge controllers are modern technology, because they
are done with, these will work more efficiently. This means that its DC to DC
efficiency is 90% to 97%. Many companies seem to offer more flexibility when it
comes to design. MPPTs can be built from small systems to large systems.
Another advantage is that they get longer warranties from the manufacturer.
Disadvantages of MPPT
- The MPPT charge controller is more expensive than the PWM
- The size will be larger
PWM vs MPPT difference in design flexibility;
Scenario 1: PWM
If a PV system is designed with a PWM charge controller. We choose to use a 250 watts solar panel with 26.31volt Vmp and 9.5 amps Imp.
Calculation: Vmp x Imp = maximum power point
26.31V x 9.5A = 250Wats
9.5A (Imp module of PV module x 12V (battery voltage) =
114W
If a 12V battery is used as the storage system. Ignoring
the charging features of the battery, the output voltage of the solar module
can be reduced to 12V to charge the battery. But if a PWM charge controller is
connected, it can be assumed that the output current is uncontrollable and the
following result will be obtained.
9.5A (Imp module of PV module x 12V (battery voltage) =
114W
Scenario 2: MPPT
Design a PV system with an MPPT charge controller. It can
be calculated using the same solar module mentioned above. The PV output
voltage has to be reduced to match the charging voltage of the battery by about
12V. However, the MPPT output current is increased at this time to maximize the
overall power transfer.
Follow these calculations to find out what the optimal
current rating of the output would be.
Maximum Panel Output Power / Battery Charging Voltage * Temperature Correction Factor
This means that the maximum output current can be obtained from the MPPT, causing very small losses.
Selection of MPPT and solar panels
Solar panels are available in 12 volt and 24 volts. E.g.
100 watts - 12 volts, 275 watts - 24 volts, 380 watts - 24 volts, 395 watts -
24 volts, 440 watts - 24 volts. Poly crystalline and Mono PERC crystalline solar
panels are available in the market today in many sizes, watts and volts. So,
choose only after you have a good understanding of solar panels. These are
selected based on various factors, mainly space constraints. Learn more about Solar Panels.
Conclusion
PWM and MPPT controllers have their own advantages and
disadvantages. Depending on the design features, cost, external control and
environment of the solar photovoltaic array, decide which scheme to choose.
If the output current of the larger panels mentioned above
cannot be adjusted, there may be a significant voltage difference causing power
loss. Only one MPPT can convert it to current as it receives more voltage from
the output of larger panels. It is in this context that the differences and
significance of MPPT and PWM need to be understood.
