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INTRODUCTION
•
PWM regulators can produce as low as 100w from a 170w panel under full sunlight condition
and a max of about 140w in ideal conditions (battery V, temp, radiation …).
•
MPPT regulators will always produce
170w in ideal conditions (temp, radiation …) no matter
what the battery voltage is.
So now that you know the 1st and foremost importance of the MPPT we can discuss some added
advantages.
It is true that a MPPT helps to improve system efficiency by allowing a higher panel voltage to be
used, because power stays the same and power = V x I it means that the panel array current will
decrease, resulting in less volt drop in the cable, resulting in less power loss in cable. What is
important here is that this is only true if you keep the cable / conductor diameter the same when or as
you increase the voltage, if you use thinner cable because the current is less then you’re only saving
on system installation cost and
not gaining any efficiency
.
This gain in efficiency is normally almost insignificant when compared to the 1st most important
reason for using a MPPT gain of up to 70% increase in power (normally around 30% because battery
voltage does not always stay at 10v).
Do not use the MPPT to increase panel voltage, increase panel voltage to make your installation
easier and more economical. W
hat is very important to note
is that there is a limit to how much you
can increase the panel voltage on the MPPT.
Why is this so?
•
The MPPT (all step down MPPT battery chargers) uses a Buck regulator circuit to do the
power conversion.
•
These circuits do not operate at max efficiency when the input output voltage ratio is very high.
•
Try to not exceed a ratio of 1:4, this is especially true on 12v systems
.
For example:
If you charge a 12v battery do not connect 120v of panels to the MPPT the ratio = 1:10.
The MPPT display
a “High Panel voltage” Warning meaning that the MPPT is now operating out of
speck.
For a 12v system your max Charge voltage is 15v, so use a panel array with a power point voltage
(Vmp not Voc) between 15v and 60v (1:4 = 15v x 4 = 60v), then the MPPT will be efficient and you
will get maximum power transfer efficiency from your MPPT.
In essence your MPPT has 2 paths where the power flow, 1 path steps down and divides the voltage
and the other increases and multiplies the current.
If the ratio is 1:10, then each circuit has to work 10 times harder then what it would have worked if the
ratio was 1:1.
Having to divide the voltage by 10 and boosting the current 10 fold (turn 1 amp from panel into 10
amps into the battery), the difference in efficiency between 1:1 and 1:4 is minuscule and not worth
stressing about but when the ratio becomes greater than 1:6 then the efficiency is notably lower.
