FWC wrote:
pianotuna wrote:
Ok,
In simple english. MPPT takes the "extra" voltage from the panel, changes it to pulse dc (or is it ac at that point?), transforms it down in voltage and delivers more amps out, than amps in. While doing so, it has an overhead (loss) of about 4%.
PWM does nothing with the extra voltage so that is "wasted" power.
The most famous example of MPPT was a unit called "heliotrope" It worked so poorly that it consumed more power doing MPPT than it produced. The unit was heavily marketed by AM Solar. It was the early days of MPPT at the consumer level.
Does MPPT work better than PWM and harvest more watts? The answer is a resounding "It depend". Often it does. But sometimes, it does not.
If you want to go MPPT, then go high voltage on the panel side, the higher the better so long as you don't exceed the input voltage. The trade off is the higher the voltage, the more loss at the charge controller. But the higher the voltage, the earlier and later in the day charging will be presented to our ever hungry batteries.
If you want PWM then go with panels that do around about 19 volts (plus or minus 2 volts).
What ever choice you make--enjoy having the nearest thing to a free lunch you are likely to find for as long as you have the system. Mine is now 15 years old and still producing its rated output. I'm as happy as a clam--even if it is rather small by today's standards.
Nice simple description.
I would add that MPPT always produces more power than PWM, how much more is variable. Contrary to the bunk from Bogart, unless the Vmp is < 4% above Vbattery (which would be a vanishingly rare situation in a properly configured system) then MPPT will produce more power. The other advantage of MPPT is that you have much more control - you can regulate both voltage and current.
Wrong, you cannot "control" the current even with MPPT.
You are "assuming" that the battery is like a fixed resistor, it is not. You cannot FORCE more current into the battery than what it can "absorb".
The ONLY real advantages to using MPPT is it allows you to use mismatched panel voltages from the battery voltage, allows panel voltages twice or higher than the battery voltage, the higher panel voltage allows for use of smaller ga wire but yet yield more panel wattage, allows charging to commence EARLIER in the day and to continue LATER toward evening which allows you to harvest longer and netting a bit more yield.
Example, two 100W "12V" panels (17.9V VMP) in parallel gets you about 11.5A (about 5.75A each panel)
same panels in series now gets 35.8V VMP at 5.75A..
Both add up to 200W..
17.9 x 11.5 = 205.85W
38.8 x 5.75 = 205.85W
The difference with MPPT is once the series panel gets at least 2V higher than the battery voltage it can start charging.. While it may start charging, it may not have enough current from the panel to be able to harvest full 200W until later when the sun is more direct on the panel.
MPPT has ZERO to do with how or what "modes" it is in for battery charging but more with getting enough voltage from the panels to start charging FASTER and LONGER over the entire day..
Your arguments are not valid because you are ASSUMING that the MPPT cares about the load attached and is regulating the load current attached, it is not.
In reality, MPPT is regulating the VOLTAGE just like PWM does to the load which regulates the CURRENT but the CURRENT is HIGHLY DEPENDENT ON THE BATTERY STATE OF DISCHARGE (IE voltage of the battery) and or load..
Voltage AND current work hand in hand, you cannot separate the relationship without affecting the other.. The battery adds in an unknown dynamic to the whole mess.
Watts is watts, you can't get more watts with MPPT only a bit longer charging cycle.
Piano gets it, BFL gets it, I get it, you don't get it..
