inexpensive panels

Boon Docker wrote:

Gdetrailer wrote:

MPPT does not always "equal" "more power" or "longer charging" either, there are limitations on how much energy the panel can actually efficiently garner from the given strength and duration of the sun that falls on it. MPPT attempts to maximize what can be harvested but in many cases you will only be talking in fractions of Ahrs per day over a PWM controller with a single 24V panel. Not uncommon for home panel arrays to be wired for 48V and higher..

Could you possibly show how many fractions of AHrs harvested: Using PWM and MPPT controllers using the panels below with all conditions being the same.
- 250 watt 24V panel (VOC 37 V - Imp 8 A)
- 250 watt 12V panel (VOC 20 V - Imp 12 A)

You attempting to use pure math, you CAN'T "assume" that MPPT will net you considerably more so your "example" is fundamentally flawed.

Not all MPPT controllers work the same, not all MPPT controllers act the same, they depend on "algorithms" in the firmware with minimal flaws and even then they may not necessarily result in any more energy harvest or even minimal extra harvest. MPPT controllers are "computer controlled" so they are not really just a straight "DC-DC" controller.

Sometimes a cheap PWM can harvest just as much as a cheap MPPT or even moderately priced MPPT.

Perhaps reread Pianotunas post..

pianotuna wrote:
Boon Docker,

For equal wattage panels, MPPT may, under some conditions, harvest about 10% more. But it has to be a quality MPPT. Research heliotrope controllers for an example of a lousy mppt.

So with 12 volt panels, given current low costs--it may be better to do an extra panel.

On the other hand, if you want every erg of power--populate the entire roof, use electronic actuators for tilting, and use a top of the line MPPT controller.

If you go that far, then consider jumping to a 48 volt battery bank, with SiO2 batteries for storage.