inexpensive panels

Boon Docker wrote:
Thank you BFL for that great explanation. Never realized that they varied that much through the day.

Now you see the "bigger picture"..

For the record, I never said that MPPT isn't worth it, just cautioning folks who think there is going to be some astronomically massive increase over PWM all the time.

You get a small increase in charging with higher voltage panel and MPPT, in a nutshell once the panel has enough sun to get it above 17V the controller now can start charging quicker (small amounts of course) and same at end of day when the sun is setting. Basically extending the time a panel can extract enough energy to start charging and maintain some charging current.

For a beginner just getting their feet wet in solar, a simple solar setup with 12V panel and PWM controller can allow them to see if spending more on solar is worth it..

Not every case will make it worth it so why muddy the waters?

Folks camping in shade for example would have to consider something more portable and moving 250W 24V panels would be a real pain to do. But yet, moving smaller 100W 12V panels would be much easier to do.

Example, Renogy 270W 24V panel HERE is 65"x40" (almost 5.5'x 4'!!!)and weights 42 lbs, you are basically wrestling a item the size and weight of a 4'x8' of a sheet 3/4" plywood!! Would be hard to store also..

A 100W 12V Renogy panel HERE is a much smaller and manageable size at 42"x20" (4'x 1.6') and weights 14 lbs. A much more manageable size and weight. AND you can ALWAYS buy two and wire in series if you really want MPPT.. Not to mention always can add more panels as you grow the system.

Large 24V panels may or may not fit on the RV roof top, not all RVs have 6'x4' open areas that would be needed for large 24V panels and yet may be able to fit more 100W 12V panels instead.

Sort of like a huge game of "Tetris"..

A 12V panel with MPPT most likely will not net very much additional charging efficiency, 24V or higher panel voltage is recommended if you really want to take advantage of MPPT.

12V panel systems can be upgraded, add more panels down the road, rewire the panels in series and add MPPT and get the best of both worlds.

pianotuna wrote:

StirCrazy wrote:


your in Sask, why not buy from blacksheep solar, thats where I got mine from, but I picked it up from one of there supliers in vancouver to avoid shipping charges.

Steve

Because their prices are far too high.

? I found them to be the cheepest I could find in Canada. I got my 24v 325watt panel for 218 most were wanting 250 for a used pannel with 75 less watts.

Steve

StirCrazy wrote:


your in Sask, why not buy from blacksheep solar, thats where I got mine from, but I picked it up from one of there supliers in vancouver to avoid shipping charges.

Steve

Because their prices are far too high.

BFL13 wrote:
If you are a salesman, percentages are a lot of fun.

when we did all this about eight years ago, using a 130w panel all day, it came out that around 8am you got 2.5 amp with PWM and 3 amps with MPPT.

So, 20% better with MPPT---wow!!!!

By high noon, it was more like 8 amps with PWM and 8.4 amps with MPPT for a percentage gain of 5%

that was where the battery voltage was held fairly constant by running a load on it so it would not get charged up. Why that? Because with MPPT, amps to the battery are output watts from the controller/ battery voltage.

So during the day, the battery voltage climbs so ever reducing percentage of amps to the battery for the same output watts. But output watts are also highest at high noon and lower in the shoulder hours.

You might still have a day where the overcast clears at noon and you are starting with best solar on a low battery. Say that is the case.

130w/12.2 = 10.6 amps , but then after an hour, with the solar strength still good, battery might be at 13.2, so
130/13.2 = 9.8 amps

So everything is in motion and as a salesman ("drummer") you can pick any percentage gain you want and not be actually fibbing--leave the scenario to the "small print"

Heck, at 6:30 am you might have 1 amp on the PWM and 2 amps on the MPPT and then be able to claim a 100% gain over PWM! Wow! But it is only 1 amp more (don't mention that!).

You do usually get a little more with MPPT. If it gets your batteries full by 2 pm instead by 3 pm with PWM is that worth anything? Depends!

people dont understand at high noon with the angle optimized then ya they will be simular outputs, where a MPPT shines is low light, partial shaded and off angle conditions.... hmm starting to sound like canadian campsites ;) on the camper I went with a 24V system and from the differences I motice over the 5th wheel I am upgrading the 5th wheel next. the 5th has 55 more watts than the camper (480 watts 12V compared to 325 watts 24v ) and I get more amp hours back to the batteries on the same day same location in the same amount of time from the "smaller system"

as far as I am concerned if you can save an hour or two of charging then ya it is worth it as that hour or two can be a big deal in inclamate conditions.

Steve

pianotuna wrote:
Hi all,


I know nothing about this firm--but the prices appear to be low:

https://www.santansolar.com/?fbclid=IwAR17Xx_DhkB3h13BFmTjqejxTlf92ZO7UsVEAiNjNmcyNzrOkJx9XgYN26c

your in Sask, why not buy from blacksheep solar, thats where I got mine from, but I picked it up from one of there supliers in vancouver to avoid shipping charges.

Steve

Thank you BFL for that great explanation. Never realized that they varied that much through the day.

If you are a salesman, percentages are a lot of fun.

when we did all this about eight years ago, using a 130w panel all day, it came out that around 8am you got 2.5 amp with PWM and 3 amps with MPPT.

So, 20% better with MPPT---wow!!!!

By high noon, it was more like 8 amps with PWM and 8.4 amps with MPPT for a percentage gain of 5%

that was where the battery voltage was held fairly constant by running a load on it so it would not get charged up. Why that? Because with MPPT, amps to the battery are output watts from the controller/ battery voltage.

So during the day, the battery voltage climbs so ever reducing percentage of amps to the battery for the same output watts. But output watts are also highest at high noon and lower in the shoulder hours.

You might still have a day where the overcast clears at noon and you are starting with best solar on a low battery. Say that is the case.

130w/12.2 = 10.6 amps , but then after an hour, with the solar strength still good, battery might be at 13.2, so
130/13.2 = 9.8 amps

So everything is in motion and as a salesman ("drummer") you can pick any percentage gain you want and not be actually fibbing--leave the scenario to the "small print"

Heck, at 6:30 am you might have 1 amp on the PWM and 2 amps on the MPPT and then be able to claim a 100% gain over PWM! Wow! But it is only 1 amp more (don't mention that!).

You do usually get a little more with MPPT. If it gets your batteries full by 2 pm instead by 3 pm with PWM is that worth anything? Depends!

Just finished reading a white paper posted on the Victron website about the difference between PWM and MPPT. An excellent in-depth read. It was stated in one example (PWM vs MPPT) that an MPPT controller could yield as much as 19% better harvest.

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.

Hi Chris,

I'd go for the 50 amp charge controller myself.