Still Don't Get It (Solar)

[Grodyman]

What will charge 2 6v golf cart batteries better, a single 270 watt high voltage panel with mppt or two 135 watt 12v panels (parallel) with PWM and why???? Thanks.

Gman

[Snowman9000]

Grodyman wrote:
What will charge 2 6v golf cart batteries better, a single 270 watt high voltage panel with mppt or two 135 watt 12v panels (parallel) with PWM and why???? Thanks.

Gman

I think as a practical matter the difference will be meaningless. Or as BFL showed, it will be a moving target. The most important decision in that scenario is probably the charging controls and specs of the controller. If you have sun, either 270W system will charge 2 6v batteries with power to spare.

[rjsurfer]

I can attest to the fact that smaller panels are the way to go on a small Rv roof. I could only find one open space to fit a large 50"x26" 200 watt panel on my roof. I could squeeze maybe one more but I couldn't walk around the roof safely, no place to step. And it was in the shadows of the antenna, vents and ac.

I went with 3 100watt panels 43"x20" for now and have space for 2 more and I'd still be able to navigate the roof safely without being on tippy toes.

Ron W.

[Canadian_Rainbi]

BFL13 wrote:
I have done it both ways now and can compare them in the same location and time of year on the same batteries.

It is the amps that charge the battery and they both do similar amps. You can set the same absorption voltage.

The charge controllers may have the same or different charging profiles but either or both could be suitable for the 6s.

The only difference for the batteries is that one set-up may get a few more amp hours in during the daylight available that day. Hit and miss on that. Sometimes the MPPT high wattage panel could do better and sometimes, such as when panel temperature is high, the PWM can do more amps and so AH.

They both work well so which to choose should be based on other things like panel size/roof clear spot areas, cost, perhaps wiring if that matters.

For portables, I have learned it is easier to lug around two 12v panels one at a time than one big 24v panel and to find places to carry them in the trailer when travelling. This is of no concern for roof installations.

I'd follow BLF13's advice. He has done a lot of definitive experimenting and real world research.

[JiminDenver]

A lot goes into properly setting up a system. Needs, wants, space, conditions, batteries, it's more complicated than a simple what is better. It is what is better for you. How much power you need and what fits where would be a good start.

[BFL13]

I have done it both ways now and can compare them in the same location and time of year on the same batteries.

It is the amps that charge the battery and they both do similar amps. You can set the same absorption voltage.

The charge controllers may have the same or different charging profiles but either or both could be suitable for the 6s.

The only difference for the batteries is that one set-up may get a few more amp hours in during the daylight available that day. Hit and miss on that. Sometimes the MPPT high wattage panel could do better and sometimes, such as when panel temperature is high, the PWM can do more amps and so AH.

They both work well so which to choose should be based on other things like panel size/roof clear spot areas, cost, perhaps wiring if that matters.

For portables, I have learned it is easier to lug around two 12v panels one at a time than one big 24v panel and to find places to carry them in the trailer when travelling. This is of no concern for roof installations.

[time2roll]

All things equal, MPPT will be slightly faster when the battery is low.

MPPT charges at full wattage less about 5% conversion loss.
PWM charges at Isc rating. Wattage will be Isc x battery voltage.

[Grodyman]

Golden_HVAC wrote:
Chances are that if you buy the 135 watt, they will fit in a area on your roof easy, like between the roof vents and sidewall. The 270 watt probably will only fit in one location on the roof, and take up a huge chunk of real estate. Or might not fit at all, if there are roof vents going down the center, and the A/C is taking up some space, and the antenna is in the front. Do you have space for a 60" X 75" panel?

For my money, I would rather have three panels in the 100 - 135 watt range and 3 PWM controller at $14 each than a 270 watt panel and $125 controller.

SunElec.com

There are many places to look for solar panels on the internet, this is one of the lowest priced places that I have found. THey have advertized in HOme Power Magazine for many years, and are reliable.

Fred.

Does this mean they will charge the same but the high voltage panel setup will cost more and take up more space? Thanks

Gman

[Golden_HVAC]

Chances are that if you buy the 135 watt, they will fit in a area on your roof easy, like between the roof vents and sidewall. The 270 watt probably will only fit in one location on the roof, and take up a huge chunk of real estate. Or might not fit at all, if there are roof vents going down the center, and the A/C is taking up some space, and the antenna is in the front. Do you have space for a 60" X 75" panel?

For my money, I would rather have three panels in the 100 - 135 watt range and 3 PWM controller at $14 each than a 270 watt panel and $125 controller.

SunElec.com

There are many places to look for solar panels on the internet, this is one of the lowest priced places that I have found. THey have advertized in HOme Power Magazine for many years, and are reliable.

Fred.