Battery vs Grid tie type PV

[Kb2yht]

I'm sure this is answered here someplace, but my search skills are failing me.

People often talk about Grid-tied panels as district from battery panels.

I assume that they are taking about "12V" panels as battery type.

I have been told, but can not find any documentation, that 12v panels are less sensitive to partial shade. Does the lower voltage allow for different arrangement of cells, and more bypass diodes ?

Many thanks for any answers, or links to previous answers or resources.

[Sunking]

No the difference is Cell Count and operating voltage. 12 volt battery panels are 36 cells period end of story. But that is meaningless and not worth discussing.

What matters is how much it cost. Nothing else matters except cost. Battery panels cost 2 to 8 times more then GT panels aka $/watt. People get sticker shock when they look at PWM vs MPPT charge controllers. You can buy a 20 amp PWM controller for less than $40, but a 20 amp MPPT charge controller will cost you $200. So they cheap out and use PWM controller. Damn foolish.

It takes a 300 watt PWM system to equal a 200 watt MPPT system. However with PWM you must use BATTERY PANELS and larger wiring and more of them. A 300 watt PWM system will cost you $700 to $800 just for th eppanels, controller, racking, and wire. A 200 Watt MPPT system will cost you $400 to $500. Not to mention th eMPPT system is physically smaller with one panel only 1 panel. to get 300 watts with battery panels requires 2 150 watt panels wire din parallel;

[PNjunction]

I have been told, but can not find any documentation, that 12v panels are less sensitive to partial shade. Does the lower voltage allow for different arrangement of cells, and more bypass diodes ?

Two different issues - and Sunking has covered why using higher-voltage grid-tie panels is the way to go. That being said, I do power up my radio gear and whatnot with a bevy of 12v panels, controllers and whatnot.

But the question about being less sensitive to partial shade has to do with the difference between a mono/poly crystalline panel, and the "thin film" panels. Voltage has nothing to do with this.

Thin-film panels are less sensitive to partial shade. If you cover up half of it, it will only produce half the rated output. If you cover up a mono/polycrystalline over just one or two cells, or even a long shadow cast by your antenna coax, the output drops to nearly unusable.

The main difference is that thin-film is less efficient (takes more real-estate to to get the same power output as a monocrystalline panel, and has a shorter lifespan.

Note too that a thin-film's ability to handle partial shade is a *temporary* ability. Day-in-day-out shadowing across the panel will eventually take it's toll, despite the material's ability to handle the reverse-bias from the shaded areas better than a monocrystalline does.

Sooo... for camping, emergency use, times where you can't babysit the panel to keep it out of the shade, a thin-film is a reasonable idea - if you can stand the larger sizes it requires. But for a permanent installation - not the best idea in my book.

[Sunking]

But the question about being less sensitive to partial shade has to do with the difference between a mono/poly crystalline panel, and the "thin film" panels. Voltage has nothing to do with this.

Just to add to this 12 volt battery panels use the same cells GT panels use, just not as many. That is why 12 volt battery panels wattage is limited to about 160 watts or so give or take. GT panels with 80 cells go up to 325 watts.

No one should ever use Thin Film panels for anything.

[Kb2yht]

Thanks for the answers.

Given the nature of the application that had me looking in to 12v systems, it may still be more efficient from a construction and maintenance view to use a 12v PWM system.

The use profile is all 12 and 5V, no inversion. Less than 1kWh daily load with long quiescent periods between use ( one day on, 3 days off) .
A single pole side mounted panel and a low cost controller will be the right thing for this.

I will need to dig in to thin film systems more, since I will not have expert installers, so am likely to end up with partial shade issues on at least some of the systems.

[Sunking]

T
I will need to dig in to thin film systems more, since I will not have expert installers, so am likely to end up with partial shade issues on at least some of the systems.

You cannot use Thin Film with PWM. You will never find a Thin Film with a Vmp of 16 to 18 volts to use on a PWM controller. Thin Flim is for Solar Farms Venture Capitalist. They re cheap, build a cheap Solar Farm and sell it immediately for a profit. In 5 to 10 years the Thin Film will fail. Sun Light destroys Thin Film. Stay away from them.

It is never efficient to use battery panels with PWM. That is a looser game. You turn a 100 watt battery panel into a 66 watt panel. Try to use say a 200 watt GT panel with PWM controller and you turn it into a 90 watt panel. MPPT is roughly 95% efficient. 100 watts in, 95 watts out. At very best if carefully designed the absolute best efficiency you get with PWM is 66%. 40 to 50% is common.

PWM Input Current = Panel Current = Output Current
MPPT Output Current = Panel Wattage / Battery Voltage

PWM is antiquated.

[Bucho]

Battery panels cost 2 to 8 times more then GT panels aka $/watt.

Except that this isn't remotely true once one looks at the cost of shipping.

[Sunking]

Except that this isn't remotely true once one looks at the cost of shipping.

What shipping? Depend son where you live. Many cities all you do is go to the store or buy surplus from an installer. I had a garage full before I gave them all away.