36 volt solar panels

[veggie]

Many of the newer panels coming from China are 36 volt Monocrystaline panels.
I have an opportunity to get some 36v modules. (my charge MPPT charge controller can accept up to 50vdc)
Is there any advantage to going with the higher voltage 36 volt modules vs. the 24 volt modules ?

veggie

[mike90045]

You just have less amps in the PV dc cables, and the MPPT manages that.  Less amps = less loss.  Some MPPT may have lower conversion efficiency the farther apart the PV & battery voltages are, but I think that would be less than the cable losses.

[BruceM]

Your nominal 24V controller if spec'd at max of 50 volts has just 6V headroom from the 44V possible open voltage on a 24V nominal panel. There will be some ringing on the wire to the panels when being pulsed so that is not much margin at all.

The unloaded voltage on the nominal 36V panel could be 64 volts.  Your solar charge controller better have a rating above 64V or smoke will result on a sunny summer afternoon when the batteries are full.

[thomasonw]

Also note that Solar Panels become more efficient when they get colder.  Depending on the panel even if things do go well during the summer you might pick up 6-7v during the winter and on a very cold sunny day find the Magic Smoke gets released. . . .

[veggie]

Your nominal 24V controller if spec'd at max of 50 volts has just 6V headroom from the 44V possible open voltage on a 24V nominal panel. There will be some ringing on the wire to the panels when being pulsed so that is not much margin at all.

The unloaded voltage on the nominal 36V panel could be 64 volts.  Your solar charge controller better have a rating above 64V or smoke will result on a sunny summer afternoon when the batteries are full.

How did you arrive at 64 volts for an unloaded panel array?
I have now installed the array and at a temp of -5C on a clear sunny day, the open voltage at the combiner box is 42. (5 X 50 watt panels wired in parallel)
I can't load the panels yet because I still have to run some conduit/wire between the combiner box and the charge controller.

here's the specs on the panels...

veggie

[veggie]

Sorry guys, Just checked the manual and my max. array voltage input for the charge controller is 80 vdc. (Whew !... heavy sigh of relief) 
I understand how the panels put out more on a very cold sunny day. But how does the vOut get as high as 64v. ?

veggie

[BruceM]

Hey Veggie,
I was estimating your open circuit voltage for 36v panels using the open voltage based on my Monocrystalline 24V panels.  (42V)  I tested them myself (including under load) before installing them and it really was as stated.

I'm sorry to be the bear of some bad news about your panels.
The spec you listed is bogus- it shows the open circuit voltage being lower (35V) than the maximum power voltage (44V).  This is impossible.  They are likely labeling this incorrectly on purpose in order to sell junk to solar neophytes. Most buyers will only check the open circuit voltage against the label...

If your open circuit voltage is 42V for a 36V panel, then what you really got was a 24V panel, or you've got some bad cells.  Check each individually.

Some of the PV panels from China are junk.  I got a set of Chinese panels "Solar Cynergy" from SolarBlvd.com that tested  25% or more below the rated capacity, every single panel (5). "Solar Cynergy" is just the name SolarBlvd uses. SolarBlvd had switched suppliers in China to get a better price and never tested the panels, and in fact didn't understand how to test them. They took them back and sold me a name brand set that tested fine. They were honest, but incompetent.  At least in dealing with a retired engineer with the ability to do a full test and send them a written report.

You really have to suspect and test all bargain, no-big-name panels- they claim to be using quality cells, but they are often defects bought on the cheap.

What company sold you these panels and under what brand name?  

Best Wishes,
Bruce

[mike90045]

Some strange panels you got there, on the other side of that spec sticker.

anyway, how a 36V PV panel produces 50V, is when it is unloaded first thing in the AM, as it's waking up the charge controller, and every time the charge controller unloads it, to sweep for MPPT.   At the times the panel is not loaded, it's producing flat out, like an engine with a fixed throttle, when the load is removed, the RPM soars.  With  PV's, the voltage soars.

[veggie]

Thanks Bruce & Mike,

Please look at this label and confirm 24V panel....
(The model number gave me the first hint)

[BruceM]

Yep, the -24 in the model number tells the tale. It's a 24V panel. 

It's not unusual for the max power voltage to be well above the "nominal" voltage.


 

[mike90045]

The other "gotcha" with Voc, is cold weather.  the 43V is for 72f.   When the panel is colder, it will be higher voltage.  If your charge controller is only rated for 50V, you may need to verify this panel will not fry your controller, on a cold frosty morning.

Mike

[LowGear]

The Big Question:

How much do you save by buying these imports over units made in your own economic district?

Perhaps your neighbors or fellow taxpayers will spend their wages buying something that you market and will never sell to the economic arena that build and market these "great deal" devices.

Casey

[veggie]

The Big Question:

How much do you save by buying these imports over units made in your own economic district?

Perhaps your neighbors or fellow taxpayers will spend their wages buying something that you market and will never sell to the economic arena that build and market these "great deal" devices.

Casey

My own "economic district" does not make solar panels.
My Country doesn't make solar panels.
Other than my mistake interpreting the voltage spec's, these panels perform perfectly.

veggie