24 volt panels

[copperhead1971]

What should a 24volt panel put out on open circuit? one of my friends have some that put out 44volts open , and I have some 12volt with 22 volts open circuit , would that mean they were 24 or 36 volt panels, I have never heard or 36 volt panels ... thanks for the replies...scott 

[gww]

Your 22 volt open is probly a 12 volt panel putting out about 17 or 18 volts under load.  I think a twenty four volt panel would be about 36 or so under load.  12 volt batteries are not really 12 volt but more like 12.8 or so resting and to get charged it takes about 14.4 or so volts. Some differance base on differant battery makers.
good luck. 
gww

[birdhouse]

What should a 24volt panel put out on open circuit?

there are a few ways to look at it.  with a standard (PWM) charge controller, i'd say a BARE minimum of 37Voc with a 30Vmp for a 24v bank.  these may not equalize all that well, but will push really hard during the bulk portions of the charge. 

you could always series two identical 12v panels for a 24v bank.  i do this with two 18Vmp panels in series yielding 36Vmp into the bank.  not matched all that well, and thus don't ever push there nameplate wattage, but they easily equalize. 

then there's mppt charge controllers where you can run upwards of 150V into a 12, 24, or 48v bank.   

my ideal set-up for 24v if i didn't have money for mppt controller(s) would be about 80% 30Vmp panels, with 20% 36Vmp with the two different types of panels on two different charge controllers.   

adam

[dnix71]

Copperhead1971 Your country shows Canada. You need to be careful about voltage in a cold climate. The ratings on panels is tropical sun at 20C. The voltages on certain panels will go way up below 0C. If you used a controller a cold day could fry it.

The Midnite Solar Classic series have 150 to 250 volt plus battery voltage (up to 48v) tolerance for clear cold weather. Those controllers aren't cheap, but the Xantrex 60 can only handle 140v. At 150v it shuts off and logs the event.

Cheaper controllers will just fry.

[copperhead1971]

thanks for the reply's ,... so I gather from this that it is possible for 24V panel to produce 44V open circuit? 

RE:dnix71... I live in Southwestern Ontario almost as low as you can go in Canada,I have only noticed slit differences from winter to summer ,
                    Winter less light hours, but smaller molecules make more power
                    Summer more light hours ,larger molecules makes less power but the longer light hours make up the difference lol

[ghurd]

Sounds like you are on the other side of the lake from me.

thanks for the reply's ,... so I gather from this that it is possible for 24V panel to produce 44V open circuit? 

Yes.  Maybe a bit more.
I tested 36 cell PVs at over 22Voc when it was not even cold.
And I had some GE or BP panels with 40 cells, so they would/could have been (40/36*>22Vov =) over 25V, which would make 2 of those in series, or a 24V version, over 50Voc.

I believe good quality controllers are either designed to handle this, or give detailed data sheets explaining why they can not.
Just a bit of current flow drops Voc a huge percentage.  It would not be hard to make something to deal with wasting a bit of current at a certain voltage, which would drop the "apparent Voc" greatly.
Pull a vary small fraction of the rated amps out, and the Voc will drop like a rock.
Some 1W Zeners and a few 1W resistors would do it?  Maybe?
G-

[ChrisOlson]

What should a 24volt panel put out on open circuit?

If it's 60 cell it'll be 37.  If it's 72 cell it'll be 44.  This varies with temperature, though.

A true 24V panel with be a 72 cell.  The 60 cell ones were made for grid-tie setups because they run at ~30 Vmpp and they can be series connected 15 in series for 560 Voc/460 Vmp grid tie inverters.  However, the 60 cell panels work nice for off-grid battery charging systems too if you series connect them to the desired voltage and use a MPPT controller.

A 60 cell panel, straight up, will bulk charge a 24V bank OK, but on a hot day it will struggle to get the bank to absorb voltage.
--
Chris

[tecker]

 Ok the factors posted to a panel design are
Pmax power max
VOC voltage open circuit
Isc current short circuit
VMPP voltage at power point
IMPP  current at power point
 The conditions for these measurement are probably unrealistic or you may see these conditions for a short
time period in the heat of summer
 You may as well start you systems with integrated meters that will give some current stats for you to track
as there's no shortage of BS in the stats the manufacturer boasts

  For the most part you can follow the Vmpp to connect your loads or the PMAX / ISC .
Panel Longevity will be effected by the panel Temp and the materials used to build the panel . Most of mine have
burned in and follow the specs for the most part but I pulse the panels at mid day.