high voltage panels?

[greenkarson]

I'm looking to help my 12v micro hydro system  with 400 watts of solar.  I have found a local guy selling BP solar panels for 1.75 a watt.  I was assuming they were 12v panels.   The guy selling them says they are high voltage panels 107v open voltage.  But he says these will be perfect for charging my 12v battery bank (2x 8dcell batteries).  I'm not overly familiar with solar.  I'm assuming that the open voltage will just clamp down to my battery voltage and convert the rest into amps.  That being said 107v seems like a high open voltage I thought most 12 volt solar panels were around 20v.   
thanks for any info
( and of course they are selling fast)

[birdhouse]

karson-  i'd be cautious!  yes, he is right, they will charge your batteries, but only at a fraction of the rated output of the panels due to the HUGE mismatch of voltages.  the only way to make them work at their rated output would be to use a MPPT charge controller between them and you battery.  then the deal becomes less of a deal due to the cost of a spendy MPPT controller.  MPPT is able to convert high voltages to whatever the battery wants to see while charging. 

adam

[Rover]

What birdhouse said.

400W is not a large amount of solar, and going into 2 8D's , (I'm gueesing 500Amp/HR for the pair ?) , is not a bad match. But adding the cost of an MPPT controller that can handle 100 +V is going to be pricey. The array is large enough to fall out of the realm of the cheaper MPPTs (The low cost BZ HV for example which will only handle 250W).

I'd find some other panels closer to your batt voltage. You can find some deals.

disclaimer : I in no way endorse the BZ, I have one though.

[greenkarson]

any  guesstimates what that actual wattage would be hooked to my 12v battery bank with just my c40 charge controller per 100watt panel?
thanks

[greenkarson]

would this mppt controller do the job or one simuliar  http://www.ebay.com/itm/BZ-MPPT500-500-W-MPPT-PWM-SOLAR-CHARGE-CONTROLLER-/150684291684?pt=LH_DefaultDomain_0&hash=item23157bd264

[ghurd]

I think when the battery reached regulation voltage, the C40 would smoke.

400W array, ~87V peak power(?), 4.6A.
Still 4.6A into a 12V battery.
That's about the same as an 80W 12V panel.

I would pass on them.
Guessing they are amorphous?  Relatively short service life.
If crystalline, that's a whole lot of solder joints in one package with the possibility of having a bad one in there somewhere to show up in 5 years.
G-

[greenkarson]

All i realy know about them is that they are BP solar  glass 107V open voltage and are supposed to be 100 watt panels

[Rover]

It would probably work, but the max array voltage is 100V... just under your open  V, so a bit of a risk. As far as C40 , I don't know... someone else that has experience with them will.

As far as BZ.. there are better choices other than BZ... based on my experience with the smaller unit. Just my opinion. I also have a Blue Sky in the same class that does quite well, but it won't handle your  array input voltage.

I'd still rather go to a different solar array, makes life simpler

Rover

[greenkarson]

OK im convinced.  I thought it may be to good to be true.

[ghurd]

Data sheet for the C40 says it will take 125Voc.
Still, rated 107Voc is a bit close to 125Voc for my comfort.
G-

[greenkarson]

Ghurd  just to see if im reading it right.  These 400watts  at 107v would be about the same as a 85watt 12v panel  when hooked to a 12v batt bank?

[ghurd]

Correct.

Think of solar panels as current sources.
It will send about the same amps into a 60V bank as a 12V bank.

So all 400W combined, into a 12V battery, will be about the same as an 80W 12V panel.
(unless you go with MPPT)

G-

[greenkarson]

ok thanks

[XeonPony]

Personaly I would waste my hard earned mony on any thing but an Mppt controller they are worth their weit in gold imo, min has served amazingly well I run my pannels at 50voc due to the 40 feet of line and been geting great amounths of charge with my meagre static array

[birdhouse]

karson-

here:  http://www.sunelec.com/sun-solar-panel-30-watts-1870-vmp-p-850.html     are some panels that aren't very cheap per watt, but they're cheap per panel because they're small, and could probably be shipped UPS.  for under $200 delivered (guessing) you could atleast have 60w worth adding to your system. 

i'd order by phone, this company has some interesting customer service! 

adam