Arco M35 PV Panels

[(unknown)]

First, can someone tell me what the rated output of Arco M35 PV panels is? I have six never used units that read 4 volts DC on my Fluke DMM on a cloudless day and pointed right at the sun. So my next question is, does anyone know how many of these units I'll need for a twelve volt system? I know that 3 times 4 is 12 but I assume that there will be voltage drop when a load is applied

[AbyssUnderground]

You will need at least 4 of these panels in series to use it for 12v, 5 would be better. 12v OCV is usually about 19-21v so 4 would make 16v. This would work, but 5 would make 20v which is considered normal for a 12v panel.

I did a quick search and I couldn't find any information about these panels.

[(unknown)]

Hey AbyssUnderground,

Thank you very much for the great information. After I posted this, I decided to look one more time for the manual and spec sheet that the company I used to work for provided with these systems. We manufactured and sold cathodic protection rectifiers that were used by oil and gas companines world wide. Well anyway I found the manual/spec sheet just about twenty minutes ago. I really didn't have much to do with the Solar side of the business so I wasn't sure about the specs. But the manual confirms your statement. Voc: 4.2V typical and Isc:  8.5A typical and

Vrated:  2.65V and I@Vrated:   8.1A minimum.

The first line of the spec sheet states that "The M35 module is designed to charge a 2 volt lead acid battery" I guess that would imply that you would need 6 modules for a twelve volt system.

Do you have any thoughts about that?

Thanks again,

bubba23

[AbyssUnderground]

You should go by OCV, so 5 should work great, 6 would just boost the OCV in lower light conditions and maybe push a little more current in low light.

[richhagen]

I would agree, in full sun, 5 would be fine, but the panels were designed apparently for 2V cells, of which a 12V battery has, of course, 6, and to charge in less than ideal conditions as well.  Rich

[ghurd]

They are old panels, well before the industry was forced to standardize.

I would go with all 6 in series. For sure.

The V rated of 2.65V, x 5 = 13.25V. Not good. Operation at a very slightly higher voltage than rated greatly reduces the output.

The 13.25V, deduct losses, like wire and a diode, and there is nothing left.

Most 12V PVs are rated at 17~17.5V at max power.

All 6 of these would only be 15.9V.  That's a big important 1.1V.

They may be an attempt at "self regulating" panels.

The idea has been abandonded. It doesn't work.

The spec sheet may prove this theory where it deals with regulation, or simply says 'connect a diode'.

ie: 2.65V-0.5V(Schottky diode)= 1 charged cell, with about no chance of overcharging under any conditions.

The saving grace is with 6 PVs in series, the diode loss only happens once.

I don't usually point to a new post, but 5 of these PVs would be operating near (past?) the drop off of the amps output. Same problem this guy has. His problems are from wire losses putting the panels in the situation of operating in the area of voltage where the amps fall fast. Yours would be from just plain starting voltages.

http://www.fieldlines.com/story/2007/4/10/161143/314

A decent solar controller uses mosfets and has much less forward V drop than a diode.

Heavy wire for the run to the batteries will keep voltage losses lower.

Using heavy wire, a decent controller, and all 6 panels will get the most power into the batteries.

Besides, what are you going to do with a single 2V 8A panel?

G-

[nothing to lose]

A bit late post Ghurd,

But I know what some of us would do with a single 2V 8A panel

Paralel charge single cells from Bruce Packs

2.65V? Could we series 2 cells? Paralel 40?