Please excuse this basic question. Can someone give some recommendations on the type of wiring I should be doing for my system?

I have 10 Sharp 185 panels going to an pair of Outback Power inverters. The specs on these panels are:

Voc = 44.9V
Vpm = 36.2V
Isc = 5.75A
Ipm = 5.11A
Max System Voltage = 600VDC
Series Fuse Rating = 10A

These panels have MC connector pigtails already connected to them.

I have gotten the recommendation from Outback Power that 2 panels should be wired in series and then connected down to the charge controller (times 5 sets, of course).

I am near Washington, DC. I think the latitude around here is 39 and the weather is generally temperate, but it can get cold for a couple of weeks during the wintertime. Summertimes are generally in the 80's to 90's.

The run from the panels on the roof to the charge controller in the garage is about 50 feet.

In trying to purchase extension cables for these MC connector equipped panels, I have com across 12ga and 10ga wires.

Using a table from Outback Power's web site, they offer wiring size suggestions for a maximum 1.5% voltage drop. They have tables for 12V, 24V, 48V, 60V, 72V arrays. Despite the Voc and Vpm figures above, people seem to want to refer to these panels as "nominal 24V" panels. Is this correct? If so, then 2 panels wired in series would give a 48V array. The maximum amps that will be put through should be around 12A, but the MPPT charge controller should try to keep it around 10A. Using Outback's table again, for these parameters (48V, 10A), they give me 72 feet with 8 AWG wire. But that is the smaller wire they list. What can I expect if I use 10 AWG wire? Will the voltage drop over 50 feet be reasonable with this smaller wire? If so, I can make 5 runs (1 from each pair of panels) down to a combiner box before putting the PV output into the charge controller. What size wire would be recommended between the combiner box and the charge controller if the run is going to be < 5 ft?

Or would it be better to place the combiner box closer to the panels if all I can get is this 10ga wire? Then run a single pair of bigger sized cables (I happen to have a supply of 4 AWG cable here in the garage) down to the charge controller?

Your thoughts would be appreciated.

Best wishes,
David Hwang

David,

I'll take a shot at answering this.

Actually each pair of panels will put out current limited by the lowest of the pair while the voltage is added. So, each pair of panels should output 73V @ 5A (or less) at MPPT. The entire array of 10 panels will be somewhere on the order of 73V @ 23-25A. If the charge controller is the Outback MX60, it is rated to 60A.

Five 50' runs of 10AWG would give you a current of ~5A per run and a voltage drop of ~1% @ 48V. Here is the table I used:
http://www.jhlarson.com/ind_table.htm Since most solar arrays are planned for a multi-decade life you really want to keep any losses as low as possible. A combiner box and 4AWG runs (25A) actually has a slightly higher loss (~1.5%) than the multiple 10AWG runs.

Overall it appears that the 50' MC cables should be cheaper and more efficient than 5' MC plus a combiner and the 'free' 4AWG you already have.

Sean

David,
where did you get your MC connectors? I have 4 Sharp 185's I need to get set up
Robert in Rockville
(are you gonna be on the Solar home tour?)