solar panel wiring

[ronsmith]

I am going to install several solar panels wired together in a series. The run from my panels to batteries will be about 100' to 120'. What size wire would carry the load without too much resistance? The panels will be in the 70 to 100 watt range.

[drdongle]

You didn't say what voltage you were using so as a general rule use the largest size you can afford, especially if its a low voltage set up (12-24 V)

[Psycogeek]

what he said for sure.

the next guage up has lots less loss of the guage your on till they call you PG&E :-)

here is one of them wire guide things

http://www.powerstream.com/Wire_Size.htm

notice the ohms per 100feet, not much huh? but in low voltage applications its all the difference in the world.

if the wire is an unruly beast, your almost there.

[ronsmith]

It will be a 12v system.

[ghurd]

Bigger is better.

To save money...

I have found sometimes a 500' roll is cheaper than 250' by the foot.

That could give you 4 wires at 120', for less money than 2 wires.

Naturally, it will all be the same color.

I mark the negative with black heat shrink and permanent marker.

Just a thought

G-

[drysider]

The wire size link is really useful. If you have a 40 amp load at 12 volts and a 120' run, you can see that you will need a very large pair of wires. Typically in solar work you try to keep the voltage drop below 2%, which, at 12 volts, is about 0.3 volts. Using the link, the wire size works out to 400 Kcmil. This is going to be both expensive and difficult to work with. You can either lower the length of run, or raise the input voltage to decrease the necessary wire size.

Pat

[ronsmith]

How can I raise the input voltage say to 24vdc with the solar panels? I intend to add more panels and possibly a small gennie later.

[ghurd]

Just like batteries.

Put 2 in series. 12+12=24. Amps stay the same.

The PVs must be the same.

G-

[ronsmith]

thanks for the info. I'm just getting started so looks like I will go with 24 volt system. I figured out and alternative location for my battery bank and its only about 75' from my panel location.

[ronsmith]

I purchased a roll of #6 gauge copper stranded wire. If I step my voltage up to 24v will the 120' run be acceptable?

[ghurd]

I'll say yes. Very acceptable.

A 5% chart shows 178' each way for 6 amps and #6.

So 2.5% is 90'.

Each way being PVs to battery.

With 100W at 24V thats about 6A, give or take.

And the losses are only when the PVs are making 6A,

which they usually are not.

The 6A is at high noon under perfect conditions,

so the losses will be more like 1% overall, maybe less.

It will even leave some decent room for expansion.

PVs are designed to make up for some loss and still make good amps.

I would not be at all concerned until you pass 15A, (500W rated PVs) at 24V.

And 20A (rated 700W) would not be out of the question, IMHO.

Just because the PVs can make 20A under perfect conditions,

doesn't mean they do 20A often.

The losses will be less than it seems, overall.

Like 20A for 1/2 hour, 15A for 2 hours, less than 10A for 1 hour,

far less than 10A for the rest of the day.

Meaning $500 extra for wire would usually be better spent on $500 in more PVs.

And when the controller kicks in as the battery becomes near control voltage,

the amps will go down even in good sun, so when the battery is near full

the amps go down either way.

Wire too small is still bad.

The chart I like...

http://www.windsun.com/Hardware/Wire_Table.htm

It has been a while so no one noticed the post.

G-