Solar Help

She is fairly good looking, must run in the family.:B

Got a name?

Hi BFL,

What! No shade? *grin*

Great spot BFL!!

Jim

MickD wrote:
Several have said that I should get 2 panels to total the necessary watts needed.

I think they (including me too) said that you should get 2 panels with same total watts as one big panel, say up to 180W. You still can go with one 180W 12V nominal panel without getting into costly MPPT controllers (read below), but 180W panel is big and heavy.

Yes, there will be 8 brackets VS 4.

There won't be "more wire" with 2 panels. You will use the panel #10 wire to the roof junction box, and then a thicker wire into the rig. With 2 panels you run #10 wire from each panel to the same junction box. You already have those #10, they come with panels unless the panel is really cheap and small, and you will need some sort of roof junction bus anyway.

when I look at the specs for lower watt panels the IMP goes way down also the volts.

Panels up to 190-200W are - usually - 12V nominal. Vmp is around 17, give or take a little, and Imp is lower when wattage is lower. 2*90W wired in parallel will provide same Imp as one 180W.

BUT... if you look into some really big panels, like 200W or 240W, you'll notice that they have Vmp around 30. This means you can't use PWM controller anymore, and need to buy more expensive MPPT one.

HiTech wrote:
I double dare ya :)

Ok.--mena's sister the mermaid in her birthday suit (seen asking about solar panels--on topic!)

I double dare ya :)

mena661 wrote:

BFL13 wrote:
You are welcome.

LOL! You are on a roll today buddy!

Be careful or I will post a picture of your mermaid sister skinny-dipping

MickD wrote:
Several have said that I should get 2 panels to total the necessary watts needed. I have no problem with that but when I look at the specs for lower watt panels the IMP goes way down also the volts. What is the effect on charging the batts? Also that means more brackets and more wire and more holes in the roof.

Mick

As long as they are nominal 12v panels they will be fine. Just make sure total Isc does not exceed controller rating.

Isc is short circuit current or max amps.

BFL13 wrote:
You are welcome.

LOL! You are on a roll today buddy!

We should note that a "17v" panel is so named for its Vmp (?) and that its Voc will be 21 or 22v, but that is also called a "12v" panel since it is for "12v" batteries.

So the same panel can be called a 12v, a 17v, or a 22v panel.

Not to be confused with higher voltage panels like 36v ones that are called "24v" panels except if they are higher voltage to go with 36v or 48v battery systems.

controller sizing depends on not going over their rated input voltage spec from the panel(s), so you need to pay attention what voltage you are talking about. also note that voltage will rise when it gets cold, so allow for that extra amount too when sizing the controller for voltage input.

controllers also have an amps rating, so you do need to have some idea of your expected max amps and allow another 20% margin on top of that.

Nobody tells you your expected max amps for any given wattage of panels--except me! :) here it is:-

use the same for either PWM or MPPT, they are nearly the same for this purpose:

expected amps = chosen wattage/130w x 8.2

EG, 230w/130w x 8.2 = 14.5a (jimindenver gets 15a from his with MPPT)

EG 80w/130w x 8.2= 5a (the Isc of an 80w panel and what I got with my 80w.) It works and its free! You are welcome.