wiring options: What do you think of this?

sprintman
sprintman Registered Users Posts: 16
My newbie questions continue-- any suggestions or ideas about this--
3--215v Evergreen solar panels wired in series....now what I'm in part having trouble grasping is what numbers would this yield. I would be using something like a xantrex mppt 60 amp charge controller on a 12 volt battery bank. 12v because in have a nice inverter. eventually would add more panels and go to 24v.
specs on the panels:
open circuit voltage 35.60 Voc
short circuit current 8.12 Isc
Max power voltage 29.0V
Max power current 7.43 Imp

My questions would be what is the total voltage of 3 panels in series, what would there total amps be and what awg would I need to use for say a 30' run?
What size fuse would I use between the charge controller and panels?
Anl last but not least........does this system make sense?
My understanding is that having the panels in series and increasing the voltage decreases the wire size required and that this controller has no problem switching everything back around for 12v battery bank (6v batteries)
Thanks so much!

Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: wiring options: What do you think of this?

    To answer your last question first, I would ask, what it it you intend to do with this system?

    A typical off grid battery based system will yield, in WH something like this.

    Tke the name plate rating of thepv, divide by 2 to account for all cumulative sstem loses, then multiply that number by 4 to represent the number of hours of good sun you can reasonably expect, per day over the course of the year.

    So your system might look Ike this:345/2=172*4=690 WH/day.

    Avaoid the Biggest pitfalls of off grid solar, the first is to avoid the , Ready, Fire, Aim! Te second is people tend to overestimate the amount of solar harvest, while at the same time under estimate their loads, leading to poor performance.

    My best advices is, do home work before you buy any hardware. Keep in mind that battery based systems don't grow very well together.

    Best of luck, welcome to the forum and keep in touch,

    Tony

    PS. I suffer you read the following links: http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    I would also suggest understand the relationship between volts, amps and watts.

    volts*amps=watts.

    Double the voltge, and you reduce the amps by have for any given load, and therefore the wire size required to run that given load.

    Also understand how loads are expressed in watts, but loading is measured and counted in watt/hours.
  • sprintman
    sprintman Registered Users Posts: 16
    Re: wiring options: What do you think of this?

    I agree I definately need more education. To clarify my situation a little: doing a room addition one side of the roof will face south. This is on a summer cottage that may become permanent when I retire. Its kind of a hobby project--I don't expect to go off grid just want to supplement maybe 25%now maybe 50% later.
    Thanks to everyone who can help with answers to my questions. In my mind, with the money I have, the system I described is what I think is best bang for the buck---but is it? For various reasons a grid tie in is not practical now.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: wiring options: What do you think of this?
    sprintman wrote: »
    My questions would be what is the total voltage of 3 panels in series, what would there total amps be and what awg would I need to use for say a 30' run?

    For panels in series the Amperage remains the same; only the Voltage goes up. So you get an array with 106.8 Voc, 87 Vmp, and 7.43 Imp. You can use the Voltage drop calculator to get a precise wire size: www.solar-guppy.com/forum/download/voltage_drop_calculator.zip
    I'm guessing even 14 gauge would handle that over 30 feet.
    What size fuse would I use between the charge controller and panels?

    No fuse is necessary in this instance as all panels are in series. You need to fuse panels when you have more than two parallel connections.
    And last but not least........does this system make sense?

    Probably not. :p Off grid when grid is available is an expensive experiment. You're looking at $1 per kW hour over the life of the equipment.
    In terms of return on the $, conservation efforts will get you more.