Need help with battery choice and wire size

System
System Posts: 2,511 admin
Hi,
I am amazed and humbled at the depth and quality of the answers I see posted here and request some help before I make (more) mistakes! I will try to give all the info you need, if I left something out please let me know.

I have a 10 year old old battery back up system in my house with manual transfer panels and 12v inverters, batteries were charged by the grid and used when the power goes out (in Breckenridge CO at 10,000 feet so it gets a little chilly and expensive if you get frozen water pipes!) typically for four days due to wet snow/downed trees n the grid.

I am "upgrading" my system to 12 Solar World sw230 mono panels mounted on my roof approximately 50 feet from the crawl space where batteries and inverters are (i know not a good idea, so inverters will be moved into the garage on the other side of the wall maybe five feet from battery bank) I have been using 12 12 volt deep cycle marine batteries from Wally World and they are dead, I would replace 2 or 3 batteries
with new ones (I know, I am learning! lol) to the bank.

I ordered 2 Morningstar mppt 45 controllers a combiner box, a disconnect box(nope, another mistake on the original design) auto fuses ebay #280633598436 in sizes from 80- 250 amps as I got conflicting advice from three retailers, I bought a variety as they are cheap but I wonder if they are up to the level necessary for my system as opposed to expensive panel breakers...

My 12v charger/ inverter is xantrex freedom marine 20 an the second one is dead, why I am upgrading everything.

So I am asking what size wire (i was looking at 0 gauge welding wire?) ground wire and how you suggest i attach the panels in series or parallel or both to get maximum power?

What type, size and number of batteries and second inverter?

Should I be setting batteries up as all 12 volt or two banks with a higher voltage second inverter?

This system will run specified circuits constantly, it will not be feeding the grid as I use more power than this system can output. I also have a well, don't know the size of the pump but its approximately 300 feet deep then runs uphill approximately 40 feet in head to a storage tank in the crawl space before going to an 80 gallon water heater (which is my next project, but that's another thread!)

Thanks in advance!

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Need help with battery choice and wire size

    Welcome to the forum.

    Since you are quite sensibly upgrading he system, why not reevaluate the needs? If you have some idea how many Watt hours you'll need to come up with everything will go much smoother.

    One thing I noticed: twelve batteries in parallel. It is almost impossible to get a set-up like that to work right. Some of the batteries will do all the work, some will do none. They'll recharge differently too.

    Considering the power potential there, it's probably a good time to up the system Voltage and get those pesky DC Amps down. It could be worth your while to buy something like an XW 6048, which can not only back up your grid but back feed it if that's allowed in your area. You have panels, so why not use them all the time? Much more economical and you still have the back-up for when the grid goes down.

    Your 2760 Watt array should support 368 Amp hours @ 48 Volts, or about 8 kw hours worth of stored capacity. You have an advantage of location: at 10,000 feet your panels should do much better than the typical 77% efficiency. Mine do 80% at 3200 feet!

    Anyway, determine how much back-up power you'll need; that's the key to building (or rebuilding) a successful system.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Need help with battery choice and wire size

    Oh, if you up the system Voltage you won't need two 45 Amp controllers: one would do.
  • System2
    System2 Posts: 6,290 admin
    Re: Need help with battery choice and wire size

    Thanks for your reply!
    I readily agree that I did not know what I was doing 10 years ago, thought I was doing it right! lol That's exactly why I am here to correct mistakes and learn.

    The thought on net metering was that it costs more to install then the credit and figuring performance or the panels due to overcast/snowing (we got over 40 feet this last winter) that the amount of electricity I will use at peak times is way more than I will generate without drawing the batteries down to low, and allow me to re-charge them for off peak or power outage use... I may be wrong, certainly been wrong before!

    The mppt's were less than what another company said I needed so I bought all of my stuff from another retailer (was delivered yesterday!) I did tell them that I may add to my panels in the future if my budget allows down the road, so I would rather have the main components in place and be able to add panels as I can afford them, was that wrong? Again I am still learning!

    12 12 volt batteries worked (kind of) at the time. I watch my big screen, vacuum and cooking Easter dinner with lights on when my neighbors were asking the first year why I had power and they didn't, they check into hotels each year and pay for frozen pipes, I don't get it and could not afford to do that every year but they seem to not care... I do take in a family that are our best friends and that we have over for Easter dinner every year when the power goes out, kinda like camping in a house!

    But I agree that it is not the optimal way, that's why I am asking for help!
  • System2
    System2 Posts: 6,290 admin
    Re: Need help with battery choice and wire size

    PS,
    I will get my last year info from Xcel so I can give actual usages, you guys will be amazed at what it costs to live here and that doesn't factor in propane, wood stoves and passive solar!
    I'm really not stupid unless you ask my wife when it's been a drinking night with the boys. lol I definitely am ignorant on the specs and correct way to maximize my system, that's why I'm here, to learn from experts and not set up my system incorrectly, again, lol.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Need help with battery choice and wire size

    The thing is, you are about to put up almost 3 kW of panels. Most of the time (we hope) the grid will be up and the batteries will be charged; the panels will sit there doing nothing when they could be selling power back to the grid. That's a better return on the investment you're going to make anyway than just using them to charge batteries for back-up power.

    The thing about the 48 Volt system is that it will allow you to store and use the same amount of over-all power (Watt hours) as a 12 Volt system but in a much more efficient and easier to manage way. When you need large amounts of Watt hours you really should go up in system size. The higher current involved in charging and discharging the equivalent 12 Volt system means more power is going to heat, not to work.

    You can add more panels later. If they are exactly the same panels they can possibly be integrated into the existing array. Otherwise having a second controller for the next array build is good. But don't try to add more batteries later: batteries "age" and old ones don't work well with new ones; they "drag them down", thus shortening life. Things that "age" batteries are time, depth of discharge, frequency of discharge, improper recharging, other abuse.

    I'll suggest you get a Kill-A-Watt meter (everyone should have one!) and measure the power use of all your "critical" loads (things that must be kept running when the power goes off) for a day. Add it up, and you have a figure for essential daily Watt hours. Some things may be 240 VAC, in which case you can't use the K-A-W; you'll have to estimate based on manufacturer's information and a bit of old fashioned "watch how long it runs" (water pump may fall into this category). Some things you need may be "hard wired", in which case you either "interrupt" the wiring and temporarily run it through a plug-in set-up or measure the current with a clamp-on Amp meter. A bit of investigation to get your Watt hour needs will be well worth it in properly designing your back-up system.