Where to put the battery room?

shastaronshastaron Registered Users Posts: 24
We are looking at a off-grid sytem. We will build it in phases adding a set of solar panels to feed into a 48 volt battery bank. We will expand as we can afford to add a new array and bank. As the family grows so will the system. Where the arrays will be placed is a fair distance from the house. We are concerned about the line loss. So here is the question:
Are we better off pushing the 48 volts down the line to a battery room at the house or but the battery room at the arrays and pushing 120 volts down the line to the house?

Thanks.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Where to put the battery room?

    In general, put the Solar Charge Controller (like an MX 60) next to the battery bank. You need the Battery Temperature Sensor (BTS), voltage sensor, control wiring, and controller to battery bus all kept short.

    Run the solar panels on their wiring/voltage the long distance... Losses are I^2 * R losses--and since you can run the arrays at 120+ VDC, vs ~60 volts at the battery bank, for the same gauge wire, your wiring resistance losses are 1/4 because of the higher voltage--allowing you to have less losses, or smaller gauge (and cheaper) wire for the long distance runs.

    Note that it is not a great plan to add new batteries to an existing (old) battery bank if it is more than 6 months than a year old... Basically, what usually happens is the new batteries will fail roughly the same time as the old batteries (the new batteries usually take more of the cycling because they are new, and "wear out" until the match the existing batteries in the bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shastaronshastaron Registered Users Posts: 24
    Mixing arrays

    Bill, Thanks for the answer. I am going to be a little dense here.

    I know to keep all the controller, sensor and inverters close to the battery bank. Are you saying that we can send greater DC voltage from the array of panels than just 12,24,48, or 60?

    When they got to the charge controller I thought the max was 60 volts?

    If we build an array to say 60 volts with a bank of batteries at 60 volts. Then latter build another array at 60 volts to supply a new bank of batteries at 60 volts. Will this still be a problem with aging as you described?

    I admit that I am a rank beginner and am trying to get this stuff straight in my head. My only experience with PV has been on my RV.

    Thanks again.
    Ron
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Where to put the battery room?

    Sorry Ron... Back to basics.

    You are going to build a fairly large battery bank and solar array (over 400 watts of solar panels). Therefore, you are going to want a MPPT (Maximum Power Point Tracking) type solar charge controller.

    A very popular brand is the MX 60 from Outback, but there are some others (and newer ones) out there now.

    A MPPT controller allows you to run higher voltage from the solar panels into the solar controller, and through a DC to DC switching power supply inside the charge controller, it matches the best power from the solar panels (Vmp and Imp -- maximum power) and converts that to the optimum charge voltage and current for the batteries. (In a way, the MPPT type solar charge controller acts a bit like the DC equivalent of an AC variable output transformer).

    So, the input to the MPPT solar charger can be between (roughly) battery bank voltage+2volt and about 130 volts maximum. And the battery bank can be 12, 24, or 48 VDC nominal (recognizing that, for example, a 48 VDC battery bank needs about 62+ volts to equalize charge).

    So, when I saw 120 Volts--I assumed that you were talking about 120 VDC from the solar panels...

    But, in reality, you where thinking of installing the solar panels, charge controller, and battery box remotely, and running 120 VAC 60 Hz to your home... Or running the 48 VDC battery bus to your home and installing the inverters there. Right?

    In the end, the highest currents will be around your battery bus--and you want to send those as short as distance as possible. You want to keep the solar charge controller (like the MX 60) and the inverters close to the batteries.

    The distance between the solar panels and the charge controller, and between the inverter 120 vac output and the home/loads can be quite a bit longer (because of the higher voltages and lower currents).

    The end question--should the battery bank (plus inverters, charge controller, etc.) be installed near the solar panels or near the home.

    In general, putting the battery bank next to (or under/in the home with proper ventilation and access) may be the better solution. You will have maintenance and monitoring to do--and walking to a remote site is a pain. Also, if you live in hot weather (or cold weather) you can use the home HVAC, propane, and insulation to help keep the batteries near 70-80F.

    Of course, you will need to do this to code (building, electrical, fire, etc. requirements). And need access to move heavy batteries around (large openings concrete floor/drive, etc.).

    And, if this is a pure off-grid, you will need to site a generator and fuel appropriately too.

    Outback Power has lots of information and drawings to help you understand and design a system using their components (you could do worse).

    Regarding adding additional batteries--if the new batteries are in parallel with the existing bank (sharing the exact same DC power bus), then you run the risk of less than full life with the newly added batteries.

    If, this is a separate set with separate charge controller and inverter (electrically isolated from the original battery bus), then there should be no issues.

    Usually, I would believe that running a home you would want to have one central battery bank--If you have, for example, two different banks and two different solar arrays for charging--you end up with trying to balance the household loads with the available charging current (say bedrooms and kitchen on one bank; heating, living room, garage, laundry on another bank)--you will have difficulty in using power without having to juggle loads between the two independent systems.

    Am I making sense here?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shastaronshastaron Registered Users Posts: 24
    Re: Where to put the battery room?

    Bill, Definitely you made sense. That was a very complete answer and I appreciate you taking the time to spell it out so good for me. I am going to sit down and digest it a little bit. But you really cleared up a lot of things for me.

    I need to be clear whether I am talking about AC or DC.

    You helped me with the MPPT which I had been reading up on. I like the Outback MX60 and several of their products.

    You cleaned up the battery bank issue in my mind.

    We are going to be using a propane generator as backup for the house and well which will be solar also. The generator will also be the power supply for the shop.

    Sounds like it is best to send as much DC up to 70-130 down the line to the Charge controller. Let it handle the battery banks and feed the inverter at that point. Everything from the controller to the inverter will be very close in the same room. Then the inverter will feed the AC 120 to the house. The generator will be nearby feeding the backup power/peak load/bad weather charging.

    The well will have its own solar that will feed a AC/DC pump and can be run off the generator as a backup. We may be able to use gravity feed for water pressure for most of our uses.

    It will all be to code!

    Thanks again,
    Ron
  • BB.BB. Super Moderators, Administrators Posts: 32,010 admin
    Re: Where to put the battery room?
    shastaron wrote: »
    Sounds like it is best to send as much AC up to 120-130 down the line to the Charge controller. Let it handle the battery banks and feed the inverter at that point. Everything from the controller to the inverter will be very close in the same room. Then the inverter will feed the DC 120 to the house. The generator will be nearby feeding the backup power/peak load/bad weather charging.

    Ron,

    I think that the AC/DC should be reversed in your above statement:
    Sounds like it is best to send as much DC to (~70-130 VDC from the solar panels) the line to the Charge controller. Let it handle the battery banks and feed the inverter at that point. Everything from the controller to the inverter will be very close in the same room. Then the inverter will feed the 120 VAC to the house. The generator will be nearby feeding the backup power/peak load/bad weather charging.

    Note that you can get Inverters that have an internal battery charger that is powered from 120 VAC from the generator. Also, these inverters will have an internal transfer switch that can take 120 VAC from the generator and pass it directly through to its output for use by your house (as well as siphoning some AC power to charge the battery bank)--basically just like a giant UPS (Uninterruptable Power Supply).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shastaronshastaron Registered Users Posts: 24
    Re: Where to put the battery room?

    Oooooooops, it was late. You are right of course. I edited the post to read correctly for others. Thanks for all the great info. You have really helped a newbie.

    Ron
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Where to put the battery room?

    Hi Ron, I had a similar situation to yours and I built a Concrete Cheese Wedge Solar Shed kept all the DC wiring very short and ran 230v AC from Shed to House. The runs from the panels to the controller are less than 3 meters and 1 meter to the batteries, Ive attached some pictures. The panels form the roof and all the control gear is inside the concrete shed.
    PS The shed started off as 8 panels 1600w Then Iwas lucky to buy 4 identical panels, and added them + A Two dog kennel extension for the Burglar Alarm System. Keeps Hugo and Boss (Jap Akitas) dry and cool Thus fit for Biting Billy Burglar
  • shastaronshastaron Registered Users Posts: 24
    Re: Where to put the battery room?

    Thanks for the pictures. Everything is helping me understand and visualize better. The more the merrier. You have a beautiful setup. In the last picture on the left side there appears to be a partial 6-pack of an essential fluid utilized for system performance!?!?!?
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Where to put the battery room?

    Thats why its called a shed;) all men need a shed to store there gear and potter
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Where to put the battery room?

    Here's how we did ours. Vented stone (insulated) room with air extractors. Extractor hoods float over batteries and vent to outside. Venting motors programmed to peak charging periods.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • shastaronshastaron Registered Users Posts: 24
    Re: Where to put the battery room?

    Nigtomdaw how long is the run from your Cheese Shed to your house?

    Mangas where did you locate the stone building in relationship to the array and to the the house (distances).
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Where to put the battery room?

    The run from the cheese wedge shed to the house is about 50ft in 6mm2 tri core 240v rated cable about $150 worth well over rated for its need,,,,, remember at high AC voltage smaller cable is required to transfer suitable power against DC low voltage;)
  • MangasMangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Where to put the battery room?

    We canabalized an old stone ranch house 100 feet from the main house as the solar mechanical room.

    The array field is located east of the old stone house and the underground DC conduit runs are about 130 feet to it.
    The stone house is located north of the main house and the AC conduit run is about 100 feet.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • shastaronshastaron Registered Users Posts: 24
    Re: Where to put the battery room?

    Thanks gang you have given me better ideas about the runs that people are doing.
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