Need help with off grid system.

Idaho solar
Idaho solar Registered Users Posts: 5 ✭
in Off Grid Solar & Battery Systems #1
We are building an off grid cabin in Idaho and have estimated we would need 3kw. It will mainly be a weekend retreat but when we retire would be a full time summer residents. If someone could look at what we have decided on getting and let me know if we need to adjust something. It would be greatly appreciated.
10 solar panels brand-Renesoalr model -JC305-24/Bbh 305 watt panel
SchneiderSolar Charge Controller. - Model -MPPT 60 150/P.N. 865-1030-1
8- Batteries Duracel badge made by Deka/68 SLIGC125 6V---235Ah at 20hr rate/#'s
Inverter Schneider Electric Conext -model-SW 4024 --24VDC Inverter/Charger For Split-Phase 120/240 VAC
Mounting system -IronRidge UNI-TP/10LL Top of Pole Mount Dual Row 115"
(Our roof will be 10/12 pitch for heavy snow load and we don't feel comfortable mounting these on the roof. So this is why we will do a pole mount)

I have questions on if the inverter and charge controller will work with these
Panels.
I have questions on if I need anything more than this inverter and charge
controller.
The above doesn’t include wiring for system as far as I know.
I don’t know what all comes with the mounting rack kit as far as brakets
and such.
I would like to understand the benefits of a 48volt vs 24 volt system.
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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Need help with off grid system.
    Idaho solar wrote: »
    I would like to understand the benefits of a 48volt vs 24 volt system.
    1. You get the total energy storage you need by using batteries in series rather than in parallel. That makes for a longer lived and easier to maintain battery system. With your existing 8 six volt batteries, to get a 24 volt system you will have to wire them in parallel as well as in series.
    2. You can use smaller wiring. For the same energy output from an inverter or charging power from a CC you can use wires that are 1/4 the size when you go from 24V to 48V. Copper costs money and big aluminum wires are hard to terminate properly and hard to bend.
    3. You really do not want to routinely run currents in the 200A + range into your inverter if you can help it. But since you have invested in the 4000W 24 volt inverter, you can resign yourself to currents in the 200A range and more during surge output or you can spend the money for a 48V inverter. Certainly do not go bigger than a 4000W inverter on 24 volts.
    SMA SB 3000, old BP panels.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #3
    Re: Need help with off grid system.
    Idaho solar wrote: »
    I would like to understand the benefits of a 48volt vs 24 volt system.

    Well for one charge controllers are rated on their output current. A MPPT 60, would be rated to output a max of 60 amps, your array at 3050 watts has the potential of 3050watts / 24 volts = 127 amps though more realistically around 100amps so you would need 2 of them in a 24 volt system and only one in a 48 volt system.

    You will also want fuses or circuit breakers, Midnite makes an Epanel that combines most of this in one unit. I read that they are working on an Epanel for the new SW inverters, they also make generic Epanels. along with the Epanel you will need a combiner box, this normally is located near your array and combines your strings of panels with fuses or breakers so you can run a single line back to the charge controller (CC). Might also suggest lightning protection and grounding rod and supplies.

    I guess they have already made an Epanel for the SW4024!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Idaho solar
    Idaho solar Registered Users Posts: 5 ✭
    #4
    Re: Need help with off grid system.

    So would you suggest using the Schneider xw4548 inverter rather than the 4024 so that my system is 48 volt instead of 24volt?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Need help with off grid system.

    It does make the DC wiring 1/2 as thick, circuit breakers 1/2 the amperage--And solar charge controllers can manage a 2x larger array vs a 24 volt system.

    But a lot of this depends on your loads... A 4kWatt inverter will power a lot of loads. And a 4kWatt 48 VDC inverter should have a minimum of ~400 AH @ 48 volt battery bank to successfully run the inverter at full/rated power (over time, temperature, state of charge, etc.) for flooded cell lead acid storage batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #6
    Re: Need help with off grid system.

    Your system as laid out, does show a somewhat imbalance as you have a battery bank of 470 Ah at 24 volts, this would take a maximum charging of around 13% or about 61 amps, yet your array would provide around 100 amps at Normal cell temps. Indeed in Idaho you might find cool days when you produce more. You can set the charge controllers to limit the amperage that they put out, and it will help on over cast days, I'm 'over paneled' myself. (I'm not sure this can be done with the schnieder/Xantrex but most can)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Need help with off grid system.
    BB. wrote: »
    It does make the DC wiring 1/2 as thick, circuit breakers 1/2 the amperage--And solar charge controllers can manage a 2x larger array vs a 24 volt system.
    If you want to maintain the same energy losses in the wiring, then indeed doubling the voltage allows you to cut the wire size in half.
    But if you are working in an environment where the percentage voltage drop determines whether your equipment works well or not, then doubling the voltage lets you double the voltage drop too, and the wire size is 1/4 what you need for the lower voltage.
    It comes down to just how you are sensitive to voltage drop.
    SMA SB 3000, old BP panels.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: Need help with off grid system.

    Another consideration is the length of the cable between your combiner box (at the pole) and your charge controller. If that distance is large, you would be better off at 48 volts. If you do go to 48 volts (with long distance), you will want to configure your array so that the series string length is 3 panels... that means you could only use 9 panels (or buy two more and have 12).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Need help with off grid system.

    #1. Skip the Schneider/Xantrex/Conext stuff entirely. Frankly it's not very good, despite what Brand X fans say.

    #2. Do not measure an off-grid system by the array size; it is meaningless. It's how many Watt hours per day you need that matters. Go with 24 Volts if you really only need 3kW hours per day. Make sure you have that number right.

    #3. 305 Watt panels are big and difficult to handle. Ten of them will give you a 3kW array capable of a system around 6kW hours AC per day. Is this sized right? Be sure: you have a 2/3 chance of getting it wrong.

    #4. Those panels would produce about 98 Amps of current on a 24 Volt system. No single charge controller will handle that much. Again, be sure you are sizing right. You'd either have to reduce the array size, clip a some power during bright days, or go up to 48 Volts.

    #5. Your eight 235 Amp hour 6 Volt batteries work out to 470 Amp hours @ 24 Volts. You do not need 98 Amps of charging potential for that. You could say the battery bank is too small or the array is too large. The bank as is would be good for up to 5.6 kW hours DC.

    #6. Work out your load requirements first and be accurate. Measure with a Kill-A-Watt everything you can, even if it is just similar items, under normal usage. What I see here is the random selection of equipment with no power planning done. This is typical and a huge mistake. I know because it's the mistake I fix over and over again on other peoples' systems.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Need help with off grid system.

    Reading material on selecting system Voltage and configuring arrays:

    http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller
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  • Idaho solar
    Idaho solar Registered Users Posts: 5 ✭
    #11
    Re: Need help with off grid system.
    Cariboocoot wrote: »
    #1. Skip the Schneider/Xantrex/Conext stuff entirely. Frankly it's not very good, despite what Brand X fans say.

    #2. Do not measure an off-grid system by the array size; it is meaningless. It's how many Watt hours per day you need that matters. Go with 24 Volts if you really only need 3kW hours per day. Make sure you have that number right.

    #3. 305 Watt panels are big and difficult to handle. Ten of them will give you a 3kW array capable of a system around 6kW hours AC per day. Is this sized right? Be sure: you have a 2/3 chance of getting it wrong.

    #4. Those panels would produce about 98 Amps of current on a 24 Volt system. No single charge controller will handle that much. Again, be sure you are sizing right. You'd either have to reduce the array size, clip a some power during bright days, or go up to 48 Volts.

    #5. Your eight 235 Amp hour 6 Volt batteries work out to 470 Amp hours @ 24 Volts. You do not need 98 Amps of charging potential for that. You could say the battery bank is too small or the array is too large. The bank as is would be good for up to 5.6 kW hours DC.

    #6. Work out your load requirements first and be accurate. Measure with a Kill-A-Watt everything you can, even if it is just similar items, under normal usage. What I see here is the random selection of equipment with no power planning done. This is typical and a huge mistake. I know because it's the mistake I fix over and over again on other peoples' systems.

    Thanks for all of everyone's insight. We will be going with a 48 volt inverter instead of 24 volt. What brand of inverter would you recommend?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Need help with off grid system.
    Idaho solar wrote: »
    Thanks for all of everyone's insight. We will be going with a 48 volt inverter instead of 24 volt. What brand of inverter would you recommend?

    You/we need some numbers.
    Do you require 240 Volts for anything? If so, how many things and of what size?
    What is the maximum Watts of everything you would be using at the same time? This is very important for sizing an inverter. It is not the sum of everything in the place.
    How many Watt hours per day?

    Picking components without knowing what power requirements are is called "guessing" and you have a 2/3 chance of getting it wrong.

    Despite what some people say Outback still has the best reputation for quality inverters. Even so there are choices to be made within the brand as to meeting the power requirements.
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  • Idaho solar
    Idaho solar Registered Users Posts: 5 ✭
    #13
    Re: Need help with off grid system.
    Cariboocoot wrote: »
    You/we need some numbers.
    Do you require 240 Volts for anything? If so, how many things and of what size?
    What is the maximum Watts of everything you would be using at the same time? This is very important for sizing an inverter. It is not the sum of everything in the place.
    How many Watt hours per day?

    Picking components without knowing what power requirements are is called "guessing" and you have a 2/3 chance of getting it wrong.

    Despite what some people say Outback still has the best reputation for quality inverters. Even so there are choices to be made within the brand as to meeting the power requirements.

    We would not use anything that would be 240V in the cabin. We are going to be running propane to the cook top and water heater. Our water pump is 220v but will be ran with a generator to fill up a 500 gallon water tank.
    The average kWh for a day would be about 20kwh. We would be running a refrigeror and all lights will be LED. Possible TV at some point but rarely. It's just the two of us so not a lot of people to use everything at once. When I did the watt estimator it came to 570 watts if I had everything going. I hope this information helps. Thank you once more for all of your help. You all have already helped us understand things that we thought we knew.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Need help with off grid system.
    Idaho solar wrote: »
    We would not use anything that would be 240V in the cabin. We are going to be running propane to the cook top and water heater. Our water pump is 220v but will be ran with a generator to fill up a 500 gallon water tank.
    The average kWh for a day would be about 20kwh. We would be running a refrigeror and all lights will be LED. Possible TV at some point but rarely. It's just the two of us so not a lot of people to use everything at once. When I did the watt estimator it came to 570 watts if I had everything going. I hope this information helps. Thank you once more for all of your help. You all have already helped us understand things that we thought we knew.

    How did you arrive at 20 kW hours per day? Our "in town" house uses 16 kW hours per day (just two people), and that includes electric hot water. At the cabin it's <3 kW hours.

    570 Watts all at once is easy to handle, but your refrigerator is going to demand about twice that momentarily for start-up. That will use around 1 kW hour in a day. You may be able to run your water pump from solar too; we do by turning it on midday when there's plenty of sun to power it and storing it up in a large pressure tank. For just the pump (especially if you want to start out with the gen power) you could use a transformer to provide the higher Voltage. We do this for our septic pump.

    It's looking pretty good for what I can see. No need for a 240 VAC inverter, no high power demand, and probably not large Watt hours.
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  • Idaho solar
    Idaho solar Registered Users Posts: 5 ✭
    #15
    Re: Need help with off grid system.
    Cariboocoot wrote: »
    How did you arrive at 20 kW hours per day? Our "in town" house uses 16 kW hours per day (just two people), and that includes electric hot water. At the cabin it's <3 kW hours.

    570 Watts all at once is easy to handle, but your refrigerator is going to demand about twice that momentarily for start-up. That will use around 1 kW hour in a day. You may be able to run your water pump from solar too; we do by turning it on midday when there's plenty of sun to power it and storing it up in a large pressure tank. For just the pump (especially if you want to start out with the gen power) you could use a transformer to provide the higher Voltage. We do this for our septic pump.

    It's looking pretty good for what I can see. No need for a 240 VAC inverter, no high power demand, and probably not large Watt hours.
    We had a cabin almost the same size just down the road that was on grid. That was the average we used when we would be there. It was running our pump, cooktop and water heater. So looking at the average used there I don't think we will ever go over 20kw a day.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: Need help with off grid system.

    Cooktop and water heater are big power users. Leaving them out can reduce the consumption by a very large amount. First thing I did with this house was get rid of the electric stove - and watch the monthly electric bill drop in half.

    If at all possible you should try measuring what you're going to use or items similar with a Kill-A-Watt meter. It's good practice whether on or off grid: see where the power goes!

    A hot water heater (which can't be plugged in to the K-A-W meter) is a 3500 Watt load and may run for 4 hours a day: there's 14 kW hours. Very good thing to take off the electric!

    I'm going on and on about this because there is a huge difference in design between supplying 20 kW hours per day and supplying 5 kW hours per day or less. If you build the system too large you'll have spent a lot of money for nothing. if you build it too small the power goes out at inconvenient times.
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