advice for system

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alter
alter Registered Users Posts: 31 ✭✭✭
in Solar Beginners Corner #1
I've been thinking about upgrading to a larger system and would like a sanity check and some comments about these products for what I'm trying to do.

I would like to build a ~1kw off-grid system, with plans to possibly upgrade to 2 in the future. This would be used in a remote cabin.

Panels - I was thinking about 4-8 205 watt Kyocera KD205GX panels or similar. From what I understand, if you have a MPPT charge controller, it doesn't really matter if the panels are 12 or 24volt, does that sound correct?

I've researched MPPT charge controllers a bit and the "Xantrex XW MPPT 60 Amp" seems decent, although not cheap. Would this handle my requirements if I decide to upgrade to more panels in the future, or is there a more obvious choice? I would like to stick with Xantrex products, all other things being equal.

I would also like a battery monitor like the Xantrex TM500A. I will use this to make sure not to use the system at all if the batteries get too low.

Inverter - Xantrex Prosine 1KW. Seems to be a good quality decent inverter that will have enough wattage to power the small number of appliances I would use.

The battery bank will be deep cycle AGM batteries of the same type, most likely 12v. I'm not too concerned about which batteries since there seem to be a wide variety of suitable ones available.

That's all for now. Basically any feedback on why or why not these products would work well together in a viable system would be appreciated.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    Re: advice for system
    alter wrote: »
    Panels - I was thinking about 4-8 205 watt Kyocera KD205GX panels or similar. From what I understand, if you have a MPPT charge controller, it doesn't really matter if the panels are 12 or 24volt, does that sound correct?
    More or less correct on the Vmp ratings... There is a spot with ~48-58 volt Vmp panels where 1 panel in series is not enough voltage to charge/equalize a 48 volt bank (need ~60-62 volts from panels), and 2 or more in series can over voltage (Voc max for most "large" MPPT charge controllers is around 140-150 VDC like "X" and "O") on a very cold day... Otherwise, most Vmp/Voc combination of panels is fine.

    Xantrex (and others too) now offer panel string calculators that help you to decide how to wire up your arrays.
    I've researched MPPT charge controllers a bit and the "Xantrex XW MPPT 60 Amp" seems decent, although not cheap. Would this handle my requirements if I decide to upgrade to more panels in the future, or is there a more obvious choice? I would like to stick with Xantrex products, all other things being equal.
    A very good choice with the Xantrex...

    The other option (that I am aware of) is the Outback FM 80 amp MPPT charge controller. There where some early teething problems with the firmware (?) that may have been fixed by now (I have not seen anything since---so I do not know).

    You have picked a 12 volt inverter--If you picked a 24 volt (or higher) inverter--Then with the same MPPT charge controller (their output is based on maximum current output), doubling the battery bank voltage will double the supported solar panels:

    P = I*V = 60 amps * 15 volts = ~900 watts max of solar panels w/ 12 volt bank
    P = 60 amps * 30 volts = ~1,800 watts max of solar panels w/ 24 volt bank
    I would also like a battery monitor like the Xantrex TM500A. I will use this to make sure not to use the system at all if the batteries get too low.
    Isn't the TM500A at end of life now? (still may be available for a good price though).

    I really like the Xantex LinkLite/LinkPro units with their Alarm Output function (digital level signal) that can be programmed to alarm at 50% (or your choice) state of charge for the battery bank. Interface this with an Inverter that has a remote On/Off input--and you can have a system that will load shed automatically if the battery state of charge goes under 50% state of charge (and/or can be used to flash a light/buzzer instead). Function may not be worth the cost for you...
    Inverter - Xantrex Prosine 1KW. Seems to be a good quality decent inverter that will have enough wattage to power the small number of appliances I would use.
    If you have not picked out a backup battery charger yet (for those "dark" days)... I would look into a Prosine 2kW version. Includes a 100 amp power factor corrected power supply and remote battery temperature sensor--really nice to run on a smaller genset for backup power. From a quick look at the manual--the Prosine with battery charger have a very detailed setup to match the genset (AC Breaker Size) and battery type/size for a very well programmed charge controller.

    A 2kW inverter is certainly much bigger than you asked for--so that may be an issue for you (extra capacity + price that is not currently needed).

    I wonder if the Honda eu2000i (manual start) would be a good backup/match genset for this unit. There is the Honda eu3000i (with electric start) or other inverter/generator units (like the multifuel Yamaha) may also be good match too (if not much larger and more costly).

    The Prosine Inverter + Integrated Internal Battery Charger looks like a killer unit to me (pricing not included :cry: )

    NAWS does carry the Xantrex Prosine family of inverter/chargers but currently on their web page:
    Xantrex Prosine inverters come in two major versions, with and without built in battery chargers. The 1000 & 1800 do not have chargers, the 2000 and 3000 have battery chargers built in.

    Availability on the 2000 and 3000 watt ProSine inverters varies so we are not listing them at this time - call for availability.
    The battery bank will be deep cycle AGM batteries of the same type, most likely 12v. I'm not too concerned about which batteries since there seem to be a wide variety of suitable ones available.
    I personally like large batteries in one series strings over smaller batteries in more than 3 parallel strings... If you do install parallel strings--you probably should get a DC current clamp/meter so you can ensure that each string is properly sharing charging/load currents since you cannot monitor electrolyte specific gravity (and battery state of charge) with sealed/AGM batteries.

    My 2 cents worth of comments... :roll:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    #3
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    Re: advice for system

    At 1KW with looking at 2KW, I would go to a 24V battery system.

    I am at 960 watts at 12 volts and have large losses in my wires. I can live with this as I am still on the grid for most of the time.
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  • alter
    alter Registered Users Posts: 31 ✭✭✭
    #4
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    Re: advice for system

    Thanks for all the good info!

    So it sounds like a 12 volt bank may not be ideal. It looks like I could support more panels if the battery voltage was increased. I've also determined that the panels may need to be placed away from the battery bank possibly about 120 feet. Does this affect which voltage the battery bank should ideally be? I would have liked a 12V bank to be able to run 12V DC appliances but I also would of course like to try and be relatively efficient and lose as little as possible over the wires. I'm guessing the wire will have to be pretty thick but I'm not sure how thick..is there a good place for me to find what gauge the wires should be?

    The Xantrex LinkLite units that can be programmed with an alarm sounds perfect.

    The idea of an inverter shutting off automatically is interesting, I'll have to see if I can find some of those and research it a bit more.

    The Prosine 2kW inverter/charger would be perfect since it combines two functions with one unit..and it even looks like it can handle more than the standalone 60AMP xantrex charge controller but I could not find any mention of MPPT. It does say "multi stage battery charger" ... is this the same as MPPT? I was under the assumption I needed that. If not I would be happy to go with this unit.

    Also the idea of combining a small generator is very good especially if it will integrate well. Would it be possible to have the generator start automatically if the battery level reaches, say 50%? Are there any other benefits of an electric start generator? If I got an electric start honda could the charge controller somehow trigger the generator automatically or will it still be manual process of starting it when needed?

    I will keep the idea of running smaller voltage batteries in a series as an option as I research.

    Thanks again for the help!:D
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #5
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    Re: advice for system

    Inverter/Chargers charge via the AC input ... you still need a charge controller to get the solar panels to charge the batterys
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  • alter
    alter Registered Users Posts: 31 ✭✭✭
    #6
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    Re: advice for system

    So if the generator is running and powering the inverter/charger, the inverter can charge the battery bank? OK that makes sense, thanks!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #7
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    Re: advice for system
    alter wrote: »
    So it sounds like a 12 volt bank may not be ideal. It looks like I could support more panels if the battery voltage was increased. I've also determined that the panels may need to be placed away from the battery bank possibly about 120 feet. Does this affect which voltage the battery bank should ideally be? I would have liked a 12V bank to be able to run 12V DC appliances but I also would of course like to try and be relatively efficient and lose as little as possible over the wires. I'm guessing the wire will have to be pretty thick but I'm not sure how thick..is there a good place for me to find what gauge the wires should be?
    Use the Wiring Drop Calculator Spreadsheet (Excel) to design your system... With long wire runs, high voltage strings are your friend (can reduce your wiring costs by a factor of 4 or more.

    voltage drop calculator

    One point--remember a 120' of wire is 240' round trip (for this calculator).
    The Prosine 2kW inverter/charger would be perfect since it combines two functions with one unit..and it even looks like it can handle more than the standalone 60AMP xantrex charge controller but I could not find any mention of MPPT. It does say "multi stage battery charger" ... is this the same as MPPT? I was under the assumption I needed that. If not I would be happy to go with this unit.
    Multi-stage battery charger is 1) high voltage/charge current until battery is 80-90% full--Bulk Charging at ~14.5-15.0 volts. 2) is the Absorb mode--current tapers down until 100% charged around 14.2 volts. 3) float charging is when the charge controller backs down to ~13.6 volts or so once the bank is fully charged. Keeps battery charged but does not "boil" the water out as overcharging would--most useful for battery banks that set for weeks and months of non-use (such as a vacation cabin, or standy by emergency power like a UPS).

    MPPT is Maximum Power Point Tracking... Most used here to discribe a Solar Charge Controller that sits between the Solar Panels and the Battery bank--and looks at the equation of P=V*I... Basically, a solar panel's optimum output voltage changes with temperature (drops as cell tempeature rises). By watching the solar panel ouputs--the controller adjusts "I" and "V" such that P is at a maximum point (some do it every 5-15 minutes, others do it much faster--both usually work OK). The MPPT Solar Charge Controller generally has a Buck Mode Power supply (which can efficiently drop higher voltage/lower current into lower voltage/higher current for use by the battery)... Effectively the DC equivalent of an AC transformer.

    You can read about MPPT power supplies here:

    All About Charge Controllers

    You can read about batteries here (a "must read"):

    Deep Cycle Battery FAQ

    About MSW and TSW Inverter here (and why you care):

    All About Inverters
    Choosing an inverter for water pumping

    By the way, MPPT can also apply to other devices--such as some digitally controlled water pumps which match P=I*V of their input to the optimum power output.

    Linear Boost Controllers used for DC motors have similar properties too (typically used for small pumps and DC swamp coolers running on solar panels without batteries):

    7 Amp Linear Boost Controller
    Also the idea of combining a small generator is very good especially if it will integrate well. Would it be possible to have the generator start automatically if the battery level reaches, say 50%? Are there any other benefits of an electric start generator? If I got an electric start honda could the charge controller somehow trigger the generator automatically or will it still be manual process of starting it when needed?
    Yes, it would be nice to use a Battery Monitor to do this--Other integrated systems have generator controllers (Outback and Xantrex) too--And I do not know the details if I would use a Batter Monitor to start a genset vs just using one of the integrated controllers instead (don't know how sophisticated they may be).... Doing it right can save you a bunch of fuel.

    A warning about auto-start... Many of the smaller gensets are not designed for autostart as they do not have a controller that monitors the starting/operating conditions of the generator. It can get quite complicated to retrofit something that will be safe and reliable to a genset with just a manual "push to start" switch... You probably would be better off if you want/need autostart to get a genset with the funtion already installed and working.

    One thing to keep track of is your end goal of the "system"... If automation/large loads are important--then it is going to cost a lot of money. And you should look at 24/48 volt battery bank and higher end controllers / gensets / etc. A good idea for industrial use, base camp support for workers/guests/spouse/kids/etc. who don't have any idea of how to operate an off grid system (i.e., you are not there and they did not spend the money installing).

    If people will be there and can start the genset manually--and your loads are not that large (vacation cabin)--then keep it simple for now until you have run the system for a couple seasons to keep the costs down and the complexity low.

    My 2 cents worth.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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