advice please

newbienewbie Registered Users Posts: 4
I'm building a cabin on my small farm in the Midwest. I'm off grid by choice and currently use a Generac 8KW generator for power. My few electric needs are the 240 volt 1 KW single phase well pump (runs app. 2 hr./wk.) and low use washing machine Except for a few led lights everything else is on propane, including frig, lights, hot water and cooking. Heat is via a wood stove.
What I wish to do now is install a battery bank and inverter with a few solar panels/charge controller to keep it all (mostly) charged. My questions are as follows.
1) Should I go with lead acid batteries or nickle/iron (Edison)? The former are a lot cheaper but the later seem to be bullet proof.
2) If lead acid, then cheap Costco 6volt golf cart, 24 volt marine, or more expensive 6 volt lead acid batteries?
3) Since lead acid batteries have a limited discharge life, will using solar charging mean that the daily charge/discharge cycle counts as 1 cycle or something else?
4) Should I install 2 battery banks and alternate use to discharge one bank to 50-75$% then charge it back up while using the other bank?
5) How many Amp Hours would you recommend? I was thinking of 220 AH.
5) A MS4024PAE Inverter/Charger, 4000 Watts, 24 VDC seems like a good for the inverter, Anybody have a better or cheaper idea?

Thanks

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Re: advice please

    Welcome to the forum!

    We like to focus on loads first... Solar/off grid power is expensive and any conservation you can do up front is a huge help down the road.

    For example, an 8kW genset and a 1 kW well pump running 2 hours a week is a big load with low duty cycle. It would take a fairly large power system to run such a load, and the rest of the time, it would hardly be used.

    For example, if you can live with the well pump and genset (perhaps run your washing machine when running the well pump once or twice a week)--And build out a very small off grid power system (say 2-4 golf cart batteries with a 300 watt 12 Volt TSW inverter, and 1-2 kW of solar panels, with a smaller backup genset + battery charger -- Say a Honda eu2000i), that would be a very cost effective system... Assuming you can justify the fuel delivery issues/costs for your genset.

    8 kW genset can drink ~ 0.5 to 1 gallon per hour just running with no load. For good fuel efficiency, you would like to run it with a ~3-4kW minimum load. The Honda can run 4-9+ hours on a gallon of fuel (~400 to 1,600 watt load). If you need a bit more power and auto-start support, there is a really nice Honda 4kW unit that one person here is using with great success (at very heavy loads to charge his large battery bank in winter/during heavy use).

    Or, look at the well pump (pumping to cistern, or pumping to a 40 gallon pressure tank--difference between 2 hours per week vs a few minutes multiple times a day--not a good candidate for generator use). You could look at adding a VFD (Variable Frequency Drive--if your pump is compatible) to soft start it, possibly reduce the RPM to reduce power needs. Or look at water pumps that are designed for use directly with solar panels/battery banks/etc. Basically "slow pump" many hours per day to keep average power low, and tend to be more efficient pumping to. Add a second pump from cistern to pressurize the home plumbing (smaller battery powered 12/24 volt DC pump here).

    Anyway--That is how I would approach the problem. I tend to the less complex system--if possible. Especially if this is your first trip off grid.

    Is this a full time home/cabin or a weekend / couple season place? Solar power tends to be a good solution for 9+ month use (in sunny area). For weekend/less than 6 month a year usage, a genset + small solar system (lights, pressurizing water, charging laptop+cell phones, TV/Radio, etc.) and propane fridge may make more sense. Also, if seasonal usage, leaving expensive gear behind, may not be the best idea (theft).

    Your thoughts/needs?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Re: advice please

    I should add, after a few months of working through this design and installation--We will have to change your user name. ;)

    Hang on tight!

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newbienewbie Registered Users Posts: 4
    Re: advice please

    Thanks for the advice.
    My cabin is a full time residence and now built and I live alone in it. I'll start the larger house in the future.
    I've already installed the propane genset and run it once a day for 20 minutes or so. Longer when the garden needs water.
    I start the morning with a shower which the charged up well pressure tank handles just fine. In the afternoon, I start the genset and do all necessary water use tasks and then turn it off. I also charge a deep cycle 12volt battery during that time. After a week that battery is charged and I exchange the genset battery which is rundown by them. Kind of a hassle that. Didn't really buy the right genset but now stuck with it. It's too big and not used for it's intended task which is grid tied emergency power.
    I'd like to install a 8 x 6 volt=48 v. x 240 volt inverter system to run the well pump and other small electrical needs. I run the genset when doing the weekly wash as you suggest.
    I think this system tied to 1 kw solar panels would allow me to be independent of the genset most of the time. Perhaps a 120 volt inverter with a transformer to 240 volt would be cheaper since I have only the well pump to run off the 240 v. I'd need (I think) a split phase inverter or split phase transformer for the single phase 240 v well pump (Grundfos 1.5 hp)
    Is any of this reasonable and could you answer some of the questions in my previous post?
    Thanks
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: advice please

    Since Bill is not off grid and I am I'll throw out a few answers from someone who's done it; me. :D
    newbie wrote: »
    1) Should I go with lead acid batteries or nickle/iron (Edison)? The former are a lot cheaper but the later seem to be bullet proof.
    2) If lead acid, then cheap Costco 6volt golf cart, 24 volt marine, or more expensive 6 volt lead acid batteries?

    The NiFe batteries are less efficient for their size and require a bit of special handling. They do last longer if they get what they need. However, the incidents of mishandling batteries among those new to solar is so high that we generally recommend starting with the cheapest per Watt hour you can get. They will eventually need to be replaced anyway, so if you ruin them quickly you're not out a lot of money and if you get 7 years out of them you're ahead. GC2's are usually the best bargain. Avoid the Marine/RV "deep cycle" batteries as they really are not suitable.
    3) Since lead acid batteries have a limited discharge life, will using solar charging mean that the daily charge/discharge cycle counts as 1 cycle or something else?

    Close enough for practical purposes. The discharge amount and rate varies through the day, and technically the predicted cycle life is based on fixed numbers for both. On the whole it doesn't matter much because real world conditions are so much different from laboratory testing. You get what you get.
    4) Should I install 2 battery banks and alternate use to discharge one bank to 50-75$% then charge it back up while using the other bank?

    Nope. No point. Been there, tried that, found no advantage. Size the bank and array according to your needs and go from there. Almost all of us recharge the bank while it's in use. Again, the amount being pulled varies through the day. If you have enough solar to meet minimum charge requirements after load draw you'll get there. And the solar can provide 'extra' power once the batteries are full and the sun still shines, providing you can make use of it (load shifting).
    5) How many Amp Hours would you recommend? I was thinking of 220 AH.

    How much load have you got? The battery bank size (Amp hours & Voltage) depends on the amount of Watt hours you need to store for daily use and how great the depth of discharge will be.
    6) A MS4024PAE Inverter/Charger, 4000 Watts, 24 VDC seems like a good for the inverter, Anybody have a better or cheaper idea?

    Good inverter. Good battery Voltage. That will handle most anything you throw at it. But make sure it's what you need first. Right back to the loads question.

    For what it's worth, my system is 24 Volts and can supply about 2.4 kW hours AC per day on a good day. It runs an electric refrigerator, plus the water pumps, satellite internet, lights, et cetera. It is a tad marginal because someone keeps upping the load requirements (not me). But the Honda EU2000i can make up the difference as needed.
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Re: advice please

    Since you will be building a larger house later--You probably would be better off leaving this system "small" for now. And keep it as a backup or even for "cabin" power once the house is built--But that is a decision that can be put off for later (two systems with two homes or one system supplying both).

    You have a choice of a "small system" with a small battery bank and array, and run the water pump/washer with a genset--And I would get a good handle on the amount of propane you use for running the genset. Propane has less heat per gallon of fuel (and propane is ~5lbs per gallon where gasoline is ~6lbs per gallon), so it is very possible that you are near the gallon of propane per hour range. You should run a little math on the problem and figure out if buying a smaller/second genset will save you any money on fuel use (a $700-$1,000 for a new genset that runs on 1/10 to 1/3 gph may or may not be worth it in your case).

    Also, for your existing setup, getting a good quality AC battery charger to run from your genset output and charge your "house battery" would probably work much better for you (and no battery swapping).

    The other thing to look at is your needs in detail. A large enough battery bank to run the water pump is going to be fairly large--And the large battery bank will probably drive you to a larger solar array just to keep the battery "happy". On the plus side, you will have more power to run other loads from your off grid system (washer, more computer/lights/appliances, etc.).

    So, here is how I would look at the issues to design an off grid system for your needs. First, the well pump. 1.5 HP is a large amount of current. Lets estimate that a 4kW AC inverter will start the load (8kW surge) and you go with a 48 volt battery bank. The minimum size battery bank to support such a starting surge reliably (using flooded cell batteries) would be:
    • 8,000 watts * 1/48 volt batt * 1/0.85 inverter eff * 2.5 maximum discharge rate = 490 AH @ 48 volt battery bank.

    A pair of strings of 8*6 volt 220 AH golf cart batteries would give you a 48 volt @ 440 AH--Good enough.

    To charge such a string of batteries would recommend a 5% to 13% rate of charge from a solar array:
    • 440 AH * 59 volts charging * 1/0.77 panel+charge controller derating * 0.05 rate of charge = 1,686 watt array minimum
    • 440 AH * 59 volts charging * 1/0.77 panel+charge controller derating * 0.10 rate of charge = 3,371 watt array nominal
    • 440 AH * 59 volts charging * 1/0.77 panel+charge controller derating * 0.13 rate of charge = 4,383 watt array "cost effective maximum"

    Note that this is not a small system, and depending on your well pump starting surge and if you can use a VFD or some other way to make it "soft start", you could try just buying one string of golf cart batteries and 1/2 the above array size (or do a ~1,686 watt array which would be a nice size for a single string of batteries) and see how it works--And if you need more power, add a second string of batteries to support starting surge.

    Next, need to figure out how much power you will get from your array (or size your array to support your loads). Let me guess that you are somewhere in the area of Minneapolis Minnesota and using PV Watts for a fixed array tilted at latitude:
    Month    Solar Radiation (kWh/m 2/day)
    1      3.85     
    2      4.72     
    3      4.97     
    4      4.91     
    5      5.74     
    6      5.91     
    7      5.89     
    8      5.64     
    9      5.21     
    10      4.28     
    11      2.95     
    12      2.85     
    Year      4.74
    

    I suggest tossing the low three months (assume you will use genset for poor weather) and use the 4th month as the "break even" point. In this case October at 4.28 "hours of sun" per day.

    So, say you wanted 3.3 kWH per day (100 kWH per month) of electric power. Enough to run a very efficient off grid home with an energy start fridge/computer/washer/well pump/lights/etc... pretty comfortably. The size of array for that would be:
    • 3,300 WH per day * 1/0.52 system efficiency * 1/4.28 hours per day = 1,483 watt array for October "break even"

    So, you need to weight the 5-13% battery charging requirements against your daily load requirements (i.e., one or two strings of golf cart batteries to start pump, vs your daily loads/needs).

    This Magnum 120/240 VAC split phase 4.4 kW inverter/charger should be a good fit for your "large" system needs.

    I will now do a post on the "Minimum" system design in a second post (5,000 character limit).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Re: advice please

    If you can "live" with the well pump/washing using the genset (get a tank for once or twice a week fill with genset, then use a small 12/24 volt pump to pressurize your cabin water system), then you could live on a 500-1,000 WH (0.5 to 1 kWH) per day pretty easily (it sounds like).

    So, a "minimum" system might look like 2x 6 volt @ 220 AH golf cart batteries with a 300 watt (600 watt) TSW MorningStar 12 volt inverter (has some very nice power savings modes that you only find in much larger/more expensive inverters). Will not power your well pump or your washer--But it will give you everything else in the small appliance category.

    Working backwards, what would a 220 AH @ 12 volt system look like. Assuming 2 days of storage and 50% maximum discharge for long battery life:
    • 12 volts * 220 AH * 1/2 days * 0.50 max discharge * 0.85 inverter eff = 561 Watt*Hours per day

    The recommended solar array would be:
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 207 watt array minimum
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 414 watt array nominal
    • 220 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 539 watt array "cost effective maximum"

    And based on my guess of 4.28 hours of sun October average:
    • 561 Watt*Hours per day * 1/0.52 system efficiency * 1/4.28 hours of sun = 252 watt array for "October" break even

    Put the two above together, the recommended array for a 2 golf cart battery bank supplying ~561 WH per day would be around 252 watts to 539 watt solar array with ~414 watt being a nice sized array.

    If you wanted to use 2 parallel strings (4 total) of golf cart batteries (or one series string of 4 into a 24 volt inverter), you could just double all of the above numbers.

    Regarding your other questions, I agree with Cariboocoot (Marc). I would avoid NiFE batteries unless you have a strong need/desire for that type of battery. They require a lot more distilled water, a change out of electrolyte (many gallons of KOH) every 5 years or so, and are much less efficient (would require a significantly larger solar array).

    If you want a longer life, you could look at forklift / industrial batteries which can give you a 15-20+ year life in lead acid (higher battery costs, a bit more distilled water usage, probably should look at 10% rate of charge minimum).

    But for a smaller system, I would start with golf cart batteries and see what your needs are... If in a couple of years you kill the bank (very common for a first time off-gridder) and/or if you need a different setup, you did not sink a bunch of money into a 20 year battery bank.

    The wild card in your system design is the well pump. I would suggest looking very closely at a VFD (Variable Frequency Drive) to provide soft start and drop the RPM to reduce peak power usage (three phase pump or pump with remote/well head located starting capacitor). VFDs are not that expensive and can help "tame" your pumping needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newbienewbie Registered Users Posts: 4
    Re: advice please

    Thanks for that, especially the real world battery advice.
    My needs are very modest as I invested in propane powered everything. Even my Bosch hot water uses a water based turbine to initiate the burner. Kinda cool that although each and every time I turn on the hot water tap, the thing kicks on. That's an unexpected hassle as I often just want a couple of seconds of warm water to rinse something.
    My main need is obviously the well pump. I'm not going to be changing that or pulling it up anytime soon as it's 335' down the hole and a damn fine new Grundfos pump ( I used to be in the business and was an electrical engineer once upon a time). It's a 3 wire so all the start controls are up in the power room and not on the pump so an easy start capacitor is an easy add on, if needed. Seems to start easy now with very little pull on the genset. 4 amp running load obviously means more in starting load but not several times more with this pump.
    A 48 volt x 220 ah battery bank giving 10kwh would seem to provide me more power than I currently need as I (now) use perhaps 3 kwh a week.
    I'd like to limit the genset use to once a week for an hour or so.
    Questions; (again)
    1) Thinking of 4x250 panels. Can you recommend a particular model?
    2) Does pulling higher amps off the battery bank harm it? Should I stick with 8x48v or just use 4x2x24 v or doesn't it matter?
    3) I can live pretty well with minimal use of electricity except for the well pump. Should I go with a 110 volt split phase inverter and transform up to 240 for the pump or go with a 240 volt?
  • newbienewbie Registered Users Posts: 4
    Re: advice please

    Thanks again Bill,
    I've used a booster pump system in Colorado for years. Pumped out of a spring with a 3hp subi. in a 1,000 tank and up a cliff into another 1,000gal tank. Wound up using 2-1.5 hp pumps plumbed in series to give the required head and volume of water for my home needs. Sailboats and RV's need a lot less but my cabin has a large garden and is 2 stories.
    I could get the forklift batteries but will probably fry them one day as you say and rather get the cheap Cosco ones and hope for the best.
    does your Xantrex inverter use much power without a load on it? Would you buy another or something else?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: advice please
    newbie wrote: »
    1) Thinking of 4x250 panels. Can you recommend a particular model?

    Panels are pretty much all the same. You get what is a good deal in $ per Watt. So long as they are a "known brand" they probably won't be any trouble. But don't guess at an array size. Four 250 Watts may or may not be right, depending on the battery bank.
    2) Does pulling higher amps off the battery bank harm it? Should I stick with 8x48v or just use 4x2x24 v or doesn't it matter?

    It makes a difference depending on what "higher Amps" is. The greater the percentage draw off the battery, the harder it is to supply. Get some actual numbers to work with. 48 Volt systems have some issues too (finding suitable breakers/fuses/disconnects for one).
    3) I can live pretty well with minimal use of electricity except for the well pump. Should I go with a 110 volt split phase inverter and transform up to 240 for the pump or go with a 240 volt?

    Some have found using an autotransformer on the one and only 240 Volt load is somewhat more efficient and slightly cheaper over-all. So long as the inverter can supply the power, either works.

    Your 4 Amps running on 240 VAC is 960 Watts. The start-up on such a pump even with a capacitor can be rough; you're trying to start it against a 300 foot column of water, after all. Having a good sine wave inverter that can take the jolt is key. The Magnum 4024PAE http://www.solar-electric.com/maenms4040wa1.html might be a good choice, for example. (Not a specific recommendation).
  • BB.BB. Super Moderators, Administrators Posts: 32,018 admin
    Re: advice please
    newbie wrote: »
    Thanks for that, especially the real world battery advice.
    My needs are very modest as I invested in propane powered everything. Even my Bosch hot water uses a water based turbine to initiate the burner. Kinda cool that although each and every time I turn on the hot water tap, the thing kicks on. That's an unexpected hassle as I often just want a couple of seconds of warm water to rinse something.
    My main need is obviously the well pump. I'm not going to be changing that or pulling it up anytime soon as it's 335' down the hole and a damn fine new Grundfos pump ( I used to be in the business and was an electrical engineer once upon a time). It's a 3 wire so all the start controls are up in the power room and not on the pump so an easy start capacitor is an easy add on, if needed. Seems to start easy now with very little pull on the genset. 4 amp running load obviously means more in starting load but not several times more with this pump.

    There are different models of Grundfos pumps--So you may be OK on the limited surge current (again, depending on model). I was a systems/electrical engineer on the computer systems side--But I do not know that much about the pumps--So, a bit of research, talking with a local well service company, and some posters here can give you some more exact answers.
    A 48 volt x 220 ah battery bank giving 10kwh would seem to provide me more power than I currently need as I (now) use perhaps 3 kwh a week.
    I'd like to limit the genset use to once a week for an hour or so.

    Except for the water pump, the minimum sized system (561 kWH per day) would be more than enough for your needs. Perhaps you start there and look at a propane version of a Honda/Yamaha genset (in the 2-4 kW range). The fuel savings would probably be significant (especially if you can run closer to 1,600 or 2kW for your pumping needs).
    Questions; (again)
    1) Thinking of 4x250 panels. Can you recommend a particular model?

    None of us volunteer moderators are in the solar business or connected with our host NAWS (except as, perhaps, the occasional customer). So, for specific recommendations on hardware, contacting our host or a local supplier you like would probably be the next step. NAWS does seem to have a good reputation and tries to keep only good quality solar RE equipment on their website/store--So, here would be a good place to start for looking at panels. Remember to include shipping and insurance costs--These costs can be very significant for larger panels (>~140 watt need to ship by truck, and small shipments need to be repacked/palletized).
    2) Does pulling higher amps off the battery bank harm it? Should I stick with 8x48v or just use 4x2x24 v or doesn't it matter?

    My suggestion, try to limit nominal current in the DC Battery wiring to about 100 amp maximum... 12 volt * 100 amp = 1,200 watt inverter/load. For example, you can see how wire sizing goes up dramatically if you do the "engineering" calculations:

    1,200 watts * 1/0.85 eff * 1/10.5 volt batt cut off * 1.25 NEC breaker/wiring derating = 168 amp minimum branch wiring/breaker rating

    And as you go up in battery voltage, the amount of "acceptable" voltage goes up (you only have about 0.5-1.0 volt of drop available in a 12 volt power system).

    And I would suggest ~2,400 watt maximum continuous power for a 24 volt bank, etc.

    And yes, high current can damage battery plates by warping them. I use ~C/2.5 as the maximum (conservative) surge current for a flooded cell battery bank. AGM can support huge amounts of current (C*4 continuous)--But there are other issues that limit this usage (heavy cables for current, you should still limit charging current to 13% to 25% maximum rate because of MPPT charge controllers can over voltage a "small" AGM bank with very large solar array).

    But--For your needs, perhaps a small battery bank setup with AGM and "large inverter" might be an acceptable solution (with a modest solar array).
    3) I can live pretty well with minimal use of electricity except for the well pump. Should I go with a 110 volt split phase inverter and transform up to 240 for the pump or go with a 240 volt?

    The problem is larger inverters have higher "tare" (or idle) losses... A small inverter may draw 6 watts just turned on. A large inverter may draw 10-20 watts or more when on.

    There are various power saving modes (search mode, inverter only turns on for 1 cycle every second looking for 6 watt AC loads) and remote on/off (12 volt signal line, inverter only is turned on when commanded) and such. You might be able to use two inverters. A small/efficient inverter for your 24x7 loads (the MorningStar 300 watt 12 volt unit does have search mode/remote on-off input). And a second larger inverter you use to start your pump.

    I am a big fan of TSW (True Sine Wave) inverters over MSW (Modified Square Wave) units.... But, perhaps for your setup, a small TSW for your cabin loads, and a large/inexpensive MSW unit for your well pump (if you can find an inexpensive 240 VAC output unit in the US). Major problem with MSW is that motors can use upwards of 20% more power (wasted as heat), and some electronics/power supplies can have problems/overheating. It is the old 80/20 rule. Probably 80% of your stiff will work fine on MSW and 10-20% will not--And it is your guess as to which appliance falls into which bin.

    Perhaps you can get some better answers here from folks with larger well pumps and MSW/TSW inverters.

    I can make guesses, but you are at the point where you need hard answers. A bit beyond where I can give you exact answers.

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