Off grid component location and sizing

sunenergysunenergy Registered Users Posts: 22
I'm in the planning stage of my first solar project. The building site has been cleared and nothing has been bought or constructed including the cabin. For now it will be primarily for summer use, mostly at the weekend. I plan to pump water 200' vertical with excess power created by the array. The array and battery bank will ideally be sized to run power tools during the cabin construction but only for occasional cuts. Much of the lumber will be pre-cut in town.

Here's the basic layout, array and battery bank sizing still a bit confusing. All input welcome, Thanks:
picture.php?albumid=51&pictureid=370

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Off grid component location and sizing

    Welcome to the forum.

    I can see a couple of problems right off. The first being no load estimation. You're going to have a very hard time planning a system without at least a target of power usage.

    The other thing is you do not want 150' of wire between the batteries and the inverter. This is where your heaviest current flow will be, and it's important to keep the wires as short as possible.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Off grid component location and sizing

    Agree with Cariboocoot... your daily estimated loads in Watt*Hours (Or Amp*Hours * bank voltage). And your peak/average watts for different loads in your system...

    For sending power long distances, you want to send that voltage as high as you can... 24 volts, will cost you an arm and a leg in copper wiring.

    120 VAC (or even 120/240 VAC split phase) will reduce your copper costs for that 150' to 1/5th to 1/10th of a 12 or 24 volt battery bank. Remember power=Volts*Current... 5x the voltage, 1/5th the current.

    Knowing your loads will help define battery capacity/bank voltage/array size.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sunenergysunenergy Registered Users Posts: 22
    Re: Off grid component location and sizing
    Welcome to the forum.

    I can see a couple of problems right off. The first being no load estimation. You're going to have a very hard time planning a system without at least a target of power usage.

    The other thing is you do not want 150' of wire between the batteries and the inverter. This is where your heaviest current flow will be, and it's important to keep the wires as short as possible.

    Thanks. I wanted to decide on a basic layout while I get myself more confused over target power usage :D
    My initial thought was having the batteries near the cabin but wouldn't the controller need to be located near the batteries? If this is the case I'm not sure how to get the excess power to the water pump without having to run an additional pair of wires 150'. I already have a few hundred feet of salvaged 4 AWG wire.
  • sunenergysunenergy Registered Users Posts: 22
    Re: Off grid component location and sizing
    BB. wrote: »
    Agree with Cariboocoot... your daily estimated loads in Watt*Hours (Or Amp*Hours * bank voltage). And your peak/average watts for different loads in your system...

    For sending power long distances, you want to send that voltage as high as you can... 24 volts, will cost you an arm and a leg in copper wiring.

    120 VAC (or even 120/240 VAC split phase) will reduce your copper costs for that 150' to 1/5th to 1/10th of a 12 or 24 volt battery bank. Remember power=Volts*Current... 5x the voltage, 1/5th the current.

    Knowing your loads will help define battery capacity/bank voltage/array size.

    -Bill
    Would you recommend locating the inverter near the array and battery bank then run wire the 150' to the building site?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Off grid component location and sizing

    The best plan is to have the longest run on the highest Voltage.
    Usually the inverter cables and the controller to battery wiring as short as possible. One way to make up for this is to have a higher Voltage array and downconvert that with an MPPT type charge controller. As in a "24 Volt" system using a "48 Volt" array.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Off grid component location and sizing

    Typically, for an off grid system you have two locations for high voltage, the 120/240 VAC inverter output and the Solar Array to MPPT Charge Controller (Vmp-array ~100 VDC typical max).

    So, you could move your batteries close to the home and have the array in the sun 150 feet away.

    But the wild card here is the well pump...

    Say we look at 6 amps and 200' at 24 volts with 3% drop (0.72 volts maximum). Using a generic voltage drop calculator:
    • 200', 6 amps, 0.72 volt drop -> 4 awg copper wire
    Depending on how much power in the home you want, placing the PV System near the well, and run the AC power to the home.

    Or, other options, 120/240 VAC well pump; local solar PV power for well pump, PV+Battery power for pump, run 120 VAC from home to a small AC charger and battery bank to run pump, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sunenergysunenergy Registered Users Posts: 22
    Re: Off grid component location and sizing

    Installation will likely be less than 1kw.

    One thing worth noting is the water source is a spring with plenty of gravity feed to the cabin site but I wanted to avoid placing the pump near the cabin because of noise. I don't know how much noise the Solar Slowpump generates and it's possible that placing it in and enclosure insulated for noise might be an acceptable option.

    But sticking with the original layout of the solar array and pump in the diagram is there any reason I shouldn't place the inverter near the array? My thinking is that in a perfect world having the controller, battery bank and inverter near the cabin would make it easier to monitor the installation. But then there's the water pump.

    Would using a controller remote display provide enough info that I wouldn't need to visit the installation itself on a regular basis? Not that it's hard to get to at all but I do have my lazy moments.

    Is there enough useful information provided by an inverter that it is nice to have it very nearby?

    Thanks for all the input, i really appreciate it.
  • mike95490mike95490 Solar Expert Posts: 7,288 ✭✭✭✭
    Re: Off grid component location and sizing

    I'd get the pump, it's own PV panel, and let 'er rip.

    I'd also want more monitor info on the charge controller, because if the batteries are happy, the inverter will be happy. All the inverter can tell you is power output, if that, and low battery disconnect.

    Run the voltage drop caculator on your plans, and see what wires are needed, then redrawm and run again.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Off grid component location and sizing

    Also look at a battery monitor. I like them. But 150 feet from shunt to monitor might be too far.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MangasMangas Solar Expert Posts: 537 ✭✭✭✭
    Re: Off grid component location and sizing

    Sidebar to our site set up.

    We set our array (DC runs) about 150' from the inverters to assure plenty of sun, no house shading and potential expansion area. The DC runs enter a rock built 12x12 solar mechanical building housing the inverters, charge controllers and batteries.

    The standby propane fueled generator is located on an elevated pad next to the mechanical room.

    The high voltage (220/120) AC run from the mechanical room to the house is about 50' into two 100 amp AC panels.

    We ran an AC line from the solar mechanical room to an insulated 500 gal water pressure tank house about 100' away. The pressure tank is charged by two adjacent underground 1,700 gal water storage tanks each set up with a 1/2 hp 220v grunfoss submersible pump.

    The pressure tank house also has its own AC circuit breaker panel.
    Ranch Off Grid System: 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 House Construction, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Off grid component location and sizing

    Since you are ultimately going to need a generator anyway, I would steer away from designing around tool use, (unless you are going to do that long term). I would prefer to run the genny for tools . It is important to realize that the running load of even a moderate sized skilsaw might be ~ 13-15 amps, (1800 watts) but the starting loads are likely to be very much higher. To design, buy and install such large system for the short term needs might not be cost effective.

    I agree with others, design around projected loads. Spend time to define those as best you can, understanding the first rule of off grid living: the loads are likely larger than you project, and they will grow with time. (The second rule is that people tend to overestimate their average solar harvest, while at the same time they underestimate their loading, leading to a double whammy of not enough power).

    My off grid rule of thumb, is to take the name plate rating of the PV, divide it in half to account for all cumulative system loses, then take that number and multiply it by four. That represents the average number of hours of "good sun" one can expect, on a daily basis, on average over the course of the the year. (Your local number can be adjusted up or down due to seasonal use, or latitude or local climate phenomenon, but it rarely much over four).

    Just as a point of reference, we have ~ 400 watts of PV, we routinely use ~5-800 watt/hours/day on average. On nearly every day we recover that without problem (into 450 ah of battery (12 vdc) We can go 3 days without sun, and nearly recover the entire drop in one good day. On a perfect, ideal, cold day with lots of reflection off the snow we can put out ~ 1.5- 2 kwh.

    Good luck,

    Tony
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Off grid component location and sizing

    Regarding 50% minimum load on genset and diesels...

    I tend to recommend a minimum of 50% load for fuel effiiciency (probably more important for gasoline/propane gensets).

    Diesels, I have seen others recommend a 60% minimum load and another poster here was very happy with 40% minimum load... Different opinions.

    But, to obtain your minimum load, look at running your optional AC loads when the generator is running... Vacuum, washer/drier, electric water heater, etc... In the field, there are people that would fill a drum with salt water and a couple of electrodes--Adjust salt content and electrode spacing dump extra power into boiling water (to meet minimum recommended loads).

    And, there have been some interesting suggestions to help keep a Diesel Engine carbon free... Adding Propane (or natural gas) to the intake air can help to keep the diesel running hot in the combustion chamber (do your own research, obviously, adding propane to the intake of a diesel engine can be dangerous).

    Here is a nice discussion page about "LP Fumigation". It is written towards vehicle diesels, but seem to apply to gensets too.

    Regarding Tony's "Icarus" experience with an increase in power production during winter... Part of that increase in power production is due to cold panels and the use of an MPPT type solar charge controller (~10-30%). A PWM type controller (less expensive type) would not see any increase in sub zero weather vs summer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sunenergysunenergy Registered Users Posts: 22
    Re: Off grid component location and sizing

    Based on all the great input I've adjusted the layout.

    I decided to take the water pump out of the equation for now. I do have flexibility on where one is placed and since I already have water storage on the property I can revisit that later. I did like the one comment from Mike "I'd get the pump, it's own PV panel, and let 'er rip" which may be what I do in the end.

    I had considered the generator option but I would want a quality and quiet generator capable of running power tools , say in the 3KW range, but those are pricey. I thought it would be better to spend the money on the solar installation itself. Definitely open to generator suggestions.

    Hopefully at the weekend I can provide my anticipated power usage for scrutiny. I'm not on too tight of a budget and want to build something I can grow into as well as be able to expand.

    New layout:
    picture.php?albumid=51&pictureid=371
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Off grid component location and sizing

    Two sizes of gensets is not the worst thing in the world either...

    The smaller Honda eu1000i or eu2000i are great as they are quiet and pretty fuel efficient down 225 watts (1000i) or 400 watts (*2000i).
    Don't bet on it: my Honda 1000 is getting pretty darn close to 8000 hours! :D

    I think Marc in another post said he had 6,000+ hours on the eu1000i right now with just normal maintenance... That is impressive--I am not sure I would count on my eu2000i lasting that long.

    And get a bigger genset for when you need to run the larger tools. If it is not used very much, 3.5kW to 5kW gasoline genset are ridiculously cheap. But they will not be very fuel efficient at less than 50% of rated load... Noisy and cheap enough to throw away--Unless you get the Honda eu3000i or similar Yamaha products.

    Also, there are some pretty practical LP conversion kits for these small generators--If that is a better choice of fuel for you.

    Regarding the 150' wire run, look at making the Vmp of the array in the ~100 volt range. That will save you a bunch on money on copper... Will require a MPPT controller that can manage 150+ VDC (Morningstar, Midnite solar, Xantrex, Outback, etc.)... The Morning Star TS MPPT and possibly Midnite are the first two you should look for this voltage class.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Off grid component location and sizing

    Why quit at 2 gennies? Why not have a dozen or more!

    Seriously, 2 Eu 2000's makes a great combination for a number of applications. Or as Bill suggests, buying a ~ 5kw 3600 rpm unit from the "home centre" for under ~ $1000 for exclusive tool use , coupled with a Inverter genny of the proper wattage dedicated for the house and it's load and charging need makes a pretty good combination as well.

    I have bought a number of used Auto idle construction gennies out of rental yard fleets for a couple hundred each. A great deal, because often they don't have a lot of hours on them, they have been serviced, and since they have been depreciated, they sell them quite cheap.

    Good luck,

    Tony
  • sunenergysunenergy Registered Users Posts: 22
    Re: Off grid component location and sizing

    Sorry it's taken so long to get back. After much head scratching I've come up with the idea of running a 24v Solar Slowpump off the battery bank for approximately 4 hours/day. The amount of time the pump runs can very flexible. The pump would be controlled by a timer and set to run maybe 4 days a week. If done correctly this would leave the weekends with fully charged batteries for other uses.

    I'd like to shoot for a minimum of a 500 watt hours a day system and maintain an ideal charge and discharge rate for the battery bank maybe using the SlowPump to help achieve that goal. For batteries it looks like 4 Trojan T105-RE 6V 225 AH batteries would be overkill. I'm unsure of a reasonable alternative and I still fantasize about having the ability to briefly run a sliding mitre saw for the occasional cut. I am willing to accept that may be asking too much. I lean towards a system I can grow into. Any thought on panel and battery bank sizing would be most welcome.

    New layout:
    picture.php?albumid=51&pictureid=379
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