New 8.5KW System

mayorbobmayorbob Registered Users Posts: 5
I've enjoyed this forum & give & take, & have learned a lot here. So now I post my first forum question for discussion:

We are approaching retirement, and planning on building our retirement home in Eastern WA on 5 acres we own (it already has a well). We will be totally off grid, so I’ve been studying solar energy and this is what I have come up with. I would appreciate any comments, improvements and/or suggestions.

Estimated daily wattage use:  7.9kW – rounded up to 8.5 kW to base my system on

10 Suntech 275W PV

Midnight Classic 150 Charge Controller

Aims 48v/8000W Inverter

16 L16 Trojan 420Ah – set up in 2 48V strings

            -or 16 Trojan T105  225Ah – set up in 2 48V strings

Plus: cables, wires, fuses, combiner box, meters, etc.

Now…a couple of questions (beyond the obvious…did I miss something, or figure this out wrong?)…considering these parameters, do I need the 420Ah battery banks, or would I get by with the 225Ah system…or is something in between better?  Also, approximately, what should a system like this cost me? I plan to do all the installation.

Any comments would be appreciated. I will not be starting this project until summer, 2016.   Bob

Comments

  • westbranchwestbranch Solar Expert Posts: 5,163 ✭✭✭✭
    edited November 2015 #2
    Welcome  to Bob the mayor... ;)

    First look at my sig line(s) that is the starting point for our OG house.. We estimated (calculated) use at ~ 3.5Kwh per day. Used CFL for all lighting, and all phantom loads minimized, we use wood heat, so no furnace or HVAC.  3 days autonomy included. We are due N of SEA about 300 miles and in the interior, so we would have similar weather to you and this year we have had so much fog and low cloud the genset has been getting a lot of unplanned exercise...

    I suggest you need to be redo your calculations and  consider a battery twice as large [email protected] 48V if your consumption will be that high... loads have a tendency to grow, somewhat exponentially.

    Go for an OB , Magnum or Schneider inverter.  Aims does not have a good reputation, search here for [email protected] 48V the field is limited...

    hth


     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭

    Welcome to the forum mayorbob,
    mayorbob said:
    16 L16 Trojan 420Ah – set up in 2 48V strings

     -or 16 Trojan T105  225Ah – set up in 2 48V strings

    Mistake.  Avoid parallel batteries.  If you can get daily consumption down to 5 kwh, you can get by with a single string of the 420 ah batteries.  Otherwise, look for larger capacity cells.

    I agree with westbranch... avoid Aims. 

    You asked about the cost of the system... not enough detail... Do you need 240 volts AC?   What are your large wattage loads and when do they run?   If a large part of your 7.9 kwh per day consumption is daytime air conditioning, then you may not need so much battery.  And if cost matters, remember that it is cheaper to conserve a kwh than to generate and store a kwh.

    One more bit of advice... take a look at Midnite's ePanels.   Consider buying one custom pre-wired for (or with) the inverter of your choice.   Even if you don't buy an ePanel, at least study their wiring diagrams carefully.

    --vtMaps

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mayorbobmayorbob Registered Users Posts: 5
    Thanks for the comments...that's what I am needing as I move along. Ok...no AC, 220 would be hot water (though I am going to explore solar hot water heating), a stove (unless we go to a propane stove) but we wanted to be totally solar if possible. That's probably it for 220. I will definitely look at Midnite's panels & wiring diagrams, & will reconsider the battery setup. Onward...
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    mayorbob said:
     220 would be hot water (though I am going to explore solar hot water heating), a stove (unless we go to a propane stove) but we wanted to be totally solar if possible.
    You will pay dearly for trying to make hot water or cook from a battery based system.... you will need a massive battery bank to power the load while the generator is starting up. 

    You will end up burning fossil fuels in the generator rather than the water heater and cook stove.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • westbranchwestbranch Solar Expert Posts: 5,163 ✭✭✭✭
    mayorbob said:
     220 would be hot water (though I am going to explore solar hot water heating),
    I am assuming you mean evacuated tube solar water heaters, or only use solar powered opportunity loads to augment  your DHW gas heater.  otherwise VTmaps has it nailed.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • inMichiganinMichigan Registered Users Posts: 50 ✭✭
    Your well is 110 or 220?
    inMichigan
    42 SP-335's (14.1kw) ->   4 FLEXmax 80's /  100 AH CALB /  FLEXnet DC  /  MATE3  -> 2 Radian GS8048A and watched over by Vantage Pro 2+ PWS
  • levsmithlevsmith Solar Expert Posts: 56 ✭✭
    I agree with vtmaps as well. Almost anything that converts electricity (water heater, stove, space heaters, etc.) to heat is a bad idea for off grid. I would seriously consider using a propane hot water heater, assuming you dont have access to natural gas, at least until you figure out your solar water heater and possibly to supliment on cloudy days.
  • mayorbobmayorbob Registered Users Posts: 5
    Vtmaps...you said to "avoid" parallel batteries. I had planned 2 banks of 8-6V batteries in series, 48V in each bank, thus doubling the Ah (ie: 420Ah to 840Ah). Are you suggesting that I can get by with just one string of 8 6V batteries in a string at 420Ah? Would that be adequate for a 5kW use?
  • mayorbobmayorbob Registered Users Posts: 5
    InMichigan...my well will be on a totally independent solar system by itself. I have that one taken care of, so it is not part of my home equation. My big draws will be from water heat, clothes dryer (only two of us, so not a lot of use), 7 cooking. That's why we are seriously looking at propane stove & water heating. We already were planning a propane fireplace for heat, but wanted to keep propane use as low as we could. Off grid...!!
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    mayorbob said:
    Vtmaps...you said to "avoid" parallel batteries. I had planned 2 banks of 8-6V batteries in series, 48V in each bank, thus doubling the Ah (ie: 420Ah to 840Ah). Are you suggesting that I can get by with just one string of 8 6V batteries in a string at 420Ah? Would that be adequate for a 5kW use?
    You can get 4V and even 2V batteries to give you the higher AH rating that you may need. That way you can go with approximately the same physical size batteries you are looking at, but arranged in one series string instead of two.
    SMA SB 3000, old BP panels.
  • inMichiganinMichigan Registered Users Posts: 50 ✭✭
    mayorbob said:
    InMichigan...my well will be on a totally independent solar system by itself. I have that one taken care of, so it is not part of my home equation. My big draws will be from water heat, clothes dryer (only two of us, so not a lot of use), 7 cooking. That's why we are seriously looking at propane stove & water heating. We already were planning a propane fireplace for heat, but wanted to keep propane use as low as we could. Off grid...!!
    We've kept our electric hot water & stove since we're grid tie hybrid and have a minimal battery bank size.  There's no doubt when looking at hourly power data when the water heater runs.  For giggles, I've explained to my wife how much larger our battery bank would have to be IF you wanted our current lifestyle in off-grid mode.   As long as we have net metering & a working grid, I'm ok with what I have.  Should that change, I've been watching for peoples experience with
    • heat pump style water heaters
    • add a tank to 'warm from cold well temperature to room temperature' to reduce the load (I'll eventually do anyway)
    • put the big tank on a timer and run it only mid-day (look for, or will do some experiments to understand the temperature drop against time)
    • Look into mixing valves if I raise the temperature of the day-time storage tank if my strategy becomes store water at as high of temperature as possible.
    • Or, add POU heater for the shower, other sinks would get what they get from the storage tank.  Then, the storage tank could be larger size but lower temperature
    I really enjoy these forum discussions since each person's system and strategy can be quite different. I like to understand the physics behind why something works or doesn't work.

    inMichigan
    42 SP-335's (14.1kw) ->   4 FLEXmax 80's /  100 AH CALB /  FLEXnet DC  /  MATE3  -> 2 Radian GS8048A and watched over by Vantage Pro 2+ PWS
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    mayorbob said:
    Are you suggesting that I can get by with just one string of 8 6V batteries in a string at 420Ah? Would that be adequate for a 5kW use?
    420 ah X 48 volts = 20,160 watthours

    general rule of thumb for off grid:  size the battery to be 4 times the daily load.

    Thus a 5 kwh per day consumption would fit that size battery bank very well.  But remember, it's just a rule of thumb... every system is different.   You still haven't described your loads well enough for me to recommend a battery.

    For example, if your load was 4000 watts for 5 minutes, that would be 333 watthours of energy, not much for a battery that stores 20,160 watthours.   BUT the battery would have to supply 4000 watts ÷ 48 volts = 83.3 amps.  Add another 8 amps or so for inverter inefficiency and you are drawing over 90 amps from the battery.

    Those 420 ah batteries are rated 420 ah only if you are drawing 21 amps from them.   They will not sustain a 4000 watt load very well... you could even damage the battery. 

    My point is that battery selection is not just about kwh.  The battery is the heart of the system... you really need to know your loads to choose a battery.  You need to know when the loads occur, how much power they draw (watts), and their energy use (kwh).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mayorbobmayorbob Registered Users Posts: 5
    Great comments, & I appreciate it. I'm with "InMichigan"...I like finding out how all this works. Ok...I'm looking at my worksheet, since we have yet to build the house I can only make assumptions. I have ordinary appliances, such as coffee maker, microwave, blender, dishwasher, vacuum, & 15-20 LED 4-5W lights, etc. Then there is a washing machine, that would probably only run 2-3x a week, dryer, same, stove (but we are seriously considering propane there), laptop, TV, printer, couple of clocks...nothing that would really draw down a system. Then there is the hot water heater, refer & freezer (both smaller, high efficient, like less than 1 Kw/day) but looking at 12V refer & freezer & trying to compare power usage. We will have a propane fireplace for heat. So that's probably the best, at this point, that I can explain our loads. Does that help? Knowing this, how would you set up the battery bank?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    edited November 2015 #15
    deleted duplicate post
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    mayorbob said:
    I have ordinary appliances, such as coffee maker, microwave, blender, dishwasher, vacuum
    <snip>
    Then there is a washing machine, <snip>  dryer, <snip> printer,
    <snip>
    Then there is the hot water heater, refer & freezer (both smaller, high efficient, like less than 1 Kw/day) but looking at 12V refer & freezer & trying to compare power usage.
    Do you intend to be doing laundry while vacuuming or using kitchen appliances?   If you expect to continue life as if you are on the grid, you should spend more time researching generators and how they interface with battery based off grid systems.   It is discouraging research.

    Off grid is a lifestyle... either you will spend a lot of time managing loads, or you will spend a lot of time dealing with the generator.  Overall the power you generate for your lifestyle will cost 5 - 15 times what your utility bill would be if you were on the grid. 

    By the way, I chose a battery that can not handle high wattage loads.... we start up the generator before we vacuum or use sustained high wattage shop tools.  I figured I needed a generator anyway (like for 3 cloudy days in a row), so since I have it I might as well use it.   I don't have any automatic generator start... they can be a real problem, especially in cold weather.  My generator is a 1600 watt portable that I keep at about 40° F in the garage.  I move it outdoors when I want to use it.   It can run anything I own, but of course, only one big load at a time. 

    If I wanted to vacuum (1500 watts) for an hour on batteries, I would have to more than quadruple the cost of my system.   Because I would have so much more battery, I would need many more solar panels to charge the battery, and a much larger generator for the same reason.  The larger generator would not be portable, so I would have to build a heated generator shed for it.  It didn't seem worth it just to avoid operating my little generator for 2 hours per week.   By the way, when you are fueling your large generator you will get a sense of just how expensive your power is.... but when you replace your batteries, that's when you will really know.
    mayorbob said:
    couple of clocks...nothing that would really draw down a system.
    Little loads for long times are big loads.   My 3500 watt 120 volt Outback inverter draws 20 watts when it is turned on and doing nothing.  That's actually a very low number for an inverter of that size.  But it does add up to 480 watthours per day.... that's as much as my ultra efficient refrigerator consumes in a day.

    You need to get realistic numbers for all the little stuff.  Many of the items and appliances you mention may draw phantom loads.
    mayorbob said:
    So that's probably the best, at this point, that I can explain our loads. Does that help? Knowing this, how would you set up the battery bank?
    You are asking for design and engineering advice... Great!  You've come to a good place for it.  Unfortunately us engineers work with numbers and formulas.   We need numbers for peak loads, peak sustained loads, and daily kwh consumption. 

    By the way, don't be too discouraged... a 5 kwh per day system is doable.   The battery selection is the hardest part of the design.  It sounds like your peak loads are large relative to your energy use, so you may want to choose a low Peukert factor battery... they cost more than flooded lead acid batteries, but may fit your needs better.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    edited November 2015 #17
    deleted duplicate post
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ArkansasoffgridArkansasoffgrid Solar Expert Posts: 118 ✭✭
    We've only been offgrid since July, but the lifestyle changes have been rewarding.
    We're in a 1150sqft cabin, that's totally spray foam insulated. 12k btu minisplit handled cooling well with fans for extra circulation. Thus far we've not been below 84% batt with a 420AH bank according to data screen on CC. We're a little over paneled, but it allows for opportunity loads.
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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