Correct wiring for a system with integrated inverter/charge controller

dakaz
dakaz Registered Users Posts: 10
Hello,

I am hoping someone can point me to a good tutorial or provide answers for me around the CORRECT way to handle wiring for our small off-grid system. The system is a small 3 panel (230W, 24V) system and we are planning on putting in the AIMS 3000W Pure Sine Wave inverter/charger. We also have a small generator to use to charge the batteries in case of emergency, so the integrated ATS and AC charge controller of the AIMS is attractive. But how do you properly wire this? I have been reading a lot and I'm fairly familiar with electrical systems (I'm no electrician though). I find this diagram good (http://www.freesunpower.com/example_systems.php) but curious where I would put the correct circuit breakers and fuses. The inverter/charger manual (http://www.aimscorp.net/documents/PICGLF30W24V120V.pdf) does not seem cover the subject in detail. I see on page 6 the unit has three DC connections: DC input from Solar, a DC output (from charge controller I have to presume??) and the main DC input block for the inverter. So do I just treat the "solar DC terminal" like a standard standalone charge controller?

Any help would be appreciated.

Thanks

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Correct wiring for a system with integrated inverter/charge controller

    Your first link does show a pretty clear drawing of the basic connection requirements for an off grid system.

    Hmmm.... AIMs inverters/systems. Always very interesting, but their documentation/actual specifications usually ends up being very problematic.

    First, the Solar input is not capable of using standard GT type solar panels that you have picked (you would need a separate MPPT type charge controller directly connected to the battery bus):
    The Charge controller built in was designed with 12/24V battery voltage auto detecting function.
    For 12VDC inverter, the output voltage of the solar charger will be accordingly 12VDC, and the qualified DC input volt range is 15v-30VDC.
    For 24VDC inverters, the output voltage of the solar charger will be accordingly 24VDC, and the qualified DC input volt range is 30v-55VDC.
    If the voltage falls out of this range, the charger will not work properly. Special attention should be paid to this when configuring the solar array.

    Next, they have a new definition for Pure Sine Wave inverter:
    The Global LF inverter/charger is built according to the following topology.
    Invert: Full Bridge Topology.
    Charge: Isolate Boost Topology
    Because of high efficiency Mosfets and 16bit, 4.9MHZ microprocessor and heavy transformers, it outputs PURE SINE WAVE AC with an average THD of 15% (min 5%, max 25%) depending on the load connected and the battery voltage.
    The peak efficiency of the Global LF series is 88%.

    TSW is 5% or less Total Harmonic Distortion... 25% THD would probably be a MSW (modified square wave output).

    Next, they are really unclear if this is actually an isolated TSW inverter:
    WARNING
    For split phase models, AC input neutral is not required in wiring. Never Connect Input Neutral to Output Neutral. Damage will result which is not covered under warranty.
    Always switch on the inverter before plugging in any appliance.
    ...
    WARNING
    The output voltage of this unit must never be connected in its input AC terminal, overload or damage may result.
    Always switch on the inverter before plugging in any appliance.

    For almost all TSW inverter, it is normal to connect input Neutral to Output Neutral--That is the way you get common Neutral Bonding throughout your power system.

    There are other issues too--But, lets back up a moment.

    What are your loads? Average maximum Watt load, Watt*Hours of Use per day? Do you have a battery bank picked out?

    A 3kW AC inverter is pretty big when compared with 690 Watts of solar panels. This inverter, if operated 24 hours per day, will eat up much of the output of your solar array (almost 40 watts of tare losses when "on").

    Lets start at the beginning and see what your needs are and then suggest a design that can support those needs.

    And to be honest, for most people, the optimum emergency/standby emergency power source would usually be a smaller generator.

    Plus, conservation--For emergencies, you want to power the minimum loads needed. Your solar array is almost large enough to power a refrigerator+lights+some other random loads (around 2kWH per day for a moderately sunny climate). If you don't need a lot of power (no fridge), you could go with 1/2... If you want a bit more power for a fridge/well pump/clothes washer/laptop computer/etc.), I would go with about 3.3 kWH per day (50% larger array than you have now).

    Jumping in and buying hardware before you have your needs defined, and before you have done a full paper design (or three)--You will probably have some wasted time and money.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dakaz
    dakaz Registered Users Posts: 10
    Re: Correct wiring for a system with integrated inverter/charge controller

    Wow, what a great reply, THANKS! Let me respond inline:
    BB. wrote: »
    Your first link does show a pretty clear drawing of the basic connection requirements for an off grid system.

    Hmmm.... AIMs inverters/systems. Always very interesting, but their documentation/actual specifications usually ends up being very problematic.

    This statement alone is making me think that this is not the right system for us! I will continue to explore other options but I do like the AC charger in the inverter and the ATS, is there another unit youd recommend for inverter/ATS/AC Charger or should I truly source them each independently?
    BB. wrote: »
    First, the Solar input is not capable of using standard GT type solar panels that you have picked (you would need a separate MPPT type charge controller directly connected to the battery bus):

    Not sure I follow. The panels I am planning on using are these: http://solarsystems-usa.net/solar-panels/et-solar/et-p672280ww
    BB. wrote: »
    What are your loads? Average maximum Watt load, Watt*Hours of Use per day? Do you have a battery bank picked out?

    Here are my loads, total is just shy of 150 aH per day.
    Device	Volts	Watts	Hours / Day	Amp Hours / Day	Qty	Total aH/Day
    						
    Inverter	24	1	24	1	1	1
    Light	120	15	6	0.75	8	6
    Fridge	120	360	24	72	1	72
    Well Pump	120	600	3	15	1	15
    Toilet	120	370	18	55.5	1	55.5
    

    BB. wrote: »
    A 3kW AC inverter is pretty big when compared with 690 Watts of solar panels. This inverter, if operated 24 hours per day, will eat up much of the output of your solar array (almost 40 watts of tare losses when "on").

    Lets start at the beginning and see what your needs are and then suggest a design that can support those needs.

    And to be honest, for most people, the optimum emergency/standby emergency power source would usually be a smaller generator.

    Plus, conservation--For emergencies, you want to power the minimum loads needed. Your solar array is almost large enough to power a refrigerator+lights+some other random loads (around 2kWH per day for a moderately sunny climate). If you don't need a lot of power (no fridge), you could go with 1/2... If you want a bit more power for a fridge/well pump/clothes washer/laptop computer/etc.), I would go with about 3.3 kWH per day (50% larger array than you have now).

    Jumping in and buying hardware before you have your needs defined, and before you have done a full paper design (or three)--You will probably have some wasted time and money.
    -Bill

    You can see my loads above. I was planning on buying 6 12V sealed batteries (lower maintenance for our occasional use cabin) like these http://www.apexbattery.com/12v-200ah-4d-deep-cycle-agm-solar-battery-ub-4d-also-replaces-210ah.html

    My goal for the batteries was to have enough power to survive 2 days without sun... 6 of those batteries should give me 600 aH total so I have met that goal at 150 aH of usage per day and a 50% drain of the batteries. I am at 48 degrees North latitude so summer time 3 panels should give me around 250 aH / Day and during the winter 80 aH / day. In the winter we'll have no well pump or toilet (the composting toilet acts as a holding tank) so power draws will be much less and we'll only spend weekends at most at the cabin.

    Thanks!
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Correct wiring for a system with integrated inverter/charge controller
    dakaz wrote: »
    Here are my loads, total is just shy of 150 aH per day.
    <snip>
    My goal for the batteries was to have enough power to survive 2 days without sun... 6 of those batteries should give me 600 aH total so I have met that goal at 150 aH of usage per day and a 50% drain of the batteries

    Welcome to the forum

    DON'T spend anything until you figure out a few more things. For starters you need to know and understand your loads.

    You wrote that your 120 volt well pump draws 600 watts (5 amps) for 3 hours per day. You also wrote that it would consume 15 amphours per day. That is NOT correct. You need to realize that your pump is drawing more than 600 watts from the batteries (because of inverter losses). Let's say its drawing 650 watts from the batteries. If you are using a 12 volt battery bank that is a bit over 54 amps, and over 3 hours that will draw down your batteries by about 162 amphours.

    You have made the same mistake on all your 120 volt loads.

    Now for the good news... your fridge does NOT run 24 hours per day. It cycles on and off.

    Obviously, there is much more to discuss before you spend money, but loads come first.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Correct wiring for a system with integrated inverter/charge controller
    dakaz wrote: »
    This statement alone is making me think that this is not the right system for us! I will continue to explore other options but I do like the AC charger in the inverter and the ATS, is there another unit youd recommend for inverter/ATS/AC Charger or should I truly source them each independently?

    We try here to first, spend your money (:p) on known good/reliable equipment. If your wallet (or spouse) does not agree, we will try to help you with other choices.

    Second, I am on grid and just use a backup generator (have not had to fire one up for 20+ years--Yet). So, I can give you some equipment to look at--Others can help with their feedback--But it will have to be your choice (us moderators are not in the Solar Business, and we have no connections with NAWS other than as volunteer moderators on this forum).
    • Schneider with the XW Hybrid inverter family has a pretty solid/reliable unit with lots of feature. A few have had isssuses. Most love their phone support, others not always.
    • Xantrex (the consumer/RV arm of Schneider now)--Has their ProSine (sp?) series which a lot of people here have used over the years and found them to be very reliable and lots of surge capabilities.
    • Outback has been a gold standard for years with their inverters and charge controller--And their tech support. They have been, at times, a bit slow to upgrading their product lines (difficult to upgrade firmware in the field) and you have to pick the "right inverter" for the optimum off grid+generator support.
    • Magnum--Really like their product line. They were among the earliest that offered split phase 120/240 VAC inverter/chargers without needing external transformers and/or "stacked" inverters. Seems to be the 80/20 Rule--80% are very happy and 20% seem to be less than thrilled with voltage stability/surge.
    • Exeltech makes very rugged inverters and if one ever fails, it is something like $100 to return to factory to get it repaired/rebuilt)
    • Samlex (and their sister brand Cotec) are good quality at lower costs.
    • MorningStar makes a killer 12 volt 300 Watt TSW inverter--But nothing else at this time.
    • SMA products are always great German Engineering--And in the US, not cheap. Not a wide product line (at least in the US). The SunnyIsland is a wonderful product for what it does (and does it very well--using GT inverters for off grid/local power AC power networks).
    • Victron (Europe) also makes good equipment too...

    So, hardly any of what I typed will help you that much... So, I like to go back to what it is you need. 120 VAC? 120/240 VAC? You want an Inverter+Charger or separate Inverter + AC charger (pluses and minuses for both). Inverter+Chargers are usually highly programmable and can make it much easier to run a smaller (and more fuel efficient generator--If your loads are not heavy) vs a off the shelf AC charger and random genset.

    Next, features. Remote metering/Control? 24x7 power (usually needed if you have an Energy Star refrigerators--they cannot have their AC power interrupted or they go into defrost mode when power is restored). Otherwise, you can use "search mode" on the AC inverter (sleeps for a second, then blips the AC line looking for >6-10 watts of AC load, inverter turns on if it "sees" AC loads).

    Check the "tare" power of the inverter--Many inverters have very high "on/no load" current (10-20 watts or more). And TSW inverters usually have higher tare power requirements vs MSW. For smaller off grid system--this can be 1/3rd of your loads or more (inverter Tare). For larger systems, the 24 hour "always on" tare of the inverter is less of an issue.

    All About Inverters
    Choosing an Inverter - Home Power Magazine

    You can pick an inverter with an Automatic AC Transfer Switch, or you can even get (or even make) simple ATS relays for not too much money.
    Not sure I follow. The panels I am planning on using are these: http://solarsystems-usa.net/solar-panels/et-solar/et-p672280ww

    That panel does have Maximum Power Voltage (Vmp)=35.54V

    As long as you are using a 24 volt battery bank--That will work OK with either PWM (cheaper) or MPPT (more expensive).

    If you have a fair distance from the array to the charge controller+battery bank--Then using an MPPT controller and putting 2 panels in series to raise Vmp-array can save you a lot on copper wiring costs.

    Here are my loads, total is just shy of 150 aH per day.
    Device    Volts    Watts    Hours / Day    Amp Hours / Day    Qty    Total aH/Day
                            
    Inverter    24    1    24    1    1    1
    Light    120    15    6    0.75    8    6
    Fridge    120    360    24    72    1    72
    Well Pump    120    600    3    15    1    15
    Toilet    120    370    18    55.5    1    55.5
    

    I am confused about your table...
    Toilet 120Vac 370Wac average load? 18hours/day? 55.5 1 55.5
    • 370 Watts * 18 hours per day = 6,660 WH per day = 6.7 kWH per day
    • 6,660 WH per day * 1/0.85 inverter eff * 1/24 volt battery bank = 326 AH per day @ 24 volts

    It may be you are confusing Amp*Hours at 120 VAC vs Amp*Hours at 24 VDC...
    • 6,660 WH / 120 VAC = 55.5 AH @ 120 VAC

    Both 326 AH and 55.5 AH are "accurate" answers... However, remember that energy is voltage dependent:
    • Power = Volts * Amps = Watts
    • Energy = Volts * Amps * Hours = Watt*Hours

    But Amps and Amp*Hours are "missing" the voltage component:
    • AH = Amps*Hours
    • Amps= Amps

    So, 2 amps at 120 VAC will look like:
    • P=VI= 120 VAC * 2 Amps = 240 Watts load
    • I=P/V= 240 Watt load / 24 volts = 10 amp load on your 24 volt battery bus (ignoring inverter losses)

    So, you will need to rethink your numbers/loads up there... Stay with Watts and Watt*Hours until you need to pick a battery voltage (and inverter losses/efficiencies). You will not get in the trap where 24 VDC current is 5x larger than 120 VAC current (and therefore needs 5x as much battery AH for storage and 5x as much solar panels for "power" and "energy").

    Watts and Watt*Hours (WH, kWH, etc.) a "complete" unit--Amps and Amp*Hours are "incomplete units" and need voltage to fully quantify what they "mean".

    If you were working on a boat or a truck with a 24 VDC power system--You can stay in Amps and Amp*Hours because everything is at "24 volts". Not so when you throw a 120/230/240 VAC inverter and 12,24,48 volt battery banks. Confusion galore.
    You can see my loads above. I was planning on buying 6 12V sealed batteries (lower maintenance for our occasional use cabin) like these http://www.apexbattery.com/12v-200ah-4d-deep-cycle-agm-solar-battery-ub-4d-also-replaces-210ah.html

    Ignore the battery choices for the moment (AGM are "ideal" lead acid batteries--Their downside is that they are ~2x as expensive and typically last a couple of years less than flooded cell--But they still may be "worth it" for you).

    Until we have your power needs nailed down--We don't need to go any further (farther?) down the battery+solar panels+hardware isle yet.

    At this point, your 120 VAC to AH calculations (and probably your load watts) are not correct. As listed, just your toilet alone consumes about as much power as my 3 bedroom suburban home consumes in a day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dakaz
    dakaz Registered Users Posts: 10
    Re: Correct wiring for a system with integrated inverter/charge controller
    BB. wrote: »
    It may be you are confusing Amp*Hours at 120 VAC vs Amp*Hours at 24 VDC...
    • 6,660 WH / 120 VAC = 55.5 AH @ 120 VAC

    Both 326 AH and 55.5 AH are "accurate" answers... However, remember that energy is voltage dependent:
    • Power = Volts * Amps = Watts
    • Energy = Volts * Amps * Hours = Watt*Hours

    But Amps and Amp*Hours are "missing" the voltage component:
    • AH = Amps*Hours
    • Amps= Amps

    So, 2 amps at 120 VAC will look like:
    • P=VI= 120 VAC * 2 Amps = 240 Watts load
    • I=P/V= 240 Watt load / 24 volts = 10 amp load on your 24 volt battery bus (ignoring inverter losses)

    So, you will need to rethink your numbers/loads up there... Stay with Watts and Watt*Hours until you need to pick a battery voltage (and inverter losses/efficiencies). You will not get in the trap where 24 VDC current is 5x larger than 120 VAC current (and therefore needs 5x as much battery AH for storage and 5x as much solar panels for "power" and "energy").

    Watts and Watt*Hours (WH, kWH, etc.) a "complete" unit--Amps and Amp*Hours are "incomplete units" and need voltage to fully quantify what they "mean".


    Hi Bill,

    Again, can't thank you enough for the completeness of your response, what an education I am getting!!!

    I see that I completely missed the conversion to 24V as you noted. I also adjusted some of the "run times" of the fridge (to 12 hours, not 24), the well to 1 hour per day (two sinks, a shower and a toilet and the composting toilet to 12 hours from 24. Adding in the inverter inefficiencies I get a total daily need of 47274 Watt Hours @ 24V and 495 aH / day. The table doesn't translate well in this forum, but I'll try attaching a picture. If I have the power correct, then we can move onto the equipment as you stated.

    Attachment not found.

    Thanks,

    Mike
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Correct wiring for a system with integrated inverter/charge controller

    doing thiss lft handed so will b short. our house uses ~ 1/4 to 1/3 of your calc'd daily use , with the same things plus elec stove 2 tv radios etc. something is out of whaack, looks like fridge, should b ~ 1/2 to1 kwh for whole day not 21

    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
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Correct wiring for a system with integrated inverter/charge controller

    looked again, you did not apply cycle on/off times
     
    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
  • dakaz
    dakaz Registered Users Posts: 10
    Re: Correct wiring for a system with integrated inverter/charge controller
    westbranch wrote: »
    looked again, you did not apply cycle on/off times

    No, they are there. They may be wrong, but they are there ;) I set the fridge run times at 12 hours, maybe its two? Not sure....
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Correct wiring for a system with integrated inverter/charge controller

    Hi Mike,

    Glad we are able to help... However, there may be still some conversion issues.

    You don't have to converter Watts @ 120 VAC to Watts @ 24 VDC... They are the same number:
    • 20 watts @ 120 VAC = 20 Watts @ 12 VDC = 20 Watts @ 24 VDC
    • P=V*I=V2/R=I2*R
    • I=P/V= 20 Watts / 12 volts = 1.67 Amps
    • I=P/V= 20 Watts / 24 volts = 0.83 Amps
    • I=P/V= 20 Watts / 120 volts = =0.167 Amps

    And the amount of Amp*Hours by voltage (assuming 20 watt load * 3 hours of usage per day):
    • Work=Power*Time (in hours)
    • Work (or energy) = 20 Watts * 3 Hours = 60 Watt*Hours at any voltage

    However, Amp*Hours is voltage dependent (basically Watts/Volts=Amps). For a 24 volt load0:
    • AH=Amps*Time (Hours) = Watts * 1/Volts * Hours ,etc.
    • AH = 20 Watts * 1/24 volts * 3 hours = 2.5 Amp*Hours @ 24 volts
    • AH = 0.83 amps * 3 hours = 2.5 Amp*Hours 24 volts

    Of course, I have lied a little bit--Yes a Watt is a Watt, however when you have conversions, there are losses... So a 24 volt input Inverter outputting 120 VAC uses a bit more 24 VDC power to get the job done:
    • 20 Watts (at 120 VAC) * 1/0.85 typical inverter losses = 23.5 Watts on the DC battery bus side...

    So, all of the battery calculations would have use 23.5 Watts or use a 1/0.85 inverter "fudge factor".

    To give you an idea:
    • 1,000 WH per day (1 kWH per day) => cabin with small loads (no fridge, just lights, small water pump, laptop+small water pump, radio, small TV, etc.).
    • 3,300 WH per day (3.3 kWH per day) => you can have a very efficient almost normal electric home (fridge, well pump, clothes washer)--Using other heating sources for cooking/hot water/heating (wood, propane, etc.).
    • 10,000 WH per day -- A pretty efficient north American home with natural gas and central heat
    • 33,000 WH per day -- The average north American home (usually with natural gas and some light A/C loads).
    • 100,000 WH per day -- Full A/C , electric heat, etc...

    1 kWH to 3.3 kWH per day--Most people can justify an off grid solar power system... ($5,000-$10,000++ or so?).

    10 kWH a day--You have to really decide if that is how much power you really want to use ($50,000+++?).

    33 kWH or more per day--That is not going to be a cheap DIY type project. That can be a huge investment (in the $X00,000 range).

    With the loads you have--I would guess that a ~3.3 kWH per day system is what you would be aiming for...

    47274 Watt Hours is still "bad math".

    Note, most people don't use, or have abandoned bio-toilets that use a heater (typically to dry liquid waste) for other alternatives. They are just too power hunger for off grid users and pretty expensive to run for on-grid folks too. We have a few threads here on the various options like this one:

    Compost Toilet


    Others will have to guide you (composting vs a "good outhouse" arguments). I am on city sewers and pay a lot in property taxes (and water fees) to flush.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Correct wiring for a system with integrated inverter/charge controller

    Just for an example with a typical Energy Star full size fridge that uses ~1.2 kWH per day... The average load is around 130 Watt*Hours:
    • 1,200 WH per day * 1/130 Watts = 9.2 hours of "on time" per 24 hour day.

    So--working with the above "knowledge":
    • 130 Watt average load * 9.2 hours (per 24 hour day) = 1,196 WH per day = 1.2 kWH per day with rounding...

    The DC AH energy per day would be (all in one formula):
    • 1,196 WattHours * 1/0.85 Inverter Efficiency * 1/24 volt battery bank = 58.6 AH @ 24 volts

    And this is why a Kill-a-Watt type meter is really nice... A frost free refrigerator may use ~120 watts 8.5 hours per day, 600 watts for 20 minutes per day, and 2 watts the rest of the day (plus 650 VA starting for a few seconds per cycle). You would go nuts trying to profile the detailed energy usage without a data logger.

    For basic planning, you just plug in the K-a-W meter into the wall, and the appliance into the meter for 1-3 days and it will tell you kWH used over XX hours, you convert to what you need--For WH per day:
    • 3,600 WH * 1/72 hour test * 24 hours per day = 1,200 Watt Hours per day (notice my units match :-))

    I suggest you just collect appliance name, average watts and kWH per day (or per time period and convert to per day as above). You can also write down the VA and PF too (useful, but not required for sizing of system).

    And then we just run it through the Rules of Thumbs equations... Don't even bother with 12/24/48 volt battery bus, conversion and storage losses, etc... It is just confusing you right now. The rules of thumbs will get a system design that is "close enough" for you to do a design/economic analysis... if you want to do the math--we can help you with that too once you have the 50,000 foot view of the project.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dakaz
    dakaz Registered Users Posts: 10
    Re: Correct wiring for a system with integrated inverter/charge controller

    Alright, despite feeling a bit foolish and embarrassed, I think I get it now. In doing a bit more research, I think I have all the WH for my loads:

    Lights = 720 WH / Day
    Fridge = 1440 WH / Day
    Well Pump = 600 WH / Day
    Composting Toilet = 4810 WH / Day

    Clearly the toilet is my major load (pun intended)! So, with the toilet I'm at about 7.5 kWH. Without it I'm at under 2.5 kWH. The good news is that we have the AC/DC (ie: Non Electric) version so we don't have to run the toilet constantly (especially on cloudy days and none at all in the winter).

    I still want to be sized for it though in case our cabin ever becomes our full time residence. So... with the inverter losses, I would have a total worst cast of 372 aH / Day of usage. By my math, 3 280W 24V panels will generate only 245 aH / Day (7 hours of sunlight) in the summer, which would still be undersized. 4 Would probably be sufficient giving 325 aH... if I ever move in full time, I could add another 2 panels I suppose.

    As for batteries, the 6 200 aH 12V batteries I had speced would only give 600 aH @ 24V (with 50% usable thats only 300), so I'd really need 12 of those truly cover my week long excursions and cloudy days.... hmmmm, this is going to be a bit more spendy than I had thought, but still cheaper than putting in a septic (we have high bedrock and would have haul in sand). Maybe I should look at water batteries, how often do I need to truly top them off?

    Thanks
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Correct wiring for a system with integrated inverter/charge controller
    dakaz wrote: »
    The good news is that we have the AC/DC (ie: Non Electric) version so we don't have to run the toilet constantly.
    <snip>
    As for batteries, the 6 200 aH 12V batteries I had speced would only give 600 aH @ 24V (with 50% usable thats only 300), so I'd really need 12 of those truly cover my week long excursions and cloudy days.... hmmmm, this is going to be a bit more spendy than I had thought, but still cheaper than putting in a septic (we have high bedrock and would have haul in sand). Maybe I should look at water batteries, how often do I need to truly top them off?

    What is an AC/DC non electric toilet? To me "AC/DC" sounds electric.

    The next step in designing a system (after the loads are figured out) is to choose batteries and a system voltage.

    As far as batteries, you should most certainly buy flooded batteries and an hydrometer. Sealed batteries are not for beginners. Most beginners murder their first set of batteries. You will need to water them every couple of months.

    Do not create a battery bank with more than two parallel strings of batteries.

    Consider golf cart batteries for your first set. If you need more than two strings of them at 24 volts, consider using L16 batteries....

    Or go with a 48 volt system... a string of batteries at 48 volts has the same storage as two strings at 24 volts.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Correct wiring for a system with integrated inverter/charge controller

    yea--You need to can the can... That alone would add ~50% to my power bill for my citified home.

    Off grid solar power is not cheap... Figure roughly ~$1 to $2+ per kWH (a few people here are under that). Very roughly if you amortized your costs (and battery+hardware replacements) over 20 years (that $1-$2 per kWH) for 4.8 kWH per day would be ~$144 to $288 per month just for toilet heater...

    So, lets start with a 3.3 kWH per day (100 kWH per month) system. Assume 24 volt battery bank. First, how big of battery. 1-3 days of storage with 50% maximum discharge (for longer battery life) with 2 days usually being a "well balanced" system.
    • 3,300 WH per day * 1/0.85 inverter efficiency * 1/24 volt battery bank * 2 days of storage * 1/0.50 max discharge = 647 Amp*Hours @ 24 volts

    Next, want to have 5% to 13% rate of charge for the battery bank:
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller derating * 0.05 rate of charge = 1,218 Watt array minimum
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller derating * 0.10 rate of charge = 2,437 Watt array nominal
    • 647 AH * 29 volts charging * 1/0.77 solar panel+controller derating * 0.13 rate of charge = 3,168 Watt array "cost effective maximum"

    How much sun do you get for your region... Using PV Watts for Kalispell Montana, fixed array, tilted to latitude:
    Month    Solar Radiation (kWh/m 2/day)
    1      2.14     
    2      2.96     
    3      4.02     
    4      4.70     
    5      5.42     
    6      5.77     
    7      6.24     
    8      6.19     
    9      5.23     
    10      4.08     
    11      2.16     
    12      1.46     
    Year      4.21      
    

    Notice that you have very little chance of 7 hours of "noon time equivalent" sun per day (changing tilt, one or two axis arrays and do better)... Normally, I would suggest tossing the bottom three months (use a generator for bad weather). So that leaves 2.96 Hours of sun (February):
    • 3,300 kWH per day * 1/0.52 over all system efficiency * 1/2.96 hours of sun per day = 2,144 Watt array for "break even February"

    So--The basic rules of thumb for a fixed array on a home that is occupied 9+ months of the year--A 2,144 Watt to 3,168 Watt array would meet your needs (as I have guessed). And if you used a minimum of ~2,437 Watt array--Your battery bank will be well taken care of.

    I did the above based on a 24 volt battery bank... If you assume a solar charge controller of 80 amp maximum rating, the largest cost effective 24 volt array that controller could support (these are rough/rule of thumb numbers):
    • 80 amps * 29 volts charging * 1/0.77 rate of charge = 3,013 Watt Array "cost effective maximum"

    So--Here is another issue... Moving relatively high amounts of power (watts) through a XX volt battery bank. In this case, you are about on the edge of wanting to go from a 24 volt battery bank to a 48 volt battery bank. The MPPT charge controllers are limited to ~60-90 amps maximum on 12-48 volt battery banks... So if you move to a 48 volt battery bank, the same controller can "manage" a 2x larger solar array (save some money).

    However, inverters are usually sized for the battery bank. If you wanted to go from 3.3 kWH to 8 kWH rated power system--You would either need to add more charge controllers+heavier cabling--Or get a new 48 volt inverter and use the same charge controller+battery bus wiring, etc...

    And notice that we size arrays for the size of battery bank used... Larger battery banks (more days without sun) force higher minimum charging current... In general, we recommend staying to ~2 day and 50% maximum discharge and use the generator a bit more in bad weather instead.

    Over sizing an off grid power system is expensive... And when the batteries wear out, expensive to replace.

    Make sense? Questions? Corrections to my assumptions? Want to tilt your array for summer sun and near vertical to shed snow in winter?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dakaz
    dakaz Registered Users Posts: 10
    Re: Correct wiring for a system with integrated inverter/charge controller

    Yup, its all starting to make good sense. As for the toilet, we already purchased and installed it, so it aint going back. BUT, we purchased the AC to DC converter kit meaning we don't have to run the heater, but it uses a 4" vent pipe for evaporation + a 20W 12V DC powered fan to help. The toilet is sized for seasonal use of up to 7 adults, so with just 2 of us (plus the occasional guest) I think we'll be OK running it in non-electric (AC) mode.

    As for the system sizing, I am good there. I do plan on changing the tilt angle summer to winter. I love letting loose my inner geek and was considering building a twin axis tracker myself until I just saw the panel numbers. Perhaps if I did 3 banks of 3 panels each on twin axis.... well, thats for another time.

    Lets talk wiring though...

    So, assuming I have:

    A) 9 to 12 Panels 24V panels
    B) MPPT Charge Control
    C) DC Inverter + ATS and Charger

    Do I need an external "combiner" for the panels? What do you recommend for fuses / circuit breaker between the charge controller and panels? Similar question between the Charge Controller and Batteries. Lastly, do most DC Inverters with chargers charge from the same input terminals? I am leaning toward the Outback VFX3024E based on today's conversations.

    Thanks
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Correct wiring for a system with integrated inverter/charge controller
    dakaz wrote: »
    I love letting loose my inner geek and was considering building a twin axis tracker myself until I just saw the panel numbers. Perhaps if I did 3 banks of 3 panels each on twin axis.... well, thats for another time.
    <snip>
    Do I need an external "combiner" for the panels? What do you recommend for fuses / circuit breaker between the charge controller and panels? Similar question between the Charge Controller and Batteries. Lastly, do most DC Inverters with chargers charge from the same input terminals? I am leaning toward the Outback VFX3024E based on today's conversations.

    I think the "E" on the VFX3023E is an export model 50 Hz 220 volt.

    As far as trackers are concerned... they are generally not cost effective anymore. They are mechanical devices that may breakdown (especially in winter). Panels are so cheap now that for the cost of a tracker you can buy more panels and come out ahead. Several of the forum members here have built "virtual" trackers... that is a southeast array and a southwest array connected to the same charge controller.

    Yes, you need a combiner box with fuses or circuit breakers... look at Midnite's offerings. I strongly recommend circuit breakers over fuses.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Correct wiring for a system with integrated inverter/charge controller
    dakaz wrote: »
    Lastly, do most DC Inverters with chargers charge from the same input terminals?

    Just to be clear--The Solar Charger (PWM or MPPT) is one black box (mounted close to the battery bank to keep wires short) between the battery bank and the solar panels. Its job is to control the energy flow from the Solar Array to the Battery bank.

    A PWM controller is a "simple on/off switch". Depending one how long the distance is and what brand/model/Vmp solar panels you get--You can use a PWM controller on a larger system.

    However, once you go to a larger array (say over 800 watts), you really should be looking at a MPPT type charge controller (much more expensive, and usually a lot more bells and whistles too).

    The two main reasons MPPT controller are really nice--One is they have a buck mode switching power supply which can take high voltage/low current and efficiently down convert to low voltage/high current needed by the battery bank (95% efficiency or so). This allows you to use higher Vmp-array voltages (upwards of 100 volts or more) and use smaller awg wire to ship the power back to the battery bank.

    The other major reason is because solar panels provide maximum Power at a specific operating point (Pmp=Vmp*Imp)... Basically there is a "sweet spot for the voltage" that the MPPT controller "holds" and as the sun changes, the Imp moves about too.

    For example, very common (and much cheaper) 240 watt panels may have Vmp in the range of 30 volts DC and Imp~8 amps. And you want to charge a 12 volt battery bank. Without the MPPT controller (PWM type), you would get:

    8 amps Imp * 12 volts Vbatt-charging = 96 watts into teh battery bank or 8 amps

    With a MPPT type controller, you would get (roughly):

    30 volts Vmp * 8 amps Imp * 0.77 panel+controller derating = 184.8 Watts into battery bank
    184.8 volts * 1/12 volt Vbatt charging = 15.4 Amps charging into 12 volt battery

    These are real numbers and reflect why MPPT controller are very popular--especially with larger installations.

    The "Inverter/Charger" is a completely different animal. It is very much like UPS you would buy for your computer (uninterruptable power supply).

    There are one or two AC power sources (grid+generator for some units). Those go into the inverter and can pass through to power your AC loads (from grid or backup generator).

    At the same time, the Inveter/Charger can bleed a little power from the AC power coming in, and recharge the Battery Bank (in parallel with the solar charge controller too--if one is present). If the AC power goes away, then the inverter cuts in and powers the AC loads from the battery bank (internal automatic transfer switch).

    Some of the never AC inverter/chargers are getting very complex... They can "blend" generator AC power and charge the battery bank or even draw from the battery bank and supply power to the AC loads--"Generator Assist" is one term you can use. You program (for example) for the generator to output a maximum of 15 amps of 120 VAC--And the inverter will split the power between the AC loads and charging the battery bank. If the AC loads exceed 15 amps, the inverter will (seamlessly) starting pulling power from the battery bank and help power the AC loads (starting a well pump, running the microwave, even running an electric stove).

    The options/capabilities of various pieces of hardware out there today are amazing... If you can think of what you want, there is a good chance that it can be done with off the shelf hardware. Chris Olsen wrote a nice writeup on generator support and some other generator topics (you will need a good genset and installation that far north):

    Choosing a good generator
    genset alternator failure (and if your generator is not generating AC? What to look for/do--Thread started by "Unicornio" from Spain)
    Demonstration of Generator Support (A couple inverters that will share AC loads with the generator--smaller generator with large load support)

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