Series or parallel panel connection to C40 Charge controller?

Converted
Converted Registered Users Posts: 9
Greetings!

I'm leaving Friday for a trip to Haiti to install a small system for our orphanage. Currently on the ground in Haiti I have the following components;

3 Philadelphia 150W panels (Vmp 18.62 Imp 8.06)
4 Interstate GC2 Batteries (6V 220Ah)
Xrantrex C40 Controller
SunElec Refrig (12/24V 85W)
400W generic 12v modified sine wave inverter for occasional use of up to 6 8W LED lamps

I will be operating at 12V and we are completely off grid in a remote village.

I was told by the supplier that the C40 can handle having the three panels connected in series.and that is how I should connect them. I've been scratching my head and doing some reading/searching. I think I should actually connect the panels to the PWM C40 in parallel to best utilize the panels capacity to charge my 12V battery bank.

Your opinions please

The installation will be very compact as far as wire length is concerned. PV array to controller will be approx 16', battery bank to controller 10', controller to inverter 2', controller to frig 15'

Comments

  • froggersix
    froggersix Solar Expert Posts: 35
    no c40 is pwm controller so panel voltage has to match battery voltage - the panels should all be in parallel plus to plus and minus to minus
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Welcome to the Forum Converted!

    Get your answers before you leave--Some of the stuff below is "questionable" as designed/installed/suggested (in my humble opinion). Some quick answers:
    Converted wrote: »
    3 Philadelphia 150W panels (Vmp 18.62 Imp 8.06)
    4 Interstate GC2 Batteries (6V 220Ah)
    Xrantrex C40 Controller
    SunElec Refrig (12/24V 85W)
    400W generic 12v modified sine wave inverter for occasional use of up to 6 8W LED lamps

    What is the refrigerator's approximate power usage (AH per day at 12 VDC, or Watt*Hours per day)?

    If possible, I would highly suggest a TSW (true sine wave) AC inverter instead... More expensive--But the AC sine wave can help your small appliances work more reliably. MSW (modified square wave) inverter have been known to damage/ruin some equipment (small wall transformers, many small AC devices/battery chargers/etc.). Roughly, 80% of your loads will work OK on MSW, and about 10% will have dramatically reduced life. To know which is which--More or less, you have to plug them in and see what happens.

    This MorningStar 300 Watt TSW 12 volt AC inverter is a really nice device--One of the best small 12 volt AC inverters out there.

    http://www.solar-electric.com/inverters-controllers-accessories/inverters/moin/mosu300wasiw.html

    There is 230 VAC 50 Hz model if that works better where it will be used.
    I was told by the supplier that the C40 can handle having the three panels connected in series.and that is how I should connect them. I've been scratching my head and doing some reading/searching. I think I should actually connect the panels to the PWM C40 in parallel to best utilize the panels capacity to charge my 12V battery bank.

    Yes, the C40 can "handle" the higher votlage--But because of the way a PWM (pulse width modulate) charge controller works--Placing these three panels in series will give you ~1x panel's worth of charging energy to the battery bank.

    The only way, for a 12 volt battery bank, to operate well with the C40 is all three panels in parallel.

    Or, you would have to buy a (proper specifications) MPPT (maximum power point tracking) charge controller--But these are usually much more expensive.
    The installation will be very compact as far as wire length is concerned. PV array to controller will be approx 16', battery bank to controller 10', controller to inverter 2', controller to frig 15'

    Keep the wiring short/heavy between charge controller and battery bank. You want only ~0.05 to 0.10 volt drop from controller to battery bank for optimum battery charging.

    You also do not want too much voltage drop from Solar Array to Charge controller... (typically 1% to 3% maximum voltage drop) from the solar array to the charge controller. Even "moderate" wiring distances can require pretty heavy (expensive) copper wire for 12 volt systems. Use a voltage drop calculator to figure out your wire run wire AWG (American Wire Gauge) requirements:

    http://www.calculator.net/voltage-drop-calculator.html

    We can go through some numbers if you need a bit of guidance.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    He must be confused... the C40 is PWM and should , correctly, be used with the 3 panels in parallel.
    You will need a combiner, with circuit protection, CB or fuse, to keep an electrical short in one panel from destroying your other panels...
    Your wiring should look like this http://www.midnitesolar.com/pdfs/Nigeria%20system.pdf

    DO you plan on expanding in the future? If so think about it and build the wiring etc to handle a larger setup.

    What wire do you have (AWG size), connectors etc?

    Wire the fridge dirct to the battery or buss bar NOT to the controller. Don't forget circuit protection again... basically you need a CB between the positive post of the battery and all items hooked to it. NOTE, a CB is used to protect the wiring from starting or preventing fires, not electronic devices
     
    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
  • Converted
    Converted Registered Users Posts: 9
    BB. wrote: »
    What is the refrigerator's approximate power usage (AH per day at 12 VDC, or Watt*Hours per day)?

    That's the $64,000 question LOL Manufacturer is not much help. Looks to be a well built frig/freezer with good insulation. I've kinda been going with a duty cycle that would have the frig running 4-6 hours per day. Ambient will get over 100 in the summer so it could be higher.
    BB. wrote: »
    If possible, I would highly suggest a TSW (true sine wave) AC inverter instead... More expensive--But the AC sine wave can help your small appliances work more reliably. MSW (modified square wave) inverter have been known to damage/ruin some equipment (small wall transformers, many small AC devices/battery chargers/etc.). Roughly, 80% of your loads will work OK on MSW, and about 10% will have dramatically reduced life. To know which is which--More or less, you have to plug them in and see what happens.

    Understood. There are no appliances. One light bulb socket in each room is it. We have a 120/240V 5000W generator next door at the church. We rarely run it except for Sunday service. The lights in the orphanage only work when the generator is running. The plan for the inverter is only to power the lights occasionally after dark. (I'll disconnect to wiring run over to the church) We also run the generator to run a well pump to feed a cistern on the orphanage bath house. I'm also taking down a SHURflo 9300 with 902-200 controller and 4 50W PV panels (had to fit in checked bags) to run that system. It will be self contained and a couple hundred feet from the orphanage. It will only pump between 1 and 2 gpm which is fine. Pump when the sun is out and overflow will be used for irrigation.
    BB. wrote: »
    Yes, the C40 can "handle" the higher votlage--But because of the way a PWM (pulse width modulate) charge controller works--Placing these three panels in series will give you ~1x panel's worth of charging energy to the battery bank.

    The only way, for a 12 volt battery bank, to operate well with the C40 is all three panels in parallel.

    Thanks for confirming!
    BB. wrote: »
    Keep the wiring short/heavy between charge controller and battery bank. You want only ~0.05 to 0.10 volt drop from controller to battery bank for optimum battery charging.

    You also do not want too much voltage drop from Solar Array to Charge controller... (typically 1% to 3% maximum voltage drop) from the solar array to the charge controller. Even "moderate" wiring distances can require pretty heavy (expensive) copper wire for 12 volt systems. Use a voltage drop calculator to figure out your wire run wire AWG (American Wire Gauge) requirements:

    I think we'll be good there. Taking #2awg down for the battery connections and have 10awg PV wiring and 8awg to feed inverter and frig.

    Just ordered the M/FFF and F/MMM MC4 connectors. Should have them in plenty of time.
  • Converted
    Converted Registered Users Posts: 9
    froggersix wrote: »
    no c40 is pwm controller so panel voltage has to match battery voltage - the panels should all be in parallel plus to plus and minus to minus


    Thank you!, much appreciated
  • Converted
    Converted Registered Users Posts: 9
    westbranch wrote: »
    He must be confused... the C40 is PWM and should , correctly, be used with the 3 panels in parallel.
    You will need a combiner, with circuit protection, CB or fuse, to keep an electrical short in one panel from destroying your other panels...
    Your wiring should look like this http://www.midnitesolar.com/pdfs/Nigeria%20system.pdf

    DO you plan on expanding in the future? If so think about it and build the wiring etc to handle a larger setup.

    What wire do you have (AWG size), connectors etc?

    Wire the fridge dirct to the battery or buss bar NOT to the controller. Don't forget circuit protection again... basically you need a CB between the positive post of the battery and all items hooked to it. NOTE, a CB is used to protect the wiring from starting or preventing fires, not electronic devices

    All wiring is marine grade tined copper with compression ring terminals except lug connections to controller.

    2awg for battery, 10awg PV cable and 8awg for inverter and frig. 50A fuse on inverter and 20a fuse on frig. Using battery disconnect switches between PV array and controller , battery, and controller and ahead of loads.

    Will look into combiner box. Probably not in the budget for this trip but looks like good advice for long term.
  • Converted
    Converted Registered Users Posts: 9
    BB. wrote: »

    We can go through some numbers if you need a bit of guidance.

    -Bill

    So I'm double checking everything since I was given some pretty flawed advice on connecting the PV panels, I want to make sure this system is going to work at least at a minimum level.

    The 3 panels are rated 150W, Vmp 18.62, Imp 8.06.

    The 4 batteries are Interstate GC2 6V 220Ahr

    The primary load is a 12V 85W refrigerator.

    The secondary load is 6 10W LED lamps

    The array is located at 19d30'11.49"N, 72d36'10.59"W

    I have a roof panel that is exactly 180d azmith with a tilt angle of 18.43.d (4/12 pitch) (My research indicates that I should mount flat to these roof panels)

    We are on the lee of a mountain range so it is almost dessert conditions, solar should be optimal conditions.

    If I use the following calculator...

    http://www.wholesalesolar.com/StartH...ml#sunhoursmap

    I have entered 12 hours per day for run time on the frig. I think it will be less than that, maybe much less. I entered 2 hour run time on the lights. 6 hours sun and a 100% system. It assumes a system efficiency and calculates that I need 247W minimum system size.

    As far as I can tell the panels should work but are probably the weak point and the batteries should stay pretty happy and not be too deeply discharged.

    What effects will the high ambient have on system performance?

    Should I adjust charge and float voltage for the high ambient?

    Am I on the right track?

    Thanks!
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    For a full year average you will want to run that program using 4 hrs per day of good solid power producing sunlight.
     
    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
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    First, the loads (rearrange your post a little bit)...
    Converted wrote: »
    The primary load is a 12V 85W refrigerator.
    The secondary load is 6 10W LED lamps

    I have entered 12 hours per day for run time on the frig. I think it will be less than that, maybe much less. I entered 2 hour run time on the lights. 6 hours sun and a 100% system. It assumes a system efficiency and calculates that I need 247W minimum system size.

    50% duty cycle is probably fine for the fridge--May go higher, but it is a start:
    • 24 hours per day * 0.50 duty cycle * 85 watts = 1,020 WH per day
    • 6 * 10 Watt LED * 2 hours per day = 120 WH per day
    • ========================================
    • 1,140 WH per day load
    Battery bank sizing (12 volt for "small" system)--1-3 days load (no sun)--2 days is usually a good optimum. 50% maximum discharge for longer battery life:
    • 1,140 WH per day 1/12 volt battery bank * 2 days storage * 1/0.50 maximum discharge = 380 AH @ 12 volt battery bank
    So your 4x 6 volt @ 220 AH battery bank looks to be a good fit (close enough to 380 AH).
    The 4 batteries are Interstate GC2 6V 220Ahr

    Next, sizing the solar array. Two different checks--One based on 5% to 13% rate of charge for battery bank. Second based on hours of sun per day. First rate of charge
    • 440 AH * 14.5 volt charging * 1/0.77 controller+panel derating * 0.05 rate of charge = 414 Watt array minimum
    • 440 AH * 14.5 volt charging * 1/0.77 controller+panel derating * 0.10 rate of charge = 829 Watt array nominal
    • 440 AH * 14.5 volt charging * 1/0.77 controller+panel derating * 0.13 rate of charge = 1,077 Watt array "cost effective" maximum
    Normally, a 5% rate of charge would be good for weekend/seasonal usage... Like to recommend 10% minimum rate of charge for full time off grid. Basically, your battery bank wants a minimum of 5% rate of charge (and taller batteries like 10% rate of charge)--Your refrigerator is taking 85 Watts (roughly 7 amps) from the array's available charging current--So, adding another (85w/0.77 panel+controller derating) 110 Watts to the 414 Watt for a 523 Watt array minimum would be "nice". If you go 10% (I would add the ~110 Watts to all of the above suggested numbers).

    Using a solar insolation tool:

    http://solarelectricityhandbook.com/...rradiance.html
    The array is located at 19d30'11.49"N, 72d36'10.59"W

    Closest I could find was: Port-au-Prince
    Average Solar Insolation figures


    Measured in kWh/m2/day onto a solar panel set at a 72° angle from vertical:
    (For best year-round performance)

    Jan
    Feb
    Mar
    Apr
    May
    Jun


    5.58
    5.73
    5.69
    5.69
    5.63
    6.26


    Jul
    Aug
    Sep
    Oct
    Nov
    Dec


    6.26
    5.77
    5.44
    5.22
    5.13
    5.29


    Looks like you have equatorial sun--Pretty steady through out the year... Using 5.13 hours minimum sun:
    • 1,140 WH per day * 1/0.61 DC system efficiency * 1/5.13 hours of sun = 364 Watt array minimum
    Now--For fixed Loads--It would probably better to plan on using no more than 65 to 75% of predicted sun per day--Unless you can use a genset and/or you have few cloudy/bad weather days:
    • 364 Watt array * 1/0.75 "safety factor" = 485 Watt array
    Because the system is in a reasonably sunny location--You could get away with around 485 to 534 Watt array pretty nicely. Although, an 829+ Watt array would not bad (less day to day monitoring).
    The 3 panels are rated 150W, Vmp 18.62, Imp 8.06.
    • 3*150 Watt array = 450 Watts total
    Your 450 Watt array is close--And in theory should work OK. I would like to see another 150 Watt panel--But this is not my money.

    Having a system with some extra panels is usually pretty cheap insurance for the battery bank (especially if the folks monitoring the system are not technical/dedicated to closely watching the system.
    I have a roof panel that is exactly 180d azmith with a tilt angle of 18.43.d (4/12 pitch) (My research indicates that I should mount flat to these roof panels)

    18 degrees from horizontal is optimum year round tilt (from above link).

    I believe you are mounting flat to a 4/12 pitch roof--Sounds good... I would suggest a minimum 5 degree tilt so that panels are reasonably self cleaning in rain (wash of dust/leaves/etc.).
    We are on the lee of a mountain range so it is almost dessert conditions, solar should be optimal conditions.

    Sounds good....

    If I use the following calculator...
    http://www.wholesalesolar.com/StartH...ml#sunhoursmap

    I have entered 12 hours per day for run time on the frig. I think it will be less than that, maybe much less. I entered 2 hour run time on the lights. 6 hours sun and a 100% system. It assumes a system efficiency and calculates that I need 247W minimum system size.

    Basically, I showed my work math above--Probably similar to your link with 6 hours of sun--Might be a bit optimistic--And there is the 5% or 10% minimum rate of charge for the battery bank.
    As far as I can tell the panels should work but are probably the weak point and the batteries should stay pretty happy and not be too deeply discharged.

    I agree.
    What effects will the high ambient have on system performance?

    It will reduce panel output--But the 0.77 derating pretty much assumes a warm climate (plus 5% controller losses) using an MPPT type charge controller. PWM type charge controller math is entirely different reasons for derating--But works out about to 77% derating too--So I use the same derating for both types (close enough for solar work).
    Should I adjust charge and float voltage for the high ambient?

    "Good" solar charge controllers have internal temperature sensor for to offset battery charging voltage (hot batteries, lower charging voltage). Very good charge controllers have a remote battery temperature sensor to measure actual battery temperature to adjust for hot/cold batteries.
    Am I on the right track?

    Pretty much. Now you need to pick hardware and wiring (lengths, gauge/cable thickness) for the next step.

    Note for 12 volt power--It really needs to be use "locally"--The Refrigerator should be reasonably close to the battery bank (10 feet or so, not 50-100 feet).

    LED lighting can be a bit farther if 12 volt--Or use the AC Inverter if you are going to send power 50-100+ feet).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Converted
    Converted Registered Users Posts: 9
    Thank you for the knowledge. It is very helpful. I'm actually an electrical engineer by trade but we don't get into any solar in our practice. I'm pretty comfortable with the wiring side of the equation and as noted this is a very compact install so voltage drop is well handled.

    I will see about getting another panel or two down on a future trip

    This is somewhat of a test case. We plan to build up to 10 units similar to the existing orphanage building and they will all get solar on the roofs. I'm picking up the CM/R for the C40 so I can keep track of system performance. The folks there will not interact with it much but we do have missions teams going down every couple months. My plan was to brief a team member on the battery equalization procedure and also have them take care of refilling the batteries.

    On the heat issue the C40 does have a plug for a BTS monitor. I was just kinda self-reasoning that it might be more of a benefit for a site that goes through a larger season swing of ambient. Since we are always hot I may just drop the bulk from 14.0 to 13.6 and Float from 13.5 to 13.1 base on the table in the manual for 95-104 ambient.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    One small potential gotcha--Most NEC/Listed lugs on solar electronics (charge controllers, inverter, etc.) don't like is very fine wire. The NEC screw clamps are usually designed for solid or coarse stranded UL/NRTL listed cable... Fine strands can squirm around and lose compression in the clamps.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Converted
    Converted Registered Users Posts: 9
    Just back from Haiti. Great news both systems are working great. :D

    The 3 150W panels on the orphanage made 165AH on Sunday. Battery voltage was at 12.2 Monday morning and the frig had frozen all the water bottles in the freezer section solid overnight. Charge controller was into float mode by 0800 Monday

    4 50W panels wired in series/parallel 24V to the SHURflo 9300 pump through a 902-200 controller are delivering in excess of 2 gal per minute to the cistern.

    19 happy orphans let out a cheer when we turned the lights on Saturday night. 3 very hard working women are very happy that they do not have to fill 5 gallon buckets out of the 65' deep well and carry them up to the orphanage any more.

    Thanks for all the help!!!

    God Bless!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Sounds great!

    Watch the battery bank state of charge... What did you decide on for the Absorb (bulk) voltage setting?

    Monitor battery voltages/specific gravity and make sure that they are charging correctly. I probably have more of a fear of under charging vs over charging at this point.

    And watch the water level in the batteries (used distilled or very clean/filtered rain water, do not use well water--minerals will probably kill the batteries over time).

    You want to have to add some water to each cell about every 2 months. No water needed, probably undercharging. Adding water once a month or more (danger of exposing plates), probably over charging.

    Going into float at 8am with significant over night loads (freezer?) may indicated you want to raise the charging voltage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Converted
    Converted Registered Users Posts: 9
    I left the voltage settings at the default midrange positions for now. I left a gauge and showed the Pastor how to check and record the individual cell specific gravity and we left him a supply of distilled water. My estimation is that we are only using a fraction of the capacity. Frig looks to be pretty efficient. Only ended up needing 3 10W LED lamps to nicely light the interior. I've asked the Pastor to take a picture of the CM/R monitor each Monday morning and email me so I can see the AH production and keep an eye on battery voltage and charge amps. He asked if he can plug in his laptop and I think that will probably not be a problem. He generally uses that during the day.

    Have a team going down in June and I thought I would instruct one of them on the finer points and maybe do an equalization while they are down. I left that jumper on manual.