Simple System to Charge Batteries

CrystalCrystal Solar Expert Posts: 115 ✭✭✭
edited June 23 in Solar Beginners Corner #1
So we've learned live very simply over the past couple years and only require power to charge a phone and a tablet. We've been trying to decide what system will be best in our unique situation.
We won't need an inverter since we charge our devices from the cigarette lighter in the camper van.

At the moment we've been charging 2 - 12volt deepcycle batteries, 2 - 12volt regular car batteries by starting the van every once in awhile. 
We'd like to get a panel with enough watts to charge these 4 batteries. They all don't have be charged at same time.

Will we need a charge control?
How many watts are recommended?
TIA

Comments

  • mike95490mike95490 Solar Expert Posts: 8,288 ✭✭✭✭✭
    My suggestion.  

    Use a couple Grid Tie panels  (where/how are you going to locate the panels ?  Do they mount on the vehicle, while traveling ? )
    and a medium size MPPT controller.

    Downside:  Having to locate the panels in FULL SUN, no shade anywhere on them.   No vent shadows, no AC / cooler box shadows, no antenna shadows.
     Driving and having a panel blow off and hit a car behind you

    Panels. Try to locate a vendor near you that you can drive in and pick up,  Shipping charges for 1 or 2 panels can be very expensive

    Controller     A real MPPT controller like this one
    Morningstar PS-MPPT-25 25 Amp Solar Charge Controller $318.00 
       You will need a input and output DC rated circuit breaker, and the right fuses at the battery to protect your wires .




    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, Administrators Posts: 29,218 admin
    What you need to do is figure out how much energy per day you are using--And plan a system to support that.

    More or less, if you are using Flooded cell Lead Acid Battery every day (charge during the day, discharge at night)... Then I would suggest you only use 1/4 of the stored energy in the battery (more or less, there is not enough hours of sun in a day to recharge an FLA battery from 50% to > 90% state of charge in one day--Typically it takes 2 days "worth of time on charge" to fully recharge.

    Another rule of thumb is I would suggest for 10%-13% (or so) rate of charge for full time off grid batteries that are used every day.

    So... Just some numbers to start with... Say your van has an 80 AH @ 12 volt battery (probably not a deep cycle battery--So discharging to 85% or 75% State of Charge is about the maximum amount you want to do anyway... Discharging a standard car battery to 50% state of charge (or lower), it will probably last a few months to a year in typical use.

    So, if you are just charging 1x "van battery" every day (discharge to 75% SoC)--The calculations would look like:
    • 12 volts * 80 AH * 0.25 discharge (to 75% SoC) = 240 Watt*Hours per day
    • 80 AH * 0.25 discharge = 20 AH per day of usage
    Assuming a fixed array in Omaha Nebraska, facing south:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Omaha
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 49° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    3.35
     
    3.66
     
    4.41
     
    4.72
     
    5.05
     
    5.44
     
    JulAugSepOctNovDec
    5.56
     
    5.34
     
    5.20
     
    4.45
     
    3.40
     
    3.09
     

    Lets say you want to (on average) use this system though December:
    • 240 WH per day * 1/0.52 off grid system eff * 1/3.09 hours of sun per day = 150 Watt solar panel/array minimum
    For a small system (single battery), a 150 Watt panel + PWM (inexpensive) solar charge controller could work OK--During winter, you would need to run a small genset or your van to make up for bad weather.

    If you were going to use a larger battery (or charge multiple batteries), then a larger array (200 Watt or more), you may want to look at larger solar panels (>200 Watts) that have Vmp~30 volts or higher and an MPPT charge controller (cheaper panels, more expensive MPPT charge controllers).

    Some other suggestions:
    1. alligator clamps do not work well for charging/heavy DC loads (higher currents). Using connections with bolts/nuts/wingnuts or actual DC connectors is much more reliable.
    2. If you are disconnecting and moving batteries around, you want to disconnect the solar panel first, then the solar charge controller (switches, breakers, etc.). And when reconnecting, connect the battery first and the solar panels second--Doing it backwards, it is possible to "confuse" the solar charge controller or even (possibly) damage the charge controller.
    https://www.amazon.com/s?k=battery+terminals&ref=nb_sb_noss (an example of many types of battery terminals)
    https://www.amazon.com/UTSAUTO-Thickened-Terminal-Positive-Connectors/dp/B0787NPBFN (an example of wingnuts+battery terminals)

    Without knowing more about your batteries, plans for use (1x battery runs a week between charging, or you recharge it daily, etc.) and how many batteries and their AH capacity, and other details, it is sort of difficult to give you a detailed answer.

    -Bill 
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CrystalCrystal Solar Expert Posts: 115 ✭✭✭
    mike95490 said:
    My suggestion.  

    Use a couple Grid Tie panels  (where/how are you going to locate the panels ?  Do they mount on the vehicle, while traveling ? )
    and a medium size MPPT controller.

    Downside:  Having to locate the panels in FULL SUN, no shade anywhere on them.   No vent shadows, no AC / cooler box shadows, no antenna shadows.
     Driving and having a panel blow off and hit a car behind you

    Panels. Try to locate a vendor near you that you can drive in and pick up,  Shipping charges for 1 or 2 panels can be very expensive

    Controller     A real MPPT controller like this one
    Morningstar PS-MPPT-25 25 Amp Solar Charge Controller $318.00 
       You will need a input and output DC rated circuit breaker, and the right fuses at the battery to protect your wires .


    Thanks for you advice Mike!
    We have currently landed and have the camper van set up permanently, so no need to mount them. We'll be putting them in full sun about 25 feet from van. 

    We'll find some in the area used or on sale online.

    Hope to find a cheaper charge control...need to keep it thrifty on our entrepreneurial income.

    Why do you suggest grid tie panels?




  • CrystalCrystal Solar Expert Posts: 115 ✭✭✭
    Thanks for the suggests BB.
    You're always so very helpful.
  • BB.BB. Super Moderators, Administrators Posts: 29,218 admin
    Just to give you an idea from our host (NAWS--Northern Arizona Wind & Sun):
    https://www.solar-electric.com/residential/solar-panels.html

    Solar Module Price List - 110 to 350 Watt PanelsPrice Per Watt
    WattsModuleSingle Module PriceSingle ModulePallet Prices
    130Solartech SPM130P-S-N 12V$224.00$1.723 
    130Solartech SPM130P-WP 24V$286.00$2.20 $2.09
    140Solartech SPM140P-S-N 12V$200.20$1.43 
    190Solarland SLP190S-24$270.00$1.42 
    270Canadian Solar CS6K 270P$155.00$0.574 
    290AXITEC 290W All Black$214.66$0.74 
    295AXITEC 295W mono$191.75$0.65 
    295Hanwha Black Q.Peak 295W$228.00 
    $0.772 
    305Canadian Solar 305W$193.00$0.633 
    305Canadian Solar 305W$218.08$0.715 
    310Silfab Solar 310 Watt$230.18$0.74 
    325Panasonic HIT 325 Watt$350.00$1.077 
    330AXITEC 330W poly$218.30$0.66 
    350Silfab Solar 350 Watt$287.00$0.82 
    Other solar panels may be available - this is what we normally stock in depth

    If you look at the $/Watt... You see the smaller (typically Vmp~17.5 volts--Used with 12 volt battery and PWM charge controller) are something like $1.40 to $2.20 per Watt (and smaller panels are generally cheaper to ship).

    The larger panels (typically >~175 Watts) are Vmp~30 volts or other "NOT" 17.5 volt panels, generally are much less (you can get down towards $0.50 per Watt)... But MPPT controller tend to much more expensive (at least the good quality ones--Cheap imports are frequently MPPT in "name only").

    However, if you order a 300 Watt panel, the shipping may be about the same price as the panel.

    That is why Mike is saying to look for local suppliers of panels in your area... You can frequently get "cheap panels" with no shipping charges (if you can pick up locally, and fit them in your vehicle).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,288 ✭✭✭✭✭
    edited June 24 #7
    You could get 4 of the 140w 12V panels and use a PWM controller. 

    Now there are 4 panels to mount instead of 2.  And you MUST use series protection on each panel in case of a panel fault (rare).  4 fuses, 4 holders, (or 4 breakers) and a combiner box.  parts count goes up, complexity goes up, more things to fail, and I'll let you figure  if you save money overall.

    Remember, in GOOD conditions, panels produce 80% of their nameplate.  So 300w of panel gives you 240w @ 12V , 20A in best conditions.

    With all the different batteries you are talking about recharging, you will still need input and output breakers for your charge controller.
    Charge controllers need to boot up on battery power first (it often sets the system voltage of 12, 24 or 48V) and it initializes the innards.  Then it's safe to connect the solar PV.  If the solar PV only is connected (lets switch from the full battery to the low battery) you get smoke and a damaged controller.  Most of the time, there is no smoke.  So you need the handy breakers to switch connections on and off before you swap batteries around.   And as with all human activity, you have a good chance of a mistake or forgetting this crucial rule.

    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 ,

Sign In or Register to comment.