Solar Power for EZ GO Golf cart

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I'm truley a beginner but willing to learn! What type of solar panels and charge controller do I need to to maintain a battery charge for golf cart. The cart has 6 batteries, 75 amps each.I have a Powerfilm Weather power Series 15.4 v/ 200 operating current solar panel. Will this work? If so, what else do I need? I don't think it came with blocking diodes but not for sure. Thanks!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,601 admin
    #2
    Re: Solar Power for EZ GO Golf cart

    I am guessing your cart has 6x 6volt 75 Amp*Hour batteries in series for a 36 volt 75 Amp*Hour battery bank?

    There are lots of ways of approaching the problem--But what I would like from you is what are your needs?
    • Do you have AC utility power?
    • How much do you drive it (daily, weekends, 9 months of the year, etc.)?
    • How many Amp*Hours do you use in a day (or % of battery usage in a day)?
    • Do you want the panels mounted on the cart? Or would a charging station be OK?
    • Do you drive it during the day and park it at night--or can it be parked during the day to charge?
    • Are you trying to "be green", conservation, save money, etc.?
    • What are your expectations? Recharge in 1 day, sunny summer weather only, 12 months a year, do you have utility/backup power?
    • Or are you looking to "trickle charge" the cart during the the off-season when nobody is around?
    Sorry to hit you with all of these questions... Normally, most solar RE charge charge controllers would require a solar array voltage of >52.5 volts and a 75 AH 36 volt battery would (if this was an off-grid cabin/home) we would be recommending around 175-500 watts of solar panels (at $3 +/- per watt or so) without even knowing how much you are driving it (just based on my guess of your battery setup).

    An Off-Grid charge controller would be around $200 to $500 or so... Plus hardware to mount the panels and wire them up. Not all charge controllers support 36 volt battery banks (have to check specifications).

    Call it, very roughly, one to two thousand dollars or so in components for a good quality, full off-grid charging system.

    If this was to be a home/shop with utility power, I probably would be talking about looking at Grid Tied system (solar panels+inverter) to power your home (and run the meter backwards--if supported by your utility).

    GT would be the most efficient and effective... Your panels generate excess power during the day (turning your meter backwards) while you drive the cart. At night, you park the cart and recharge using grid power (turning meter forward again). In some areas, you would be paid $0.30 per kWH during the day when running the meter backwards, and at night you would be charge $0.09 per kWH (Time of Use billing+Net Metering).

    If you can tell us more about your needs--we can rule out other options and keep things from getting too confusing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Solar Power for EZ GO Golf cart

    Thanks Bill!I'm truely lost but determined to learn this!! The golf cart is driven 1-2 hrs daily. On the weekends it's driven for about 6 hrs daily by my 10 yr old son.It's parked at night. I would like to mount the panels on the cart. What I'm trying to accomplish is a constant charge so the batteries don't go dead while we're riding out in the country.I do have a back up charger. Is there a way I can use the panel I have?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Solar Power for EZ GO Golf cart
    jenone wrote: »
    Thanks Bill!I'm truely lost but determined to learn this!! The golf cart is driven 1-2 hrs daily. On the weekends it's driven for about 6 hrs daily by my 10 yr old son.It's parked at night. I would like to mount the panels on the cart. What I'm trying to accomplish is a constant charge so the batteries don't go dead while we're riding out in the country.I do have a back up charger. Is there a way I can use the panel I have?

    Of course solar panels don't work at night. :p

    You might want to read through this previous thread: http://forum.solar-electric.com/showthread.php?t=9680&highlight=golf+cart

    Basically there isn't enough room on a cart to mount sufficient panels for full re-charge, but anything you can add will slow the discharge to some extent. The problem is that the panel outputs 15.4 Volts and the cart's nominal Voltage is 36. You'd really need to get three matched "12 Volt" panels in order to match Voltage. There are ways of "upping" the Voltage (DC to DC converter) but it's probably not practical in this application.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,601 admin
    #5
    Re: Solar Power for EZ GO Golf cart

    That is a tough one...

    As Marc says, it is difficult to get enough panels on the roof to have significant charging current...

    Assuming your son and the area he drives in would not run the risk of breaking very expensive glass panels on the roof (trees, buildings, other obstructions), a possible configuration:
    So, first mount the panels as a 60" x 79" "roof" (5' x 7').

    Assuming that the cart will run "6 hours" per day between charging. And that you are somewhere near Savannah Georgia, using PV Watts to estimate "hours of full sun equivalent per day" for flat mounted solar array (ignore the kWH and cost of power--just using for hour of sun calculations):
    "Station Identification"
    "City:","Savannah"
    "State:","Georgia"
    "Lat (deg N):", 32.13
    "Long (deg W):", 81.20
    "Elev (m): ", 16
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 0.0"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.9 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 2.66, 37, 2.92
    2, 3.67, 50, 3.95
    3, 4.84, 71, 5.61
    4, 5.73, 82, 6.48
    5, 6.27, 89, 7.03
    6, 6.21, 83, 6.56
    7, 6.26, 87, 6.87
    8, 5.54, 77, 6.08
    9, 4.71, 63, 4.98
    10, 4.11, 58, 4.58
    11, 3.16, 43, 3.40
    12, 2.57, 36, 2.84
    "Year", 4.65, 775, 61.23
    You can get between 2.57 to 6+ hours of sun per day (20 year average).

    For about 1/2 the year, you get around 5 hours of sun (or more) per day.

    For a 6 hour day, assuming risk of running the battery bank flat gives you a usage of:
    • 36 volts * 75 Amp*Hours * 1/6 hours per day = 450 Watts average load
    The solar panels will provide ~6 months of the year:
    • 3x 135 watts * 0.77 system eff * 0.80 battery efficiency * 5 hours of sun per day = 1,247 Watt*Hours per day
    This should extend the usage of the cart around if operated/parked in full sun (at least between 9am and 3pm):
    • 1,247 WH / 450 Watts average load = 2.8 hours
    All the above is pure guess work and is no more accurate than +/- 20% (I showed all the digits so you can reproduce my math). But I did try to be conservative in my estimates on the information you provided.

    In winter with ~2.5 hours of average sun, you will collect 1/2 the energy. In summer, another 20% more.

    Also, depending on the accuracy of the battery capacity meter in the golf cart, you may want to look at adding/replacing with a Battery Monitor (or Victron's version).

    Tell your son to head home when the state of charge is less than 40% (or whatever) and that he call for help/plug in the charger when the battery hits ~20% state of charge to avoid killing one or more of the batteries.

    On the next battery change, you might consider using AGM batteries instead (if you are current using flooded cell). The are sealed so less mess and no water level maintenance. Plus AGM's are about 90%+ efficient vs 80%+ for flooded cell batteries--so you can get 10% more range from the solar panels/save a bit on charging costs. Down side is AGMs are 2x the price as flooded cell.

    You could possibly do without the solar charge controller--but it would probably extend the life of the battery bank if the cart is left outside (parked in sun) for days at a time without use (charger will switch to float mode once the batteries are charged).

    There are nice MPPT type charge controllers--but I don't see that they really offer you any advantages for the extra cost (unless you need more computer connectivity, etc.).

    Anyway, my two cents... How does it look for you?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: Solar Power for EZ GO Golf cart

    what kind of area do you have on the roof for mounting pvs? that will probably be the determining factor on how much charge you can get from the sun outside of the costs for doing this. here are some of the higher powered pvs and remember you will need a vmp of around at least 50v to get a 36v charge.
    http://www.solar-electric.com/hiposopa.html

    if you fit 2 of the larger pvs you will notice vmps that are around 29-35v or so. 2 of these will certainly be high enough to charge the batteries, but too high may show losses so in the area of 55v or more you may wish to consider the possibility of an mppt controller to cut losses to a minimum and with much higher costs. in deriving the correct voltage range the pvs' voltages can be added when in series and one should require the imp current to be within about 5% or so noting that others give a tolerance of up to 10%.

    it is possible to mix and match by that current and derive a correct voltage with different pv voltages to be added when in series. for instance a pv with a 34v vmp and a pv with an 18v vmp will series together to get 52v which is a good voltage to use for a cheaper pwm controller. all that is needed is to roughly match the currents in this case and here are some smaller pvs that may work with the larger ones. of course you can also do 3 pvs with vmps in the 18v range in series.
    http://www.solar-electric.com/1to39wasopa.html

    of course this depends on what physically fits on the top of the golf cart and how much current you may wish to supply to the batteries. generally we state that a range of 5%-13% of the battery current capacity (in this case 75a) so at 5% that's 3.75a (20hr rate) and on the other end at 13% that's 22.5a (about 8hr rate). if it is on while charging from the sun, the sun's energy will most likely be consumed first and if there's any leftover then the battery can use that power to recharge and i doubt recharging will be the case as electric motors draw heavily and odds are a bit of power may be consumed from the batteries. we don't know the draw from that motor so we don't know what would be the case for you, but in any case longer run times will be realized.
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