Newbie Help Needed; system not running off solar

MrSpenceMrSpence Registered Users Posts: 4
Hello everybody! First let me say that i am very new to this forum and to the whole solar world in general. I want to explain the setup that i currently have and i am hoping that somebody will be able to help tell me why my setup is not working like it should.

I have a 120watt 12V solar panel and that is connected to a 30AMP PWM charge controller using 12gauge wire (I think one of the problems is that i needed larger sized wire as the distance between charge controller and solar panel is approx. 75 feet and that may been causing a large voltage drop). I am using 8gauge wire to go from the charge controller to two 12V marine dual purpose batteries that i have hooked up in parallel to maintain 12V because my power inverter can only handle 12V. i have a cobra 1000W power inverter connected to the batteries.

The problem is that when i plug my 400 watt light into the power inverter it causes the battery to discharge (as it should i guess) but it seems as if the solar panel is not charging the batteries fast enough. The solar panel should be charging the batteries enough as to where they do not drain during the day because the system should be running off of solar anyway right? My system seems to not run off the solar panel and just off the battery and i have to turn off the inverter and wait for hours as the batteries charge up again. Any help would be GREATLY appreciated. Thank you!

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Newbie Help Needed; system not running off solar

    Well some specs for your charge controller and panel might help. You have one 120 watt panel, consider the derate factor 0.77 that is about 95 watts in ideal conditions. You add a 400 watt load, it is bound to run off the battery. There are losses in the inverter as well.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Newbie Help Needed; system not running off solar

    Welcome to the forum.

    solar_dave is on the right track here: your single 120 Watt panel simply isn't enough to do anything for this set-up. It probably is capable of around 6 to 7 Amps of current and no more. The size of the charge controller is irrelevant. The marine batteries are probably around 90 Amp hours each, so that panel would barely be adequate for recharging one. With two the charge rate would be well below the 5% recommended minimum.

    Then there's the load draw. 400 Watts on 12 Volts is 34 Amps. To this you'd need to add the inverter's consumption which would be another Amp or so. If the batteries are the size I suspect, they'd run this for about 2.5 hours before they were dead.

    Now look at how well that panel will replace the power. 120 Watt will average about 77% over the good sun hours. That's 92 Watts for about four hours or 368 Watt hours per day. Not enough to run the 400 Watt light for one hour, never mind recharge the batteries. There is simply no way 120 Watts of panel can keep up with 400 Watts of load.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Newbie Help Needed; system not running off solar

    And I'll add that the 75 ft of 12g wire is a serious problem as well, but even without that loss, I totally agree with both Solar_Dave and Cariboocoot that there is no way you're relatively HUGE 400 + watt load can be supplied by a 120 watt panel. It's like expecting a vehicle that gets 10 miles to the gallon, to take you for a 60 mile drive on just one gallon of gas. It ain't gonna fly.
  • MrSpenceMrSpence Registered Users Posts: 4
    Re: Newbie Help Needed; system not running off solar

    Some specs for the charge controller are DC charge voltage 14.4, floating charge 13.7, 30A for both rated cable charging current and rated load current. The panel is Max Power:120Wp, Open Circuit Voltage (Voc): 21.6V, Short Circuit Current (Isc): 7.4A, Maximum Power Voltage (Vmp): 17.6V and Maximum Power Current (Imp): 6.82A.

    So i would need another panel at the least? I was thinking about upgrading to a MPPT charge controller, dont know how many amps yet. Please tell me your suggestions on solar panels and charge controller for my setup..
  • MrSpenceMrSpence Registered Users Posts: 4
    Re: Newbie Help Needed; system not running off solar

    I also replaced that 75ft of 12gauge with 30ft of 8gauge. I did some shifting and move my setup closer to the panel. It still didnt make any difference in performance of my operation but i figured it was something that needed to be done.
  • Earnest TilleyEarnest Tilley Solar Expert Posts: 56 ✭✭✭✭
    Re: Newbie Help Needed; system not running off solar

    You had the same thought i did when i got my first solar panel i thought wow a solar panel 85watts wooo huuu i can power my whole house!!! you will quickly realize that if you want to run maby a 100 watt light you need to produce at least 150 watts of power just to power the light in the day and charge the batteries back up so you can run it at night if your running it 24/7.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Newbie Help Needed; system not running off solar
    MrSpence wrote: »

    So i would need another panel at the least?

    How many more panels you will need will depend on how much power you want to use each 24 hour period. Just that 400 watt light alone, if used day and night, would consume 9600 watt hours per day. That's a HUGE amount for any off grid system, and considering we can usually only assume 4 hours of full sun per day, you're panels would need to produce that 9.6kwh PLUS the extra needed to cover system losses and days without sun, in just that 4 hour window. Thus you'd be looking at over 15,000 watts in solar panels, or to put it another way, one hundred and twenty five more panels like the one you have now, plus one HECK of a huge battery bank to store the energy needed to run your loads at night and on cloudy days. And don't forget the many controllers needed to handle all that power. And no, I'm not joking.
    Bit of an eye opener eh?
    It's very unfortunate, but there is an idea floating among the general population not familiar with solar power, that all one needs do is mount a $300 panel on the roof and all their energy needs are solved. If only that were the case :cry:
  • MrSpenceMrSpence Registered Users Posts: 4
    Re: Newbie Help Needed; system not running off solar

    WOWWWWWWW!! yes that is definitely an eye opener. I wish i had found this forum and talked to you guys before i tried to set anything up. Ok so im pretty much going to need more everything..panels, charge controllers and batteries. When (and if) i do get more can you break it down to me how i would have everything connected in order to get it to run properly. Would i have to run the batteries and charge controllers in series, and how do i hook up multiple charge controllers?? any suggestions on the type of charge controllers to get?

    I really appreciate all the help and feedback from everyone. I really would be completely lost without it.
  • solar_davesolar_dave Solar Expert Posts: 2,382 ✭✭✭✭
    Re: Newbie Help Needed; system not running off solar
    MrSpence wrote: »
    WOWWWWWWW!! yes that is definitely an eye opener. I wish i had found this forum and talked to you guys before i tried to set anything up. Ok so im pretty much going to need more everything..panels, charge controllers and batteries. When (and if) i do get more can you break it down to me how i would have everything connected in order to get it to run properly. Would i have to run the batteries and charge controllers in series, and how do i hook up multiple charge controllers?? any suggestions on the type of charge controllers to get?

    I really appreciate all the help and feedback from everyone. I really would be completely lost without it.

    Step one is look at conservation, it is always cheaper to save a watt than generate a watt. If your on the power company grid, I assume you are, read about grid tie system, much better return on your investment using the grid as your "battery".
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Re: Newbie Help Needed; system not running off solar

    Next is to understand your loads... A good place to start is to measure kWH (kilo Watt*Hours) per day usage of your load(s). A Kill-a-Watt meter or similar is a very good start.

    A rough rule of thumb is your grid power (in North America) runs from $0.10 to $0.20 per kWH (in California, it can get to $0.50+ per kWH).

    Again, roughly, pure off grid power with solar, battery bank, and AC inverter will cost you in the range of $1-$2+ per kWH (assuming ~5-7 year life for battery bank, ~10 year for electronics, and ~20 year for solar array)... And you are paying a large chunk of money up front (plus replacement/maintenance costs).

    As the other guys have already said, conservation will be your friend here. And if the power needs are short term (weeks or a couple months a year), frequently, a good quality genset plus fuel may cost you less money overall.

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