Help pick new panel and charge controler

bc buck
bc buck Registered Users Posts: 59 ✭✭
in Solar Beginners Corner #1
I spend most weekends in my cabin off grid. I have a old inverter/charger and my battery bank consist of two 12 volt Trojans wired in parallel. The AH rating of the battery bank total a little over 200. I need to run the Honda 2000 about 5 hours a day to keep them charged. What size panel and charge controller would you recommend to help cut down on generator use. I am in Northern Mo so the equipment will need to be shipped.
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  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    #2
    Re: Help pick new panel and charge controler

    What size Charger? What is the Bank Voltage when you decide to recharge?
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  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    #3
    Re: Help pick new panel and charge controler

    I live in gaconade county in mo. I can't answer your question. I put about 150 watts home made solar panels with a $12 dollar ebay charge controller and two car batteries down at the creek where we parked an old rv. The solar panels are shaded and facing more north then they are south. We use a cheep 400 watt ($40) inverter. We are on the second inverter. We do not use it every weekend. I think it draws about 20 watts for the small amount of lighting an a radio that we use. We have whatched a movie or two with a projection thingy hooked to a vcr. It has run out of power before when using for several hours. It has been there for about 4 years. I think the biggest thing is the fact that we never use more then 20-25 watts per hour at night. What do you use power wise?
    gww
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  • Plowman
    Plowman Solar Expert Posts: 203 ✭✭✭✭✭
    #4
    Re: Help pick new panel and charge controler
    bc buck wrote: »
    I spend most weekends in my cabin off grid. I have a old inverter/charger and my battery bank consist of two 12 volt Trojans wired in parallel. The AH rating of the battery bank total a little over 200. I need to run the Honda 2000 about 5 hours a day to keep them charged. What size panel and charge controller would you recommend to help cut down on generator use. I am in Northern Mo so the equipment will need to be shipped.
    200 ah battery bank @ 10% charge rate = 20 amps

    That's about 375-400W of panel, not including derate factor (~450W would be better).

    For charge controller sizing, you multiply that 20 amps by 1.25 (or 1.56 to be extra safe). So 25 to 30 amps should suffice. Bigger if you think you might expand the # of panels down the road.

    That's for a 12V system. Sizing will be different if you use an MPPT controller and grid-tie panels.
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  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    #5
    Re: Help pick new panel and charge controler
    Plowman wrote: »
    200 ah battery bank @ 10% charge rate = 20 amps

    That's about 375-400W of panel. For charge controller sizing, you multiply that 20 amps by 1.25 (or 1.56 to be extra safe). So 25 to 30 amps should suffice. Bigger if you think you might expand the # of panels down the road.

    That's for a 12V system. Sizing will be different if you use an MPPT controller and grid-tie panels.

    What Plowman said, though for weekend-only use, you might be able to downsize the panels a little bit (they should begin to float-charge your battery bank during the weekdays when you're not using your cabin).
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #6
    Re: Help pick new panel and charge controler

    how old are the batteries? what are the specs of that inver/charger? Sounds like you are seeing the sulphation effect if you have to charge them 5 hrs...
     
    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
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  • bc buck
    bc buck Registered Users Posts: 59 ✭✭
    #7
    Re: Help pick new panel and charge controler

    This is a system I put together about 10 years ago. I have a Trace inverter/charger designed for a 18 wheeler. 1100 w with a 50 amp 3 stage charger. My Trojans are one year old SCS225 rated at 130ah each. The inverter is set up to stop working at 11.8v. Im not familiar with this term. (Sounds like you are seeing the sulphation effect if you have to charge them 5 hrs...) Also how many AH would you think im not using buy the system shutting down at 11.8 volts?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Help pick new panel and charge controler
    bc buck wrote: »
    This is a system I put together about 10 years ago. I have a Trace inverter/charger designed for a 18 wheeler. 1100 w with a 50 amp 3 stage charger. My Trojans are one year old SCS225 rated at 130ah each. The inverter is set up to stop working at 11.8v. Im not familiar with this term. (Sounds like you are seeing the sulphation effect if you have to charge them 5 hrs...) Also how many AH would you think im not using buy the system shutting down at 11.8 volts?

    So what you've got is two 130 Amp hour batteries in parallel: 260 Amp hours total.
    Minimum size of 5% peak current: 13 Amps * 17.5 Vmp (for PWM charge controller) = 227.5 Watts. Round that up to the nearest available.
    Best case would be to try for around 10% on an MPPT controller: 26 Amps * 12 Volts / 0.77 = 405 Watts. You may find a couple of "GT style" 200+ Watt panels & a MidNite Kid 30 Amp MPPT controller costs less than the 'standard' panels & PWM type controller for equivalent power.

    Sulphation (hard) occurs when the SOC stays below about 70% for extended periods of time due to insufficient charging. It decreases battery capacity.

    You should not let the batteries go as low as 11.8 Volts really; that is below 50% SOC (if resting Voltage) and will shorten battery life significantly. You can not actually use 100% of the capacity of lead-acid batteries and expect them to last long at all. Plus, as Voltage goes down current goes up for any given Watt draw. It gets pretty high pretty fast for large loads and the Voltage sag experienced at the inverter will usually shut things down anyway.
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  • bc buck
    bc buck Registered Users Posts: 59 ✭✭
    #9
    Re: Help pick new panel and charge controler

    I looked at the Schnider c35 PWM and was about $85. Started looking at the MPPT controllers and where quite a bit more money. Look to be more efficient. Also looking at panels is overwhelming too with so many brands in the same power class. Do you think I would be better off looking for a kit that was matched correct in the 250 to 350 watt range?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Help pick new panel and charge controler
    bc buck wrote: »
    I looked at the Schnider c35 PWM and was about $85. Started looking at the MPPT controllers and where quite a bit more money. Look to be more efficient. Also looking at panels is overwhelming too with so many brands in the same power class. Do you think I would be better off looking for a kit that was matched correct in the 250 to 350 watt range?

    MPPT controllers are really only about 10% more efficient. But they allow for more flexibility in array design and can work out cheaper. Here's why:

    PWM controller needs "standard" array Vmp to best utilize PV output. That means 17-18 Volt range for a 12 Volt system. Panels that produce their power at that Voltage tend to cost twice as much as "GT style" panels with their "oddball" Vmp around 30. So when you need a lot of Watts the GT panels & MPPT controller can work out to be cheaper than standard panels & PWM controller for the same size system. If you save $1 per Watt on the PV then by the time you're around 400 Watts that's an extra $400 to spend on the MPPT controller. With the advent of MidNite's 30 Amp Kid MPPT at <$300 the game has definitely changed.

    If you use the GT panels on a PWM controller you get only the current rating. So a 250 Watt panel with Vmp 30 and Imp of 8.3 functions the same as a panel of Vmp 17.5 and Imp of 8.3: 146 Watts. Loss of over 100 Watts, which you might as well interpret as $100 - per panel.
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