Solar Power diagram...Will it work?

grpark20
grpark20 Registered Users Posts: 16 ✭
in Off Grid Solar & Battery Systems #1
Hello all! I'm the new guy here and have been searching everything to try and get my design and questions answered. Hopefully, some of the experts will chime in and help me out. He goes the story....

I'd like to add solar power to my 7 x 14 enclosed trailer. The trailer is parked in an RV lot and probably gets 4 hrs of sunlight a day in the summer. The trailer is in direct sunlight, but I like to plan for worst case scenario, so let’s say 3 hours direct sunlight. Reasons for solar power in the trailer are because I need to power a 12 volt DC fan that draws 1.6 amps. I'd like to run this fan as long as possible every single day. I also have a fairly large 120 volt AC light that draws 216 watts. I will use this light for an absolute maximum of 2 hours a day and at the most this will happen 2 times a month. The light will only be used at night and I'm rounding way up on the usage time. The reasons for the set up in the enclosed trailer is because I will be storing some valuable cargo inside the trailer for 4+ years (military thing) and will occasionally be able to go out and check on it. The fan is needed for the vent in the trailer to circulate some air to keep the condensation out. Light is so I can see at night if I decide to check on things. Now to the proposed set up....

I'd like to run (2) 100 watt 12 volt monocrystalline silicon panels that claim 5.42 amps each. I'll be permanently mounting these flat on top of the trailer. I plan on using rubber bushings under the panels so they have some flex while I'm traveling. I need to know if that will work? I'll wire the panels up parallel and run them to a Morningstar SL10-12 Lighting controller with LVD. This solar controller will handle 10 amps and has a load output, and battery charger. I highly doubt the panels will ever put out 10+ amps in direct sunlight with all the inefficiencies. What do you think? Off the load terminals on the controller I'll run the 1.6 amp 12 volt DC fan as long as possible. The battery charger will be hooked to 1 Marine deep cycle battery that is rated at 85 amp hours. Tied in to the battery will be a 400 watt continuous DC-AC inverter, and from the inverter I'll run the 120 volt AC / 216 watt load lights. Usage of lights stated above. Here is the kicker....I'd like to run the 12V DC fan 24/7. If I can't, how long do you think I can run fan since my controller allows me to regulate how long the load will be powered. So that’s the scoop. Here is my research...

By my calculations my daily wattage with fan running 24/7 will be 2 amps (rounded up from 1.6) times 12 volts equals 24 watts per hour time 24 hour run time equals 576 watts daily use. Remember I can cut this down if I need to.

With the lights being converted to AC, I have no clue how to figure out the numbers.

So let's say on a normal day I get 3 hrs good sunlight and the panels bring in 150 watts that'll give me 450 watts back in per day. This is as far as I've gotten. I need your expertise now. If this will not work for what I'd like to do please suggest the next cheapest option or component I can add on to make this work. My diagram is attached for what I see in my head. Please share your expertise and thanks for taking the time to read this story. LOL

Panel.png
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Comments

  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #2
    Re: Solar Power diagram...Will it work?

    On most CC's the load connection only provides power when there is excess solar power. So the fan will run 3 hrs/day. You've posted both a 1.6A and 2.0A fan draw. Which one is it? 1.6 seems high. My fantastic fan draws 1.3 and it can move significant air. Can you use a smaller fan? Does it really have to run 24/7?

    But from your numbers: The fan uses 2*24=48AH/85AH battery = 56% discharge which is to much - think clouds, rain etc. Panels are 200W*3hrs*60% efficiency/12V = 30AH. They won't keep up with a 2A fan. And the fan has to be connected to the battery for 24 hr use.

    If you really want a 2A fan to run 24 hrs you need both more panels and more batteries.

    The light use is small in a month but why 120V? Why not just the rig 12V lights? Recommend you measure he actual inverter draw. You might find that it alone uses 20% of the power, so a 100W light is now 120W.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
    Re: Solar Power diagram...Will it work?
    CATraveler wrote: »
    On most CC's the load connection only provides power when there is excess solar power. So the fan will run 3 hrs/day.

    That was my first impression too, but then I noticed the word Lighting Controller in the product name. The Morningstar SL10-12 Lighting Controller is not primarily a Charge Controller, although it does that too. It is designed to control output from the battery to the (lighting) load, and on all but one setting it turns off at sunrise, and also turns off on Low Voltage.
    Not sure whether the LVD is set too low (11.7 volts, under load) for long battery life. I suspect that the voltage was set low assuming that the full 10 or 20 amp output would be drawn from it. With only a 1.6 amp load, it would drain the battery deeper.

    From what I know of MorningStar, I would expect the battery charge function to be well implemented, but it only mentions Float voltage in the spec page.

    For a 1.6 amp fan running 24x7 the battery load would be 38.4 AH. Call it 40. Running only 12 hours, (but at night, is that when you want your ventilation?) it would be only 20AH. By the 20% rule of thumb, that would take a 200 or 100AH battery depending on the run time choice.
    And the panels would have to replace 40 or 20 AH during perhaps 4 solar hours, so that calls for a panel array with an Imp of around 10 or 5 amps, corresponding to 180 or 90 watts nominal for an 18 volt Vmp panel. You would have to increase that for losses in the charge controller and charging process.
    SMA SB 3000, old BP panels.
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  • grpark20
    grpark20 Registered Users Posts: 16 ✭
    #4
    Re: Solar Power diagram...Will it work?

    Thanks all for the help so far....the fan is rated at 1.6 amp by the manufacturer. It's just a vent fan on a pop up vent in my trailer. The fan doesn't have to run 24/7 but I always factor worst case scenario. As far as the lights....I've already got a really clean set up hard wired in the trailer with a single 15 amp breaker box that goes to 4 120v AC outlets, a switch and then the lights. I have an external hook up for shore power and I also have a honda eu 2000i generator. I just stumbled across solar and this new situation. If I cannot run the fan 24/7, it will not matter to me wether it runs day or night. My thinking is that in the day time the sun will heat up my trailer and if the fan kicks on at sunset it'll cool trailer the same way the outdoor temp cools at night. What about this option......ditch the conrtoller with the load output terminal and run the fan off the battery and add another battery and panel. I've just found a deal on Schott 80 watt panels. Are they any good? I can get 8 for $500. I know that'll meet my needs but I'll need a place to store all the energy and a larger controller. I was thinking of getting 4 of those panels and 2 of the 85 amp hour batteries. Once again all.....I'm factoring in worst case. I've been told that the vent's in my trailer will keep the temp regulated just fine and not cause condensation. I really appreciate all the help so far.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5
    Re: Solar Power diagram...Will it work?

    Just wanted to toss in, that vent fans, work much better if they have some where to draw air into the trailer, sounds like this is a closed box trailer (not a camper?) so putting a few small screened vents around the bottom of the trailer (or even in the bottom of the trailer if your looking for stealth) will help keep the fan from just cavitating (moving the same air around in circles)
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • CATraveler
    CATraveler Solar Expert Posts: 98 ✭✭✭✭
    #6
    Re: Solar Power diagram...Will it work?

    Sounds like you have options. See if you can find a device that will only run the fan when you have some minimum battery voltage like 12.2V (50% SOC). With good sun it would run longer and with clouds and discharged batteries not at all.
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  • grpark20
    grpark20 Registered Users Posts: 16 ✭
    #7
    Re: Solar Power diagram...Will it work?

    I'm thinking of other options. I'll be in Florida for work soon, so may pick up 3 of DM Solaris 145 watt panels and piece everything else together now. I'm still all ears. Has anyone ever heard of a voltage timer that lets you set run times by the hour?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Solar Power diagram...Will it work?

    if that controller is a sunsaver 10 pwm or even the ss 20 pwm cc then the load connection does not just activate for excess power as it is an lvd or low voltage disconnect point. the load stays on unless it drops to 11.5v. this is meant to help prevent killing the battery.
    http://lib.store.yahoo.net/lib/wind-sun/sunsaver.pdf
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #9
    Re: Solar Power diagram...Will it work?
    niel wrote: »
    if that controller is a sunsaver 10 pwm or even the ss 20 pwm cc then ....

    The exact controller the OP mentioned is actually the "Morningstar SL10-12 Lighting controller with LVD" (http://www.solar-electric.com/sunsolligcon.html). Which seems to have a lot in common with the SunSaver, but with extra bells and whistles such as a selectable timer and use of the PV array as a photocell to control when the "lighting" load is energized.
    SMA SB 3000, old BP panels.
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  • grpark20
    grpark20 Registered Users Posts: 16 ✭
    #10
    Re: Solar Power diagram...Will it work?
    inetdog wrote: »
    The exact controller the OP mentioned is actually the "Morningstar SL10-12 Lighting controller with LVD" (http://www.solar-electric.com/sunsolligcon.html). Which seems to have a lot in common with the SunSaver, but with extra bells and whistles such as a selectable timer and use of the PV array as a photocell to control when the "lighting" load is energized.

    The llatest cand greatest is this....Going to get all set up with (1) 100 watt panel, (1) 85 amp hour marine deep cycle batter, and a controller/charger rated for 20 amp minimum with lighting controller. With this I'll atleast be able to run the lights at night. I'll grow into (4) 100 watt panels and (2) 85 amp hour batteries. I think that will meet my needs. Now I just have to decipher bad panels from good panels.... Home Depot has grape solar 100 watt panels for $200. Are they any good? Home depot reviews look good.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #11
    Re: Solar Power diagram...Will it work?
    grpark20 wrote: »
    Now I just have to decipher bad panels from good panels.... Home Depot has grape solar 100 watt panels for $200. Are they any good? Home depot reviews look good.

    A few concerns to keep in mind:

    There have been problems in the past with Grape-branded panels being built with the + side of the array connected internally to the frame, and therefore to ground. If these panels do not have either end of the array connected to the frame, a non-issue.

    They are made in China by a company which does not have an established track record. Will Home Depot honor the manufacturer's warranty if the panels outlast the company?

    The reviews, by their nature, do not address long experience with these particular panels. We know the design, and maybe even the manufacturer, has changed in the past.
    SMA SB 3000, old BP panels.
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  • grpark20
    grpark20 Registered Users Posts: 16 ✭
    #12
    Re: Solar Power diagram...Will it work?
    inetdog wrote: »
    A few concerns to keep in mind:

    There have been problems in the past with Grape-branded panels being built with the + side of the array connected internally to the frame, and therefore to ground. If these panels do not have either end of the array connected to the frame, a non-issue.

    They are made in China by a company which does not have an established track record. Will Home Depot honor the manufacturer's warranty if the panels outlast the company?

    The reviews, by their nature, do not address long experience with these particular panels. We know the design, and maybe even the manufacturer, has changed in the past.

    Thanks for the heads up. After doing more research I've noticed it's a lot easier for me to find 24 volt panels. Would it make more sense for me to just get (2) 24 volt 200+ watt panels and run an Xantrex C35 controller to keep my 12 volt batteries charged. I'll run that 1.6amp fan off the batteries versus a load controller and then just hope I have enough battery amp hours to keep up.....I'm all ears. Sorry for going 100 different ways, but I want to get this right the first time.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #13
    Re: Solar Power diagram...Will it work?

    Be careful... you need to check the panel/array Vmp voltages... Many "24 volt" panels are ~24-30 volts. For charging a 24 volt battery bank, the panel/Array Vmp needs to be around 35-38 volts (for PWM, for MPPT ~35-38 volts minimum).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • grpark20
    grpark20 Registered Users Posts: 16 ✭
    #14
    Re: Solar Power diagram...Will it work?
    BB. wrote: »
    Be careful... you need to check the panel/array Vmp voltages... Many "24 volt" panels are ~24-30 volts. For charging a 24 volt battery bank, the panel/Array Vmp needs to be around 35-38 volts (for PWM, for MPPT ~35-38 volts minimum).

    -Bill

    Please correct me if I'm wrong, but won't the Xantrex C35 work for this? Input voltage up to 55 volts (from all the inefficiencies I've been reading about I'll never see over 30 volts or 20 amps with 2 panels) and then select battery bank voltage for 12 volts. Essentially a step down? Or am I way off?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #15
    Re: Solar Power diagram...Will it work?

    A PWM charge controller is, more or less, simply an On/Off switch. If the longer the on time, the more "average" current is let through.

    The batteries, depending on charging cycle, bank temperature, type of battery, etc. need around 14.5 volts (~29 volts) charging (bulk/absorb set point) at 77F. Higher temperatures, the voltage requirement drops, the lower the battery bank temperature, the higher the charging voltage needed.

    For equalization, you need around 15-15.5 volts (30-31 volts). For float, ~13.2-13.6 volts (26.4 to 27.2 volts).

    You need to add a couple volts for controller+wiring drop. And solar panels are rated at ~77F/25C, but really operate at much hotter temperatures (from ambient temperatures and the sun beating down on the panels)--This all serves to depress the Vmp operating voltage of the panel from 17.5 to 18.6 by a couple of volts (again, depending on temperatures).

    MorningStar has a string calculator for both their MPPT and PWM controllers... Just input a PWM controller type and play with the numbers.

    Solar panels are very "imperfect" batteries and it takes some study to ensure that they will meet your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • grpark20
    grpark20 Registered Users Posts: 16 ✭
    #16
    Re: Solar Power diagram...Will it work?
    BB. wrote: »
    A PWM charge controller is, more or less, simply an On/Off switch. If the longer the on time, the more "average" current is let through.

    The batteries, depending on charging cycle, bank temperature, type of battery, etc. need around 14.5 volts (~29 volts) charging (bulk/absorb set point) at 77F. Higher temperatures, the voltage requirement drops, the lower the battery bank temperature, the higher the charging voltage needed.

    For equalization, you need around 15-15.5 volts (30-31 volts). For float, ~13.2-13.6 volts (26.4 to 27.2 volts).

    You need to add a couple volts for controller+wiring drop. And solar panels are rated at ~77F/25C, but really operate at much hotter temperatures (from ambient temperatures and the sun beating down on the panels)--This all serves to depress the Vmp operating voltage of the panel from 17.5 to 18.6 by a couple of volts (again, depending on temperatures).

    MorningStar has a string calculator for both their MPPT and PWM controllers... Just input a PWM controller type and play with the numbers.

    Solar panels are very "imperfect" batteries and it takes some study to ensure that they will meet your needs.

    -Bill

    Thanks for the knowledge. I'll keep researching. This is a lot of research just for a measly 461 watt set up.....
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