Newb RV questions

Billw
Billw Registered Users Posts: 5 ✭
in Solar Beginners Corner #1
So I was doing some bartering and ended up with a Shell 165 PC. Just the panel. I have no other equipment but I do have a 32ft Toy Hauler that the guy said "it will work great". Me being the optimist was hoping he wasn't yanking my chain. But after being in the market to get a solar system to compliment the generator I knew how much panels can cost and realized it was a little too good to pass up.

So I have been doing a little bit of reading here and I think I am ready to ask my questions.

First, will this panel work? Is there a way to test it with a DVM? I am a mechanic by trade and understand enough about electricity that I can figure out most problems.

Second will this panel work on my 12V trailer? I would like it to allow me to use the lights, stereo, ceiling fan etc... and still charge the battery at a minimum.

Third what type of convertor or switch box will best suit my needs. This panel is rated with Peak power of 35V and Peak current of 4.72a

Fourth if I bring the voltage from 35v to 12 will I increase my amperage equally?

Fifth how much power will this panel really put out? I know it is rated at 165watts but is that realistic being mounted flat on top of an RV?

Hope I am clear enough in my intentions here. Like I said, I am usually pretty good at figuring things out but this is my first venture in to solar power so go easy on me.

Thanks
Bill
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Comments

  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #2
    Re: Newb RV questions

    That is probably the Shell SQ165, which is about a 32 volt panel. You can use it, but will need an MPPT controller, like this one http://store.solar-electric.com/mosumpsochco.html

    On an RV you will get anywhere from roughly 120 to 170 watts in full sun, depending on temperature and sun angle.

    To test it just put it in full sun and measure the voltage output, should be around 45 volts open circuit.
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  • Billw
    Billw Registered Users Posts: 5 ✭
    #3
    Re: Newb RV questions

    Thank you for the quick reply. So I take it this panel will do what I want then? Charge my batteries and run the lights and other 12V accesories during the day?

    Also what type of charge rate would that controller put out? I imagine it would be equivilent to a trickle charge of say 2 amps? It would cut out on it's own so there would not be an overcharge situation?
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  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    #4
    Re: Newb RV questions

    Will the panel work? It should. How well it will work can only be determined by defining your needs as accurately as possible. For example, how much current will your loads draw and for how long? Also, what is the Amp Hour capacity of your battery?

    You can test the panel with a voltmeter connected to the panel's terminals.

    A popular rule of thumb for determining the real world power output of the panel is to divide the name plate rating (165W) by 2 to account for efficiency losses and then multiply that by the number of hours of "good" sun. usually about 4. So you have about 330 Watt-Hours. That assumes that the panel is oriented toward the sun. Flat mounting on the trailer roof will yield considerably less.

    You could connect the panel directly to the battery but I do not recommend it. It could be harmful to the battery. In any case, you will still only get the rated current out of the panel. An MPPT charge controller would protect the battery and deliver more current. However, MPPT charge controllers are relatively expensive and may be difficult to justify for your needs. I'm not sure a PWM controller would work with the large voltage difference between the panel and the battery. Other people here can advise on this better than I can.

    Welcome to the forum and good luck!

    Kamala
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #5
    Re: Newb RV questions
    Billw wrote: »
    First, will this panel work? Is there a way to test it with a DVM? I am a mechanic by trade and understand enough about electricity that I can figure out most problems.

    Assuming these are the ratings for your Sell 165-PC panel:
    Pmax @ STC 165 W
    Pmax @ PTC 149 W
    Vmp at Pmax 35 V
    Imp at Pmax 4.72 A
    Voc @ STC 44.5 V
    Voltage change -145 mV/C
    1. Set DVM to VDC--Read Open Circuit Voltage (Voc)
    2. Set DVM to 10 Amp full scale and read Isc (short circuit current)
    3. The first two will give you a 95% confidence the panel is good. If you had some small load (a few amps at 35 volts) you could measure voltage and current again to get ~Vmp and Imp for 100% confidence.
    Second will this panel work on my 12V trailer? I would like it to allow me to use the lights, stereo, ceiling fan etc... and still charge the battery at a minimum.

    Third what type of converter or switch box will best suit my needs. This panel is rated with Peak power of 35V and Peak current of 4.72a
    Mounting on the trailer is critical... Frame needs to be secure and no "twisting forces" imparted to the glass (thin, tempered glass).

    For RV's, it can be nice to mount in such a way that it can be laid flat for traveling, and tilted to capture noon-day sun.

    Some folks will put the panel on a nice heavy extension cord. Park in the shade, put the panel in the sun (secure for theft and wind damage). A high voltage panel (Vmp) with MPPT controller is very nice for this type of application.

    Because your panel is Vmp=35 volts--you will have to pick a MPPT type controller with Vpanel input rated for that voltage/current.

    The Morning Star MPPT 15 amp controller would be an ideal fit. Not cheap. Fro a 12 volt system, it will max out around 200+ watts (useful)... So that 165 watt panel is about its limits:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller

    For a larger controller--at a bit more price--you can look at the Rogue 30 amp MPPT unit. However, to use this controller, any additional panels will have to be rated at Vmp ~34-35 VDC.

    You can, of course, go to larger MPPT unit$--but probably not practical for your trailer.
    Fourth if I bring the voltage from 35v to 12 will I increase my amperage equally?

    Yes,
    • P=I*V
    • Power = Imp*Vmp = Ibatt*Vbatt (less ~5% losses or so)
    Fifth how much power will this panel really put out? I know it is rated at 165watts but is that realistic being mounted flat on top of an RV?
    For a panel that is tilted to noon-day sun, assuming 5+ hours of sunny full sun summer weather, flooded cell battery, and AC inverter--assume 52% derating factor:
    • 165 watts * 5 hours of full sun * 0.52 = ~429 Watt*Hours per day
    Mounting the panel flat will reduce your collection (depending on where you will be camping).

    About the equivalent of a 1/10 gallon of gasoline in a Honda eu2000i genset running between 400-1,600 watts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Billw
    Billw Registered Users Posts: 5 ✭
    #6
    Re: Newb RV questions
    Kamala wrote: »
    Will the panel work? It should. How well it will work can only be determined by defining your needs as accurately as possible. For example, how much current will your loads draw and for how long? Also, what is the Amp Hour capacity of your battery?

    You can test the panel with a voltmeter connected to the panel's terminals.

    A popular rule of thumb for determining the real world power output of the panel is to divide the name plate rating (165W) by 2 to account for efficiency losses and then multiply that by the number of hours of "good" sun. usually about 4. So you have about 330 Watt-Hours. That assumes that the panel is oriented toward the sun. Flat mounting on the trailer roof will yield considerably less.

    You could connect the panel directly to the battery but I do not recommend it. It could be harmful to the battery. In any case, you will still only get the rated current out of the panel. An MPPT charge controller would protect the battery and deliver more current. However, MPPT charge controllers are relatively expensive and may be difficult to justify for your needs. I'm not sure a PWM controller would work with the large voltage difference between the panel and the battery. Other people here can advise on this better than I can.

    Welcome to the forum and good luck!

    Kamala


    If it means spending a few hundred bucks on a quality controller I am fine with that. The money I saved on the panel is considerable so compared with the $2000 price tag some of my other RV friends have spent on solar panel installations I am way ahead of the game. It helps to that I am capable of installing them myself. I am not against going with more panels. I have a lot of room on the roof of the trailer and it is a full walk on roof so I will add more if it is needed. I am just at the point where I want to have enough to keep my batteries charged so I can start the generator when needed. The rest of the electrical load is relativly minor. I have already switched some of my lights to flourecent which use considerable less energy and I am searching for some reasonably priced LED lights to replace the small incandecent that are remaining. So right now it is the choice of going with just enough or I cover the whole roof and get enough power to turn on my coffee maker :roll: no thanks.
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  • Billw
    Billw Registered Users Posts: 5 ✭
    #7
    Re: Newb RV questions
    BB. wrote: »
    Assuming these are the ratings for your Sell 165-PC panel:


    1. Set DVM to VDC--Read Open Circuit Voltage (Voc)
    2. Set DVM to 10 Amp full scale and read Isc (short circuit current)
    3. The first two will give you a 95% confidence the panel is good. If you had some small load (a few amps at 35 volts) you could measure voltage and current again to get ~Vmp and Imp for 100% confidence.

    Mounting on the trailer is critical... Frame needs to be secure and no "twisting forces" imparted to the glass (thin, tempered glass).

    For RV's, it can be nice to mount in such a way that it can be laid flat for traveling, and tilted to capture noon-day sun.

    Some folks will put the panel on a nice heavy extension cord. Park in the shade, put the panel in the sun (secure for theft and wind damage). A high voltage panel (Vmp) with MPPT controller is very nice for this type of application.

    Because your panel is Vmp=35 volts--you will have to pick a MPPT type controller with Vpanel input rated for that voltage/current.

    The Morning Star MPPT 15 amp controller would be an ideal fit. Not cheap. Fro a 12 volt system, it will max out around 200+ watts (useful)... So that 165 watt panel is about its limits:

    Morningstar SunSaver 15 Amp MPPT Solar Charge Controller

    For a larger controller--at a bit more price--you can look at the Rogue 30 amp MPPT unit. However, to use this controller, any additional panels will have to be rated at Vmp ~34-35 VDC.

    You can, of course, go to larger MPPT unit$--but probably not practical for your trailer.



    Yes,
    • P=I*V
    • Power = Imp*Vmp = Ibatt*Vbatt (less ~5% losses or so)

    For a panel that is tilted to noon-day sun, assuming 5+ hours of sunny full sun summer weather, flooded cell battery, and AC inverter--assume 52% derating factor:
    • 165 watts * 5 hours of full sun * 0.52 = ~429 Watt*Hours per day
    Mounting the panel flat will reduce your collection (depending on where you will be camping).

    About the equivalent of a 1/10 gallon of gasoline in a Honda eu2000i genset running between 400-1,600 watts.

    -Bill

    I like the idea of the extension cord but I wonder if it is more of a pain than it's worth. Really I have to decide if the whole thing is more of a pain than it's worth. My dad put one on his RV and says it's the greatest thing. Of course he spent a pile of $ so I don't expect him to say it's no good I got hosed. I don't want to be constantly worried about how I park for optimum solar exposure. Ideally of course I want my trailer in the shade or I end up needing the A/C and so much for the solar panel. I think if I can find the storage space then I will build a collapsible stand for the panel and just put the panel in the sun. When you live as far north as I do you are constantly going to be moving it but I suppose that is better than losing efficiency by mounting it flat.

    Sorry just thinking out loud.
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  • Kamala
    Kamala Solar Expert Posts: 452 ✭✭
    #8
    Re: Newb RV questions

    The Morningstar SunSaver-15 MPPT charge controller is just the ticket, then.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #9
    Re: Newb RV questions

    Assuming start around Massachusetts -- You can use the PV Watts program to figure out how much various options will affect your power. Assume 1 kW of solar panels (sorry, smallest the program will accept), 0.52 derating, and fixed mount tilted to lattitude for Worcester:
    "Station Identification"
    "City:","Worcester"
    "State:","Massachusetts"
    "Lat (deg N):", 42.27
    "Long (deg W):", 71.87
    "Elev (m): ", 301
    "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:"," 42.3"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","11.8 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.37, 56, 6.61
    2, 4.35, 66, 7.79
    3, 4.84, 78, 9.20
    4, 4.86, 72, 8.50
    5, 5.26, 77, 9.09
    6, 5.34, 73, 8.61
    7, 5.60, 79, 9.32
    8, 5.31, 75, 8.85
    9, 4.94, 69, 8.14
    10, 4.32, 66, 7.79
    11, 3.21, 49, 5.78
    12, 2.87, 46, 5.43
    "Year", 4.52, 804, 94.87
    Look at minimum for 9 months of the year (assume winter will be with genset)--66 kWhrs for October/February per 1,000 watt panel, per month:
    • 66,000 WH per month / 30 days = 2,200 WH per day per 1kW of panel
    • 2,200 WH per day per 1 kWatts * 0.165 kWatts of panel = 363 Watt*Hours per day average
    Anyway--you can run the program with panel 0 degree tilt, or if you turn the panel to follow sun, etc...

    Ground mount + cord is nice if you park in shaded areas--but a wind gust can easily knock it over and turn it into shattered glass in just a couple seconds.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Billw
    Billw Registered Users Posts: 5 ✭
    #10
    Re: Newb RV questions

    Awesome BB thanks for the program. Very helpful forum. I will be lurking around from time to time. Thanks to everyone for their help.
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