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Old 08-24-2014, 08:07 AM   #1
ftroop82
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Amps vs Volts Solar Panel

Looking to get a solar panel for the RV. Question is do I get one with more amps or more volts? 8 amps with 18.5 volts or 5.56 amps with 36.2 volts?
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Old 08-24-2014, 08:10 AM   #2
kellydog98
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I believe that the more amps you have the more you can run in your rig. That being said, there are so many different solar products out there your research has just begun.
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Old 08-24-2014, 09:35 AM   #3
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Originally Posted by ftroop82 View Post
Looking to get a solar panel for the RV. Question is do I get one with more amps or more volts? 8 amps with 18.5 volts or 5.56 amps with 36.2 volts?
You can sort of look at it this way: Amps is the "working unit" or the "power" of the electrical charge. Voltage is the "pressure" by which the amps are "pushed" through the wire. Your RV electrical system (battery side) is limited to about 13.5 volts as an average. So any solar array with a voltage greater than about 15 volts would have to be "converted" to appropriate voltage to be stored in the batteries. That conversion process produces heat (lost/wasted energy) and makes the system less efficient.

So, there is a "best mix" to consider, but you'd be more concerned with the amperage than with the voltage. Your battery charger is going to reduce any input voltage from the solar arrays to a voltage that's appropriate for your battery bank. Higher voltage solar arrays would be appropriate where the "amperage" needed to be "pushed" for a long distance to the "storage/conversion site". As an example, you had solar arrays located along a mile of highway, you'd want high voltage developed to push the amperage for that distance. In your situation, you're only pushing for 10-15 feet, so keeping the voltage lower, increasing the amperage at the solar array eliminates the conversion (and energy lost in heat) that would be necessary in your battery charger/converter assembly.

This is very simplistic and not "exactly correct in all terms" explanation of how DC energy works, but is "sort of" a layman's explanation of what's happening. There are "more appropriate" ways to define how amperage and voltage relate, but it would take an engineer to explain/understand it.

I hope this sort of clears up your question.....
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Old 08-24-2014, 11:11 AM   #4
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Originally Posted by JRTJH View Post
You can sort of look at it this way: Amps is the "working unit" or the "power" of the electrical charge. Voltage is the "pressure" by which the amps are "pushed" through the wire. Your RV electrical system (battery side) is limited to about 13.5 volts as an average. So any solar array with a voltage greater than about 15 volts would have to be "converted" to appropriate voltage to be stored in the batteries. That conversion process produces heat (lost/wasted energy) and makes the system less efficient.

So, there is a "best mix" to consider, but you'd be more concerned with the amperage than with the voltage. Your battery charger is going to reduce any input voltage from the solar arrays to a voltage that's appropriate for your battery bank. Higher voltage solar arrays would be appropriate where the "amperage" needed to be "pushed" for a long distance to the "storage/conversion site". As an example, you had solar arrays located along a mile of highway, you'd want high voltage developed to push the amperage for that distance. In your situation, you're only pushing for 10-15 feet, so keeping the voltage lower, increasing the amperage at the solar array eliminates the conversion (and energy lost in heat) that would be necessary in your battery charger/converter assembly.

This is very simplistic and not "exactly correct in all terms" explanation of how DC energy works, but is "sort of" a layman's explanation of what's happening. There are "more appropriate" ways to define how amperage and voltage relate, but it would take an engineer to explain/understand it.

I hope this sort of clears up your question.....
nuff said!!
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Old 08-25-2014, 06:58 AM   #5
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Thanks for the info... Second question would I need a MPPT solar controller or could I use a PMW type

Max System Voltage (IEC/UL) 1000V / 600V
Maximum Power Pmax 160 W (-5%, +5%)
Voltage at Maximum Power Point Vmpp 18.5 V
Current at Maximum Power Point Impp 8.65 A
Open Circuit Voltage Voc 22.2 V
Short Circuit Current Isc 9.46 A
Temperature Coefficient of Voc -0.084 V/ºC (-0.38% /ºC)
Temperature Coefficient of Isc 4.6x10-3 A/ºC (0.05% /ºC)
Temperature Coefficient of Pmax -0.79 W/ºC (-0.50% /ºC)
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Old 08-25-2014, 09:44 AM   #6
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If you were building a system for 24/7/365 use where absolute reliability and maximum power capacity were essential regardless of the potential for sustained weather/temperature extremes, I'd say using an MPPT controller would make a difference, but realistically, you're talking about a system intended for recreational use when the temperature is moderate (meaning not arctic/Antarctic conditions) and the sun shines at least part of most days so there's not a "huge" benefit to paying a premium for a MPPT based system. You'd get better overall performance by using the extra money to buy more efficient solar panels or to add "one more panel" to a PMW based system. In other words, most of us use a solar system for RV use on "bluebird days" not in "even the ducks won't fly" weather conditions, so we're talking about "nice, moderate conditions" for using the RV solar system.

I'd say whichever is the best value would suffice in an RV solar system. I personally wouldn't get too "wrapped up" in the ideas of extreme performance or squeezing the ultimate "last bit" of power from the system's capabilities. Rugged endurance and "good" performance are much more relavent goals to achieve in a mobile roof mounted or portable "hand positioned" collection system.

Squeezing an extra 10-15 watts (at a premium cost) isn't usually the goal for most RV'ers. rather being able to maintain sufficiently charged batteries without relying on the backup generator is more important.
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Old 08-25-2014, 10:23 AM   #7
ftroop82
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Thanks for all the helpful info... now to get the Bogart 30 amp solar controller with the Bogart Tm-2030rv meter or a Morningstar 30 or 45 amp controller
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Old 09-02-2014, 09:31 AM   #8
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You might find that there are other factors to consider when setting up your solar system. Firstly - is cost a consideration? Higher wattage solar panels are sometimes cheaper than lower wattage units simply because many more of the higher wattage are sold. For example, EcoDirect list 100-150 watt panels from $270-$450 while 250 Watt panels are available for $200-$250. So your cost per watt drops considerable with the larger panels. Size isn't just about electrical power - you also have to consider physical size. Some of the 250 watt panels can be as large as 5.5ftx3.5ft and weigh 40lbs. Personally I'm planning on using a 200watt panel that is 5ft by 2.5ft. Most of the larger wattage panels are 24volt nominal while 100-150 watt can sometimes be found that run on 12v. If you are planning on using a 24v panel to charge a 12 volt battery I believe that you need to use an MPPT controller to get the full wattage output from the panel. (BTW wattage is voltage times current so a 100 watt light bulb at 110 volts uses about 0.9 amps, while on a 12 volt system it would use 9 amps).
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