bkirkpatrick
Brea / Orange County, CA
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Which is better: Higher or lower volt solar panels? I am looking at two different solar panels... both put out about 7.75 amps but one is a 29v (240 watt) and the other is a 36v (270 watt) panel. They are both around the 2.00/watt range. I heard that a MMPT controller will convert the higher volts to more amps. Or is that already factored into the amps on the sticker which would make the 36v panel more inefficient?
I am actually looking at putting about 1000w (or 20+ amps) on my rig but would like a good solar controller and a remote monitor. Any suggestions from the solar gurus here? Thanks, Brendan
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TechWriter
Green Bay, WI USA
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bkirkpatrick wrote:Which is better: Higher or lower volt solar panels?
Higher voltage - less I^2R loss + more of a chance your array will exceed battery bank voltage.
This info from Jack Mayer's site and MidNite Solar forum.
For a controller, look at MidNite's Classic.
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mena661
Southern California
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You can use smaller gauge wire with higher voltage panels. Also, they tend to be cheaper than 12V panels.
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sonicsix
Jerry n' Cynthia
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My panels put a consistent 20v into my MPPT controller. Very pleased with the setup. Make sure your controller can handle the volts you throw at it.
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pianotuna
Regina, SK, Canada
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Hi,
Look not at amps but at watts, or "power". Efficiency between the two panels is probably nearly identical. To choose look at cost per watt.
Since both panels would require an mppt controller, I'd choose the higher voltage. If staying below 500 watts maximum, my favorite controller is the Rogue 3024.
Above 500 watts I'd go to the Morningstar 60 amp MPPT unit.
From the midnight solar site:
"NOTE ON HIGH VOLTAGE-HIGH POWER INPUT SOURCES... When using an unlimited power source, it is recommended that the input voltage not be much higher than 4 or 5 times the output (battery) voltage. i.e. Don't try to charge a 12V battery from an unlimited input power source sitting at, say, 200 Volts."
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Regards, Don
Kustom Koach Class C 28'5" 256 watts solar, 875 amp hours in two battery banks 12 volt batteries 2500 watt inverter.
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Salvo
California
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Shade is the biggest killer of solar current. Forget about the minor advantage higher voltage has on IR losses. The greater the number of solar cells in series, the worst shade will effect current. Or, the lower the voltage the more shade tolerant the system is.
A lot of people say they won't park in shade or partial shade. But they will.
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Salvo
California
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I believe what they are getting at is efficiency. IIRC, lower voltage MPPT controllers are more efficient.
pianotuna wrote:
From the midnight solar site:
"NOTE ON HIGH VOLTAGE-HIGH POWER INPUT SOURCES... When using an unlimited power source, it is recommended that the input voltage not be much higher than 4 or 5 times the output (battery) voltage. i.e. Don't try to charge a 12V battery from an unlimited input power source sitting at, say, 200 Volts."
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pianotuna
Regina, SK, Canada
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Hi Salvo,
Yes that's true about the higher the voltage the lower the efficiency--but the only information I've seen about that is at the Rogue site shows 96% after about 26 volts? (working from a faulty memory so it may be slightly higher)
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Salvo
California
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The Rogue spec states a 17V panel is 1% more efficient than a 34V panel.
A 51V panel (if the controller can operate at this voltage) is probably more than 2% less efficient.
So much for the argument go higher voltage and reduce IR drop in the cable. You can always get a bigger cable. You can't do anything to help converter efficiency (other than keeping voltage low).
Sal
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TechWriter
Green Bay, WI USA
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Salvo wrote:. . .the lower the voltage the more shade tolerant the system is . . .
So a 0V system would be the best, right?
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