Quote:
Originally Posted by Bill
This issue is often over-hyped and misunderstood. It is a really important issue when you have really long runs of wire, real small wires, or a large current flowing. But that is not your situation.
Think of it this way - 100 watts of power at 14VDC is about 7 amps. Number 10 copper wire has a resistance about 1 ohm per thousand feet, so if you had 1000 feet of wire, you would lose about 50 watts. But in 20 feet of wire, you would lose less than a watt.
Check my numbers, folks, but I think you are OK on the front shell.
Bill
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That's a pretty good example. But the maximum power loss is even less than that, for two reasons:
#1, a "100 WATT" panel will never generate a full 100 watts, if mounted flat on the roof of a TM Trailer in most of North America. (Even at the perfect moment on June 21, at high altitude, at exactly "solar noon", you will not see more than 80 watts). This is because the panel(s) have not been "tilted" to create a perfect 90-degree angle with the overhead sun.
#2, Although the average battery charging voltage (for the solar charge controller) should probably never exceed 14.2 Volts, the Voltage of the Solar panels is higher - most "12v" solar panels generate power at 17.9 volts (or even more). The resulting maximum real-world solar current (for a single "12v" panel, at that "perfect moment of the whole year) will therefore be just is 80 watts / 17.9 volts = 4.47 Amps.
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Next, we go to an actual calculator, in order to obtain the "power loss" within the Solar Wire circuit. Moving to the front shell, the total length of wiring might be around 20 feet, one for the negative wire and again for the positive wire (a total "round trip" of 40 feet. Here's a pretty good calculator URL, with numbers already plugged in AGW-10 wire:
https://www.calculator.net/voltage-d...y=24&ctype=nec
The result is 1.19% power loss for AWG-10 Solar wire, or 2.01% for AWG-12. This only occurs at the best, highest-powered second of the entire year. I frankly wouldn't bother with the extra expense for AWG-10, if I was installing only a single "100 watt" panel.
To be any more precise, we need to know your panel's MPP "voltage" and current". (I'm assuming a 100% efficient 'MPPT in this simple calculation. If you're using only a "PWM" type solar controller, you will lose around 15-20% of the panel power at the controller).