Flexable solar panel UNDER rear seal

[Kmikesell]

UPDATE! Took out the TM for the Memorial Day weekend and had a great test of the Panel, the Eternabond, and how well the panel kept the batteries charged.

My 100-watt panel allowed us to use just about everything we could throw at it, including watching a movie on our TV/DVD combo, using a 400-watt inverter. We had a HUGE storm blow in, that destroyed our easy-up.... But the panel did just fine. Even without a full day of sunshine, the two Trojan 105's were running at 12.8 by noon!

[rickst29]

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

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).

[Kmikesell]

Originally Posted by rickst29

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).

Wait, WHAT!!!

IF I'm using a PWM controller I'm losing 15/20%? WTH!

If I'm losing that much and the panel is lying flat (and only being 70% effective) that's too much to lose!.

Besides price what is the difference between an MPPT controller and a PWM?

[rickst29]

If you format your non-google search carefully, you will have found two posts I wrote previously, starting with https://www.trailmanorowners.com/for...ad.php?t=20204.

A PWM controller "wastes power" by leaving a portion of panel-provided power within the panels (by disconnecting and then reconnecting the panels thousands of times per second). The average (lower) voltage provided to the batteries is reduced to the Voltage which the batteries need to have, for that State-Of-Charge. They can be built small, simple, and reliable at costs around $15-40 delivered. If you need "14.2 volts" into your batteries, but your panel voltage is even higher than 17.9 Volts, you lose a higher share.

An MPPT controller never disconnects the panels while feeding a hungry pair of batteries. Instead, they convert the power being obtained from the panels (at a voltage which is too high), into more current, at lower battery charging voltage. This is a complex process, involving expensive electronics within a much larger box. The bigger box provides a heat sink for a smaller amount of wasted power (5-10%) dissipated as heat while the controller runs in MPPT mode.
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With only a single "100w panel", it would be a poor investment to spend $130-$150 on a decent MPPT Solar controller - gaining only about 15 watts from that panel. It would be far better to add a second solar panel, gaining more "final watts for possibly less money.

The cross-over occurs at about 300 watts of panel power. At that point, adding a 4th panel versus switching to MPPT begins to make the MPPT switch a better deal. For higher power panels (I have about 500 watts, configured at about 80 volts) MPPT definitely wins.

[Kmikesell]

Excellent advice... Much appreciated.

[Kmikesell]

Great advice!

[Kmikesell]

Originally Posted by gerargliuchnaglaz

While placing the panel on the rear shell might be convenient, you'll definitely want to ensure there's enough flexibility in the seal to avoid damage and scratches.

I placed in on the rear shell so as to not be under the seal.... So far so good!