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-   -   Solar: Several questions (https://www.fiberglassrv.com/forums/f95/solar-several-questions-25845.html)

wes harris 05-31-2006 05:38 PM

I've been looking into the solar option, & have several questions

1) The cost I've seen here talks of solar panels for $10.00(U.S.) per watt, plus controller, plus meter, plus wiring, plus battery. A cursory search yields many under $5.00 per watt for the solar panels. Does mounting hardware bump this price up that much? Of course, this does not include the other hardware.

2)I live in the southeast. I want to park in the shade in the summer when I camp. If the panel is mounted, I would think the efficiency would be low. Does anyone know approximate loss of efficiency in the shade? I would think it would be terribly inefficient, or nonexistent.

3)If one has a portable solar panel, or several panels, what kind of line loss is expected going from the panel to the battery, on a per foot basis? My question is, how long a cord can one have & get the solar panels out from under the trees, without major voltage loss to the battery? Is there a safe low voltage for charging?

Any opinions, or advice would be appreciated.

Brian B-P 05-31-2006 05:52 PM

While US$10/watt is a nice round number for conservative estimation, I agree that it may now be high. Canadian retail prices are more likely CDN$10/watt (which is what I paid at Canadian Tire for a 30 W panel on sale last year), and are lower (per watt) with larger panels; many egg owners have panels which are small by RV standards. Larger setups which I have seen offered for sale as packages by RV stores in the Edmonton area are roughly $10/watt including the controller and mount.

Since the battery is not specific to the panel power output, it doesn't make sense to me to include it in the solar system "per watt" pricing, although of course to charge by day and consume by night you need battery capacity. For instance, a 60 W panel with controller may cost about double what a 30 W panel which controller does, but the 80W panel doesn't necessarily need twice as big a battery.

I was surprised to find last summer that in moderate shade my 30 W (rated) panel was still pushing about an amp at over 12 V (that is, over 12 W) into my powerpack battery.

Mike Taylor 05-31-2006 09:55 PM

You can extend the power leads to the panels and not loose too much in voltage drop if you use larger gauge wire. The smaller the wire, the more resistance loss.
My panels are mounted on the roof of trailer and I find they charge ok even if partially shaded or cloudy. Under deep shading they won't charge. The nice thing about roof mounting is they don't walk away when I'm away from the trailer. Mike

Gina D. 05-31-2006 10:27 PM

Mine are on a 20 foot 10 guage tether. I have measured as much as 22 volts in full sun with this arrangement. (4 15 watt panels, total 60 w.) 20 feet should be more than enough to find a spot in the sun. Unless you are in a parking garage...

loss per foot.. don't know exactly, but keep in mind, your controller is going to limit the input to the battery at 14.5 volts. I'd say anything OVER that going into the controller is for good measure, but you will do OK in the 12 to 15 volt range. (Depending on current draw and how fast you deplete the battery.)

Oddly enough, using my "Old" 15 watts panel, I got didly in the shade, but in overcast, I still get over 12v. Have not seen it drop below that at anytime when out from under trees etc even in a rainstorm.

I notice the same with my newer larger array. To the "eye" it seems to be the same brightness out, but the direct solar UV is the key.

Solar is NOT the end all to free power needs. It will work great for you as long as you know the limitations and learn how to conserve, (Not go without, but CONSERVE wisely) install less power hungry items and be prepared to cut back at times when the sun is not co-operative.

Things I did to conserve:

Installed LED lighting. Soon to have cold Cathode like Mikes.
Have back ups for powered systems like hand pumps etc.
Swapped out my powered vented cat heater for an unpowered one.
Use invertors matched to the task (Like only having a 100 watt one for my comp instead of running the 400 watt one I need for the TV/DVD)
Fantastic Endless breeze fan as well as a roof vent fan. The roof vent one is a power sucker, the endless breeze runs for days on a single 20Ah Gel Cell.
Speaking of.. back up batteries for non essentials LIKE the comp.
Car is wired to charge the house battery. In a pinch, I can always run the car connected for a bit to help things along.

I am like you, I don't want them on the roof for various reasons, but one of the biggest is what happens when parked in the shade.


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