Community Forums

69RoadRunner · 01-27-2010, 09:24 AM

AM Solar's panels are 100 watts, but are rated at 21 volts. The Kyocera's are 135 watts but 17 volts.

AM Solar says their panels produce the same or more juice (sorry for the technical jargon, my term, not theirs), and the AM Solar panel is smaller.

Can anyone explain which is better, 100w/21v or 135w/17v?

RVRoadTrip · 01-28-2010, 06:13 AM

All solar panels are rated in Watts. The watt rating is how much power (amps times volts) the panel will produce in full sunlight at 25 degrees C (77F). High voltage panels can be used on battery charging systems when using MPPT controllers and they create a bigger boost charge. The AMsolar and Kyocera designs are both good, but the AMsolar allows you to get 100 watts in a smaller footprint. If you are comparing the two, it really is as simple as comparing output... one gives you 100 watts, the other gives you 135 watts. For many, the cost per watt is the deciding factor.

Another note: Voltage loss due to heat and wire length are offset by higher voltage panels. Use big wire from your panels to your charge controller (we used #6 AWG) and use even bigger wire from the charge controller to the batteries. Make the wire runs as short as possible. Remember, the most convenient route for the wires is not always the best route.

Luv2go · 01-28-2010, 08:46 AM

Quote:

Originally Posted by 69RoadRunner

Can anyone explain which is better, 100w/21v or 135w/17v?

Short answer: 135W 17V.

Long answer: As RVRoadtrip pointed out, solar panels are rated in Watts. However to get the power out of the AM solar panels you have to use an MPPT controller (they point this out on their website). Unfortunately, MPPT controllers are less efficient than PWM controllers and the manufacturers are unwilling to disclose efficiency with a 12V load (Blue Sky rates efficiency at 24V, AM Solar has no specs), so it is difficult to figure out exactly how much, if anything, you will gain by using an MPPT controller with higher voltage panels.

If I were to re-do our system, I'd pick panels with a 17-19V MP output and use a 3-stage PWM controller (like the old standby Xantrex C40). I believe we'd get more real-world power out of my roof-mounted panels than we do with 26V MP panels and an MPPT controller.

BTW, with your coach roof area (from the looks of your pic in another post), you should check out these modules: SUN ES-A-200-fa3 200 Watt Solar Panel. When you add shipping, you can buy 2 of these for about the same price as 2 of the AM Solar and have double the power output. I installed 3 of an earlier version (Sun 190W 26V MP) of these on our coach and am very happy with them. Shading is not a problem (see pic). PM me for details if you would like to go this route, I can get info on mounts, cabling, etc. that I used.

Attached picture was taken at Monument Lake Campground (Big Cypress Nat. Preserve, Fl) in Jan 2010. During our week stay, we did not run the genny at all and had power to spare, running inverter all the time, dishwasher, microwave, etc. and even some cloudy days.

Stewart

69RoadRunner · 01-28-2010, 11:44 AM

Thanks for the info, and I apologize for the thread hijack.

TheDubs · 02-04-2010, 09:25 AM

Hey Luv2go do you ever run you fridge off of just solar? I want to run mine off of solar but I think I need to get another panel and maybe 2 more batts to handle it, because it wont make it thru the night.

Luv2go · 02-05-2010, 07:34 AM

Justin, I have not run the fridge off solar. It takes about 30A when cooling.

Assuming it is cooling 1/3 of the time, it would take about 240A/H out of the batteries every day, so just for that you'd need a 500A/H bank and about 500W of solar to recharge in 5 hours. If my assumptions are pessimistic you'd need less, perhaps 250W of solar and 120A/H of battery.

My understanding is the Gas Absorption fridges are much less efficient than well-designed compressor-based fridges, so I suspect you'd want to change yours out if you were to want to run it on electric (when I looked at that, it was way too much money unless my fridge was already broken).

Stewart

two sailors · 02-05-2010, 07:38 AM

With everything turned off, our coach draws about 2.5 amps. mult. by 24. Our 2 100 watts will put out about 14 amps peak, mult. by maybe 6.
If our 6 6v batt. were in better shape we can get by pretty well if we leave the inverter off except when we need it.
Talk to AM SOLAR in Springfield, Or.

TurtleBack · 02-08-2010, 05:39 PM

See my comments to Read and Learn's post and/or check out www.amsolar.com for additional technical info.

jeepsrule · 02-09-2010, 09:50 PM

Quote:

Originally Posted by TurtleBack

See my comments to Read and Learn's post and/or check out www.amsolar.com for additional technical info.

Looking into Amsolar system for my coach and they seem to recommend dropping the cables down the refrigerator vent from the roof. Is this a good way to get cables down?? Any problems with this route??

UFO Pilot · 02-09-2010, 10:50 PM

Solar Bill's routed the wires on my solar panel thru the bathroom vent pipe.

Luv2go · 02-10-2010, 06:32 AM

Quote:

Originally Posted by jeepsrule

Looking into Amsolar system for my coach and they seem to recommend dropping the cables down the refrigerator vent from the roof. Is this a good way to get cables down?? Any problems with this route??

The roof vent is a fine way to route the cables. Ideally the shortest route from the panels to the batteries is best, but longer distances can be compensated for by correctly sizing the wire. Just make sure AM Solar sizes the wire for less than 3% voltage drop at the rated panel current. If you are installing it yourself you'll have to give them an estimate of the wire length from your controller to your panels.

Handy Bob has a lot of good information in his blog, just be prepared for a long read and some rants:

Hello world from HandyBobSolar! « HandyBob's Blog

Stewart

jeepsrule · 02-10-2010, 07:54 AM

Quote:

Originally Posted by Luv2go

The roof vent is a fine way to route the cables. Ideally the shortest route from the panels to the batteries is best, but longer distances can be compensated for by correctly sizing the wire. Just make sure AM Solar sizes the wire for less than 3% voltage drop at the rated panel current. If you are installing it yourself you'll have to give them an estimate of the wire length from your controller to your panels.

Handy Bob has a lot of good information in his blog, just be prepared for a long read and some rants:

Hello world from HandyBobSolar! « HandyBob's Blog

Stewart

Great info. I'm re planing my cables and studying up on equipment.

jeepsrule · 02-11-2010, 06:24 AM

OK my wire run is not to bad. Around 10 feet down and 5-8 ft to the compartment next to the batteries where I'll put the solar controller, but how hot does the refrigerator vent get? The wire is rated for 105 degrees C and high abrasion resistance. Amsolar doesn't think the heat is a problem and and this looks like a slick installation.

jeepsrule · 02-11-2010, 06:36 AM

Quote:

Originally Posted by Luv2go

The roof vent is a fine way to route the cables. Ideally the shortest route from the panels to the batteries is best, but longer distances can be compensated for by correctly sizing the wire. Just make sure AM Solar sizes the wire for less than 3% voltage drop at the rated panel current. If you are installing it yourself you'll have to give them an estimate of the wire length from your controller to your panels.

Handy Bob has a lot of good information in his blog, just be prepared for a long read and some rants:

Hello world from HandyBobSolar! « HandyBob's Blog

Stewart

I read most of HandyBobs blog and picked up some tips. I'll go with heaver wire and I already planned my wire runs as short as possible with the controller in about one foot from the batteries in the next compartment. This is where my inverter is located, so it should be a good location.