how small of a solar panel can i get away with

[Ultrasport12]

Originally Posted by larrie

What is the Ebay link to the panel?

Larrie (or anyone else) you might try just calling around to Solar dealers in your area. They sometimes have units not used on a job or warranty replacements. I bought a Kyocera 135watt unit from a local dealer who only had one left over from a job they did and I bought it for $150 cash. It is a few years old (it was made in 2008 or 2009) but still brand new in the box and has a 20 year warranty. For us 135 watts is more than enough as by mid day all of the time the float charge light is flickering on and off.


..Jamie

[stanw909]

It's been a while and I held off on the solar but I bought a Dometic Freezer/fridge for my ice.I got's to have my ice.I added another optima taking my my amp hours to 110. 2 X 55 amp hours.The freezer mode will draw 3 amps per hour and in theory I should get 30 hours but in a test with full batteries and no other draw I only got 12 hours.I believe this is due to the circuitry in the unit that senses low voltage for protecting the batteries and the fridge.I've got a line on a brand new Monocrystaline 135 watt for $175 ( $1.15 per watt) don't know the brand.Using a calculator on the web I calculated 11.25 amps.This should solve my usage for daylight hours and help in overcast situations right?I will be buying a 20 amp controller but unfortunately not an MPPT due to budget constraints.Also my top is corrugated so I plan on a flat mounting.I realize there needs to be air flow but I still want to keep low profile.Thoughts anyone.Thanks

[daveb]

I don't know Stan, I actually think you'll get about half that figure. I don't think I've ever got over 16 amps on a perfect day with the sun at the best angle and I have twin 135's plus a MPPT controller. Most of the time I see 12-14 amps. I'd figure you might get +/-7 amps out of them on the most days if you're lucky. Wire losses take a toll by the time the juice gets to the controller. I actually don't think tracking is that important either when dealing with an RV set up but the sun quality is huge. I have two 4-D batteries so my twin panels are better suited for that size of bank but even a single 135 would work IMO. I just like peaking faster in the morning and grab a bit more power in hazy conditions. Because I only take my AGM's down to 60% as a rule, and because AGM's charge up so fast, 2-135's is slightly overkill. The twin panels are more suited to a standard wet cell battery bank that gets pulled down to 30% or lower.

Dave

[BroncoHauler]

Part of the delta between theoretical output and real-world output is due to the poor aspect angle of the panels with respect to the sun. This more of a factor with mounted panels vice portable panels. A few people have made tilting mechanisms for rooftop mounted panels which helps in some regards, but even then the panels cannot 'track' the sun like portable panels can, provided you're willing to relocate the portable panels every hour or so to maximize the panel output. Rooftop panels are decidedly simpler however, and you don't have to worry about setting them up, or having them blow over in the wind. They're also great for just keeping all your batteries topped-up if you park outside.


Herb

[daveb]

Yes I did mean tilting not tracking. It would be very difficult to install self tracking panels and the motors would eat up too much power on such a small array. I agree that the amount of gain with tilting panels isn't usually worth the effort in most cases. A portable panel is much easier to move about but has it's own issues.

[stanw909]

Just flat mounting them. No room for portable panels. Thanks for your thoughts gents.

[stanw909]

I finally installed a 155 watt ( 12.9 amps full sun) monocrystaline solar panel and a cheap 20 amp controller. I will add a mppt controller at a later date. I noticed the panel was not charging but realized that the controller has an auto matic shutoff if the batteries are full so I turned on a couple of fans and my freezer. It started charging right away. I live in the Inland Empire in SoCal so although I don't like to do it that way,I did the install at night. I took it real slow so everything works fine. Started about 10:30 and finished at 1:30