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Darkspeed · 06-12-2011, 08:41 AM

Has anyone here seen a large solar install on an airstream trailer.

I know it would require removal of AC / vents / etc... to get the room on a large airstream like a 31'. Maybe - low profile vents could work..

I have designed / installed a number of large systems so i know it is physically possible.

The limiting factor is battery capacity but it could be set up as a real time system where any overcharge on the system could trigger a diversion load like an AC.

Any thoughts? I have a big stack of MSX120's collecting dust and I am about to build a new frame /floor with room for additional battery capacity ( without turning the trailer into an anchor )

barts · 06-12-2011, 10:06 AM

I'd have to ask what you anticipate doing with that much solar power. You're in Florida which means that you're going to get about 5 hours of full power a day... w/ the right controller that's 375 amp-hours/day.
Unless you're planning to add 500 lbs of batteries, it just doesn't make sense unless you need the power only when the sun is shining.

Of course, if what you're doing is running a pirate radio station....

Just because we can do something doesn't mean we should....

= Bart

Airstream25 · 06-12-2011, 10:41 AM

Why not mount a panel right over the AC? It might only increase your overall height by 4" or so. More panels could be hinged to fold up glass to glass while traveling then opened up to extend over the sides when you are parked.
You could add an electric heating element to your hot water heater to use some of the power. Some refrigerators can also be run on 12v.

Darkspeed · 06-12-2011, 02:20 PM

I have run split system ac and Dan foss refer units on solar and I am fascinated with the idea of doing this in an airstream.

I have an evacuated tube solar water heater that I may be able to incorporate as well

AirsDream · 06-12-2011, 05:22 PM

No reason you can't to that ... it's especially easy if you've got the extra panels not being put to good use. You may need to mount panels above the roof vents, and as noted, perhaps over the top of the a/c unit if you leave it in place. And probably relocate the tv antenna or do away with it.

That's a lot of generating capacity for a little trailer, though. My even smaller 23 footer has two panels (130w or 150w, I can't remember) and three Group 27 Lifeline AGMs, and if there's any sun, the panels keep the batts. charged up all the time.

One thing I considered and did not do, was to put several more batteries in the front of the pickup truck bed, with large (e.g. welding) cables and high amperage connectors at the end of the cables and the front of the trailer. Then I could plug in the truck and charge the in-bed batteries as well. That would have given me something like 750 amp hours of storage. But I haven't needed the extra storage. I simply forgo the a/c and the microwave when I'm boondocking (which is most of the time), and everything else runs just fine on this system. In fact, I'm usually fully charged by noon or so, which means I'm not using most of my battery bank very hard as it is ... [I run LED lights throughout, pc boards for the fridge and water heater, vent fans for stove and shower, water pump, fantastic vent, computer, printer, tv, stereo, a fan or two and a couple of phone and flashlight chargers.]

Lewster sized it, and if you're not talking to him, you ought to be. He'll have some practical tips for you, and he's putting a bigger system than you're talking about on the roof of his moho.

Do keep us informed if you decide to do this - inquiring minds want to know how it works out.

UAPachyderm · 06-13-2011, 04:49 AM

Lewster installed 800w (eight 20x40" panels) without covering any vents on a 28' (see pic below). You definitely should be able to fit 1000w if you so desired.

Lewster is the consummate professional. As stated above, he would be the one to talk to. I think he's going to tell you that the Puekert Effect is the obstacle for AC ... Lithiums will likely solve that here in the next year or two.

Darkspeed · 06-13-2011, 06:49 AM

Where is Lewsters thread on his 800w solar install?

UAPachyderm · 06-13-2011, 06:55 AM

There isn't a thread. The most helpful and educational solar thread is the one where Evan, Bart, etc discuss their installs in detail. BTW, thanks to those guys for sharing.

Lewster has a lot of installs under his belt ... he just doesn't tout them on this board. If you PM him, he'll talk you through whatever you are curious to accomplish.

tr0y · 08-15-2011, 07:29 PM

I know this is a bit late but I have a 500 watt install, charge controller, 1500W inverter charger and 1KW worth of AGM batteries, if you are still looking for more info I would be glad to share with you.

Darkspeed · 08-16-2011, 06:53 AM

Quote:

Originally Posted by tr0y

I know this is a bit late but I have a 500 watt install, charge controller, 1500W inverter charger and 1KW worth of AGM batteries, if you are still looking for more info I would be glad to share with you.

What loads do you power with your system?

tr0y · 08-16-2011, 08:42 PM

Our power use is very much like we are at home; we live off the grid on solar as well. We run the following:

Start-up of 13.5K AC ( longer runs we will run Honda 2000 generator )

6 CuFt 120 volt refrigerator runs 24/7/365 ( beer storage when at home)

Brew coffee plus one to two hours of warming

15 to 20 minutes a day of 1000 watt microwave

12 volt water pump for faucets and showers

6 to 15 - 12 volt 20 watt interior lights a few hours a night after dark and before bed

6 to 10 hours daily of automotive audio system with power amp and 4 speakers

2 laptop computers either in use or charging 24/7

Assorted small electronics charging ( gps, smartphones, ipads, etc )

We usually watch a movie at night on a 16” TV in the bedroom

We have external Christmas lights for decoration we run at night

And I am sure there are some things we are forgetting. We chose to go modified sinewave in the trailer and it is fine no issues with electronics not running or charging, overall we just live like we are plugged in. Solar can do a lot the AC is about the only thing we don’t have on solar only.

I have attached a drawing of what we have, I have made some slight changes since it was drawn but it is close.

t

Darkspeed · 08-17-2011, 08:06 AM

So I'm guessing you are generating around 3kwh per day from your solar. How many kwh from your generator?

tr0y · 08-17-2011, 08:20 AM

I haven't really been watching as I didn't install the digital meter on the CC, I'll take a look and try to get you some numbers. We are spending the summer in Northern WI, and even this far north we are usually into float by 2 PM. So between 1.5 and 3 kwh seem reasonable. The generator is a Honda 2000, we haven't needed AC for the last week or so so it has not been run.

Wabbiteer · 08-17-2011, 10:23 AM

Solar panels loose output the hotter they get, with a 1000 watt 25°C rating at 80°C in full sun would be around 750w output (minus 0.4 to 0.55 of a percent output per degree centigrade heating) so a kilowatt of PV is not that extreme of a number to handle

tr0y · 08-17-2011, 10:38 AM

I haven't really noticed that the panel output starts to degrade till quite a bit hotter, in my off the grid home with better monitoring, up to about 105 F outside temp, the panels will still output at full voltage.

On the other hand, Jan and Feb are even more fun to watch them put out amazing amounts of power on a bluebird day when it is below freezing. I have seen my 2.2Kw array put out almost 4Kw and well over 60A at times.

This is just from watching the numbers in a day to day off the grid solar only home. I am also seeing similar but smaller numbers on the trailer.

Darkspeed · 08-17-2011, 11:10 AM

I have noticed that the older panels put out a lot more than rated. Some of the newer china panels output are overrated

tr0y · 08-17-2011, 11:40 AM

I don't think it is age, I would stay away from "most" of the China panels. I tend to buy Evergreen made in the US. If you know of a China made panel that is great quality I would like to hear about it.

Darkspeed · 08-17-2011, 12:16 PM

No china that I know of. I'm always willing to pay the premium for USA / German / etc... quality.

arodriguez60 · 08-17-2011, 01:09 PM

Looks like evergreen is moving to China

Wabbiteer · 08-17-2011, 02:07 PM

Depending on the panel types the voltage itself may not lower much but the total power output HAS to drop with heating - What type panels are you using?

I should've specified panel types - thin-film PV panels losses with heating are quite a bit less (-0.2%/°C), its physics of the expansion of the mono/poly crystaline silicon with heat that makes the exchange of electrons less easy so output drops. Solar water heaters can and do make steam (sometimes too easily) so its not a great stretch that the PV wafers in the panels itself can reach 100°C.

Count any sun at 100%: Panel sees 8-14% escaping in reflection or from glass surfaces (both inner & outer) and reflected away from wafer surface, then subtract energy converted to electricity 12-18% so already the 1000w per square meter sunlight means 68 to 80 percent of sunlight converted to heat - 680 to 800 watts heat having to be dissipated. (hot?)

Heat is exchanged three ways - convection, conduction and radiation.

The smooth outer surface of a PV panel is not a lot of area to bleed off heat into air, if the panels are getting a breeze that is a plus.

The glass and plastic of the PV panels actually are on the insulation side of the heat Conduction equation, some heat is carried away into the supporting frame work but very little.

So Radiation is where most of the PV waste heat is dumped - panels up away from any reflector that could bounce the Infrared back at the panel, and also not 'shining' on another panel to add to its heat load is best-effort design. That is the bad thing about panels on a travel trailer, to keep them aerodynamic and strong you're loosing by having the RV shell bounce the heat right back at the panels.

Something else is the rated power output, some OEM's are +/-5%, +10/-5% etc. so straight out of the box you could be dropping watts, but then normal aging also drops wattage so if the OEM ships low* output panels the likelihood of them having a warranty issue on them is higher. I believe Evergreen is minus zero tolerance on new panel output but that is likely advertising spin since their panels may suffer a little faster output loss over time versus other silicon foundry methods so its really just covering their own bases... BUT their 10-year limited warranty on materials is kind of rare in the Industry.

I have a mix of panels - some Sharps, Photowatts, Schott Solar and some Sun Electric 'house' brand. Most are ancient but the Sun Electrics are newer surplus German wafers with 21-23% conversion efficiency cells that are usually only sold 'in-house' by a packaged system installer (dark, almost black square cells w/ beveled corners and no front mounted conductor traces). If I had to start fresh I think the wafer efficiency and cheap price would win any argument which cells to buy as long as the panels did NOT have to be UL listed. I think they still have them and will mention German made cells but its been a while since I've followed them...