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Old 02-15-2003, 04:31 PM   #15
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I'll be on the lookout for your pictures, Kevin. Thanks. And thanks to mtbob for the reply. Are those 80W panels? And can I assume that you are using gel batteries? If so, do they fit in a slideout battery compartment? It sounds like you have the system I wish to end up with.
Brian
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Old 02-15-2003, 08:28 PM   #16
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Keep in mind if you're looking at solar panel ratings, that they are rated with a solar insolation of 1000W/m at a panel temperature of 25C (77F). That solar insolation occurs with the sun at 90 to the panel in both directions.

With a horizontally mounted panel, you'll only get that much solar insolation at solar noon on June 22 on a boat one degree south of Key West, Florida. This determines the current (amperage) output of the panel.

You'll also only get that low of a panel temperature with an ambient temperature below 50F, which isn't going to happen anywhere near Key West on June 22.

When you look at the spec sheets, use the 800W/m curve for amperage and the 45C curve for voltage, and you'll find a more realistic rating of the panel. Some manufacturers show a combined 800W/m and 45C curve.

Shell gives a realistic rating called typical data at Nominal Operating Cell Temperature (NOCT) conditions, i.e. 800W/m insolation (an average solar angle of 37 degrees away from perpendicular) and a 20C (68F) ambient temperature with a 1m/s (2.2mph) wind which should result in a panel temperature of 45C.

This spec sheet says that under real-world conditions, their "110W" SM110 panel is really an 80W panel, and if you divided that by the 16 volts, you get a 5A charge rate.

If you want to play what-ifs with insolation and see the effects of tilting the panels, go here.
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Old 02-15-2003, 10:32 PM   #17
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You're good help, Maurice -- Apples to apples makes sense. I didn't realize the potential for skewing panel ratings. It would seem that perfect tilt/no track capability would make 100% difference in winter. Now the issue is 'how much less than perfect gives how much benefit...' I see why people are just adding more horizontal panels.
Brian
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Old 02-16-2003, 07:36 AM   #18
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Tilt/tracking mounts are great when facing south, but that is not always possible. I beat this around a lot, finally decided the expense wasn't worth it and mounted mine flat. I would buy a charge controller that will handle future expansion, if you decide to add more panels later you don't have to upgrade the controller.

John
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Old 02-16-2003, 08:40 AM   #19
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Something I was surprised not to see in this thread was how good the constant charge is for lead acid battery's. Alowing the system to operate when the camper is not being used should extend the life of the batteries by years. Lead acid loves being charged and the constant charging prevent the plates for sulfating (layer of unproductive lead to form on the plates causing them to not hold a charge). This become very problematic at a low charge state. Even a small 3-5 watt set up will help with this when not in use and keep your batteires ready to go.
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Old 02-16-2003, 09:17 AM   #20
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Yeah... tilting depends on being able to have the panel oriented due south or real close to it. The odds of getting such a site are pretty low.

There are other things you need to look at too...

As big as my AS is, with the Fantastic Vent in the living room, followed by a skylight, followed by the air conditioner, followed by another skylight, and then another Fantastic Vent. there's not much room for panels. The two gaps that are there are a little short for KC120 panels, but could take SM110 panels.

What's really bad is the solar prewire. From the frig compartment on the curbside, it goes up and over the trailer to forward under the oven on the streetside, where the wires break for a controller, then forward around the front to the batteries. That's 32' of only 10 gauge wire, and by the time you'd go up from the frig compartment to the panels, add another 10'. The most current that 42' of 10 gauge would support, with a .5V drop, would be about 5A.

My choice would be to try to recable from the frig compartment, down under the trailer and forward to the batteries with heavier gauge cable. Or to use the factory prewire, wire the panels in series, butt splice the wires under the oven, and mount the controller by the batteries. There are more expensive controllers that take a multiple of 12V panels, with higher voltage and lower current, and step it down to 12V with increased amps.
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Old 02-16-2003, 12:19 PM   #21
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Brian,yes they are 80w panels. Solar Elect had a special on and provided them at the same cost of the 75's. The batteries are lead acid as they were already purchased and in use when we went the solar route. One is in the battery compartment and the other two are inside under one of the sofas on the street side.
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Old 02-17-2003, 12:10 AM   #22
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Thanks to all for replies... a picture is beginning to form!
Maurice -- how about stringing parallel or shorter route 10g and making the connections (fwd galley, refer comp and battery) with two 10g wires instead of the present one?
mtbob -- any problems w/ the under couch lead acid batteries... are they vented outside? If not what means are used to manage the H gas?
John -- I agree and see more benefits in the flat roof mount.
Brian
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Old 02-17-2003, 07:11 AM   #23
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Yes, one could run the two wires parallel for the + side and run a new - cable under the trailer. That would support two panels.

The batteries under my couch are in compartments that are only open to the outside. The door to that compartment isn't sealed tightly allowing the hydrogen to escape to the outside. The door is on one battery end, so on five sides the compartment is warmed by interior air.
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Old 02-17-2003, 08:56 AM   #24
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Maurice,
Any thoughts on the Maximum Power Point Tracking controllers (like the RV Power Products Solar Boost 2000E) ? Is there any value to these? I am going to install something this spring for our weekend dry camping trips to the MN Northwoods.
Thanks!
JC
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Old 02-17-2003, 10:56 AM   #25
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They use a DC to DC converter to step down the panel voltage a little to get a little more current at the charging voltage. This process is only about 80% or so efficient, so you don't see all of that gain.

The greater the difference between:

panel voltage minus voltage drop of the panel to controller wiring,

and

battery voltage plus voltage drop of the controller to battery wiring,

the more gain they give. And when this difference is small, they can actually lose a little charge current. Minimizing voltage drop of the cabling is critical with an MPPT controller.

The colder the panels, the higher their voltage, and the more gain an MPPT controller gives. They do better in March and Sept than in June, so they tend to help offset the loss of lower sun angle and shorter days a little bit.

The deeper the battery is discharged, the lower its voltage, and the more gain an MPPT controller gives.

Expect a 5-15% gain in the real world, depending on time of year, except when it's hot outside, when you might see a slight loss.

The SB2000 is only a two-stage charger with a bulk mode and 14.0V constant voltage mode to do the last 10%. Odds are you'll run out of daylight before the 14.0V mode gets much above 90%, and the evenings use will take it down well below that, so it won't be the battery-boiling problem that this voltage might lead you to believe it would. That would be a problem with a 24 hour converter though.

MPPT controllers are probably a good idea unless you mainly camp where its really hot.
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Old 02-17-2003, 06:10 PM   #26
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Maurice -- I'm in awe... I need to plug one ear so that all of this info doesn't spill while I'm getting more!
The 120W panels that a vendor described to me were said to be 60x28x4". Quick measurements (it's raining again) look like I've got that and a little more between AC and FF roof vent. Could mount two it seems.
So about these MPPTs... if you treat your batteries the way they like to be treated (no deep discharge) by conserving, generator, alternator or large battery bank use, are they a good investment? If so, recomment one or two. If not,recommend a preferable controller. In other words, what's Maurice's ideal setup? Thanks.
Brian
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Old 02-17-2003, 06:58 PM   #27
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flexible panels

I purchased 6 120w flat panels based on measurements taken from the roof of my 1981 28' Excella motorhome. Before installation was begun it became apparent that the final result would be Coyote ugly. I went back to the internet and found the following sources for flexible panels. They are less efficient than the flat SCC cell panels but would look much better because they would conform to the Airstream shape. By the way; the flat panels have never been installed and are for sale.

http://www.solaraenergy.com/Solara_E...duct_List.html

http://www.gosolar.u-net.com/flexibl...s_Unisolar.htm
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Old 02-17-2003, 08:18 PM   #28
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From measurements I took on the roof, I don't think two 28" panels side by side and flat would look very good on the curved roof. In fact, I think they'd be ugly. I don't want the panels visible. I'd want the center about 2" off the roof for cooling, so they'd be really high off the roof 28" on either side of center. You could mount them in an inverted V, but then one panel would be tilted toward the sun and the other away from it. In that case, I'd want them hinged in the middle so that you could lift the panel on the far from the sun side and tilt it to match the tilt of the other panel.

About the most flat panel width I'd want to have would be 40" and three 13" wide Shell SM55 would fit within that. I'd have room for two banks of three of those, and I'd wire them for 36V and 2.5A in each bank, and feed their 180W/5A to a Solar Boost 6024 that can step down 24, 36, or 48 nominal volts to 12V batteries... maybe get as much as 60-75AH/day out of this.

Alternatively, the Kyocera KC80 are 38" long by 25.7" so two would mount sideways in about 52" of length. I could get four in series for 48V at 4A (192W), but the reality is that peak voltage could be as much as 68V, exceeding the 50V rating of the prewire. Or in series parallel for 24V at 8A but that's more than I'd want to run through my long prewire... one could get maybe 65-80AH/day out of four of these. And four of these at $1342 plus shipping are a lot cheaper than 6 of the SM55 at probably $1650.

If I redid the solar wiring with shorter, heavier cable, I'd probably go for a Solar Boost 2000 if money was a factor.

But for this much money, I'll buy two Honda EU2000s and have air-conditioning.
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