My Solar Installation in a Lil Snoozy - Page 3 - Fiberglass RV

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Old 08-25-2014, 07:37 PM   #29
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This great I've been thinking about how and where to place my flexible solar panel

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Old 02-23-2015, 07:44 PM   #30
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Name: Denny
Trailer: Lil Snoozy
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Solar Power Revisited

After four nights camping in a state forest campground with no services we used 50% of our 220 Ah battery capacity. We went back to my in-laws house for a night to recharge and are now back camping off the grid.

I was disappointed we had to leave to recharge the batteries as our experience last winter was that one sunny day would easily replace the energy we consumed over a 24 hour period. Last week, despite 3.5 of the 4 days being clear, we only able to offset about a third of our energy use with the sun.

It turns out that as with most technical issues, you have to do the math. I added the 100 watt solar panel just before we left for our trip out west to Texas and New Mexico. Our "solar" experience was in the desert - clear, dry, 5000' altitude, no trees to shade the roof of the trailer. Pretty much perfect solar energy conditions. Also we were camping off the grid the first week of April at Big Bend National Park so it's latitude of 29 degrees means the sun is 66 degrees above the horizon at noon. Here in Southern Florida at latitude 27 degrees the sun angle is 51 degrees in the middle of February. That angular difference means the horizontal solar panel got 20% more energy on our reference trip last April. Another factor is that April 5 is 12% longer than Feb 15 at this latitude. So date and location differences reduce the available solar energy by about one third.

The effect of the trees here is hard to quantify. I try to get the trailer in the sunniest spot but some shading is inevitable over the course of the day. Just a little shade kills the panel output so it's not hard to see how here in Florida in the February we are getting only a third of the solar battery charging we got last April in Texas.

I anticipated camping in partial shade and built a nice aluminum frame to support the solar panel on the ground at the best angle to catch the sun and have a 25' extension cord to give some ability to place the panel in the sun. We never had to use the frame last year in Texas and it was a pain to store so of course I left it home this winter. I built another cheesy plywood one a few days ago and we are using it now to see how much we can improve our solar performance by 1) keeping the panel in a sunny spot and 2) reaiming it every couple of hours as the sun moves from east to west. Compared to a flat (horizontal) panel one aimed at the sun at noon on this date and latitude will produce 30% more energy. The advantage is even greater as the sun moves lower in the sky. An experiment at 4:00 PM yesterday showed the panel aimed at the sun put out 5 times more energy than when it was flat on the ground.
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Our first day (100% clear sky) with the portable panel we were around the camp site most of the day and checked every hour or so to be sure it was aimed correctly and in a sunny spot. With this level of attention we were able to recover all the energy we used the previous night and finish the afternoon with a fully charged battery.

The second day (90% clear) we guessed where the panel should go at 9:00AM and left, so no adjusting until we returned at 2:00 PM. Then we moved to a more shady site but fussed the rest of the afternoon to make sure the panel was aimed at the sun. The battery meter showed -10 Ah at sundown so the panel provided about 75% of our days energy use.

The third day (60% clear) and still in the shady site we aimed the panel at 9:00 AM and didn't return until 5:00 PM. We were -32 Ah in the morning and -26 Ah at sundown so this day the panel provided about a third of our daily energy use.

The conclusion is that it's possible to fully meet our energy needs, even in the winter, with the solar panel if we can keep it aimed at the sun throughout the day. With the panel mounted on the roof four days camping used about 50% of the battery capacity. These three days camping with the solar panel in a portable frame used 20%.

Denny Wolfe

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Old 02-23-2015, 08:08 PM   #31
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Name: Dave & Paula Brown
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Denny, thank you for the detective work and the nice write-up. I went with 2 100 watt panels, and utilized the frontal curve of the Lil Snoozy to hopefully not have to use our generator. So far so good, but have only used it in the summer in Michigan and here in sunny Az this winter. We'll be traveling for 5 months this summer in various states, including the Pacific Northwet, so we will see how well it works out.
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Old 02-23-2015, 08:54 PM   #32
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One could always carry an additional portable panel, and hook it into the circuit only on days when more energy is needed to catch up. Of course the controller must be sized appropriately for the current; the SG-4 controller I have right now won't handle it, for example.
To every thing there is a season, and a time to every purpose under the heaven... --Ecclesiastes 3
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Old 02-24-2015, 07:32 AM   #33
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Trailer: '04 Scamp 19D, Tacoma 4.0L 4door, SB
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Solar power revisited

That is an excellent update on the solar panel usage. Solar is great when done right, and Denny is doing it right. He has shown that one has to be careful not to set his expectations too high. The cost of a panel will jump dramatically when automatic solar tracking is added. I am glad to see many people trying it out, but at the same time I am afraid a number of them might end up disappointed. As Denny said, do your math, and I might add, do *all* the math you can think of and be careful about all necessary assumptions. Still thinking about it and learning from others.

For example, I am disappointed about this one. I am an unwilling part-owner/investor in this installation, unfortunately:
Why not solar power??
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Old 02-24-2015, 09:29 AM   #34
Name: todd
Trailer: Casita liberty deluxe 17
New York
Posts: 64
VEry Nice Write up

Good Job, I added solar to my casita using the 30 amp version of your charge controller, haven't got to use it much but its fun. I did add a battery monitor which gives you real time usage and recharge. THis one doesn't have all the bells and whistles but the cost is reasonable.
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Old 02-25-2015, 07:50 PM   #35
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Name: Denny
Trailer: Lil Snoozy
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I miss-posted this on the linked thread above.

One other fact I've learned is that the 100w panel puts, at most, 67 watts into my battery.

I'm no expert, like most here I got my degree at Google U, but I think the main reason I get 67 not 100w is that the panel puts out 100w (5.7 amps at something like 18.5 v) and 25 degree C. My xantrex controller (not MPPT by the way) cuts that to 13.2 to 14.2 volts depending on battery state of charge. 5.7 times 14 is 80 w. The max I've seen on my BVM energy meter is 5.1 a at 13.2 v. That's 67 w.

I have 50' of 10 gage wire and two sets of connectors between the panel and the controller. I'm assuming the wiring and the controller resistance account for most of the loss between 80w and 67 watts. A black pv cell in the full sun is surely hotter than 25C. That reduces the output too.

I didn't get an MPPT controller because Google told me it would not produce very much extra power for the extra cost. The Xantrex unit let me adjust the three stage charging voltages to exactly what Trojan recommended.

Denny Wolfe

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