Simple Solar Question (kinda of a Poll ?)

I used actual lat and lon, and entered 8 for hours west of GMT. Maybe should have been 9?

Don't forget that my table posted above was on "fast time" so 1300 is "noon." However another wrinkle is that the sun is near its highest at "meridian passage," which is not "noon" by the clock.

So now you have the difference between your time zone "noon" (taken from the middle of your 15 degree time zone-not your real time zone either, but just by dividing up 360 evenly) and where you actually are within that zone by longitude.

So where we camp, actual "high noon" (ignoring that bit about "high" and "noon") is more like 1315, because we are farther west than the middle of our time zone.

So to move the panel at equal intervals either side of "noon" for us, means move it at 1145 and 1445 so we get three hours in the middle.

My table posted above does not reflect that very well, because I was moving it too soon (based on 1300 as noon) in those days, before I smartened up and remembered my navigation training :)

smkettner wrote:
RJ, you have an adjustable system.... why not measure the amps flat vs optimal tilted into some low batteries.

I have done that several times, and under several conditions, and using kinda crude measurments, I always come up w/ the same conclusions,..... that I would need near double the watts if laying flat....zero track/tilt. But I am "true tracking", not just tilting. My mount has skew built into it so I can track the sun's arc at any time of the year, and any place.
Purpose of the question, to gather others thoughts on it. But it seems there are few if any doing "true tracking" except those that are prop tracking w/ portable panels.

BTW if anyone wants to play the same game with BFLs readings, here is the solar altitude chart for his data. First number is altitude, second is azimuth, which is of no concern. Let's hope it formats somewhat.

05:00 3.4 64.6
05:30 7.9 70.0
06:00 12.6 75.4
06:30 17.4 80.7
07:00 22.4 86.1
07:30 27.3 91.7
08:00 32.3 97.5
08:30 37.2 103.8
09:00 41.9 110.6
09:30 46.5 118.2
10:00 50.7 126.9
10:30 54.4 136.8
11:00 57.4 148.2
11:30 59.5 161.2
12:00 60.6 175.3
12:30 60.4 189.7
13:00 58.9 203.4
13:30 56.5 215.9
14:00 53.2 226.8
14:30 49.3 236.3
15:00 45.0 244.6
15:30 40.4 251.9
16:00 35.6 258.5
16:30 30.6 264.6
17:00 25.7 270.3
17:30 20.7 275.8
18:00 15.8 281.2
18:30 11.0 286.5
19:00 6.4 291.9
19:30 2.0

Calculator I used

TomG2 wrote:
I guess I don't know how to ask a question. Will a 200 watt portable array that is aimed at the noonday sun in a place like South Texas be the equal of a XXX watt system laying flat on the roof? I am not asking for exact numbers (those seem to be nearly impossible to come by anyway). Forget about the difficulty in propping up the panels, I need the exercise and own a generator.

I'm going out on a limb and guessing you mean in mid-winter in south TX. So I went to a sun position calculator. I put in Vancouver BC for May 15, and Mission TX for Jan 15. Then I looked at the amps that BFL got for certain sun angles that I could use on the Mission chart.

I didn't go to the trouble of plotting it out and adding it up, but my educated guess is that 200 watts tilted and moved (tracking) 2 or 3 times during the day in Mission on Jan 15 would be about the same output as 500 watts or more, flat.

Examples: BFL's 0800 reading would be your 1030 and 1500 readings. At those readings, 200 watts of tilted panels would equal 570 watts flat.
Your 1200 noon reading would be BFL's 0900. At noon, your 200 watts of tilted would be equal to 400 flat. That's about as close an answer as you'll get, I think. If you want a different date, just say so. Mid winter is worst case for flat panels, and best case for tilted & tracked.

TomG2 wrote:
I guess I don't know how to ask a question. Will a 200 watt portable array that is aimed at the noonday sun in a place like South Texas be the equal of a XXX watt system laying flat on the roof? I am not asking for exact numbers (those seem to be nearly impossible to come by anyway). Forget about the difficulty in propping up the panels, I need the exercise and own a generator.

I thought I posted way back that two 130s flat at 56 AH/day each makes 112AH, where the one 130w tracking gets me 90AH. What are you really asking? it is all proportional BTW so you can do a bit of math on that to get the equals.

EG. to get the same as 90AH from one 130w tracking, you would need 90/56 x 130 = 209w lying flat

Almot, that is exactly right! I have posted elsewhere that you can end up floating between 12.3 and 12.5 as your "morning voltage," which will make it look like you don't need to run gen, but it will kill your batts eventually.

Of course running gen won't help, because you can't run it long enough to get to 100%-- you must get some shore power.

You can try to do the split bank trick for equalizing with solar ever month or so, if you have a set-up for that, which will let you "get away with it" longer, but sooner or later you need some serious shore power time to "recover" before you can dive back in off-grid.

I guess I don't know how to ask a question. Will a 200 watt portable array that is aimed at the noonday sun in a place like South Texas be the equal of a XXX watt system laying flat on the roof? I am not asking for exact numbers (those seem to be nearly impossible to come by anyway). Forget about the difficulty in propping up the panels, I need the exercise and own a generator.

Learning is good for brains. Keeps them off the Alzheimer.

Individual goals vary. Once and again people are asking about simple 100-200W system that has to be portable because they are not ready to take the drill to RV roof yet. But such a system will have a lot of cons, be it with or without tracking. In the end, it could keep you afloat for a few days in the boons, if this is the goal. Then a proper 120V or generator charging will be needed anyway, even if you manage to stay above 50%, because very-very likely a small system won't charge the batts to more than 80-85% by the evening.

I have tried to post what really happens the way we do it in various situations but people have to interpret those results for how it might apply to their own situations.

One point however, is that I do not regard the generator as a necessary evil. I love my Honda 3000 and my 100a PowerMax charger! In fact, one thing with the solar going , is how seldom I get to use those neat things. Several cloudy days in a row kills the solar, so now I get to use my other toys! :)