If I have 200 watts on a polar mount now, and I track the Sun thru the day,....moving at least 3 - 4 times a day,......sometimes every hr if not doing anything any better, about how many watts would I need to do the same job w/ all panels laying flat on the roof ?(don't need no detailed long drawn out posts)

This question is unanswerable with the information given. It depends on the season and location. You'll get more further south (where the sun's angle of incidence on the panel is less), and you'll get more during the summer than winter (duh).From my single 115W panel laying flat on the roof, I've gotten anything from 8 amps (at Assateague in August) to 5 amps (in Northern Ontario in July) to 3 amps (at home in the winter).

I did measure my results with the 130w panel (it is all proportional, so you can work it out for your 190w) in May at 49N when tracking was moving it three times a day.Flat-56AHTilted aimed South all day-70AHTracking with fixed tilt-90AHYou can see that two of those 56s is 112--more than the 90. But that was in mid-May at 49NYou can't escape the details (the Devil is in the details!)When the sun is higher you get less difference between tilted and flat. Longer daylight time gives more diff between tracking and not. With the longer daylight you get more angle the sun goes around where it rises and sets more north of east and west up to 23 degrees more each side in June.So in March and Sep it is 180 degrees and in June it is 226. Dec gets you only 134. The sun moves around at 15 degrees an hour. (Earth rotation) So June gets you 226/15 = 15hrs, Dec is 134/15 = 9 hrs and Mar or Sep is 180/15= 12 hrsTilting is affected by the sun's declination changing that 46 degrees back and forth every six months too. That's 7.7 degrees a month to change your tilt. (about 2 degrees a week)When you move south for the winter, you get under a higher sun than up north but you still have the shorter daysIn summer with more than 180 degrees of sun travel sunrise to sunset, you get the problem that your rig casts a shadow part of the time when the panel is placed on the ground to the south side. This is why I put my first tracker on the roof so it could see all around

No long drawn out posts....I find flat mounted 560watts does me good, if I had room would go to 800 wattsIt all depends on your location time of year and loads Never have any time while camping or would even remember to move a portable panel

BFL13 wrote:I did measure my results with the 130w panel (it is all proportional, so you can work it out for your 190w) in May at 49N when tracking was moving it three times a day.Flat-56AHTilted aimed South all day-70AHTracking with fixed tilt-90AHYou can see that two of those 56s is 112--more than the 90. But that was in mid-May at 49NYou can't escape the details (the Devil is in the details!)When the sun is higher you get less difference between tilted and flat. Longer daylight time gives more diff between tracking and not. With the longer daylight you get more angle the sun goes around where it rises and sets more north of east and west up to 23 degrees more each side in June.So in March and Sep it is 180 degrees and in June it is 226. Dec gets you only 134. The sun moves around at 15 degrees an hour. (Earth rotation) So June gets you 226/15 = 15hrs, Dec is 134/15 = 9 hrs and Mar or Sep is 180/15= 12 hrsTilting is affected by the sun's declination changing that 46 degrees back and forth every six months too. That's 7.7 degrees a month to change your tilt. (about 2 degrees a week)When you move south for the winter, you get under a higher sun than up north but you still have the shorter daysIn summer with more than 180 degrees of sun travel sunrise to sunset, you get the problem that your rig casts a shadow part of the time when the panel is placed on the ground to the south side. This is why I put my first tracker on the roof so it could see all aroundGreat info' I made another print copy of a BLF post. Keep 'em comin'O$S

I don't know if my terminology is the same for us all.When I say "tracking the sun", I'm talking keeping the sun perpendicular w/ the panels, or maybe better defined as the panels shadow directly behind the dish ?I doubt that is the same as "tracking w/ fixed tilt"Is the difference coming into play here ? From what I have seen, I'm getting double the AH in a day by "tracking the sun", verses laying flat.When I go south this winter, I doubt I'll see those percentage numbers change by much. But maybe I have much more to learn.

Simple Solar Question (kinda of a Poll ?) | Good Sam Community

36 Replies

MEXICOWANDERER
Explorer
Sep 16, 2013
Flat versus tracking I figure 25-30% less amp hours daily. Close enough for thermonuclear targeting.
BFL13
Explorer II
Sep 16, 2013
Snowman9000, that is an interesting table. You can see what I was saying for here that "high noon" or meridian passage (they aren't quite at the same time but ignore that for this work) is between 1300 and 1330 when the sun is bearing 180 (South)

The angles work for the afternoon being a mirror image of the morning, but of course, in real life the afternoon sky isn't the same as the morning sky for how much sun you get. Often there is a morning haze that takes some time to "burn off" or some other difference.

ALSO-- I need to review my "8 degrees a month change of tilt" based on that altitude of 60.7ish for 15 May. That means Dec was about 19N close to about 23N for 21 June, and up from zero on 21 March. So Dec change can't be linear, which I never noticed before (no reason to notice that!)
Snowman9000
Explorer
Sep 16, 2013
Corrected data for Victoria BC 15 May 2013
GMT -7
Lat 48-25
Long 123-22

Peak sun is around 1300, as BFL noted.

Altitude Azimuth
(E of N)

h m o o
04:30 -9.2 47.3
05:00 -5.4 53.3
05:30 -1.2 59.0
06:00 3.4 64.6
06:30 7.9 70.0
07:00 12.6 75.4
07:30 17.4 80.7
08:00 22.4 86.1
08:30 27.3 91.7
09:00 32.3 97.5
09:30 37.2 103.8
10:00 41.9 110.6
10:30 46.5 118.2
11:00 50.7 126.9
11:30 54.4 136.8
12:00 57.4 148.2
12:30 59.5 161.2
13:00 60.6 175.3
13:30 60.4 189.7
14:00 58.9 203.4
14:30 56.5 215.9
15:00 53.2 226.8
15:30 49.3 236.3
16:00 45.0 244.6
16:30 40.4 251.9
17:00 35.6 258.5
17:30 30.6 264.6
18:00 25.7 270.3
18:30 20.7 275.8
19:00 15.8 281.2
19:30 11.0 286.5
20:00 6.4 291.9
20:30 2.0 297.4
21:00 -2.6 303.0
21:30 -6.6 308.9
22:00 -10.3 315.0
Snowman9000
Explorer
Sep 16, 2013
TomG2 wrote:
Thanks Snowman for this, "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."

I was curious as to the approximate efficiency with flat mounting versus tilted. Thanks for not trying to snow me (pun intended) with a lot of jargon.

You're welcome. I might be off because of putting the wrong time zone into the calculator. In that case maybe the answer is 400 instead of 500. But you get the idea. Even in the summer, BFL's results were close to 2 to 1.

edit: okay, I corrected my error. At 1030 and 1500, your ratio would be 2 to 1. At noon, 1.6 to 1. So I feel like 400 watts is a nice round answer to your question.
TomG2
Explorer
Sep 16, 2013
Thanks Snowman for this, "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."

I was curious as to the approximate efficiency with flat mounting versus tilted. Thanks for not trying to snow me (pun intended) with a lot of jargon.
Almot
Explorer III
Sep 16, 2013
Ok, here is a brief summary for those who don't want to calculate but need to know if tilt is worth the pain and how much to tilt and how often to adjust:
http://www.macslab.com/optsolar.html

See the tables for all-year optimum tilt, or for 2-season, or 4-season.

You can see that it depends not only where you are, but also WHEN you need this energy the most. If winter output is your biggest concern, then set it at winter angle. You will still get 0.9% of optimum in summer, but your summer output will be more than winter output because there is a lot more sun in summer. (Correction - with fixed winter tilt you will get 0.9 of WINTER output in summer, which is less than winter output).

You can also see - in the very 1st table - that while there is 25% improvement of annual output with 2-axis tracking over annual fixed tilt, there is only 4% improvement with 4-season adjustment over annual fixed tilt. But this is annual output.

Note that optimum tilt in these tables assumes that the panel is aimed South. For any other scenario they will calculate your optimum angle for pay.

It doesn't answer the question "how much more AH" you will get with tilt, or tracking, or both, VS flat panel. For that, you need to use the previously mentioned calculator.
BFL13
Explorer II
Sep 16, 2013
I think the 15 degrees you see a lot of, comes from an "average" declination between 23 and 0 degrees for those who pick a tilt and leave it there for months instead of moving it up or down by 8 degrees a month.
Almot
Explorer III
Sep 16, 2013
Snowman9000 wrote:
I'm going out on a limb and guessing you mean in mid-winter in south TX.

We are peaceful people, no hanging tonight :)

What he needs is a calculator like this
Click on the closest town in Texas. Enter 1 KW panel size (the calculator is for large home system, it won';t accept less than 0.5 KW value). Enter "fixed tilt" and either 0 degrees for flat or whatever the value is for a latitude tilt, or Lat+15 or Lat+20 for winter, or Lat-15 for summer. Compare the results for those months that yo are interested in. They will be in daily KWH/sq.m or monthly KWH, not AH that we normally use in RV, but this doesn't matter. He wants to know how much more the tilt will get him, so this is what it will.

BFL will sure chime in and say that all the science is cr-ap and only his measurements are the truth :) but for a very rough estimate I think this calculator should be given a chance.

And there are other data, statistical averages for 30 years of observation, including Texas among other places, but I won't mention those for the same reason as before.
BFL13
Explorer II
Sep 16, 2013
Snowman9000 wrote:
I used actual lat and lon, and entered 8 for hours west of GMT. Maybe should have been 9?

We are in +8 Standard time, so it is +7 on summer time. Also we are not in the middle of our proper (not political) time zone, but farther west, so our high noon is later. You can be up to 30 minutes out from that.
camperpaul
Explorer
Sep 16, 2013
Snowman9000 wrote:
I used actual lat and lon, and entered 8 for hours west of GMT. Maybe should have been 9?

CST is Z(GMT)-6.

CDST is Z(GMT)-5.