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

TomG2
Explorer
Sep 15, 2013
"Why is it even important?"

It may not be, to most on this forum, but for us who want to learn, it is very interesting. My friends spend a lot of money putting panels flat on top of their motorhomes. It would be interesting to see how their gain compares to panels tilted to face the noonday sun. My guess is that a somewhat smaller array would provide the same output. But, I am only guessing.
Almot
Explorer III
Sep 15, 2013
I forgot to ask - why is this even important?

A portable system, with the best tracking, won't supply enough AH for a comfortable generator-free life for most people. BFL is the living proof :)
Unless you are really into minimalist's camping, it will merely delay the point when your batts go flat and you have to run a genny or go home.

A roof-mounted system, even a flat one, has better chances to be a source of generator-free power except for situations when A/C is required. Any rig that is longer than 20ft, will have enough roof for that - you put more wattage than if it were tracking. Some adjustments in your energy habits and devices might still be necessary. Making it tilting, with a fixed tilt through the season, makes sense, if you camp for at least 2-3 days. I wouldn't want climb the roof more often then once a week, but maybe somebody else would. Making it 2-axis automatic tracking - possible, not very easy, I think you will be the first person on this board to do this.
BFL13
Explorer II
Sep 15, 2013
smkettner wrote:
RJ, you have an adjustable system.... why not measure the amps flat vs optimal tilted into some low batteries.

When I did the above posted tests, I used the Trimetric with only the solar across the shunt, and I had to leave lights on all day to keep the battery bank from charging up and skewing the results for the afternoon.

In fact, you only see a smaller portion of the "daily AH haul" that is available unless you are running loads to use those AH. Battery charging tapers off from:

- rise of battery SOC to near the "full" point at those low solar amps
-panel IV curve where higher panel=battery voltage reduces Isc.

The usual thing is for most of the action to take place earlier in the day till batteries rise in voltage. However, with a swivel contraption , you can get those morning results in the afternoon on days when it is clagged in for the morning and does not clear up till noon.
time2roll
Nomad
Sep 15, 2013
RJ, you have an adjustable system.... why not measure the amps flat vs optimal tilted into some low batteries.
BFL13
Explorer II
Sep 15, 2013
Snowman9000 wrote:
Tom_M wrote:
The simple thing to do is measure current with panels pointed direct toward sun then lay them flat and take another reading.

If you do that test at 8AM and again at noon, you'll get big differences in the results.

130w, mid-May, 49N

Time, Flat , Tilted, Tracking- Amps

0700- 1.0, 0.6, 3.7
0800- 2.0, 1.7, 5.7
0900- 3.6, 3.6, 7.3
1000- 5.1, 6.2, 8.1
1100- 6.3, 6.8, 8.2
1200- 6.9, 7.7, 7.7
1300- 7.2, 8.3, 8.3
1400- 7.1, 7.7, 7.7
1500- 6.4, 6.9, 8.1
1600- 5.0, 6.6, 8.1
1700- 3.9, 5.4, 7.3
1800- 2.0, 3.3, 5.7
1900- 1.0, 1.7, 3.7

Flat 56AH, Tilted 70AH, Tracking 90AH

Mid-day dips in tracking amps from only moving panel three times a day.
Almot
Explorer III
Sep 15, 2013
There is no exact answer. Depending on the latitude and time of the year, the gain with a 2-axis tracking (i.e. changing both azimuth and elevation) VS flat mount can be anywhere from 1.1 (i.e. 1.1 times more) to 1.7 (i.e. 1.7 times more). Less in Ca, more in Ak. Less in summer, more in winter.
time2roll
Nomad
Sep 15, 2013
Golden_HVAC wrote:
That solar system, while tracking helps produce about 25% more power than a non-tracking flat mounted panel, still is only going to make about 85 - 100 amp hours per day.

My 415 watt solar system will also make 120 amp hours per day, and that solar system is not that impressive. Mine are flat mounted, and I no longer take time to tilt them. When I would park either northbound or southbound, I could tilt the larger panels, and expect to get about 150 AH daily.

Now days it is less expensive to buy an additional pair of 150 watt solar panels ($350) than it is to install a tracking system on a 300 watt solar system (trackers cost about $2- $8 per rated watt in the 300 watt size range for home based systems that are mounted into a cement pole in the ground. I have no idea what that guy spent in hours and materials, as well as some sort of tracking system to control the motors that move the system, but I would not be surprised at $500. Under $250 would surprise me.

Fred.
Snowman9000
Explorer
Sep 15, 2013
Tom_M wrote:
The simple thing to do is measure current with panels pointed direct toward sun then lay them flat and take another reading.

If you do that test at 8AM and again at noon, you'll get big differences in the results.
Snowman9000
Explorer
Sep 15, 2013
I've been playing with my new portable panel setup. I don't have full data yet but my guess for your answer is 1.5x more watts flat to get the same watts produced in a day, in Illinois, near the autumn equinox.
Tom_M1
Explorer
Sep 15, 2013
The simple thing to do is measure current with panels pointed direct toward sun then lay them flat and take another reading.

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