Tilting Solar Panel

[ajriding]

I did a little experiment.

I have a new poly 100 watt panel. Before installing

I tilted the panel to face directly into the sun. 19.6 volts.

I tilted it the same angle, but away from the sun, so at a very bad angle to still have sun hit it. 18.4 volts, was not that less of a tilt to be 19.6 (1 volt less).

I tilted it to be in the shade, only ambient light. 17.x volts.

I don't feel so bad that the panels lay flat on the roof. The bad angle was about 5% less volts. Shade was 6.x% less volts.

The controller will drop the voltage down to 14 or so, but amps will still be lower, probably 5% too.

5-6% is not bad for being able to just lay the panels flat. I see RVers with rigs where they can angle the panels perfectly and get that 5%, maybe they need it.

Am I missing something?

[ktmrfs]

profdant139 wrote:
Interesting discussion! I wonder why home solar panels aren't built to track the sun -- they are almost always stationary. My guess is that the cost and maintenance of tracking outweigh the gain in extra power.

if the panels are facing south, and your in most of the U.S. normal roof pitch of 4/12 to 6/12 gives a pretty good angle to start with, so there isn't much to be gained. And if the panels are layed out to tilt very much you need to take into account a shadow of a lower panel on an upper panel. So in some cases, panel spacing needs to increase which decreases the number of panels so there is little advantage, possibly actually a loss.

Large arrays where area is not a big limitation often do have trackers.

[BFL13]

Itinerant1 wrote:
If you have room on the roof just add another panel or two. Chasing the sun with tilting would be a pain in the butt unless maybe you're using a ground deployed system and looking to do something during the day.

With 1,280w flat mounted,
Nov/ Dec will average 6-750w peak or 2.5-3 kwh +/- daily.
Jan/ Feb average 7-800w peak or 3.1-3.7 kwh.
Mar-Oct average 8-1,150w or 3-7 kwh daily.

With a ground tilted twirler, you only need to move it three times a day to get almost as much as a continuous twirl. After sunset to SE so it is ready in the morning before you get up, to S mid-morning, and to SW mid -afternoon.

You can just twirl it whenever you are going by the rig anyway, no special trips watching the clock needed. If you will be away all day, just aim it S before you leave in the morning.

People with a small portable set have been seen with the panel on a chair tilted, and they turn the chair toward the sun every so often. that gets the most from their solar.

It is all situational what is "worth it". It is easier if you are on a trip moving often, to have it all flat on the roof, and you don't have to park a certain way wrt the sun with the panels flat. (With a twirler same thing, but fixed tilt on roof you need to park so they aim South)

Stick house roof panels are tilted with the roof, and good luck if your roof ridge is E-W. Don't buy a house that is lined up N-S if you want solar on the roof!

[Itinerant1]

If you have room on the roof just add another panel or two. Chasing the sun with tilting would be a pain in the butt unless maybe you're using a ground deployed system and looking to do something during the day.

With 1,280w flat mounted,
Nov/ Dec will average 6-750w peak or 2.5-3 kwh +/- daily.
Jan/ Feb average 7-800w peak or 3.1-3.7 kwh.
Mar-Oct average 8-1,150w or 3-7 kwh daily.

[2oldman]

profdant139 wrote:
I wonder why home solar panels aren't built to track the sun -

If you have the bucks they do. The panels at the South La Posa LTVAs at Quartzsite do.

[profdant139]

Interesting discussion! I wonder why home solar panels aren't built to track the sun -- they are almost always stationary. My guess is that the cost and maintenance of tracking outweigh the gain in extra power.

[BFL13]

I also did some measurements. This was in May at 49N latitude, using a 130w panel where I was able to take all-day AH hauls over three days with the same perfect sun conditions.

Tilted up and also aimed during the day- 90AH
Tilted up fixed aim South- 70AH
Flat- 56AH

A second panel lying flat would be 56 x 2 = 112AH, more than the single panel tilted and aimed getting 90AH.

It is situational what to do about that. When we went there for a few years seasonal off-grid all summer with the 5er, I chose single 255w panel ground- mounted in a tilted, twirler contraption. With the MH, and not seasonal anymore, but still off-grid a lot, I chose more panels flat on the roof.

[red31]

ajriding wrote:
It would be interesting to see the amps change as the panel is tilted

set your meter to amps and redo!

takes very little light to yield voltage (Voc) but the current (I) is approx directly proportional to the light, in the graph, full sun perpendicular to the panel is ~ 1000 W/m2, panel operates @ battery voltage (PWM) or mppt voltage.

[TomG2]

Some good information here.

http://www.solarelectricityhandbook.com/solar-irradiance.html

[pianotuna]

Harvey51,

Thanks for that lovely morsel of knowledge!

Does that extend to infrared and ultraviolet?

I know my panels are "triple junction" to respond to 3 different frequencies of light.

And how come you know this stuff???? * chuckle *

[Harvey51]

The physics of solar energy is that the voltage (energy per charge) is determined by the colour of the photons hitting the molecules in the panel. V = hf where h is Planck’s constant and f the frequency of the light which determines the colour. Angle has no effect on the voltage. Each photon hits one electron transferring its energy to the electron. Angle does affect the current or number of photons that hit the panel, determining the number of electrons carrying solar energy.

[pianotuna]

ktmrfs,

Thanks for the correction on "constant voltage"!

Since I don't monitor incoming voltage which is nominally 33, the Blue Sky controller jumps from "off", to "on", at something above the overnight float voltage (which is depended upon how much I've drawn the bank down). It starts charging at 0.1 amps about 30 minutes after sunrise.

[ktmrfs]

pianotuna wrote:
Hi ajriding,

Thanks for taking the time to experiment and share it with us.

Solar panels are a 'constant voltage' device. You may loose 25 to 30% by not tilting. But NO WAY am I climbing the roof in a storm to stow the panels.

I'd consider a remote controlled tilting mechanism--but it is cheaper just to add another panel.

I trust folk's opinions when they have actually done an experiment, rather than guessing.

solar panels are not a perfect constant voltage device, but close enough for most first order calculations.

[ktmrfs]

ajriding wrote:
It would be interesting to see the amps change as the panel is tilted

been there, done that, what I found pretty much matches the math.

the drop in power is related to the cosine of the angle error in the vertical and horizontal plane. as an example if the error is 45 degrees, power drops to 70% of max. a 60 degree error drops power by 50%. depending on your latitude and time of year and time of day the error can be insignficant or noticeable.

And measuring voltage or current alone is NOT a good way to determine the loss. you need to measure both voltage AND current.

to get "perfect" alignment, place a tube, like an empty tp tube perpendicular on the panel and adjust for no shadow. easy to do on portable panels. almost impossible to do on roof panels since most only allow tilt in one axis.

and unless you have a tracking system, perfect alignment only lasts a short time. On my portable panels I just set them for best alignment around noon and live with what I get.

[ajriding]

It would be interesting to see the amps change as the panel is tilted