Tracking parabolic PV

[Sparky01]

I currently am running a 350W panel rack with the simple satalite dish conversion with a redrok tracker. But a just found a deal on 11 75W PV panels and need more room.

I have been looking into some parabolic troth systems and wondering why I do not see more of these being used? (similar to these http://www.solar-trackers.com/solar_trackers.htm )  

My new (used) panels are 47.5" tall and I have several extra 20' tower sections that are 4' wide so the panels would bolt to the tower using unistrut. I would have very little fabrication invested in the frame and it would hold all 11 panels.

My second question is at what angle should the reflectors on each side be if I do go this route?

[Sparky01]

No one has an opinion?

[TomW]

Well, Sparky, I think you are just asking questions way beyond what most likely have hands on experience with.

That and most of the info is actually online already  like the declination angle for your latitude which is needed to tell you what angle to use.

Too bad Dwayne's 4 gigs of graphics per page site is dead or you could ask him how to use his tracker?

Common belief is that concentrators on PV are bad, too so there is that bit

Just an opinion.

T

[dinges]

Tom, I believe Sparky asks for the angle of the soft concentrators, not the declination.

The exact angle will depend on the concentration ratio (C) you desire. As you no doubt know, too high concentration ratios (2-3) cause overheating and damage to the PV panels.

I have done a bit of ray-tracing a while ago to determine the angle; there's no information to this effect to be found on the Poulek site. If I remember correctly, for a concentration ratio of 1.5 (a conservative, safe value I think) I ended up with an angle of 65 degrees.

I wanted to show you the sketch I had made so you could determine your own angle for the concentration ratio you desire. But alas, I have this nasty habit of doing such drawings/calculations on the back of a piece of paper that is usually entirely unrelated to the subject. So it got archived under a very different topic

But, I found a similar sketch I had made about 2 years ago which I have scanned and uploaded; hopefully this is useful to you (the part that's interesting to you is at the bottom right):

http://www.anotherpower.com/gallery/dinges/solar_concentrator?full=1

Notice that not only would it have to be the correct angle (64 deg. in my case) but also of the proper height, so it would shine on the entire area of the PV panel. Easiest thing would be to make a few sketches for yourself, remembering that for a mirror the angle at which a ray strikes it is the same angle at which it leaves the mirror again (Law of Snellius).

Turns out that for a concentration ratio of 1.55 an angle of 64 deg. would be needed.

Personally I like the Traxle design very much, along with its concentrator, and intend to build one in the future.

BTW, you may do a patent search as well; I remember several interesting patents of him coming up at the time as I was looking into it.

Hope this helps,

[jimjjnn]

Concentrators for PV aren't the best way to go as it causes deterioration of the PV cells . Lower output is the consequence which is the last thing you want.

New PV cells are being developed for concentrators that are a part of the cell is going on now. Requires different materials like Gallium Arsenide and other technology.

[Sparky01]

Thank you for the reply. Yes this is the info I was looking for. Ideally It would be great to build it in a way to use the parabolic in the winter and maybe on cloudy days.

Depending on which design to go with, the winter only approach (this is when there is little daily output) would be to install the mirror's or mylar or whatever when the temperature gets cool enough to keep the PV's from overheating (I live in Maine).

Or option 2 would be to have the mirror frame run from a linear actuator that would be run from a controler to limit the amp output.

[Clifford]

Some cells actually have higher efficiency ratings with concentrators.

I.E.  Not only do you get more light, but better efficiency of light conversion.

I'm not sure if this is true with all silicone cells...  but I did notice it as a comment with the Boeing/Spectrolab/Emcore Triple Junction Cells (which are expensive and tiny).  Presumably cooling is an issue that you have to deal with.

Also Note,

Rather than Parabolic,

You could consider a Fresnel Mirror.