Dual PV Array Orientation

[watermanhfl]

Hi,

Well my 10' windmill wet my appetite for RE so now I am doing solar PV, grid-tied.  Install has started and I have a debate going with a few locals.

Normally one would aim each of my two new 1,700 watt arrays due south but I like the idea of one 5-10 degrees East of south and the west one 5-10 degree west of south.  Forms a V facing south.

Idea would flatten the output curve over the day and allow inverter to run a bit cooler.  But would there be a net Kwhr gain for the day assuming full sun all day?

Qty 18 of the Evergreen 190's, 9 per 8" x 11' high poles.  To big to just turn them a bit later.

Tks for your thoughts.

Ant

[GaryGary]

Hi,

If its a fully sunny day, then a panel facing due south will always get more total solar radiation than one (or two) set slightly off south.  For 5 or 10 degrees the difference will be very small.

If your weather has any tendency toward cloudy mornings or cloudy afternoons, then you can gain somewhat in total radiation for the day by pointing the rig a little east or west of south so its centered on the sunny part of the day.

The first link on this page:

http://www.builditsolar.com/References/SunChartRS.htm

has a good paper that tells you what the best direction to point your collectors is for  different areas of the US.  It takes into account regional cloud patterns.

Its good as a general guide, but you should also take into account any local variations in cloud patterns you have.  If you look at the charts in the paper, its apparent that there is a pretty big window of bearings and tilts that all perform very close to the optimum -- that is, getting the tilt or bearing wrong by a few degrees is not going to make a lot of difference.

Gary

[TomW]

Gary;

Good points.

I would add that, if you have shading [I do, early] early or late, that favoring the sunny side may boost the total.

Cheers.

TomW

[watermanhfl]

Gary & Tom,

Tks for info.  Lots of reading.  I have no shading for 180 degrees so I am in good shape.  Pond on the East side so that may give a little boost.

Ant

[wpowokal]

With that size investment I would definatly track them, payback in half the time.

allan down under

[TomW]

Allan;

Uh, darn, I missed that elephant in the room!

I guess, to me anyway, tracking panels is a no brainer . I guess I just can't see a valid reason not to. Used to be lots of donor mounts [old satellite dishes]  and something like a traxle [tm] would be dead simple to build out of common stuff. I also know you pull in a good bit more than some stated figures online from tracking. Plus a handy person can build a tracker from common stuff or junk and so far I haven't seen a large number of successful homebrewed PV arrays. Lots of solar heat devices but making electricity is trickier.

 Thanks for pointing out tracking. To me cars have tires and PV arrays have tracking. Kind of goes without saying.

Just the view from "the trenches".

Cheers.

TomW

[dinges]

Tom,

I assume that anyone who invests in such a large amount of PV panels has done some research into it, including the options of tracking and soft concentrators.

I agree with your comment on satellite mounts (polar mounts) for PV tracking, they're abundant and free, begging to be used. I'm building a tracker right now using one:

However, for anything more substantial (more than, say, 100 W) I wouldn't go with a polarmount but with a Traxle, most likely with a soft concentrator (with only a limited concentration ratio, C=1.5 or so). The traxle mechanism seems simply, sturdy and durable.

http://www.solar-trackers.com/solar_trackers.htm

Have no idea about price; if I'd want one, I'd build it myself...

[TomW]

Dinges;

Well, my polar mount had a sticker on it "Maximum dish weight 1500#" so I had no concerns slapping 300 watts of SP75 Siemens panels on the thing. I hope to double that one of these days and will use the same mount with some additional framing to hold them.

Cheers.

TomW

[wpowokal]

When I built my last one a mate sugested using a LandRover front axel, well one side of. The ball joint gave you adjustment in both required planes, unfortunatly he got buisy so I built it the same way as the first one, but it may be an idea worth following up on.

Allan