Question on solar array orientation

[RandomJoe]

In short, what is the effect on output if you have half of a solar system array facing south and the other half facing west?  Each half would be a series string of four panels, then those two strings would be paralleled and connected to a single charge controller.

I know for a voltage source (say batteries or power supplies) the lower-voltage one is going to do no work (or worse, rob from the higher) until it equals the output of the other.  But I don't remember how two current sources (such as solar panels) react when in parallel...!

Reason I ask, I've been bitten by the upgrade bug and bought four more panels for my system.  I have the room to mount the next set right below the first on the south face of the roof, but wondered about putting it on the west face of my roof instead for a couple of reasons.  

First, I was surprised to find when playing with the PVWatts calculator that while I get more wintertime power from a south facing array, I actually get more power overall (thanks to summertime production) from a west-facing array!  (So they say, anyway...)  

And second, I'm not looking forward to crawling into the attic area where the south face is at to install the braces for the racks.  It's going to be cramped and very dusty - if I could get away with staying in the much roomier area under the west face, I'd be happy! :-)

(If this double-posts, I'm sorry!  The forum is really giving me fits today...)

Thanks,

Joe

[dnix71]

I do that, too. In the winter a neighbor 2 houses away has a very tall tree that shades me in the middle of the day. The panels mounted south get very early light and the panels mounted west get the late afternoon sun.

I can't roof mount them because I don't own the place and the wind rules here won't allow for it anyway (the panels are non-UL).

[wooferhound]

It can depend on your afternoon weather too. If you live in Tampa Florida, it clouds up and rains every afternoon at 3:30pm so west pointed panels wouldn't do much good there.

[dnix71]

I was born and raised in Tampa. If it rains every afternoon, you should be happy. You all need the rain, otherwise you have to recycle your beer, or drink desal from the Bay.

The Sunshine State is sunny in the winter, not so much in the summer.

[stuie]

yeah this is not unheard of, pointing two smaller arrays in different directions instead of them all in the same direction, instead of getting one big power bulge in the middle it is a slightly lower but more sustained bulge see this guys page urlhttp://www.unisun.com.au/url

dunno if that link will work but just cut the middle out and copy and paste.

this installer seems to do it qutie a bit and a interesting site very excentric way

Stu

[DamonHD]

My grid-tie on my roof is split with two thirds on the east-facing side (with a bit of shading from a big tree at this time of year) and the rest facing west.

It does reduce total annual power generation a little (for my 23 degree roof pitch, by about 10%--20%) but I think it is more grid-friendly sending a longer flatter wedge of energy onto the grid.

For my little off-grid system I take whatever I can get on our tiny plot, including a few basically facing straight up to get the most from overcast conditions!

Rgds

Damon

[RandomJoe]

Well, in this case I'm probably better off with the west-facing array!  Seems most days we have overcast, the sun will peek out from behind the clouds toward the end of the day  Did that yesterday, in fact but, of course, the angle was too far west and low for the south-facing panels, only got to about 10% of capacity.  A west-facing array would definitely do better in the summer, when the sun is just about due west.  Not too sure how well they'd perform in winter, the sun is pretty much southwest at that point.  

I did some more browsing online, found some electrical theory sites that say two current sources in parallel will add, so that sounds promising.  May just have to do that.

Looks like my biggest problem now is getting the racks I need!  I was worried about the panels changing before I bought more (in fact the ones I bought have already changed, they are about 1/2" taller than before) but apparently the rack system I used has been discontinued!  Waiting to hear back from them, if they have something equivalent.

Guess that's another point in favor of building your own! :p

[Ungrounded Lightning Rod]

Morning overcast or fog and shadowing objects to the east are a classic reason for pointing your (non-tracking) array, or a section of it, more westward than due south.

Any given panel set will typically give you the most amphours per day by being pointed in the direction of the sun at approximately the middle of its unobstructed time.  (Or maybe a tad south, due to the longer passage of sunlight through atmosphere at times other than local noon.)

But if you have a surplus of generation you can trade some of it for a longer generation time by split-aiming.  This may get you more power total if you have a shortage of storage - and even if you don't, you'll reduce the depth of cycle on the batteries.

I'd go for extra capacity on the batteries and point 'em all south at the NV place.  But I'm about in the middle of a slight valley and have nearby mountains to the east and west that narrow the day.  I also have essentially no overcast there except for REALLY exceptional weather (high desert in rain shadow).  So the NV place is good for south-pointed panels.

At the CA place I've got some neighbors on the SE with high trees, and a schoolyard to the south and west.  So I'd probably point the panels a bit west to get the middle of the sun time.

[RandomJoe]

Finally!

After plenty of delays, I finally got the new panels installed yesterday.  First a long time in shipping, then a LOT of cold weather and snow (for us, anyway!) and even yesterday seemed like everything fought against me finishing the job...  (Most notably, the manufacturer sent me the wrong mounting hardware - AGAIN!  The bolts were too short for the clips that hold the panels on!  Grumble...)

I now have a total of 1080W STC / 760W PTC up, half facing south and half facing west.  Both sets are at an angle of roughly 35 degrees.  Winter insolation for this area suggests I should see about 5.4kWh/day (3.8kWh PTC) from an ideally positioned array, and I hit 2.8kWh today - that's even with some clouds bouncing the output all over the place and the system backed off around 2PM during Absorption.

Can't wait for a good clear day to see what my real peak currents will be.  Today it spent some time just before absorption at 14.3V / 52A.  That's 743W, so right at PTC which is promising.  The first set usually performs a bit better than PTC, although not as high as STC except on rare occasion.

Now to find something to do with my extra power!  (Yeah, like that'll be any sort of challenge...!)

Took a couple of pics just now.  The second one shows my weather station and one (of many!) ham radio antennas. ... Okay, the "Insert Image" button at the bottom isn't doing anything...  They are in my files, Panels-1.jpg and Panels-2.jpg in case you care to see them! :p