South facing vs East facing on very low slope roof

[dennydotco]

Hi there,
I have 26 ET solar 250 watt panels and Ironridge rails. This was part of a package I ordered from Wholesale Solar.

I'm in Phoenix, and my home has a mid-century low slope roof. Not quite flat, but under 20 degrees (I haven't measured yet).

I would like to mount them across the street facing south roof, but I have a nice big tree I don't want to cut back that far, and it shades the house well.

I have plenty of space on the east facing roof.

Would I be better off trimming/cutting down the tree and mounting south face, or taking a loss on power and putting it on the low slope east face?

How much would I be losing by putting it on the east side?

[russ]

You can play with PV Watts to see the difference in output

http://pvwatts.nrel.gov/

[domii]

I'm up in Ontario, Canada, so I don't get as much sun as you do. Like the above poster said, I'd take a look at the pvwatts calculator and see what it says. But from my own experience with my roof, I get pretty close performance as the east sun is stronger in the morning and makes up allot of the difference.

With my older Enphase D380 inverters, 199w max before clipping, with CSI 230w Mono panels, I generated the other day (average value per panel):

East facing 1.2 kw,
South facing 1.4 kw
West facing 0.9 kw

You could also use longer L-brackets on one side of the panel, to change the tilt more due South, (I believe ironridge also sells adjustable tilt legs). That would be a relatively inexpensive way to accomplish that.

Take a look at this picture of a rather neat racking system, that does an even better job (this guy is getting south facing on his east roof):

http://www.buildingenergyvt.com/assets/Uploads/Solar-PV/schumann-montpelier-solar-pv.JPG

[Naptown]

I'm up in Ontario, Canada, so I don't get as much sun as you do. Like the above poster said, I'd take a look at the pvwatts calculator and see what it says. But from my own experience with my roof, I get pretty close performance as the east sun is stronger in the morning and makes up allot of the difference.

With my older Enphase D380 inverters, 199w max before clipping, with CSI 230w Mono panels, I generated the other day (average value per panel):

East facing 1.2 kw,
South facing 1.4 kw
West facing 0.9 kw

You could also use longer L-brackets on one side of the panel, to change the tilt more due South, (I believe ironridge also sells adjustable tilt legs). That would be a relatively inexpensive way to accomplish that.

Take a look at this picture of a rather neat racking system, that does an even better job (this guy is getting south facing on his east roof):
http://www.buildingenergyvt.com/asse...r-solar-pv.JPG

except he wasted more than half the roof.

[Volusiano]

Hi there,
I have 26 ET solar 250 watt panels and Ironridge rails. This was part of a package I ordered from Wholesale Solar.

I'm in Phoenix, and my home has a mid-century low slope roof. Not quite flat, but under 20 degrees (I haven't measured yet).

I would like to mount them across the street facing south roof, but I have a nice big tree I don't want to cut back that far, and it shades the house well.

I have plenty of space on the east facing roof.

Would I be better off trimming/cutting down the tree and mounting south face, or taking a loss on power and putting it on the low slope east face?

How much would I be losing by putting it on the east side?

It also depends on whether you're on a TOU plan or not. If you are, the south facing roof will give you even more value because you'll be able to get more credit into the on-peak bucket as compared to your east facing roof.

A low slope roof would probably minimize the difference between south vs east placement.

Also remember that if you cut down or trim your shading tree a bit, the new additional heat beating on the house due to less shading now may negate any extra production you gain on the south facing roof. Also, you may have to continually keep your tree trimmed to keep the shade out. And if you don't, you may have to consider microinverters or SolarEdge optimizers on the roof to deal with the shading -> not a good idea to have electronics up on the roof in Phoenix, AZ.

Another consideration is aesthetic. If the panels on the east roof is not as visible as the street facing south roof, and you like to keep a low profile, the east roof scores some points there.