CSI EPBB Calculator Question

[J.P.M.]

west is far better than east. east is not good - only gets the early morning sun and that's it. our 48 panels are on south-to-west facing, at 159 degrees and also at 249 degrees

Probably not correct. All things being equal, which they never are, production can be nearly the same for east or west azimuths symmetric about south. In the real world, at least in S.D. (for however real it is around here), taking all the pertinent weather variables, SAM and TMY3 data including temp., wind, irradiance, etc., west orientations have a slight advantage over east orientations with the optimum, depending on location about 5-10 degrees west of south. This appears to be due mostly to morning clouds. As in Slopoke's situation, shading usually plays a much greater role in determining optimum orientation, primarily for azimuth and thus for tilt as well if tilt options are available. As Volusiano points out, east may be better considering increased panel output at (assumed) lower panel temp. due to lower ambient temp. However, increased morning fog/clouds/mist patterns tend to mitigate some or all of that. Afternoons tend to be windier around here, and that probably lowers plate temps some. Hr./hr. simulations address some of this, but are still little better than an educated guess. - useless for any particular point in time, somewhat better for long term patterns. Shading is probably the much larger consideration in this and most applications where sunshine is abundant or more isotropic in a temporal way.

[silversaver]

The image is a satellite view of my house.



[ATTACH=CONFIG]3665[/ATTACH]

No wonder the installer choose SE than NW. You should put panels on the South and East other than West if necessary. Your East is better than West base on Sat image. That tall tree will have very little affect to your South facing array during Summer at late afternoon depends on how tall it was, but I don't think you should worry about it.

[Volusiano]

Bando, thanks for the reply. I'm wondering why two different installers are maximizing the roof area on the east roof, instead of the west roof. They are both utilizing all of the south roof, all of the east and overflow panels to the west. Strange.

I would surmise that the east facing production should be the same as west facing production, all things being equal, with ideal exposure, no shading issue, no morning fog, etc. But one thing not equal is that the morning temperature usually is cooler than afternoon temperature. And panels produce more in cooler temperature. So that would most likely be the reason why your installers prefer to place panels on the east roof over the west roof. Your neighbor's redwood may also make the installers apprehensive about putting the panels on the west roof. Shading will be an issue in the later winter afternoon.

Why does the CSI EPBB calculator say 270 azimuth produces more than 90 azimuth? Did you double check to make sure that the convention used by this calculator is the normal convention? I know in the SMA Sunny Design page, they use a different convention altogether: 0 for south, 90 for west, -90 for east, 180 for north. So make sure the CSI EPBB calculator uses the same convention as you think it does.

Did your installer ever ask you whether you're on any kind of TOU plan? If yes, and on-peak is in the afternoon (most likely), than a west facing orientation may give higher energy "value", even if the actual production may be lower due to higher temperature causing the panels to be less efficient compared to east facing.

[bando]

i see what you mean about hips and valleys! you have quite a lot of "sections" to work around

that redwood is pretty close and looks tall. is that neighbor slightly above you also

[slopoke]

those redwoods could still impact your production on the west, depending on how big they are and how far from your house. like silver was saying - anything can impact your production, even satellite dishes. and if by hips and valleys you mean like peaks in various roof sections, perhaps those have a lot to do with their proposal too.

The image is a satellite view of my house.



Roof Image.jpg

[bando]

those redwoods could still impact your production on the west, depending on how big they are and how far from your house. like silver was saying - anything can impact your production, even satellite dishes. and if by hips and valleys you mean like peaks in various roof sections, perhaps those have a lot to do with their proposal too.

[silversaver]

try this in 3 different directions. What are the actual azimuth and tilt?

http://pvwatts.nrel.gov/

Just remember, what ever towards the South will be the best if no shade. For example, my roof is facing SW 245, so I have to move top roll to the right side to avoid late afternoon shade from chimney.

[slopoke]

???? what are you saying?

Sorry, I gotta quit making posts while having a beer. I should have said that they are using the south roof area first, all of the east, and a couple on the west roof. My south roof is small because of the hips and valleys that require the setback, the east roof and the west roofs are similar in size, but the west has more hips and valleys, compared to the east. I don't have a real shading issue, just two redwoods in my neighbors yard at the south west corner of my house.

[silversaver]

Bando, thanks for the reply. I'm wondering why two different installers are maximizing the roof area on the east roof, instead of the west roof. They are both utilizing all of the south roof and overflow panels to the west. Strange.

It is depend on orientation of the roofs, chimney, shade...etc. Most of solar companies are pro, they know what will bring the max output for you

[slopoke]

west is far better than east. east is not good - only gets the early morning sun and that's it. our 48 panels are on south-to-west facing, at 159 degrees and also at 249 degrees

Bando, thanks for the reply. I'm wondering why two different installers are maximizing the roof area on the east roof, instead of the west roof. They are both utilizing all of the south roof, all of the east and overflow panels to the west. Strange.

[bando]

on a side note, east is a great place to put outdoor inverters. our inverters are on the east facing wall outside and are only in direct sunlight until about 10am.

[bando]

west is far better than east. east is not good - only gets the early morning sun and that's it. our 48 panels are on south-to-west facing, at 159 degrees and also at 249 degrees

[slopoke]

Ok, so I'm playing around with panel placement on my roof. I take a panel, inverter, plug in all of the variables and get an annual output for just one panel. I then change just the azimuth and then get an output. Is not the azimuth the way the panel faces? 0 degrees is north, 90 is east, 180 south, 270 west? If that is correct, why is a panel at 270 in the calculator producing more than the same panel facing 90? I thought an east facing panel produces more than a west facing panel. All of the panel placement drawings from the installers are using all of the south, east roof space and overflow is going to the west roof. Thanks in advance for any responses.