Shading?

[wstevew]

East west split 90 degree azimuth 2 strings of 8 suntech STP240S-20Wd, SB4000TL-20, Roof pitch is 22.5 degrees.

Afaik the only shading is on the east side is a soil pipe that casts a shadow across 1 panel as the sun rises but im pretty sure it soon goes as the sun comes up.

Over the last two days sunny apart from today until approx 9:30am, I have noticed a dip in production around 10:30am to 11:15.

I haven't been around during the day to look for shading but at that time the sun should almost be at its highest.

Production not bad considering east/west 6.5kwh 02/02/2012 and 6.03 03/02/2012




View attachment 10490
02/02/2012 10.20.00 0.768
02/02/2012 10.25.00 0.792
02/02/2012 10.30.00 0.816
02/02/2012 10.35.00 0.816
02/02/2012 10.40.00 0.816
02/02/2012 10.45.00 0.816
02/02/2012 10.50.00 0.804
02/02/2012 10.55.00 0.816
02/02/2012 11.00.00 0.804
02/02/2012 11.05.00 0.804
02/02/2012 11.10.00 0.888
02/02/2012 11.15.00 1.020
02/02/2012 11.20.00 1.032
02/02/2012 11.25.00 1.068
02/02/2012 11.30.00 1.092
02/02/2012 11.35.00 1.104

View attachment 10491

 

[SolarCity]

It's not quite a dip in production - more of a plateau.

It seems to be fairly constant which makes me wonder if it is an issue with the MPPT. Is it like this on every day?

 

[wstevew]

I notice it only on the best sunny days. I could try global peak but if not clear tomorrow would have to wait for a good day.

 

[wstevew]

2 more sunny days in January, (apart from that dirty great cloud on the 15th!)

 

[FB.]

If one array faces East and one West.........an hour or two either side of lunchtime, the sun will be shining onto the metal edges of all the panels and not much onto their faces - especially given their relatively flat pitch of 22.5 degress.

As the sun gets higher in the sky in summer, the sun will no longer shine onto the South metal edge of the panel, but will shine from above-but-to-the-side and should be harvested reasonably well.

Or, more precisely, hour-by-hour relative sun position to your panels at this time of year:

8-9am:
60degress below your East panels.
30degrees to the right of your East panels.
West panels in shade.
East panels probably at 25% capacity.
West panels probably at 5% capacity.

9-10am:
50degrees below your East panels.
60degrees to the right of your East panels.
West panels in shade.
East panels probably at no more than 30% capacity even with clear sky.
West panels probably at 10% capacity.

11am-1pm:
Sun shining onto the edge of both East and West arrays, but barely striking the face of the panels.
East panels probably at no more than 15% capacity even with clear sky (10% capacity with cloud).
West panels probably at no more than 15% capacity even with clear sky (10% capacity with cloud).

1-2pm:
50 degrees below your West panels.
60 degrees to the left of your West panels.
East panels in shade.
East panels probably at 10% capacity.
West panels probably at no more than 30% capacity even with clear sky.

3-4pm
60 degrees below your West panels.
30 degrees to the left of your West panels.
East panels in shade.
East panels probably at 5% capacity.
West panels probably at 25% capacity.

 

[wstevew]

I can see where you are comming from, but would i not expect to see the plateau on the west side too?

I always thought of an east west system as 2 curves (overlapping) one for each array and when you merge them you get a lower peak than south but for longer time.

But if i have got it right your suggestion is that in winter the curves for each array would have a dip in the centre due to the sun being so low.

 

[methley]

Here's what my system is up to. This is a plot from yesterday, a perfectly sunny day. One panel is east, one west and one south. It's fairly obvious which is which! All panels are about 42deg.

 

[FB.]

methley

Yes, I'm seeing from others' arrays that East-facing or West-facing only generates about half the output of a South-facing array, while a SouthEast or SouthWest generates about three-quarters of a South-facing array.

The difference is more pronounced at this time of year because the sun rises in the SouthEast and sets in the SouthWest. By summer time it will rise in the NorthEast and set in the NorthWest, so the East and West-facing panels will mostly catch up when summer arrives.

 

[wstevew]

Pretty much what I expected, but with mine I would expect a more of a crossover due to the 22.5 degree pitch.

 

[wstevew]

Solar Azimuth

 

[SolarCity]

methley

Yes, I'm seeing from others' arrays that East-facing or West-facing only generates about half the output of a South-facing array, while a SouthEast or SouthWest generates about three-quarters of a South-facing array.

The difference is more pronounced at this time of year because the sun rises in the SouthEast and sets in the SouthWest. By summer time it will rise in the NorthEast and set in the NorthWest, so the East and West-facing panels will mostly catch up when summer arrives.

We're finding East/West systems performing at around 60% of a South facing system between Nov-Jan. You're right that the system does catch up in the summer. Depending on the pitch, they should be performing at around 80% of that of a south facing system over the course of the year.

 

[wstevew]

When I did the calcs my system had an estimate of 2800 kWh/year and would be an estimate of 3400kWh/Year for south. 82%

 

[wstevew]

Enabled Optitrak global peak and first clear day since.



11/02/2012 10.00.00 0.852
11/02/2012 10.05.00 0.864
11/02/2012 10.10.00 0.864
11/02/2012 10.15.00 0.900
11/02/2012 10.20.00 0.960
11/02/2012 10.25.00 0.984
11/02/2012 10.30.00 1.008
11/02/2012 10.35.00 1.020
11/02/2012 10.40.00 1.044
11/02/2012 10.45.00 1.068
11/02/2012 10.50.00 1.080
11/02/2012 10.55.00 1.128
11/02/2012 11.00.00 1.140
11/02/2012 11.05.00 1.176
11/02/2012 11.10.00 1.188
11/02/2012 11.15.00 1.224
11/02/2012 11.20.00 1.224
11/02/2012 11.25.00 1.272
11/02/2012 11.30.00 1.284
11/02/2012 11.35.00 1.332
11/02/2012 11.40.00 1.320
11/02/2012 11.45.00 1.344

Although there appears a slight plateau on the graph, more even i think.