PV-System, Power as function of View & Time

The Solar PV-system comprises a compact panel-array on the tilted roof looking East (= +115 degrees from North), in combination with a rather flat array looking South (= +205 degrees from North).
A panel-array looking West on the tilted roof would be a fitting supplement for full, daylong coverage, but considering it's viewing direction of -65 or (+295) degrees from North (and the shade from neighbour's roof from that direction) not a good investment.
This configuration provides PV-production as long as light is available.

The background for selecting this configuration?

Expected output-efficiency is related to the viewing direction, as indicated in this diagram, although consider also that output is variable with daytime & season.
According to this diagram the max. sun elevation has a variation between approx. 15 degrees on december 22 till approx. 62 degrees on june 22.
Mid-position is applicable in march and september.
Examples for PV-production on clear and sunny days around those dates.
PV_winter PV_mid PV_zomer PV_mid











Totaal = total, cumulative production this day from the whole PV-System (kWh)
Upper P / blue line = 1960Wp/Involar&SAJ-inverters, actual output (Wh) and achieved day-efficiency (kWh/kWp)
Lower P / red line = 2950Wp/STECA&Solis-inverters, actual output (Wh) and achieved day-effiency (kWh/kWp).
These 2 graphs have the following split-up of nominal panel-power over azimuth & elevation:

  • 1960Wp = 1530Wp to East/ elevation 55 degrees + 430Wp to South/ elevation 15 degrees ~ 80% / 20%
  • 2950Wp = 580Wp to East/ elevation 55 degrees + 2370Wp to South/ elevation average 15 degrees ~ 20% / 80%
This distribution and orientation shows in the graphs:
  • blue line has peak output at approx. 11:30 due to eastward orientation of it's panels
  • red line has peak output at approx. 13:00 due to southward orientation of it's panels
  • in midwinter the blue peak is higher than the red peak, because the low sun elevation better matches the higher panel elevation
  • contrary, in midsummer the red peak exceeds the blue peak, because high sun elevation well combines with low panel elevation
  • in spring and autumn the blue and red graphline are equivalent, mirrored.
  • the cumulation of blue line and red line always yields a broader (= less peaky) coverage than the individual segments
Due to installation history, with shifting of some panel-groups to get/test better positions, after several upgrades&modifications the 1960Wp-segment has a southward-component of approx. 20% and the 2950Wp-segment has an eastward-component of 20%.
Important is that the 20%-components have their own inverter, avoiding effects on the 80%-components!
Result: the peaking for each segment is not as clear as for segments which are 'purely' 100% aimed along a main line-of-sight: in this case, the 20%-component aimed in other direction slightly smooths the peak at the main line of sight, and generates a 'shoulder' at the offset line-of-sight.

Conclusion: looking South at one fixed elevation, with production peaking at noon is not the "one&only" solution to get year-round a good daily PV-production.
A combination of viewing directions (such as one segment Eastward and another segment Westward, or mixing segments aimed in various directions, with own inverter/segment) very often will provide a good (if not better) PV-production spread over the days and over seasons, due to a broader cumulative peak and the advantage of production running from sunrise till sunset.
The more uniform availablity of power over the day also means that consumption of PV-power more easily can be spread over the day.

September 1st, 2018 another 330Wp has been added to the group of 2950Wp => within that group 28% is looking eastward:
now cumulatively 2440Wp is pointing east and 2800Wp is pointing south.
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