This is further to my post regarding Roof pitch and orientation. I did a comparison over 7 days of my system to those of 2 friends of mine who have the same inverter and panels - one friend has 2 extra panels than my system. The results are in the attached spreadsheet (Excel 2003 version). Wondering if anyone has any ideas on the readings - the 3 of us have decided to compare again in summer to see what the results are then.
Hi Tony G. I've done some calculations for your 3 systems presented, assuming Sunshine Coast at 27 deg South and the Winter solstice, which is close enough for the dates you mention. I have had to apply a derating factor of 0.73 to bring my theoretical calculations close to the observed (I have averaged over the observed days but removed obviously low values - possible cloud). My calculations include BOTH pitches for Tony G.
Have a look at the included figure.
Calculations of System performances for the Sunshine Coast.
PV_Comp.jpg (26.75 KiB) Viewed 2458 times
This shows Dave C's data re-scaled to 30/32 to bring the system size to the same as the others. Note the observations in comparison with eachother and their respective calculations.
(1) All 3 are low in the afternoon (2pm) relative to theory. Maybe the sky is hazy in the afternoon? (2) Tony G's is low for all 3 times while Tony M's is good for 10am and 12pm. Dave C's is good at 10am but low at 12pm. (3) The different orientations and tilts have a large effect. As expected, Tony G's favours the afternoon (29 deg W) while Dave C's slightly favours the morning (12 deg E) and is noticeably higher due to 30 deg pitch. (4) The original comparison at 10.55am was most unfair to Tony G's system. (5) A better time to compare is from 1-2pm, when all systems (Dave C's X 30/32) should produce about the same.
A better comparison than hour-by-hour is the daily kWh produced. My calculations give approximately: Tony G: 8.1kWh Tony M: 8.6kWh Dave C*: 9.3kWh. These all assume no cloud. Perhaps Tony G can get these readings from the systems and compare?
It would be interesting to add a 4pm observation to compare when Tony G's system should be outperforming the others. This might also shed some light on why the systems seem to output low at 2pm. Happy reading. c*p