As mentioned in the information on PV Modules presented on the PV Features Page, the potential electrical power from a PV panel falls as the temperature of the panels rises. High panel temperatures are usually caused by bright sunshine; overall the high level of sunshine usually compensates for the temperatures de-rating of the panels and PV output rises with increasing sunshine levels. The interplay of sunlight and panel temperature and ambient air temperature is complex, however.
Actual panel temperature is recorded for a number of arrays at the St Lucia campus but the data is not yet accessed by the Live Data Feed. The Live Data Feed taps into ambient air temperature data and to a degree this can be used as a proxy for panel temperature. Furthermore, high ambient air temperatures reduce the transfer of heat gained by panels, from the sun, to the surrounding environment. For a given amount of incident sunlight, PV output will normally drop with higher ambient air temperatures.
Cool yet sunny conditions can occur in Brisbane, especially after southerly wind change has moved through SE Queensland. Such conditions along with a clear sky can be expected to produce high power outputs. The most dramatic effect of temperature can be seen when the sun breaks through on a cool, very cloudy day. As the cool panels are suddenly exposed to bright sunshine, the power output will soar.
This effect is well illustrated for the UQ Centre where the best power day in 2011 was the 18 October, which was generally a cloudy day but with the sun frequently breaking through for short periods (please enlarge the two thumbnail screen shots below). The weather records for this day show a good level of sunlight levels and the same pattern of broken cloud cover (for example, 9 December 2011), but these days had higher ambient air temperatures than in the 18 October 2011. The ambient air temperature when the peak power output was recorded on this day, was only 20.7° C.