RE: Thought I would share4 Nov 2018 08:58
Thaba Hotel - of course the 15kW-75kWh VRFB that is there is rather small compared with the 100KWp (p='peak' power when illuminated with a standard of 1,000 W/m² ) of the PV array to which it is attached.
It is interesting work out whether the Thaba Hotel array ever outputs more than 100KW - i.e. is the solar irradiation ever greater than 1000 W/m2.
When averaged over a year with average weather the average daily sum of the power is known to be around 7 KWh/m2 for that region ( https://en.wikipedia.org/wiki/Renewable_energy_in_Africa#/media/File:SolarGIS-Solar-map-World-map-en.png ) At a guess we might expect to get an average of 8 KWh a day in summer and 6 KWh a day in winter (it's much closer to the equator than we are so the seasonal variation is much less)
The question is what is the distribution - if all this arrives in only a couple of hours then the peak intensity would be over 1KW /m2 - clearly the average number of hours when the sunlight is zero is 12 for all latitudes so the average number of hours when sunlight is falling on the array is 12 also - this may work out as maybe 14 hours in the summer, 10 in the winter.
If the distribution were triangular then the peak would be double the average. In this case the if we have to average 8KWh over the summer day but we've only got 14 hours to count to that, then the average in those 14 hours needs to be 8 / 14 = 0.57KW - the peak would be double this at 1.14 KW.
However we suspect that the triangular peak assumption is a bit too 'sharp' and the real distribution is going to have the top flattened off somewhat - this is going to reduce the peak to less than double the average , so 1.14KW/m2 of 114% of 'peak' PV power is an upper limit.
To get a precise answer you need to do all the analysis properly, which is not particularly illuminating if you will forgive the pun, but it keeps engineers in jobs.
There is an easy to use calculator here:- https://pveducation.org/pvcdrom/properties-of-sunlight/calculation-of-solar-insolation . Put in the latitude as -26 degrees, which is the latitude of thaba and you will find that the peak summer irradiation is about 1.03 kW/m2 - looks like our 1.14 kW was a pretty good initial estimate for the maximum, also see how the summer day is only 3 hours longer than the winter one - we estimated 4 hours.
Then put in a latitude of 51 degrees (London) and prepare to be surprised.
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