Good question. I simply did some googling for comparative efficiency per unit area between PVC and solar thermal -- the 3x factor seemed to come up regularly

Good question. I simply did some googling for comparative efficiency per unit area between PVC and solar thermal -- the 3x factor seemed to come up regularly from different sources. The kWh/m2 was the unit most of those sources were using. Time of day is very interesting, as PVC's are going to be useful earlier in the day, and solar thermal can still be providing good power output well after sunset. Consequently, in practice, I'd see a combination of both technologies (combined with good storage and grid capabilities, etc) as being most effective way of harnessing sunlight in the short to medium term. Averaging over a year ... geo / climate variations (eg distance from equator, monsoon cycles, etc) are likely going to affect both technologies similarly.