Shading rooftops with solar panels

Another well-known argument for rooftop solar panels is that they help cool buildings through the shade that they provide.  Anthony Dominguez, Jan Kleissland Jeffrey C. Luvall of UCSD and NASA recently published a paper in Solar Energy “Effects of solar photovoltaic panels on roof heat transfer” in which they claim (via minor testing and a heat flux model) a 5.9 kWh m−2 (or 38%) reduction in annual cooling load as well as some (not quantified) reduced thermal stress on the roof.  The effect of the wind circulating under the panels is part of this energy savings.
The panels also reduce warming the building in the winter during the day, but the paper claims there is a compensating reverse “blanket” effect at night.  To me, it is a little counter-intuitive that the blanket effect would totally compensate for the loss of winter warming, especially taking into account the additional cooling effect of wind blowing under the panels.
The bottom line is a quantification of the additional energy savings, which they calculate at about 5%.  This 5% was for San Diego, but I would expect similar savings for most regions that use solar panels.
They used PV panels which I assume were fixed inclination.  I would imagine CPV panels with a dual axis tilt mechanism would yield slightly better shading effects, but the extra energy savings might be negligible.
It would be nice to have a statistical study of this extra savings over a large number of buildings and a large number of geographic regions.
-gayn
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