Solar Energy Perspectives - IEA

Solar Energy Perspectives: Buildings
relatively small solar collector fields, and building integrated or building adapted PV
production may offer viable options in a relatively large variety of situations in temperate to
cold countries.
Photo 4.6 Solar steam cooking system at Shiridi for 20 000 meals
Source : Deepak Gadhia.
Key point
Solar cooking works best for community kitchens in developing countries such as India.
Zero-net energy buildings or positive energy buildings will likely have on their roofs and
façades, whether very visible or concealed, both solar thermal collectors and PV collectors
(Photo 4.7). Solar thermal is significantly more effective in capturing the energy from the sun
(70% peak efficiency) than PV (20% peak efficiency), as long as the heat is effectively used
for heating water or space heating, directly or with heat pumps. These applications do not
require very large collector surface areas, so they leave enough room for PV systems, which
have the advantage of production being usable either locally or by distant customers, so it is
never wasted – an option usually not available for solar heat.
The photo also shows that the tilt angle of solar thermal collectors, identifiable by their
storage tanks, is greater than that of PV modules in the foreground. This maximises heat
collection in winter, when the sun is low on the horizon. This suggests that placing the PV
modules on the roof and integrating thermal modules in the façades could help maximise the
collection of solar energy.
Another option is to use hybrid photovoltaic and thermal (PVT) modules, which combine PV
generation and heat collection on a single surface. This can be done with glazed water
collectors or with unglazed air collectors mounted as “transpired walls” covered with a PV
layer on their sunny side (see Chapter 7). While it is unclear whether this combination works
well for both systems, as some manufacturers claim, it certainly extracts the most energy from
a given collector surface area and represents an interesting option when the available surface
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© OECD/IEA, 2011