Solar Energy Perspectives - IEA

Solar Energy Perspectives: Buildings
Day lighting
“Day lighting” describes the practice of maximising during the day the contribution of
natural light to internal lighting. The difficulty is to provide ambient light while avoiding
glare, and also overheating the buildings’ interiors. Day lighting may use windows of
many types, skylights, light reflectors and shelves, light tubes, saw-tooth roofs, window
films, smart and spectrally selective glasses and others. Hybrid solar lighting, developed
at the Oak Ridge National Laboratory in the United States, links light collectors, optical
fibres, and efficient fluorescent lights with transparent rods. No electricity is needed for
daytime natural interior lighting, but when the sunlight gradually decreases fluorescent
lights are gradually turned up to give a near-constant level of interior lighting.
Lighting represents an important share of electricity consumption in industrialised
and emerging economies, but also important costs to consumers in least-developed
countries (IEA, 2006). Solar light is naturally a prime candidate to replace daytime
artificial interior lighting (see, e.g., IEA-SHC, 2000).
Active solar space heating
Active solar space heating requires more complex installations based on solar collectors of
various types and some storage (see Chapter 7). Unglazed air or water collectors can be used
as “solar walls”. They offer a transition between purely passive and active systems. Combisystems
covering a larger fraction of heating loads (as well as water heating loads) may
require collectors from 15 m 2 to 30 m 2 in Europe. Heat costs about USD 225/MWh to USD
700/MWh. The cost-effectiveness of solar space heating systems does not only depend on
solar resource, but also on the heat demand. In France, for example, space heating systems
offer better economic performance in the east or the north while solar water heaters are more
profitable in the south. The most cost-effective applications are usually found in mountainous
regions or countries, such as Austria and Switzerland, where reduced atmospheric absorption
of solar energy drive up both the heating loads and the solar resource. Only in Austria and
Germany has the share of combi-systems in single-family houses recently exceeded 50%
among all newly-built solar thermal systems. It has exceeded 70% in Spain, but only for
multi-family dwellings.
At country level, recent experience suggests that costs are reduced by 20% when the
cumulative capacity doubles, according to the European Solar Thermal Industry Association.
The technology is still improving rapidly in many applications, and most national markets are
still immature, leaving ample room for cost reduction. The costs are expected to decline by
2030 to USD 140/MWh th to USD 335/MWh th for combi-systems, and USD 40/MWh th to
USD 70/MWh th for large-scale applications (>1 MW th ). Cost reductions will come from the
use of less costly materials, improved manufacturing processes, mass production, and the
direct integration into buildings of collectors as multi-functional building components and
modular, easy-to-install systems.
Active solar heating faces an intrinsic difficulty: over the year, the demand for heat is in inverse
proportion to the availability of solar energy. Solar collector yield is maximum in summer and
minimum in winter (Figure 4.5). The higher the intended coverage of the heat demand, the
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© OECD/IEA, 2011