Solar Energy Perspectives - IEA

Solar Energy Perspectives: Solar heat
The most simple devices, so-called “unglazed collectors”, used for example to warm the
water of swimming pools (mostly in Australia, Canada and the United States) or outside
showers, are just black hoses lying on the ground or attached to the shower structure.
Unglazed systems can also warm the air (see below under flat-plate collectors).
For higher temperature applications, including ensuring the availability of sanitary hot water,
one must use flat-plate collectors or evacuated tubes. Advanced flat-plate and compound
parabolic collectors (CPC) allow working temperatures of 100°C to 160°C. Concentrating
collectors (Fresnel, parabolic troughs, dishes and towers or central receivers, ovens) allow
much higher working temperatures – up to 2 500°C. Figure 7.1 illustrates various uses of solar
heat and their respective levels of technology maturity.
Figure 7.1 Various uses of solar heat at different technology maturity
Market development
Small solar water heaters
Solar water heaters
for multi family houses
District heating
Solar space heating
Facade integrated systems
Sea water desalination
Industrial applications
Solar cooling
Time
Research and
development
Source: Weiss, 2011.
Early market
Mass market
Key point
Solar water heating for domestic use is the most wide-spread application.
Flat-plate collectors
Flat-plate collectors are appropriate for lower demand hot water systems. They are also often
more appropriate when snow accumulation is a problem, because the heat loss through a flat
plate collector will often melt the snow.
Assembling a black surface in an isolated box with a glass cover makes a flat-plate collector.
To retain as much heat as possible, it must be prevented from escaping through the back,
sides or front. The radiation emitted by the heated surface is long-wave radiation, while the
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© OECD/IEA, 2011