**10. Conclusion**

16 Solar Radiation

Spectral splitting coatings can be used to divide solar spectrum into various broad band regions. By this, various regions of the solar spectrum can be separated for use for different

A "cold mirror" device has opposite spectral response to that of the "heat mirror". That is, cold mirror films reflect highly (low transmittance) in the VIS region of solar spectrum and reflect poorly, but transmits highly in the IR region, thus splitting the spectrum into short wavelengths and long wavelengths. The high energy waves i.e. the short wavelengths are used for photovoltaic generation while the low energy waves, the long wavelengths (IR) are used for photo thermal heating. This device can be used in "green house" with special arrangements of baffles on the roofs. The device will reflect the photosynthetic active radiation (PAR), 0.35 ≤ λ ≤ 0.75 µm waves into the green house while transmitting the IR into the air channels which can be redeployed to maintain a suitable warm temperature in the green house. ZnS/ MgFs and Ti O2/ Si O2 have been used to achieve these coatings.

Solar control coating is a design intended to reduce the incoming heat radiation through windows of a building by reflecting off the heat radiation (IR). To achieve comfortable indoor temperatures, that is, to achieve cooling in a building, solar control coating surfaces that are transparent at 0.4 ≤ λ ≤0.7 µm and reflecting at 0.7 ≤ λ ≤3 µm may be used for the material of the windows in the building. By this, the infrared part of the solar radiation is reflected back, which is possible through the use of solar control windows. A 50% reduction in the internal heating of a building without noticeable reduction in the lightning of the interior of the building had been achieved. The use of such windows may achieve the same objective of a controversial air conditioner in a building. Solar control coating are

In solar control and energy conserving windows, low transmittance windows are employed. If the medium is generally opaque to the passage of radiation but selectively transmits a particular small range of radiation, it is said to operate as a window in that range. A low thermal transmittance window reduces the heat radiation through the window. To achieve low thermal transmittance window therefore, surface coatings that transmits at 0.3 ≤ λ ≤ 3 µm and reflects at 3 ≤ λ≤ 100 µm may be used. This means that maximum use is made of the solar energy in the short wavelengths range while the transmittance of thermal radiation is

A thin homogeneous metal film is found capable of combining transmission in short wavelengths up to about 50% with high reflectance in long wavelengths (Okujagu, 1997; Wooten, 1972). The required thickness of such film, using copper, silver and gold is about 20mm. if the films are thinner, they will break up into discreet islands of strong absorptance of visible

Enhancement of luminous transmittance to more than 80% without significantly impairing the low thermal transmittance can be achieved by embedding the metal in anti-reflecting dielectric

purposes such as photovoltaic or photo thermal devices (Lambert, 1985).

particularly applicable in hot climate countries such as Nigeria.

**9.4 Solar control and low thermal emittance materials** 

**9.2 Cold mirror coatings** 

**9.3 Solar control coating** 

minimized.

wavelengths.

Energy is necessary for the growth of any nation, and for improving the standard of living of the nation. Therefore energy has to be made available and cheap by the nation for rapid and quality growth of the economy.

Fossil fuels energy, the main source of energy for the world for now, is unable to meet the world's demands of energy and it is, at the same time, rapidly depleting, hence the fever of the world's search for alternative sources of energy. Each country therefore faces the challenges of developing her energy resources.

The renewable energy sources, some of which are: **wind, marine, geothermal, biomass, biodieses, hydro-power, land fill and solar energy** have become object of research, because they could be the alternative dependable and feasible sources of energy that the world is looking for to meet her energy demands. They are truly possible alternative sources of energy if their technologies are developed and mastered. Out of them all, solar energy seems to be the most capable of meeting world energy demands if properly harnessed and made cheap. The amount of it received per second during the daylight on the earth's surface is 10,000 times more than the total energy requirement of the world today. The varieties of solar energy applications and advantages are enormous, only a few are mentioned and discussed very briefly in this chapter.
