Solar Concentrator

From Thermal-FluidsPedia

Figure 1 Parabolic trough and parabolic dish.

Table 1 Solar Concentrators.

Figure 2 The largest solar furnace in the world is in Odeillo, France. A heliostat consisting of 63 mirrors (not shown here) automatically track the sun and reflect its rays into a fixed parabolic mirror reaching temperatures of 3800°C for a maximum of 1 MW of power.

When temperatures higher than 100°C are demanded, solar energy must be concentrated (1, a) The degree to which solar energy is concentrated by a given collector is called the concentration ratio and is defined as:

C.R. = Collector Aperture Area/Receiver Surface Area

Concentrators come in two basic configurations: parabolic troughs and parabolic dishes (Figure 1). Parabolic troughs are basically long sheets of metals bent along an axis to concentrate sunlight on a tube containing a liquid and placed along the focal line. Parabolic dishes are similar except that they are bent to form dishes. Since parabolic dishes distribute the energy over a smaller collector surface (around a focal point), they have a higher concentrating power than parabolic troughs. Furthermore, it is a matter of common sense that the bigger and more curved the collector area is, the higher the degree of concentration and collection efficiency will be. As Table 1 shows, parabolic dishes with concentration ratios as high as 1000:1 can be constructed; these can heat water to superheated steam at 1,200°C. Temperatures as high as 4,000 °C have been reached by a combination of various concentrator methods (Figure 2).

References

(1) Manchini, T., et al., Solar Thermal Power, in Advances in Solar Energy, Vol. 11, American Solar Energy Society, Boulder, CO, 1997.

(2) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Additional Comments

(a) Readers interested in detail designs of solar concentrators should refer to Solar Energy Systems Design by W.B. Stine and R.W. Harrigan (John Wiley and Sons, Inc. 1985. An updated copy of text is available electronically at http://www.powerfromthesun.net).

Further Reading

Markvart, T., and Castanar, L., Solar Cells: Materials, Manufacture and Operation, Elsevier Publishing Company, 2005.

Galloway, T., Solar House, Elsevier Publishing Company, 2004.

Stine, W. B., and Harrington, R. W., Solar Energy Systems Design, John Wiley and Sons, Inc., 1985.

Solar Energy, Direct Science Elsevier Publishing Company, the official journal of the International Solar Energy Society, covers solar, wind and biomass energies.

External Links

National Renewable Energy Laboratory: Solar Research (http:// www.nrel.gov/solar).

Energy Efficiency and Renewable Energy: Solar Energy, US Department of Energy (http://www.eere.energy.gov).

American Solar Energy Society (http://www.ases.org).

Solar Electric Power Association (http://www.solarelectricpower.org).

California Solar Center (http://www.californiasolarcenter.org).