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A Primer on Solar Radiation Data

A correctional institution in Tehachapi, California, uses solar energy to supplement the existing boiler system to provide hot water and space heating for 5100 people. This privately owned system provides energy at a cost below the commercial rate for natural gas heating. Sunlight striking the 2 acres of troughs is reflected and concentrated onto tubes carrying a glycol/water antifreeze solution that runs the length of the troughs. The solution, heated to 270° F, is piped away and circulated through a heat exchanger to provide hot water for showers, kitchens, laundries, and space heating.

Engineers based their design of the system, built in 1990, on the available sunshine, the efficiency of the existing boiler system, the effectiveness of the collector troughs in tracking the sun and concentrating its rays on the tubes carrying collector fluid, the efficiency of the heat exchanger, and the system reliability. All this information was vital not only to the design of the system but also to its evaluation, its operation, and even to the decision to go ahead and build the system.

Accurate information is important for designing energy systems. This primer examines one of the most important pieces of information-- solar radiation data. It explains what solar radiation data are, why they are needed, what data are measured, how the data are used, and how data uncertainties affect performance and economic projections. It also examines how climate, geography, and atmospheric conditions cause the amount of solar radiation to vary, and discusses solar radiation data bases and products available (now and in the near future) for engineering and economic analyses.

Chapter 1: What are solar radiation data?

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