SOLAR HEATING INFORMATION

The world’s supply of fossil fuels is finite and is expected to be depleted in the foreseeable future. Though nuclear energy systems are not similarly constrained, particularly since the asdevelopment of breeder reactors, nuclear waste problems still reremain unresolved.

The future of fusion technology, where the fuel is essentially unlimited, is also uncertain at the present time. As a result, there is a great potential for alternative renewable energy sources, such as solar energy.

Humankind has a very long history of solar energy utilization dating back to prehistoric times. The total solar radiation incident on the surface of the earth is on the order of 80 trillion kW, which is more than 10,000 times the annual global energy consumption for all human activities at present.

Although energy availability is not an issue, its direct use is constrained by three factors: (1) the low energy flux (a maximum of about 1 kW/m2); (2) the large variations and unpredictability of the incident terrestrial radiation due to localized weather conditions; and (3) the need to convert the energy to forms that are more easily transported/stored (e.g., electricity, chemical fuels).

These increase the overall cost of energy obtained from solar radiation, so that solar energy systems are uneconomical for most large-scale industrial and commercial applications.

In spite of these limitations, direct solar heating systems have become more acceptable, and in many cases, commercially viable because of the increasing economic and environmental costs of energy. This is particularly true for many low temperature applications ( 100 C to 150 C), such as water and space (i.e., building) heating and industrial processes, such as distillation, salt/brine production, and drying.

A number of other applications, such as cooking, power generation, cooling/air conditioning, and detoxification/disinfection have also been investigated over the years. Most of these are still in the developmental phase though a few designs have been commercialized to a limited extent.

The applications of direct solar heating applications are quite diverse. However, the basic design in all cases is determined by three factors:

• the availability of solar energy at a given location
• the energy collection and storage requirements
• the end use of the energy as related to the actual application relevant to each of these are discussed separately