Solar energy collectors, requirements

Imagine, if you will, a solar energy collector that simultaneously stores the collected energy for use at anytime - day or night, rain or shine, summer or winter. This collector/storage system has no moving parts, uses the cheapest materials available, and requires very little maintenance. 

What is the value of the solar constant If energy falling on Earth at the top of the atmosphere could be collected with 100% efficiency, estimate how many square meters of solar energy collector would be required to provide the energy needs of a medium-size house. Explain why only a small fraction of this energy could be utilized in practice. 

The interfaces of importance in SECS are the solid/solid (S/S), solid/gas (S/G), and solid/ liquid (S/L) (4). The area-intensive nature of SECS components was established in the previous section. The major problem is collecting solar energy at a cost that is competitive with other energy forms. Thus, low initial cost is required for the materials, support structures, and production processes in the SECS of interest in Fig. 1 (6). This requires, for example, using thin films in mirrors, in photovoltaic systems, for antireflection coatings on windows, for passive collection, etc. in addition, these films must be made from inexpensive, durable, and easily processed materials (5). Inexpensive long-life materials in flat-plate collectors and durable, stable absorber coatings are also necessary. 

Another concern is keeping the solar collectors clean. Grime and dust deposited on the mirror surface can rapidly reduce the amount of energy reflected. This in turn decreases the output of the plant. The collectors require windshield wipers to perform frequent cleaning cleaning and/or windshield wiper maintenance causes a significant increase in operating cost. 

The benefits of solar thermal collectors, as the rooftop panels that heat water using the sun s energy are called, are numerous they require very little maintenance they have virtually no running costs they usually only take a day to install and, in some cases, you don t require building permits. 

Passive Solar Heater - A solar water or space-heating system in which solar energy is collected, and/or moved by natural convection without using pumps or fans. Passive systems are typically integral collector/storage (ICS or batch collectors) or thermosyphon systems. The major advantage of these systems is that they do not use controis, pumps, sensors, or other mechanical parts, so little or no maintenance is required over the lifetime of the system. 

Thus, the nature of solar radiation has innate problems that require means (heat stores, auxiliary energy source, control system, and large-surface solar collectors) for their solution, and so the investment costs are considerable. Obviously, a prerequisite to utilizing solar energy is economics and the need to achieve an acceptable rate of return. 

FIGURE 12 (a) Details of the actual profile shape and collector design for the integrated stationary evacuated concentrator (ISEC) tube, which has achieved a thermal efficiency of 50% at 200°C. (b) Ray trace diagram showing how essentially all the solar energy incident within 35° is directed onto the absorber tube. Because the reflector cannot physically touch the absorber, as required for an ideal concentrator, a small fraction is lost in the gap between the reflectors and the absorber. 

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