Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

Solar Systems

Using various technologies, solar radiation can be converted into useful forms of energy, such

as heating water or air, or generating electricity. The economical feasibility of solar systems

depends on the amount of solar radiation available at a location. In many countries, radiation

data for solar-water heating and space-heating systems is expressed in watts per square meter per

day (kW/m

2

/day). In the U.S., some of the radiation data is given in British thermal units per

square foot per day (Btu /ft

2

/day). The radiation data for solar-electric (photovoltaic) systems are

represented as kilowatt-hours per square meter (kWh /m

2

).

There are two basic types of active solar heating systems, liquid and air. The liquid

systems make use of water or water-antifreeze mixture (in cold climates) to collect solar

energy. In such systems, the liquid is heated in a solar collector (Figure 13.22), and then

transported via a pump to a storage system. In contrast, in air systems, the air is heated in

“air collectors” and is transported to storage or space using blowers. Most solar systems

cannot provide adequate space or hot-water heating. Consequently, an auxiliary or back-up

heating system is needed. The main components of an active liquid hot water solar system

are shown in Figure 13.23. A photograph of a home in Golden, Colorado using a liquid solar

system is shown in Figure 13.24.

In moderate climates, solar hot water systems are also used to heat swimming pools. The

goal of this type of system is to extend the swimming season. Swimming pool solar heaters

operate at slightly warmer temperatures than the surrounding air temperature. These types of

systems typically use inexpensive, unglazed collectors made from plastic materials. Because these

systems are not insulated, they require large collector areas, approximately 50 to 100% of the

pool area (Figure 13.25).

400 Chapter 13 Energy and Power

■Figure 13.22

A schematic of a solar collector.

Source: U.S. Department of

Energy

Flow tube

Glazing frame

Flat-Plate Collector

Glazing

Outlet

connection

Absorber plate

Inlet connection

Enclosure

Insulation

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