How a Solar Hot Water System Works
A solar hot water system collects and converts solar radiation into usable energy for the purpose of heating water. The use of solar radiation for heating water is an inexpensive and environmentally responsible substitute for heating by gas or electricity. The main parts of a solar hot water system are a collector, a hot water storage tank, and a distribution system. The main steps in the process of heating water by using the sun’s rays are (1) trapping the sun’s energy, (2) heating and storing the hot water, and (3) dispensing the water at points of use.
The first step is to capture solar radiation. That is, the sun’s energy must be absorbed by a solar heat collector, which is usually built in a south-facing roof. The collector has several layers of material. It has a glass plate and a metal absorber plate, which is painted black to increase its ability to absorb heat. Next to the absorber plate are copper tubes, which are filled with transfer fluid. The tubes are surrounded by foam insulation and aluminum casing to help hold the heat in them. The process of trapping the sun’s radiation is as follows. As the sun shines through the glass plate, its thermal energy is absorbed by the copper absorber plate. This heat is conducted from the plate to the tubes. The heat from the tubes is then conducted to the fluid flowing through them.
After trapping heat from the sun, the second step is to transfer this heat to water which is stored in an insulated tank. The hot fluid from the collector is circulated by a pump through copper coils inside the tank. The heat is conducted by the coils to the water. When the supply of solar radiation is reduced on cloudy days, an auxiliary system can take over.
Dispensing the hot water is the final step in the process. The water flows from the outlet valve through pipes to faucets throughout the house.
In summary, the process of collecting and converting solar energy for use in a solar hot water system involves three steps. First, collectors absorb the sun’s energy, which is then transferred to fluid in copper tubes. These tubes run from the collector to a tank, where the water is heated and stored. Finally, the hot water is distributed through pipes to wherever it is needed. Although initially expensive to install, solar heating systems are economical in the long run —— at least until utility companies figure out how to charge us for sunshine!
III. Compose an essay. (60%)
Write an argumentative essay of about 250 words on the following topic:
Effects of China’s Single-child Policy
You are to write in three parts.
In the first part, state specifically what your view is.
In the second part, support your view with two or three reasons.
In the last part, bring what you have written to a natural conclusion or a summary.
