Question

A solar water heater cannot be used to get hot water on

• A. A sunny day
• B. A cloudy day
• C. A hot day
• D. A windy day

Answer 1

The correct option is B

A cloudy day

Explanation for the correct option,

1. Solar energy is the energy that we receive from the sun.
2. On a cloudy day, heat radiation coming from the sun does not reach the solar water heater.
3. Therefore, the heater will not get enough solar energy and the water will not heat.
4. After obtaining solar energy from the sun’s radiation it can be converted to electricity or heat.
5. Initial solar water heaters were basically large metal containers painted in black because black color is a good conductor of heat and absorbs a lot of heat getting heated quickly.
6. As the container got heated with the heat of the sun, water stored in these containers also got heated.
7. Batch collectors, also called Integrated Collector-Storage (ICS) systems, heat water in dark tanks or tubes within an insulated box, storing water until drawn. Water can remain in the collector for long periods of time if household demand is low, making it very hot.
8. Flat-plate collectors typically consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with tempered glass.
9. Evacuated tube collectors are the most efficient collectors available. Each evacuated tube is similar to a thermos in principle. A glass or metal tube containing the water or heat transfer fluid is surrounded by a larger glass tube. The space between them is a vacuum, so very little heat is lost from the fluid.

Explanation for Incorrect option,

In the case of option A,

1. Solar energy is obtained from the sun’s radiation.
2. Solar energy can be converted to electricity or heat.
3. So on a sunny day, we can use a solar heater to get hot water.
4. Hence option A is incorrect.

In the case of option C,

1. On a hot day we get sun rays from the sun which is the main source of solar heaters.
2. So the heater will get enough solar energy and the water will heat.
3. So we can use a solar heater on a hot day.
4. Hence option C is incorrect.

In the case of option D,

1. Even on a cloudy day we can experience heat radiation from the sun but it is not adequate in amount to heat the water.
2. Solar water heater can only be used in the presence of sun's radiation.
3. So heat radiation coming from the sun reaches the solar heater, therefore we can use a solar heater to get hot water.
4. Hence option D is incorrect.

Hence Option B is the correct answer