Mention any four areas where solar cells are being used as a source of energy.

4 Mention any two differences between a box type and a concentrator type solar heater. 5 Why is it not possible to make use of solar cells to meet all our energy needs? State atleast two reasons to support your answer. 7 Why can wind energy farms be established only at specific locations? Give reasons to support your answer. 8 It is difficult to use hydrogen as a source of energy, although its calorific value is quite high. Explain.