Name any two renewable sources of energy.

21 State the two forms in which energy is mainly utilized at our homes. 22 Explain why fossils fuels are classified as non-renewable sources of energy. 24 Why is the use of wood as a fuel not advised although forests can be replenished? 25 How much solar energy will be received by 1m² area in one hour, if the solar constant were 1.4 kilowatt per square metre?