Energy is a conserved quantity, while entropy is a quantity that generally increases. Entropy is often associated with disorder and the second law of thermodynamics is sometimes cast as a statement that the disorder of a closed system always increases. Thus disorder of an isolated system never decreases.
In accordance with second law of thermodynamics, the entropy of the universe tends to a maximum. We know that that Sun-Earth system is not a closed system. Entropy measures the total disorder of the system or degree of randomness of the system. This signifies that, entropy measures the amount of energy in an isolated system. As heat energy flows from the Sun to the Earth, the thermal energy of the Earth will increase. As the thermal energy increases, therefore change in entropy of the Sun-Earth system will increase
