‘Renewable energy’ is an interesting use of words because the first law of thermodynamics tells that energy is always conserved while the second law implies that during all processes the quality or usefulness of energy is degraded. Both energy ‘generation’ and ‘consumption’ are processes in which energy is converted from one form to another with some degradation in quality or usefulness; how much degraded energy is produced compared to useful energy or electricity in a generation process is a measure of the efficiency of the process. Whereas in a consumption process we expected most of the energy to be degraded to the point of uselessness, often in the form of heat or noise. So the concept of renewable energy suggests that we can somehow refresh or recover the quality and usefulness of energy degraded in consumption processes. In practice it is not possible to refresh or renew the energy, instead we replenish it with new ‘high quality’ energy arriving from the sun.
The picture shows Old Faithful Geyser in Yellowstone National Park in the USA.