Solar energy in progress and future research trends
Natural energy sources
All types of energy, renewable or non-renewable, can be traced back to either atmospheric activities in the past or to the present and future activities within the atmosphere. The renewable energy sources are regarded as related to present atmospheric movements, but non-renewable sources have been deposited in the depths of the earth. The latter types are also referred to as the fossil fuels. By burning the fossil fuels the stored energy of the past atmospheric activities is added to the present energy demand. Consequently, their burning leads to the altering of the weather in the short, and climate in the long terms in an unusual manner.
So far as the nuclear power plants are concerned, they are relatively conservative. However, nuclear energy prospects are affected by several important questions, such as increasing production costs, their unsuitability for the large rural areas of the world, risks of nuclear weapon proliferations and from a market point of view, the potential prohibitive cost of commercial insurance against accidents and waste disposal [96]. Although, nuclear energy stands as an unlimited alternative, but its public alertness on serious risks and controversial waste disposal problems remain as major hindrance for worldwide use. There is also national and international political arena for its choice as
an alternative among the energy sources. Nuclear energy is often mentioned as a viable alternative, but the nuclear reactor industry has seen serious setbacks due to public awareness of the risks involved, and the controversial waste disposal practices. For this reason, future progress in the nuclear energy option depends on considerations that belong mainly to the political arena and decisions, which lie outside the scope of the present paper.
After the industrial revolution in the middle of the 18th century, human beings started to require more energy for consumption. Hence, non-renewable energy sources in the form of coal, oil and wood began to deplete with time. Their limited reserves and environmental pollution potentials led to search for alternative and renewable energy sources.
All the renewable energy sources have their origin in the sun. The sun’s rays that reach the outer atmosphere are subjected to absorption, reflection and transmission processes before reaching the earth surface. On the other hand, the solar radiation shows different appearances depending on the earth surface topography as explained by Neuwith [87].
The renewable energy sources are primary energy alternatives, which are parts of the everyday weather elements such as sunshine and the wind. Extraterrestrial sources of energy are the solar radiation and moon’s gravitation that appears in the form of tides. The terrestrial sources are the earth’s heat through conduction and earth’s gravitation and rotation. These external and internal sources are constant energy supplies to the atmosphere. Apart from balancing each other, they both contain thermal and mechanical forms depending on heat and mass, respectively. The solar radiation is the main source of heat energy, and earth’s motion and gravitation exert influence on the masses. The atmosphere is fed by continuous flux of radiation from the sun. In general, there are six different heat and mass exchanges within the atmosphere. These exchanges play the main role in the energy distribution throughout the whole system. The major energy source is radiation between the atmosphere and space as one of the external sources.
This source initiates the movement of heat and mass energy from the oceans (seas) into the air and over the land surfaces. The next important heat energy transfer occurs between the free surface water bodies (oceans, seas, rivers, reservoirs) and the atmosphere. Thus water moisture as a result of evaporation is carried at heights towards the inlands by wind effect having the kinetic energy. Such a rise gives the water vapor potential energy. After the condensation by cooling, the water vapor appears in the form of precipitation and falls at high surface elevations forming the surface runoff, which due to gravity flows to the seas. The energy cycle along with the hydrological cycle is presented by Sen [126]. During its travel toward the earth’s surface, raindrop loses its potential energy with the increase in its kinetic energy. Water is the intermediator in such a dynamic system. Finally, the water is returned to the seas via streams and rivers, because the gravity ultimately takes over the movement of masses. The energy cycle explained herein, appears as an integral part of the water (hydrological) cycle. During this cycle, no extra energy is produced within the atmosphere. Such movements result from the fine balance that has existed for so long between the output of radiation from the sun and the overall effects of earth’s gravitation.
