Preface

One of the greatest problems facing humankind in the 21st century is the lack of available potable water. The reason behind the origins of this precarious problem is the limited natural water‒resources available on the planet earth. The rate of potable-water use is growing drastically with time and has almost quadrupled over the past century. Therefore, it is now necessary to find alternatives to challenge water-related problems to protect the limited natural water‒resources remaining on the earth. In this universe, only the sun is available as one of the most ample and unlimited energy resources. There would be no life on the earth without sunlight. Electromagnetic radiation in the form of sunlight reaches the earth through the atmosphere. Sunlight consists of ultraviolet, visible, and infrared light. Statistically, every year 6 10 J/m of solar radiation is incident on the earth (based on an average of 6 hours of sunlight a day), which is a very large amount. For a 10-m roof, the amount of energy received is approximately three times more than the energy used in a typical house per day. These are the reasons that solar energy has gained much–attention worldwide. For efficient utilization of solar energy, is essential to understand the basic science of solar energy, including solar radiation and heat transfer.