The Physics and Applications of Solar Energy: Understanding Solar Fusion, Radiation, Technologies and Modern Utilisation; NJRER - Vol. 1, No. 5 - 2025:

ABSTRACT The sun is the primary engine driving nearly all natural and technological energy systems on Earth. This article presents a comprehensive exploration of the scientific mechanisms by which the sun generates and delivers energy, beginning with nuclear fusion processes that convert hydrogen into helium via the proton–proton cycle. These reactions release immense quantities of thermal and electromagnetic radiation that sustain life and form the basis for renewable energy systems. The paper examines the structure and temperature profile of the sun, the historical evolution of theories about its energy source, and modern understanding of mass–energy conversion and binding energy. It further explains solar radiation behaviour, including atmospheric scattering, diffuse and direct components, and spatial–temporal variation in solar irradiance. The study then transitions to contemporary solar technologies, detailing photovoltaic mechanisms, silicon doping, solar cell generations, concentrated photovoltaics, and solar thermal systems such as flat-plate collectors, evacuated tubes, parabolic troughs, and thermal energy storage techniques. Global renewable energy trends based on IEA projections are reviewed, highlighting solar PV as the fastest-growing energy technology and a major contributor to future electricity supply. Additionally, diverse applications of solar energy—including ventilation, water and space heating, pumping, lighting, cooking, and battery charging—are discussed alongside the environmental, economic, and operational challenges that limit its large-scale deployment. Despite issues of intermittency, land demand, manufacturing pollution, high initial costs, and low efficiency, solar energy remains one of the most promising long-term renewable resources. The article concludes that ongoing innovation in materials science, storage technologies, and system integration is essential for achieving cost-effective, efficient, and sustainable solar utilisation in the decades ahead.