This chapter focuses on solar energy harvesting, which is one of the most important renewable energy sources that has gained increased attention in recent years. Solar energy is plentiful; it has the greatest availability among other energy sources. Sunlight has been used as an energy source by ancient civilizations to ignite fires and burn enemy warships using "burning mirrors." A photo voltaic (PV) cell converts sunlight into electricity, which is the physical process known as photoelectric effect. The chapter deals with I–V characteristics of PV systems, PV models and equivalent circuits, sun tracking systems, maximum power point tracking MPPT systems, shading effects, power electronic interfaces for grid-connected and stand-alone PV systems, sizing criteria for applications, and modern solar energy applications. PV devices can be made from various types of semiconductor materials, deposited or arranged in various structures. The three main types of materials used for solar cells are silicon, polycrystalline thin films, and single-crystalline thin film.