Photovoltaic power systems are becoming a significant source of energy in our energy resource mix today. It is essential these systems are reliable, safe and secure. Precise engineering design is required to insure these new power systems meet these requirements. In particular, interconnected systems with existing utility power systems must operate in synchronism and improve overall quality of the electrical power grid. This book is intended to identify and explain engineering procedures for the design and operation of photovoltaic systems. It includes a review of conventional electrical power systems as implemented in the United States and common to all electrical systems throughout the world and introduces other types of renewable energy systems. The heart of the book is focused on the design of interconnected and stand-alone PV systems-battery storage is becoming an integral part of PV systems, and a significant portion of the text is dedicated to energy storage for stand-alone and back-up power systems. The author also highlights how economics and structural considerations are an essential part of the engineering design process.