Book excerpt: Presently there is no single publication available which covers the topics related to photovoltaic (PV) or photovoltaic thermal (PV/T) technologies, thermal modelling, CO2 mitigation and carbon trading. This book disseminates the current knowledge in the fundamentals of solar energy, photovoltaic (PV) or photovoltaic thermal (PV/T) technologies, energy security and climate change and is aimed at undergraduate and postgraduate students and professionals. The main emphasis of the book is on the design, construction, performance and application of PV and PV/T from the electricity and thermal standpoint. Hot topics covered in the book include: energy security of a nation, climate change, CO2 mitigation and carbon credit earned by using PV or PV/T technologies (Carbon Trading). This information will prove helpful in filling the gap between the researchers and professionals working on the application of photovoltaic and global climate change. It also covers economic, cost effective and sustainable aspects of photovoltaic technologies. The book gives a detailed history of the new technological developments in PV/T systems worldwide with system photographs and references and elaborates on the fundamentals of hybrid systems and their performances with thermal modelling. Energy and exergy analysis, techno-economic analysis and carbon trading are key chapters for research professionals. The book also includes important case studies to aid understanding of the subject for all readers.