There are two main kinds of solar energy:
Solar photovoltaic (PV) directly converts solar energy into electricity using a PV cell made of a semiconductor material.
Concentrating solar power (CSP) devices concentrate energy from the sun’s rays to heat a receiver to high temperatures. This heat is transformed first into mechanical energy (by turbines or other engines) and then into electricity – solar thermal electricity (STE).
Over the period 2000‐11, solar PV was the fastest‐growing renewable power technology worldwide. Cumulative installed capacity of solar PV reached roughly 65 gigawatts at the end of 2011, up from only 1.5 GW in 2000. In 2011, Germany and Italy accounted for over half the global cumulative capacity, followed by Japan, Spain, the United States and China.
Concentrated solar power is a re‐emerging market. Roughly 350 megawatts (MW) of commercial plants were built in California in the 1980s; activity started again in 2006 in the United States, and Spain. At present, these two countries are the only ones with significant CSP capacity, with respectively about 1 GW and 500 MW installed, and more under construction or development.
According to IEA analysis, under extreme assumptions solar energy could provide up to one-third of the world’s final energy demand after 2060. Solar Energy Perspectives outlines a bold ‘what if’ scenario for reaching this ambitious target. A number of assumptions are made to see what might be possible in terms of solar deployment, while keeping affordability in sight. These include policy makers successfully reducing greenhouse gas emissions beyond the current international targets, and electricity-driven technologies fostering significant energy efficiency improvements and displacing fossil fuels in many uses in buildings, industry and transportation. While a broad range of aggressive policies will be needed, this target is achievable.