
30-1
30.1 Introduction
e amount of energy coming from the Sun and hitting the Earth surface in one day might be enough
to fuel human activities all around the world for almost 1 year. e solar energy available on Earth
changes with latitude, but it has been estimated as 7 kWh/m
2
/day in the Arizona desert area [1] in the
United States, and as 2 kWh/m
2
/day in Russia [2]. Up to now, this natural and free resource of energy
has been largely underutilized due to the full availability of fossil fuels, e.g., oil, carbon, and natural
gas, and a sleeping environmental awareness. Further motivations for such vacancy are the high cost of
the electric