This Discovery Guide is not about passive solar, but about more ―active‖ uses of solar as a direct
means of replacing energy currently generated mainly by fossil fuels, such as coal, oil, and natural
These more ―active‖ solar energy uses can in turn be divided into two main groups. The first is
Solar Thermal, which traditionally has been used to heat water and is increasingly being used, in
a more centralized fashion, in large energy plants. The second is solar cells, which can in turn be
divided into bulk or wafer based, usually employing silicon, and thin film, which employs a variety
of metals and is easily manufactured and installed, but currently requires more square footage
to do the work of wafer based cells.