Solar Energy
It is no understatement that solar energy is the lifeblood of our planet. Weather,
oceanic circulation, and life owe their existence to the energy output of our sun.
Although it is true that solar energy is responsible for heating up our planet, there
is a common misconception that solar energy and thermal infrared energy are syn-
onymous. In fact, only a small proportion of the direct solar beam is composed of
thermal infrared energy.
The sun is a star that has natural variation in output but the variations are currently
insignificant enough to maintain life onEarth. The evolution of the sun and certain
prehistoric output changes has been known to forceclimatechange, but the present
status of the sun is not such that we do not expect large changes in the next thousands
of years. Sunspots are dark features on the sun’s radiating photosphere some 1,500°C
cooler than their surroundings. They are caused by disturbances in the interior solar314 Solar Energy
Table 4. USDA Taxonomy World Soil Orders
Order General characteristics
Alfisols Mature soil, extensive in low and middle latitudes, transitional environments,
subsurface clay horizon, plentiful nutrients
Andisols Volcanic ash as parent material, not highly weathered, minimal profile
development, dark color, usually fertile
Aridisols Light colored, in arid and semiarid climates with little water to leach soluble
minerals, sandy, thin, productive if irrigated
Entisols Least well-developed order, horizons sometimes nonexistent, thin and rela-
tively infertile except on floodplains
Gelisols Recent soils associated with permafrost, found in the arctic and subarctic,
mixing of materials because of freeze/thaw
Histosols Least extensive of any order, organic soils, always saturated, lack of oxygen
slows decay, acidic, briefly fertile if drained
Inceptisols Immature but possessing faint horizons, parent materials “young,” steep slopes
and floodplains, various climates
Mollisols Surface horizon dark, thick, and fertile, typical of grasslands, most fertile of all
orders, most extensive order on Earth
Oxisols Deep, warm, and wet climates, highly altered from parent material, tropical,
not usually fertile
Spodosols Cool, moist climates, coniferous forest cover, upper layers light in color and
heavily leached, tend to be infertile
Ultisols The most heavily weathered soils of middle latitude soils, reddish, subsurface
clay accumulation
Vertisols Alternating wet and dry climates of tropics and subtropics, large amounts of
clays prone to swelling and shrinking