Fossil energy and nuclear energy are considered nonrenewable energy
types.Nonrenewable energy is obtained from sources at a rate that exceeds
the rate at which the sources are replenished.For example,if the biogenic
origin of fossil fuels is correct,we could consider fossil fuels renewable
over a period of millions of years,but the existing store of fossil fuels is
being consumed over a period of centuries.Because we are consuming
fossil fuels at a rate that exceeds the rate of replenishment,we consider
fossil fuels nonrenewable.Similar comments apply to nuclear fuels such
as uranium,as we observe in later chapters.Solar energy is considered
a renewable energy for the following reasons.1
Renewable energy is energy obtained from sources at a rate that is less
than or equal to the rate at which the source is replenished.In the case
of solar energy,we can use only the amount of energy provided by the
sun.Because the remaining lifetime of the sun is measured in millions
of years,many people consider solar energy an inexhaustible supply of
energy.In fact,solar energy from the sun is finite,but should be available
for use by many generations of people.Solar energy is therefore considered
renewable.Energy sources that are associated with solar energy,such as
wind and biomass,are also considered renewable.
Solar radiation may be converted to other forms of energy by several
conversion processes.Thermal conversion relies on the absorption of solar
energy to heat a cool surface.Biological conversion of solar energy relies
on photosynthesis.Photovoltaic conversion generates electrical power by
the generation of an electrical current as a result of a quantum mechanical
process.Wind power and ocean energy conversion rely on atmospheric
pressure gradients and oceanic temperature gradients to generate electrical
power.In this chapter we focus on thermal conversion.We first discuss the
source of available solar energy,and then consider solar energy technology
in two of its three forms:passive solar,and active solar.The third form of
solar energy,solar electric,is discussed in the next chapter.We end this
chapter with a discussion of solar power plants.
