The large-scale expansion of hydro power, for example, relies on being
able to find enough new locations appropriate to the damming of large
rivers, but such sites are already becoming quite scarce. Expansion of
nuclear power is politically difficult for the simple reason that this method
of power generation carries its own considerable environmental
challenges—the safe storage of nuclear waste and the ongoing risk of
nuclear accidents. Wind power and solar power, though currently
growing in use, both require large amounts of land, and this land often
has a considerable opportunity cost. In addition, the capital costs for both
types of renewable power are considerable, and without government
subsidies, operators are currently unable to cover their costs if they must
compete with cheaper, conventional carbon-based power. Another
disadvantage of wind and solar power is their inherent intermittence; as
the wind dies down or the sun moves behind the clouds, power
generation naturally falls off. A major challenge for wind and solar power
is therefore the development of efficient, large-capacity, and low-cost
storage batteries.
In summary, the large-scale substitution away from carbon-based energy
and toward alternative, cleaner energy is not feasible in the short term.
The various alternative energy sources have their own limitations, which
probably explain why they are currently so rarely used as compared with
carbon-based energy. Such a large-scale substitution, however, is possible
over a much longer time frame. In the next section we will discuss several
policies that encourage a substitution toward alternative fuels.