Solar energy, past and
future
With the exception of nuclear, geothermal and tidal
energy, all forms of energy used on earth originate
from the sun’s energy.
Some are renewable, some are not. Renewable is the term
used for forms of energy that can be regenerated, or
renewed, in a relatively short amount of time. The regeneration
process may be continuous and immediate, as in the case
of direct solar radiation, or it may take some hours,
months or years. This is the case of wind energy (generated
by the uneven heating of air masses), hydro energy (related
to the sun-powered cycle of water evaporation and rain),
biomass energy (stored in plants through photosynthesis),
and the energy contained in marine currents.
The energy contained in fossil fuels – coal, oil and
natural gas – likewise comes from the sun's energy,
but it was stored in plants millions of years ago, and
once used, it cannot be regenerated on a human time
scale. The earth's remaining fossil fuel reserves can
probably provide us with energy for another 100 to 500
years, but this is an insignificant amount of time in
terms of the whole past history of human civilisation
and (one hopes) of its future.
The flow of renewable solar energies on earth is essentially
equal to the flow of energy due to solar radiation.
Every year, the sun irradiates the earth's land masses
with the equivalent of 19 trillion toe. A fraction of
this energy could satisfy the world's energy requirements,
around 9 billion toe per year.
For thousands of years, the sun's renewable energy was
humanity's sole source of energy. Its role started to
decrease only a few centuries ago, with the progress
of industrialisation, the diffusion of new technologies,
and the discovery of new fossil fuels (coal has been
used since ancient times) and eventually nuclear power.
Today solar sources provide around 10% of the energy
used worldwide, but in the developing countries their
share is still of the order of 40%. This contribution
could start growing again, thanks to progress in solar
technology and the pressure of recurrent energy and
environmental crises related to fossil fuels and nuclear
power.
To raise the contribution to 50% of world energy use
by 2050, as suggested in the Shell Renewables report,
would require sweeping changes in our energy infrastructure.
These changes can be achieved only through the parallel
development of a new, more sophisticated way of thinking
about our environment and how we generate and use energy:
a new culture that should pervade every part of society
and shape the responsibilities of each.
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