00 years ago.
But the first hydroelectric dam was
built in England in 1870. Hydroelectric power is now the most common
form of renewable energy, supplying around 20% of world electricity.
China's Three Gorges Dam, which
has just been completed, is the largest ever. At five
times the size of the US's Hoover Dam, its 26 turbines will generate the
equivalent energy of 18 coal-fired power stations. It will satisfy 3% of
China's entire electricity demand. Surprisingly, some argue that hydroelectric
dams significantly contribute greenhouse
In 2003, the first commercial power station
to harness tidal currents in the
open sea opened in Norway. It is designed like windmill, but others take the
form of turbines, oscillating hydroplanes,
flexible eel-like generators, or
are made of floating pontoons that rise up and down with the waves and tide.
As prices fall, wind
power has become the fastest growing type of
electricity generation - quadrupling worldwide between 1999 and 2005. Modern
wind farms consist of turbines that generate
electricity. Though it will be more expensive, there is more than enough wind
to provide the world's entire energy needs.
Wind farms come in onshore
and offshore forms. They
can often end up at spots of natural beauty, and are
often unpopular with
residents. And turbines are not totally benign - they can interfere with radar
and leave a significant ecological footprint; altering climate,
sending wildlife diving for cover and
killing sea birds. Migrating
birds may have more luck avoiding
Scotland is building Europe's largest wind farm,
which will power 200,000 homes. The UK's goal is to generate one-fifth of power
from renewable sources, mainly wind, by 2020. But this may cause problems, because wind
Future buildings with integrated turbines
could generate 20% of their own power. Other visions see wind-power revived for
shipping, floating wind farms, or
28-kilometre-wide flying behemoths
powered by high speed winds in the upper atmosphere. There are also plans to
construct a 1-kilometre-tall tower
that would harness wind energy from heated air in the Australian outback.
Catching some rays
Using solar power to
generate electricity has been considered since Victorian times and
clever building designs that use it to regulate temperature
have been around for millennia. Today solar power is used in several ways. In thermal solar power,
sunlight directly heats water in rooftop panels for household supplies, while
sunlight can also be converted to electricity
using photovoltaic cells,
which use semiconductors to turn photons into electricity.
Both types of power are
intermittent sources, as they can only work in good light. Photovoltaic cells have
been too expensive for widespread use, but are already popular for supplying
electricity to remote locations and filling gaps in
ramshackle electricity grids. Solar panels often power spacecraft too,
and solar cars and aeroplanes.
New cheaper versionsof
photovoltaic cells could mean more energy is generated from solar
than nuclear power by 2020.
In the future we may
generate solar power using flexible coverings that
"clothe" both buildings and people. There is even a
scheme for an orbiting solar power station.
Running on empty
When oil runs out what will
we fuel our cars with? This question, plus the fact the exhaust fumes are one
of the greatest contributors
to greenhouse gas emissions, means the race is on to find a
new solution to getting around.
Biofuels have been around since the internal
combustion engine. Ethanol is added to
petrol in the US, and millions of cars in Brazil are run on it
too. Vegetable oils are
already used in Europe to produce biodiesel. Soya oil could be used
for aviation too. Biofuels such as
fast-growing elephant grass or saplings could be used
to provide heat and electricity. Even sewage is being
considered as a biofuel.
Hydrogen fuel cells have enormous potential if
technical problems can be solved. Essentially a kind of battery that can be
continuously refilled, fuel cells chemically
react hydrogen with oxygen - producing just electricity an