How Energy Is Produced - The Renaissance of Renewable Energy - page 83

regions is on small-scale projects, as the potential of the major waterways has already been
tapped. Today, the biggest hydropower projects are being built in Asia and South America.
Hydropower is the only renewable energy sector with an output comparable to
conventional energy sources. Indeed, it is the world's third most important electricity
source after coal and natural gas. In 2010, global capacity was around 1,000 GW with an
output of roughly 12 exajoules per year (3,400 TWh per year), equivalent to 2.3 per cent of
primary energy production, 16 per cent of global electricity production (IEA 2012a ; JRC
2011 ; REN21 2012 ; Chapter 7 , this volume).
According to the International Journal on Hydropower and Dams , the total worldwide
technical potential for hydropower is 52 exajoules per year (14,576 TWh per year) or
roughly 10 per cent of current global primary energy (IJHD 2010 ). Estimates of
undeveloped capacity range from about 47 per cent in Europe and North America to 92 per
cent in Africa. Asia (led by China) and Latin America (led by Brazil) are the new leaders
in large-scale hydroelectric development, but Africa has the most untapped resources.
Additional power may come from upgrading old power stations. Compared with new
power plants, such projects are cheaper, quicker to develop and usually have lower
environmental and social impacts. Furthermore, most of the world's 45,000 large dams are
used for non-energy purposes (e.g., irrigation, flood control, navigation and urban water
supply schemes), with only 25 per cent used for hydropower. Significant potential can be
developed from existing infrastructure that currently lacks generating units (e.g., barrages,
weirs, and irrigation dams) by adding new hydropower facilities (Kumar et al. 2011 ) .
4.3 Wind Power
Why Dogs Like to Sleep on the Couch
Atoms are like people on a dance floor. As they dance to the music, they naturally bump
against one another; to create more space to dance, they move apart and occupy a greater
space. In a similar way, when a substance is heated, its atoms vibrate, move apart, and the
substance expands to fill a greater space. We can observe this principle in a hot-air balloon.
The air inside the balloon is heated using a burner, causing it to expand. This air becomes
lighter (less dense) than the air outside, causing the balloon to rise.
At the north and south poles the air is cold, therefore dense or compressed. Hence, it
is referred to as high air pressure. At the equator, the opposite applies: the air is warm, its
atoms more sparse, and so we call this a low-pressure area. Like the dancers who try to
nab a spot on the dance floor with a bit more wiggle room, air automatically moves from