What Is Energy? - The Renaissance of Renewable Energy - page 15

wheeled wagons. Thus, about 6,000 years ago, the ox became our first beast of burden. A
millennium later, the first wild horses were captured from the steppes of Central Asia and
bred for food. Again, it wasn't long before this animal's potential as a source of labour was
discovered and (literally) harnessed. By the middle of the second millennium BCE, horses
were central to almost every human activity, from agriculture to industry and from trade
to war. The horse accompanied us well into the industrial era, and as late as the 1930s,
horse-drawn carts were a common sight in industrialised cities (Kavar and Dov č 2008 ).
Prime Movers
Humankind's quest for energy began with tools that concentrated our own muscle power;
continued with the use of fire for heat, light and cooking; later involved the cultivation
of secure, high-energy foods; and eventually led us to harness the muscle power of larger
animals. The most recent leap forward has been the invention of machines that can run
without the involvement of human or animal muscles. Scientists refer to such machines,
which convert a naturally occurring source of energy into mechanical power, as 'prime
movers'.
Around the third century BCE, the power of running water was first harnessed by the
ancient Greeks. Over the next millennium, waterwheel technology spread throughout the
Mediterranean and to most of Asia and northern Europe. While the design and efficiency
of these machines improved steadily over time, medieval watermills had a power output
of only a few kilowatts, roughly equivalent to a modern hair dryer. Nevertheless, the
waterwheel remained the most efficient pre-industrial prime mover and was a key factor in
Europe's technical supremacy during the early stages of industrialization.
The second most important pre-industrial prime mover was the windmill. Windmills
were first used in Persia around the tenth century. As the name suggests, these were used to
mill grain, and later to pump water for irrigation (Smil 2008 ). Despite these and numerous
other innovations, the way energy was used did not substantially change from prehistoric
times to the eighteenth century. By 1800, people were still using animal muscle for work
and transport, animal and vegetable fats for lighting, biomass for heating and methods of
agriculture that had not greatly changed for millennia.
This all changed with the Industrial Revolution. What began in England, thanks to
plentiful and easily accessible coal reserves, spread to France, Germany, Italy and the
United States, and eventually reached most of the world. New machines and tools allowed,
for the first time, thermal energy to be converted into kinetic energy, driving a wide variety
of machines. While many of the applications, such as mining and weaving, had been
practiced for centuries or even millennia, the new machines allowed for great advances