Introduction: Hierarchical Nanostructures for Energy Devices - Hierarchical Nanostructures for Energy Devices - page 2

exhaustible natural resources and their environmentally hazardous com-
bustion, more scientific efforts should be directed toward reducing the cost
of energy production from renewable sources. 2
Developing sustainable renewable energy sources has been a major
research topic in an effort to solve the environmental problems caused by
fossil fuels. Significant progress has been made in increasing the eciency
of various renewable energy technologies including solar cells, fuel cells,
nuclear energy, wind power and so on. 3 Since the nuclear power plant
disasters at Japan and Ukraine, the safety issue has become the most
important factor.

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1.2 Energy Cycle
Energy devices do not mean only energy generation devices but also include
energy storage and energy consumption devices. To fully understand
ecient energy usage and to increase the eciency, the term Energy Cycle
should be understood. Energy Cycle is the complete life of energy from birth
to death: energy generation, energy storage and energy consumption
(Figure 1.1). Eciency is a major concern in energy devices and the total
eciency of energy devices is limited by the one with lowest eciency (just
like a chemical reaction rate is dominated by the slowest process). Even
though one may develop an extremely ecient energy generation device, if
the generated energy is stored in a poor eciency energy storage device or
used for a poor eciency energy consumption device, the eciency will be
low from the total energy cycle viewpoint. Therefore, to approach the energy

.

Figure 1.1 The Energy Cycle is the complete life cycle of energy from birth to death:
energy generation, energy storage and energy consumption.