This textbook analyzes the full range of renewable energy supplies available to modern economies worldwide. It is widely recognized that
these are necessary for sustainability, security, and standard of living.
The renewable energy systems covered include power from solar radiation (sunshine), wind, biomass (plant crops), rivers (hydropower), ocean
waves, tides, geothermal heat, and other such continuing resources. All
of these systems are included within the following general definition:

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Renewable energy is energy obtained from naturally repetitive and
persistent flows of energy occurring in the local environment.

An obvious example is solar (sunshine) energy that ‘persists’ and ‘repeats’
day after day, but is obviously not constant but variable. Similarly, plants
have an annual growing season, which stores energy from sunshine in
their structure that is released in combustion and metabolism.

with a renewable energy resource, the energy is already passing through the environment as a current or flow, irrespective of there being a device to
intercept and harness this power. The phrase ‘local environment’ refers
to the location of such a device to intercept the flow. The natural energy
flows that are commonly harnessed for energy purposes are indicated in
§1.3. Such energy may also be referred to as green energy or sustainable

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Non-renewable energy is energy obtained from static stores of energy that remain underground unless released by human interaction.

Examples are nuclear fuels and the fossil fuels of coal, oil, and natural
gas. With these sources, the energy is initially an isolated energy potential, and external action is required to initiate the supply of energy for
practical purposes. To avoid using the ungainly word ‘non-renewable’,
such energy supplies are called finite supplies or brown energy.

It is also possible to include energy from society’s wastes in the definition of renewables, since in practice they are unstoppable; but are
they ‘natural’? Such finer points of discussion concerning resources are
implicit in the detail of later chapters.

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For renewable energy the scale of practical application ranges from
tens to many millions of watts, and the totality is a global resource.
However, for each application, five questions should be asked:

The first three are technical questions considered in the central chapters of this book by type of renewables technology. The fourth question relates to broad issues of planning, social responsibility, sustainable development, and global impact; these are considered in the concluding section of each technology chapter and in Chapter 17.

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The fifth and final question is a dominant question for consumers, but is greatly influenced by government and other policies, considered as ‘institutional factors’ in Chapter 17. The evaluation of ‘cost-effectiveness’ depends significantly upon the following factors:

  • Appreciating the distinctive scientific principles of renewable energy (§1.4).
  • the efficiency of each stage of the energy supply in terms of both minimizing losses and maximizing economic and social benefits (§16.2).
  • Considering externalities and social costs (Box 17.2).
  • Considering both costs and benefits over the lifetime of a project (which may be > ~30 years).

In this book we analyze (a) and (b) in detail, since they apply universally.
The second two, (c) and (d) have aspects that depend on particular economies, and so we only explain the principles involved.

The definitions of renewable energy and of fossil and nuclear energy
given at the start of this chapter are portrayed in Fig. 1.1. Table 1.1 provides a comparison of renewable and conventional energy systems.


There are five ultimate primary sources of useful energy:
1 The Sun.
2 The motion and gravitational potential of the Sun, Moon, and Earth.
3 Geothermal energy from cooling, chemical reactions, and natural radioÂ
active decay.
4 Nuclear reactions on the Earth.
5 Chemical reactions from mineral sources.

Renewable energy derives continuously from sources 1, 2, and 3. Note
that biomass and ocean heat are ultimately derived from solar energy

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