Environmental Engineering Reference
In-Depth Information
is the sun. On average the rate of solar radiation intercepted by the earth's surface is
about 8000 times as large as the average rate of world primary energy consumption. With
the present world population this amounts to a staggering average power of 20MW per
person.
The fi gure shows that this energy fl ux can be accessed directly using solar thermal
or photovoltaic technology, or indirectly in the form of wind, wave, hydro and biofuels.
Two other energy sources are often regarded as renewable in view of their sustainable
nature: energy in the tides caused by the gravitational fi elds of the moon and the sun which
can be tapped using tidal barrages or tidal stream technology; and geothermal energy from
the earth's core accessible in some locations through hot springs, geezers or boreholes. The
available average power from these resources is a small fraction of that available from the
sun.
A substantial proportion of the incident radiation is refl ected back to space. Over the last
several millennia and up to the onset of the industrial revolution, energy inputs and outputs
have been in equilibrium at a global temperature level suitable for the development of the
earth's biosphere. Exploiting the incident energy through the application of renewable energy
technology
does not
disturb this balance. Intercepted natural energy fl ows, for example con-
verted to electricity and then converted again by consumers into mechanical, chemical or
light energy, all eventually degrade into heat.
Most renewable energy forms are readily converted to electricity. Solar energy, geothermal
energy and biomass can also be used to supply heat. Renewable energy can in principal
provide all the energy services available from conventional energy sources: heating,
cooling, electricity and, albeit with some diffi culty and cost, transport fuels. It has the
additional advantage that being a naturally distributed resource, it can also provide energy
to remote areas without the need for extensive energy transport systems. It is worth noting
that it is not always necessary to convert the renewable energy into electricity. Solar
water heating and wind-powered water pumping are fi ne examples of systems that can
work very well without involving electricity at all. However, the major contribution that
renewable energy will be increasingly making in supplying people's needs will be in electrical
form.
Renewable energy is currently experiencing dramatic growth. Wind power and solar PV
are leading the growth with global companies such as GE and Siemens entering the wind
energy market, and BP and Shell playing a major role alongside Japanese companies like
Sharpe and Sanyo in PV. In China fi ve of the largest electrical aerospace and power genera-
tion equipment companies have recently begun to develop wind turbine technology. Most
large oil companies have expanded their research and development in ethanol and biodiesel
production from biomass. The fastest growing RE technology is currently grid connected PVs
with 40% annual year on year growth, but the RE technology that has made the largest con-
tribution to date (excluding conventional hydro) is wind power with over 60 GW installed in
EU countries and 95 GW worldwide by the end of 2007.
At least 48 countries have national targets for RE supply including all 25 EU countries.
Figure 1.11 shows the intended increase in contribution of the EU countries from 2002 to
2010. The EU has Europe-wide targets of 21% electricity and 12% of total energy by 2010.
Table 1.2 shows the intentions of the EU over a wider period, with expected contributions
in TW h per annum from various RE technologies.
