Environmental Engineering Reference
In-Depth Information
Gravitational
(Hydro tidal)
Nuclear
Wind wave
Fission
(Fusion)
Heat
engines
Electric
generator
s
Thermal
Mechanical
Electrical
n < 60%
n = 90%+
Photovoltaic
n = 90%+
Fuel
cells
Solar
thermal
Chemical
(Coal, oil, gas,
biomass,
hydrogen)
Solar
Figure 1.8
Conversion from a variety of energy forms into electricity
effi ciencies between 35 and 40% although in the last two decades conversion has been sub-
stantially improved to over 50% through the development of combined cycle gas turbines
(CCGTs) a technology discussed in Chapter 2. It follows that when coal, oil or gas is used
only 35-50% of the primary energy is successfully converted, the remaining being discharged
into the environment in the form of waste heat.
One way of getting around the Carnot limit is simply to make use of the waste heat. This
is the principle of combined heat and power (CHP), used extensively in Scandinavia and of
growing importance elsewhere. In such schemes, the waste energy from the thermal genera-
tion of electricity is distributed through heat mains to local industry and/or housing. This
requires substantial infrastructure and is therefore only viable if the power station is reason-
ably close to the heat users. An alternative arrangement made possible by recent develop-
ments is to transport the fuel (mainly gas) to the consumer using the existing supply
infrastructure and install the CHP system at the consumer's premises. Such systems are
known as
micro - CHP
and are discussed in Chapter 8.
Direct paths that bypass the Carnot bottleneck are also available. The leading example of
this approach is the fuel cell, which now borders on commercial viability in a number of
forms: solid oxide, molten carbonate, and proton exchange membrane (PEM) to name the
main ones. Another direct path is through photovoltaics, a technology that perhaps is the most
promising in the near to far future.
The conversion effi ciencies of the various routes indicated in Figure 1.8 are dealt with in
greater detail in Chapter 2.
1.3.2 The Nuclear Path
The topic of electricity generation from nuclear power elicits strong emotions from supporters
and critics. Although nuclear power supplies only the equivalent of 5.7% of the world primary
