Environmental Engineering Reference
In-Depth Information
nondepletable and will be there as along as the sun is shining;
indigenous, hence reducing dependency on imported fuel from other countries with unsta-
ble regimes;
virtually nonpolluting, with some small emissions produced during manufacture and end-
of - life disposal;
diverse and complementary in their time dependence;
generally small and geographically distributed and can often be located near to the demand,
reducing transmission and distribution losses;
robust in system terms because of the very large numbers of individual generators and the
statistical robustness of such a collection compared to centralized generation;
particularly suited to the needs of developing countries, where systems based on renewable
energy technology can be simpler to manufacture than traditional fossil fuelled or nuclear
power stations.
However, renewable energy sources involve relatively new and underdeveloped tech-
nologies that have the following disadvantages:
In general, the cost of electricity from some, but not all, such sources is at present higher
than that from conventional energy sources. This comparison, however depends impor-
tantly on the inclusion or exclusion of external costs;
Except for biomass based generation, they are nondispatchable;
Their distributed nature may require restructuring of the electricity supply infrastructure.
This last area may be of particular interest to readers of this topic who are now in a posi-
tion to understand the key technical features required of future electricity supply systems.
These will be explored in more detail in the remainder of this chapter alongside projections
for the expected evolution of the individual renewable energy technologies.
8.2 The Future of Wind Power
8.2.1 Large Wind Turbines
Recent progress in wind turbine technology has been breathtaking. At the time of writing
5 MW wind turbines are commercially available. Ten years ago, the largest wind turbine on
the market was typically an 800 kW machine with most manufacturers offering 600 kW units.
At present, most wind turbines are fi tted with rotors of 60-90 m compared to the 35-45 m of
the mid-1990s. Due to economies of scale, larger machines generate electricity at a lower
cost per kW h , particularly in offshore applications.
This increase in size has been evolutionary in nature with successive but incremental
scaling up of proven designs, allowing manufacturers to progressively improve their under-
standing of and confi dence in the design process and key issues such as fatigue. However, is
this the best recipe for future expansion? Might not step change innovations provide a faster
path to lower cost larger machines? And is there a limit to the size of wind turbines imposed
by material strength limitations? Since the emergence of the fi rst commercial wind turbine
in the mid-seventies experts have been predicting defi nite limits to turbine size. All these
limits have now been exceeded, pointing up the hazardous nature of such predictions.
