Environmental Engineering Reference
In-Depth Information
schemes if the conclusion is that they have an important role to play in the long term future
electricity supply.
It may be that concerns about the ecological side-effects will result in alternatives to the
straightforward barrage schemes. One such alternative has been suggested by FoE in which
tidal lagoons are created. These are claimed to be capable of producing even more energy
than barrage schemes as well as being less environmentally intrusive. The newer technology
of tidal stream, introduced in Chapter 2, suites different sites and is generally seen as promis-
ing despite its present lack of development. It is widely anticipated that reliable and cost-
effective technology will be developed. This will make a useful contribution, but only in very
specifi c geographical areas where suitable stream velocities exist.
Wave power is perhaps the least developed renewable energy source, although the resource,
especially around the UK coastline, is huge. Since 2000, a number of large scale wave power
prototypes have been demonstrated around the world, but the technology is still up to 15
years behind wind energy. In the UK only one wave energy device (Pelamis, see Chapter 2)
has been demonstrated at near full scale in the open sea. The fi rst commercial wave energy
farms using the Pelamis device are being planned in Portugal, Orkney and Cornwall. Design-
ing devices to survive in the open seas is challenging but enthusiasts for the technology are
projecting signifi cant electricity generation from this source in the future.
8.6 Distributed Generation and the Shape of Future Networks
Many reports have been published covering the need for changes in the structure of power
systems. Key reports include References [7] to [10] and these have been drawn on in this
section.
8.6.1 Distribution Network Evolution
Traditionally, engineers have regarded electricity distribution networks primarily as passive
conduits of power from the high voltage transmission system to the loads and have been
installed on a 'fi t-and-forget' basis. However, some active control elements are now being
introduced as far down as the 11 kV network for fault restoration to improve customer supply
reliability. Some limited voltage control is also incorporated as described in Chapter 6, but
these networks can generally been viewed as passive in operation. All this is changing with
the growth of distributed generation.
The connection of smaller CCGTs at distribution voltages has been increasingly common
in the European community over the last 15 years and similar trends are occurring elsewhere.
Much of the UK's wind energy capacity, especially the older smaller wind farms, were
connected at 11kV, and so embedded in the distribution system. In the USA, distributed
generation consists primarily of standby diesel generator sets that add to system security
by operating at times of high network stress. In addition there is coming on to the market a
wide range of very small generators (micro-chp, PV and micro wind) that are designed for
use in domestic and small commercial premises. These trends are expected to continue. As
regional penetrations rise new ways of designing and operating distribution networks will
evolve. There are presently a number of major research programmes around the world specifi -
