The future - Wind Power Integration: Connection and System Operational Aspects - page 259

Chapter 8
The future

8.1 Introduction

Wind energy is now, after hydro-power, the main source of renewable electricity. It
has made a substantial contribution to the reduction of CO 2 emissions, especially in
Europe. Wind energy has also helped countries such as Denmark, Germany, Spain
and Ireland to diversify their electricity supplies at modest cost, improving energy
security.
The perceived success has, however, come at a price. Wind energy is often seen
by policy-makers as the main credible solution to global warming. Hence ambitious
targets for 'green' electricity supply tend to rely heavily on wind power. Many
technical and economic challenges stand in the way of these ambitions (Ackermann,
2012). In particular, the variability of wind power and its limited capacity factor
place a limit of about 30 per cent on the wind energy penetration which can be
achieved without significant curtailment. Further development beyond this level
requires large-scale energy storage or interconnection, or both. These solutions
would add significantly to the cost of wind energy, and hence the financial burden
on consumers. Also, the visual and environmental impacts, especially in densely
populated countries such as Britain, are a deterrent (MacKay, 2009).
Offshore wind offers a less visible solution, but with many technical chal-
lenges. It remains stubbornly expensive. Large-scale deployment will require fur-
ther cost-saving solutions. Perhaps the most ambitious proposal to facilitate major
offshore energy development, including wave and tidal power, is the use of under-
sea HVDC grids. Such grids could be cheaper for long ( > 500 km) transmission
distances, but require the solution of formidable technical challenges. Fault currents
could be an order of magnitude greater than in an equivalent AC grid. The diffi-
culty of interrupting a direct current without the zero-crossing characteristic of
alternating current remains, but a solution has been announced recently (ABB,
2013). There are concrete plans to build HVDC grids in both the Irish Sea and the
North Sea.
Where conditions and population density are favourable, there is scope for
cost-effective expansion of onshore wind energy. In addition, capacity can be
increased when re-powering existing wind farms. The early wind farms, built in the
1990s, employed fixed-speed wind turbines. When they reach retirement, there is
an opportunity to install more modern, variable-speed turbines. It is likely that there