Operation of power systems - Wind Power Integration: Connection and System Operational Aspects - page 215

example, a well-lagged domestic hot-water tank of reasonable size can deliver
adequate hot water over 24 hours derived from 7 hours of supply during the off-
peak night time period (McCartney, 1993). However, communication is unidirec-
tional and commands are normally only sent every 24 hours. Telecommunications
technology has advanced to the point where real-time bi-directional control of
air-conditioning loads is possible (Kirby, 2003). Using a pager system, thermostats
can receive curtailment orders while returning acknowledgement/override signals
and system status reports. The thermostats may be accessed collectively, indivi-
dually or even as a group, so that local network constraints can be addressed
directly. Approaches using text messaging and mains signalling are also possible.
More conveniently, perhaps, loads such as air conditioners, refrigerators, etc. could
be designed to be frequency sensitive, increasing the load when the frequency is
high and decreasing the load when the frequency is low - just like the governor
control on a steam-turbine-generator (Vince, 2005). Many modern offices and
buildings incorporate energy management control systems that provide the cap-
ability of controlling electrical equipment associated with heating systems, air
conditioning and lighting. Off-site monitoring is generally provided, but few uti-
lities currently exploit such features in their own regional control centres.
5.5.3 Hydrogen energy storage
Hydrogen has been proposed as the energy store (carrier) for the future, and the
basis for a new transport economy. The reasons for this are simple: hydrogen is the
lightest chemical element, thus offering the best energy/mass ratio of any fuel, and
in a fuel cell can generate electricity efficiently and cleanly. Indeed, the waste
product (water) can be electrolysed to make more fuel (hydrogen). Hydrogen can
be transported conveniently over long distances using pipelines or tankers, so that
generation and utilisation take place in distinct locations, while a variety of storage
forms are possible (gaseous, liquid, metal hydriding, etc.). For transport needs, fuel
cells in vehicles combine multi-fuel capability, high efficiency with zero (or low)
exhaust emissions and low noise. Portable applications including mobile phones
and laptop computers can also employ such compact storage. Fuel cells also
encourage the trend towards decentralised electrical generation and/or the growth
of CHP schemes, through exploiting the waste heat.
Iceland has set itself the target of being the first hydrogen economy in the
world, totally eliminating the need for fossil fuels within the next generation
(2030-2040). The country meets virtually all its electricity and heating require-
ments from renewable (hydroelectric and geothermal) sources, with excess energy
used to generate hydrogen through electrolysis ( ´ rnason and Sigf ´ sson, 2000).
Similarly, the United States Department of Energy is aiming for at least 10 per cent
of annual energy consumption to be provided by hydrogen-powered fuel cells by
2030. A study by the Danish Department of Energy has forecast that by 2030 the
growth in wind power would allow 60 per cent of transport energy needs to be met
by hydrogen (Sorensen et al. , 2004). A further 20 per cent of vehicles could be
expected to run on methanol, obtained by biomass gasification, again derived from
wind power.