Tidal Current Energy

The Prospects for Electricity and Transport Fuels to 2050
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installed nuclear capacity in 2002 or, in terms of wind energy, some 2000 GW of
wind turbines (50 times the world capacity in 2003).
If the electricity is to be used in an electrolyzer specifically to produce hydrogen
to displace petrol consumption in vehicles, then approximately double the
capacity of renewable or nuclear electricity is required. A typical petrol-driven
passenger car emits about 50 g�km � 1 of carbon. If the annual range is assumed
to be 16 000 km, then the annual emissions are about 800 kg; allowing 25% carbon
overheads results in the useful emissions benchmark of one tonne of carbon
per vehicle. One wedge is therefore represented by an additional 1 � 10 9 vehicles
by 2050 (2% annual growth from the current world vehicle fleet of around
540 � 10 6 vehicles). A similar sized wedge might be represented by the growth
in freight transport and air travel. The size of the wedge can be reduced by
restricting demand (fewer vehicles or lower annual driving range), improving
vehicle fuel efficiency and/or substituting a lower carbon fuel, such as biofuels
or hydrogen.
2.5 .
Disruptive technologies: fuel cells, hydrogen, and electric vehicles
A key problem in developing energy scenarios is how to deal with so-called
‘ disruptive ’ technologies. A good example of a disruptive technology is the mobile
phone, which forced existing telecommunications companies to rethink their
whole business strategy and changed the way a lot of people in the developed
world live and work. And, extremely relevant to projecting the development of
energy markets, mobile phones enabled new consumers in developing countries
to leapfrog line-based networks.
The most obvious potentially disruptive energy technology is the fuel cell,
which can potentially provide quiet, clean electricity on demand wherever
there is a suitable supply of fuel. Applications include not only mobile power,
vehicles and remote, stationary power, but also hybrid systems crossing the
boundaries between these applications; thus, a car could become a mobile
power station, providing power to the electricity grid in times of local shortage,
or off-grid power for remote homes or camping, for example. Low-temperature
fuel cells require hydrogen and oxygen (usually obtained from the air)
and emit only water vapor at the point of use, the catch being how to produce
all the required hydrogen cleanly in the first place and how to store enough of
it on board a vehicle to permit a reasonable range. High-temperature fuel cells
will accept hydrocarbon fuels, but clearly then would emit carbon dioxide into
the atmosphere at the point of use. At present, the most economic way to produce
hydrogen is from steam reforming of natural gas, a process that inevitably
releases carbon dioxide. Many proponents of the ‘ hydrogen economy ’ assume
that bulk hydrogen will eventually come from renewable power via electrolysis,
while power sector projections of electricity mix rarely project levels of renewable
electricity above 50% of ‘ conventional ’ demand (i.e. extrapolation from existing
markets, not considering any massive increase for the transport sector). Any
such transition would be highly disruptive to the traditionally slow-moving,