Reducing the Energy Carbon Content - Energy and Climate: How to Achieve a Successful Energy Transition - page 85

weight of the storage system. It has been estimated that this value would
have to be approximately doubled in order to fit a storage system carrying
the 8 kg of hydrogen required to achieve autonomy of about 500 km on a
vehicle equippedwith a fuel cell [69]. Since the lowheating value (LHV) of
hydrogen is 120MJ/kg, a storage density of 4%by weight corresponds to
an energy storage density of 1.33 kWh/kg. This density is already much
higher than that which could be obtained using electrochemical batteries,
since the storage density of the best batteries does not currently exceed
70Wh/kg, as we saw in Chapter 5.
Large-scale distribution of hydrogen for a range of decentralised uses
and for transport, creating a 'hydrogen civilisation' [70], is likely to take
several decades and therefore seems uncertain.
The fact still remains that the energy transition will require the imple-
mentation of newenergy vectors and newenergy storagemeans. From this
perspective, the use of hydrogen is one of the avenues to be explored.

Hybridisation of sources

The energy transition will be favoured by setting up hybrid systems,
powered by different energy sources.

- In the field of transport , plug-in hybrid propulsion systems will play

this role.
The autonomy of the current hybrid vehicles, for example the
Toyota Prius, is extremely limited (about 2 km) in purely electric
mode. In addition, all the energy consumed is produced from the on-
board fuel.
Increasing the capacity of the electricity storage systemandmaking
the electric battery rechargeable will offer far greater possibilities,
such as most urban transport requirements. The petroleum fuel
consumption of this type of plug-in hybrid vehicle (PHV) can there-
fore be considerably reduced. In France, 60%of the daily trips would
be covered by a PHVwith an electrical autonomy of 30 km (PHV30),
this proportion reaching 70% for an electric autonomy of 40 km
(PHV 40). Long-distance trips in France represent only 30% of the
annual mileage.
With a PHV offering autonomy of 60 km in purely electric mode
(PHV 60), the average emission level would be about 40 g CO 2 /km, a
figure four times less than current emission levels. This assumes,
however, that the electricity consumed is itself decarbonised.