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856 ELECTROCHEMICAL STORAGE FOR PHOTOVOLTAICS<br />

hour with the hydrogen system must come down to the values of today’s lead acid batteries<br />

and thirdly, the technical reliability of the complex hydrogen system must be as high as<br />

with conventional batteries. The hydrogen storage system is far away from all these goals<br />

and these goals will be hardly achieved within the next decade.<br />

One interesting line of development is the reversible fuel cell RFC. RFCs fulfil<br />

the functionality of the electrolyser and the fuel cell at the same time. As the process<br />

is completely reversible, this is an obvious solution. Technical problems concerning the<br />

catalysts and the gas and water management within the cell have to be solved [37]. No<br />

commercial products for field applications are available in this technology today.<br />

Applications in autonomous power supply systems will have a combined storage<br />

system made from a conventional battery and the hydrogen system. Figure 18.30 shows a<br />

principle system design as it is currently under development within an R&D project [38].<br />

The hydrogen system here substitutes the conventional motor generator, which is used<br />

today in hybrid systems to bridge the energy gap between summer and winter. A conventional<br />

lead acid battery (five days of autonomy) is assisted by the hydrogen storage<br />

systems. During summer, the energy excess from the PV generator is used to produce<br />

hydrogen in the electrolyser (oxygen is released to the atmosphere). The hydrogen is<br />

stored in a metal-hydride tank. During winter, in long periods with low energy supply<br />

PVG<br />

Photovoltaic generator<br />

and charge controller<br />

CC<br />

TE<br />

Telecommunication<br />

equipment<br />

EMS<br />

Battery<br />

BAT<br />

Electrical energy flow<br />

Hydrogen flow<br />

Signals,<br />

communication links<br />

DCDC<br />

FC<br />

Energy<br />

management<br />

system<br />

Fuel cell and<br />

DC/DC<br />

converter<br />

HSS<br />

ELY<br />

Electrolyzer<br />

Hydrogen storage<br />

system<br />

H2<br />

EMS: energy<br />

management<br />

system<br />

Figure 18.30 Example of an autonomous power supply system for telecommunication with a<br />

PVgenerator, a lead acid battery for short-term storage (five days of autonomy) and a hydrogen<br />

storage system for seasonal energy storage. The system and components have been developed by<br />

partners in the EC co-financed project FIRST [38]

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