Portable and other small-scale systems

Consuming patterns have over recent years seen a dramatic increase in the use of portable equipment for entertainment and work (such as music and video players, laptop computers and mobile phones with multi-functionality). This has increased the demand for batteries, but at the same time found limitations of the battery technology that seem difficult to avoid even with increasing conversion efficiencies. Fuel cells with small-scale stores are an obvious solution to these problems, because the technical performance is already far beyond that of batteries (e.g., operating a state-of-the-art laptop computer for a few days rather than a few hours). The difference between these otherwise similar technologies is the external storage of chemicals for a fuel cell versus the internal storage in batteries. 

A cellular phone in use will need less than 200 mW of electric power, a video camera will need less than 6 W, and a laptop computer or a portable 

CD player will need less than 20 W. More specialised portable equipment includes field environmental monitors, medical mobile life-support systems and soldier commvmication and signalling devices used in military operations (Palo et al, 2002). Power requirements for such equipment would be in the range of 10-400 W. A standard size Li ion battery has a storage capacity of 750 mAh, and the largest one convenient for a laptop computer has a capacity of 3600 mAh. For a portable video camera, the standard Li ion battery may deliver 5 W at 7 V for about 1 h, while for the laptop at 12 V, the larger battery provides about 4 h at an average power consumption of 10 W. 

The high price paid for Li ion batteries today (except for power users, the cost may be some 15-25 euro or US per kWh for typical average operational use of cameras and laptops over an assumed 4-year lifetime of the battery) makes portable applications an inviting niche market for new technologies such as fuel cells. 

For the best metal hydride stores, the capacity (hours of operation) could be increased 5-fold over Li ion batteries of the same volume, and this option has attracted some attention. Giither and Otto (1999) describe a Siemens-Nixdorf experimental laptop computer with such a store, obtaining a 3-fold 

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