Fuel Cells vs. Batteries

In the area of fuel cells, reliability and availability have much improved. Recent U.S. military experience with phosphoric acid fuel cells found that the mean time between failure (MTBF) was almost 1,800 h and the availability was 67%. This is comparable with the MTBF service intervals for diesel generators. These fuel cells also favorably compare with the service interval needed for a typical gas turbine generation set. Still, much more development is required to obtain a commercially viable product. Today, the typical fuel cell system still requires servicing every 3-4 days to replace its scrubber packs. 

The early electric cars used the old lead-acid batteries. Today s hybrids are provided with more robust nickel-metal units. The EVs of the future are likely to be provided with lithium-iron batteries, found in today s laptops and cell phones. Much work remains to be done in this area to increase safety and life span (to 100,000 mi of driving), while reducing their cost. Nissan and Mitsubishi are both making major investments in building lithium-ion battery mass production plants. 

New battery developments include the ultracapacitor hybrid barium titan-ate powder design (EEStors). These devices can absorb and release charges much faster than electrochemical batteries. They weigh less, and some projections suggest that in electric cars they might provide 500 mi of travel at a cost of 9 in electricity. But these are only the projections of researchers. 

Another direction of battery development involves high temperature and larger units. NGK Insulators, Ltd., in Japan uses sodium-sulfur batteries operating at 427°C (800°F) that are able to deliver 1 mW for 7 hours from a battery unit. The size of these units is about the size of a bus. Such units could be used at electric filling stations that are not connected to the grid. 

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