5 - Uninterruptible power supply/backup

Abstract

This chapter aims to look at the use of fuel cell technology for uninterruptible power supply (UPS) services. UPS systems provide security against the loss of power in a grid failure, or grid fluctuations, either sags or spikes. In the case of power loss, the UPS system is scaled to provide one of two functions that include either enough power to safely shut all systems down once work is saved or extended run-time UPS systems that provide continuous power during the period. Currently, three types of fuel cells are being used or considered for UPS systems. One of the types is proton-exchange membrane (PEM) that is used in over 99% of new UPS units. Another is solid oxide fuel cell (SOFC), a high-potential technology for standby power. SOFCs are high-temperature fuel cells which are experiencing intense levels of research and development (R&D) which in turn is having the impact of bringing unit sizes and costs down, while increasing power densities. Another is alkaline fuel cell (AFC), and only a few companies are pursuing the technology and developing UPS applications. Molten carbonate technology is another high-temperature fuel cell. Different regions of the world have varying levels of interest in UPS systems. In Japan, the electricity grid is not only ubiquitous but also very stable, so interest is higher in systems that take some of the primary load off the grid, such as residential systems, rather than providing power in the case of grid failure. In Europe and North America, where the grid is also widespread but not as stable, interest in UPS is intense.