Adaptive State-of-Charge Determination HJ Bergveld, NXP Semiconductors, Eindhoven, The Netherlands D Danilov and PHL Notten, Eindhoven University of Technology, Eindhoven, The Netherlands V Pop, Holst Centre/IMEC-NL, Eindhoven, The Netherlands PPL Regtien, University of Twente, Enschede, The Netherlands PHL Notten, Philips Research Laboratories, Eindhoven, The Netherlands & 2009 Elsevier B.V. All rights reserved. Introduction One of the challenges that face modern society is the search for sustainability. Sustainable economic develop- ment requires the existence of clean renewable energy sources and efficient energy storage media. Wind, solar, and tidal powers are examples of renewable but irregular energy sources that require storage media to harvest energy at the peak and to consume it when necessary. Figure 1 illustrates the need for energy storage in various applications. Until recently, energy storage devices such as rechargeable batteries, fuel cells, and su percapacitors were mostly used in portable electroni c appliances (notebooks, cell phones) and stand-alone equipment (reserve power supplies, construction-site tools). Now- adays there is a strong tendency to extend the area of application of energy storage devices in two directions: to higher energy-storage levels for automotive and indus- trial-scale facilities, on the on e hand; and to lower energy-stor age levels in micro-size electronic devices, on the other hand. The automotive sector will be one of the largest consumers of energy storage devices in the coming decades. The overwhelming success of hybrid vehicles illustrates such successful large-scale appli- cation. The industrial-scale energy production will un- avoidably suffer a shift toward sustainability when natural fossil resources will be exhausted. The top right-hand side in Figure 1 corresponds to automotive and indus- trial-scale applications. On the other hand, micro-size energy sources are going to be the key elements of nu- merous wireless autonomous devices and medical im- plants. These devices will change the face of our homes and offices, reorganize logistics, and introduce new op- portunities to modern medicine. A first generation of such devices is already in the state of mass production. This is a prospective and challenging area of great eco- nomic importance. The micro-size energy sources are shown at bottom left in Figure 1. Automotive Micro heat power Portable Autonomous devices Application mWh Wh kWh Ener g y stora g e needs Hydrogen Membrane Electrodes Bipolar plate Electrical consumer bipolar plate Air (oxygen) Air (oxygen) Figure 1 Various battery applications and necessary energy storage capabilities. 459 . Adaptive State-of-Charge Determination HJ Bergveld, NXP Semiconductors, Eindhoven, The Netherlands D Danilov