Powering devices using ultra-capacitor batteries

We explore the use of ultra-capacitors as backup storage for solar powered electronic devices. We discuss two use cases: routers in off-grid broadband networks consuming a few Watt and wireless sensor network nodes using a few mW when operating and a few μW in quiescent mode. We have been testing batteries with ultra-capacitor based cells, both EDLC and LIC, in the range from 40 to 3000F. We found them viable alternatives in some applications and started long term field tests to sort out some unclear aspects regarding maximum discharge levels. Besides the traditional function of a backup battery storage in low-power applications, the very low internal resistance of capacitors make them useful also in hybrid solutions to accommodate transient needs for high currents that traditional batteries cannot deliver. Due to the low resistance, charging/discharging can be very fast. We also show how a very simple design requiring only one LIC capacitor can power a WSN mote sending at 1 packet/minute for 6 weeks on a single charge.