Using Solar Cells to Extend Standby Time of Handheld Computers

Abstract

Handheld computers are becoming increasingly popular in today's mobile information applications. Due to their battery energy limitations, the batteries in these computer systems need to be periodically recharged to regain the system's power. In this paper we design and implement a low-power handheld computer system with a rechargeable battery that is automatically charged by solar cells. From the feasibility analysis of the queueing model for the stochastic charging and discharging process of the battery system, using the random characteristics of weather conditions and the user's operation behaviour, we estimate that the average operation time in our model will depend on the power generation efficiency of solar cells and the power consumption of a handheld computer. By including experimental system parameters, we can obtain a duty cycle of less than 5%, which is the ratio between the charging and discharging period. With such a low-duty cycle, solar cells cannot currently be a feasible power source for normal operation of handheld computers. However, from both modelling and experiment results, we learn that solar cells can be a partially supportive power source for the extension of the standby time of handheld computers. In our experiment, with the half of the area of a typical handheld computer, common solar cells can generate the power to extend the standby time of a low-power handheld computer by 50%.