Off-grid mobile phone charging: An experimental study

• We determine the power and energy requirements of bulk mobile phone charging.
• We quantify the efficiency of low power inverters used for mobile phones charging.
• We present optimal size batteries, inverters and solar panels to charge phones.

Global demand for electricity and mobile phone (MP) service is increasing rapidly as a result of emerging markets in developing countries. Compared to the growth of mobile networks, the relatively high cost and technical limitations of extending electricity grids have left over 500 million MP users without access to electricity. MP charging has become one of the major end-use demands in rural electrification projects, where MP users spend disproportionate amounts of time and money seeking charging services.This study investigates the energy and power requirements of MP charging. The energy and power demands of MP charging are determined experimentally using the charge configuration commonly found in developing countries: an inverter powered by a 12 volt car battery. The objective is to quantify the power and energy demand for MPs, and the overall efficiency of the systems used to charge them. By analyzing the charging configurations on an energy efficiency basis and identifying the major losses, recommendations for improvement are made.Results show that the average energy requirement per MP charge is 7 Wh, but due to efficiency losses in the inverter, the total energy requirement can reach up to 13 Wh. The efficiency of the inverter increases with the number of MPs being charged simultaneously, ranging from 50% for a single phone to 85% for 15 phones. The peak power requirement per MP is 7 W.