Determination of Number of Days of Autonomy for Battery Sizing in Lagos, Nigeria.

Abstract

The study investigated the number of days of autonomy for sizing a photovoltaic cell (PV) panel and a battery bank in Lagos State, Nigeria. The calculations were based upon the data of monthly mean and daily mean global solar radiation obtained from Department of Physics, University of Lagos weather station (6.31^oN, 3.25^oE); over a period of 6 years (2007 to 2012). The global solar radiation on the horizontal surfaces from the weather station was analyzed using Microsoft excel and the average watt-hour radiation per day was obtained. The month with the worst solar radiation in the year was determined to be July with average daily solar radiation of 1435.07 Wh/m²/day. This radiation value in the month of July was used in sizing the PV panel and the battery bank. For a PV system to comfortably supply the required energy load needed in Lagos State, the panel must be able to provide a minimum of 1435.07 Wh/m²/day energy to the battery after a consecutive number of cloudy days. The number of days of autonomy for sizing a battery bank for a PV system was determined to be 5 days. Using this number in sizing the battery bank, the system is expected to power the load for consecutive five cloudy days without being recharged by the panels. It was found that the solar noon in Lagos is around 1.00PM and is expected that more load be channeled to the solar noon to safeguard the battery life.