A study of photovoltaic-powered billboard lighting systems in Chiang Mai, Thailand

In the municipal zone of Chiang Mai there are nearly 32 billboards of government buildings. These billboards are illuminated by tubular 36-W (watt) fluorescent lamps (FL) or by high energy-consumption tungsten halogen lamps. We proposed to substitute AC lamps by photovoltaic-powered (PV) lighting systems. We experimentally investigated the number of fluorescent lamps while changing billboard sizes in our laboratory. PV lighting system is assembled with a 42-W/sub peak/ single crystalline silicon solar cell panel, a 60 Ah lead-acid battery and two 18-W FL lamps with local electronic ballasts. The charging time and discharging time were controlled on each day. We found that after several weeks of testing we still have surplus energy in the battery. Because of the limited power of 42-W/sub peak/ panel and average daily solar irradiation data in Chiang Mai, it is suggested that for two 18-W lamps the operating time of the lamps should not be more than 4 hours in this tested system.