Hybrid Daytime Lighting System with Photovoltaics and Short-term Storage

Most efficient utilization of electrical energy takes place when energy is consumed locally, avoiding its distribution over long distances or costly storage technologies. Finding such applications for renewable energy sources, like wind or solar, is difficult. The main obstacle is the their limited predictability and the mismatch between energy availability and demand. Nowadays the daytime lighting in modern urban architecture causes a considerable electricity consumption. For such applications, there exists an excellent match between energy availability (solar irradiance) and consumption demand (interior illumination). Moreover, the demand can be met with relatively small PV-generators with modern energy efficient lighting technology. In this paper a hybrid lighting system for daytime, using both natural and artificial light, has been proposed. The supply for artificial lighting is provided from photovoltaic (PV) system or the utility grid, when solar irradiance cannot meet the illumination and electricity demand. The paper presents the results of simulation of full year energy savings in a daytime lighting system. The system maintains the indoor illumination level to be equal or higher than required by the norms, using natural sunlight and artificial lighting. The artificial lighting is used only to compensate the deficiencies of sunlight and is powered with autonomous PV-system in the climatic conditions of Central Europe. The PV-system is also equipped with short-term energy storage, based on super capacitor, allowing for only several minute of backup supply. Such storage is used only to mitigate the rapid solar power fluctuations, providing energy from PV supply at more stable power level during the day, but the excess of energy is not fed to the utility grid. The numerical simulation is using the solar irradiance data collected with 5 s time resolution during the whole year 2010 at Lodz University of Technology, in center of Poland.