Power distribution architectures to improve system efficiency of centralized medium scale PV street lighting system

• Narrow DC voltage bus distribution has been proposed for street lighting system.
• Analytical tool using MathCAD for various distribution voltages is presented.
• Overall system efficiency improved between 13% and 17% in DC grid against AC grid.
• Length of Power distribution line is doubled for 380 V DC in comparison to 220 V AC.

Typically, stand-alone/decentralized off-grid solar street lighting solutions are designed for autonomy of 3–5 days to meet 3–5 days of low or no-insolation period. These decentralized systems meet the lighting load requirements even under bad weather condition but more than two–third of the year, the surplus solar energy remains unutilized. The small amount of unutilized surplus energy from a single street pole may not be sufficient to meet local energy needs. On the other hand centralized system will have enough energy capacity to meet many of the energy needs of rural community, such as by establishing solar charging stations (energy kiosks), or electric vehicle charging stations or even feeding to grid . This paper investigates various centralized power distribution architectures with the objective of improving system efficiency and simultaneously reducing system complexity. Among various distribution architectures for centralized street lighting system, narrow DC voltage bus architecture is most efficient and has higher reliability. Analytical work using MATHCAD has been undertaken to identify the boundaries of efficient distribution network; and is presented in this paper. During analysis, factors like load at each point, distribution range, type of distribution network, extension to grid and safety are taken into consideration. The analytical work though has been undertaken for centralized street lighting system, it is equally relevant to cluster of homes in off-grid or grid connected systems. One such 220 V DC centralized street lighting system has been designed and tested in lab as well as in field. Experimental results of 220 V DC centralized street lighting system are presented to illustrate system efficiency improvements over conventional 230 V AC system.