Solar powered motorized blinds: A case study on using energy harvesting to power internet of things applications

Abstract

Smart devices capable of harvesting their own energy have advantages over their wired or battery-powered alternatives including improved portability, simplified installation, and reduced maintenance and operating costs. This thesis studies energy harvesting technology through a case study of a solar-powered motorized window shade. An analytical and experimental evaluation of window attenuation found that windows reduced the ability of solar cells to produce photocurrent by 30%-70%. This still allows significant potential to power small electronics so a prototype motorized window blind was designed and assembled. The solar array was mounted to the roller blind's bottom rail and power is conveyed to the control electronics and motor in the unit’s top cylinder through wires embedded in the shade’s fabric. A simple battery system was implemented to ensure the prototype could remain powered in the absence of light.

Various forms of powerflow in the prototype were evaluated. Experimental evaluation of joule heating within the conductive textile indicates that a temperature gradient that is less than 10 °C develops, meaning it is safe for use. The prototype was designed with artificial friction to prevent the blinds from slipping when not in use. An experimentally validated motor model was developed and used to determine that the system could use up to 46% less energy if the artificial friction was removed. A pseudo-empirical system model was developed to simulate the interaction between system electronics. Simulation results indicate that the system would remain consistently powered if placed behind a south-facing window that receives a consistent supply of direct sunlight and attenuates that light by less than 75%. These results also indicate that the unit would remain powered in the absence of light for 13 days. Similar methods could be used to evaluate future energy harvesting systems.