Inexpensive solar garden light provides valuable energy system learning tool

Solar powered residential garden lights, also called landscape lights, are ubiquitous and provide an inexpensive and convenient means of low-power outdoor illumination. A typical solar garden light fixture consists of a small solar cell, rechargeable battery, white LED, and controlling electronics all contained within a weatherproof enclosure mounted on top of a short plastic stake that can be pressed into the ground. The solar cell charges the battery during daylight hours and the battery powers the LED during the evening. The battery charge/discharge cycle is carried out daily under the control of an application-specific integrated circuit. This small system contains the same functional components as many large-scale solar energy systems (residential, utility-scale, satellites, etc.) and thus provides an excellent tool for demonstrating the concepts of energy generation, storage, and efficiency. First-year students in an electro-mechanical engineering technology program have used the garden lights in an introductory electrical systems course laboratory. Prior to working with the garden lights, the students have become familiar with basic circuit analysis techniques (Ohm's law and Kirchhoff's laws), energy, power, and efficiency as well as basic diode and solar cell operation. These concepts come together and are solidified by the solar garden light laboratory exercises. Most students have seen the garden lights outside of class but are not familiar with their components and operation. Several manufacturers and models of garden lights were investigated, and all were found to be easily disassembled without damage and modified as necessary to allow access to the required system parameters (voltages and currents). This paper describes the operation of the garden lights and how they can be modified to provide various laboratory exercises. Examples of laboratory exercises are presented, and experimental results are discussed.