Exploring the impact of passive direct current microgrids on off-grid energy transition: Concept development, testing, and implementation in a remote amazonian community

Abstract

Implementing Direct Current (DC) microgrids in isolated communities offers significant benefits such as energy efficiency, robustness, and reliability but introduces challenges, primarily due to technical complexity. DC microgrids necessitate specialized equipment and control systems to integrate renewable energy sources, energy storage systems, and loads. This integration is particularly challenging in remote locations with limited expertise and maintenance support. The proposed microgrid operates passively, meaning it does not use additional devices or communication between power conditioners to manage the grid's voltage. This alternative approach employs conventional equipment from Solar Home Systems (SHS) using a passive open structure because, despite the global use of SHS in electrification projects for their simplicity and cost-effectiveness, there are limitations in capacity, generally restricting energy use to only one home. A more reliable system with enhanced power delivery capacity can be achieved by interconnecting SHS to form a microgrid. This paper discusses the development of a 24 V DC microgrid using commercial off-the-shelf components, contrasting with the sophisticated equipment typically required. The laboratory testing and the implementation in an Amazonian community are described. The laboratory facility has three SHSs and three independent loads used to evaluate the concept and design, demonstrating operating principles and system capabilities, such as load sharing under typical operating conditions and operation under contingencies. The community DC microgrid is then implemented with five interconnected SHSs, one without batteries, in a remote Amazonian community to run productive end-uses and domestic loads, which were monitored, and the practical results evaluated. The laboratory and community systems demonstrated improved reliability over an individual SHS. When failures occurred within the system, the other generation nodes continued to supply power to the loads. It was also found that 55 % of the total consumption (1963 kWh) was serviced from the battery and that generation curtailment often occurred during the day as most loads did not coincide with the peak generation time, indicating a significant potential for optimizing the energy usage from the load side. At the main nodes, the voltage range is between 0.96 and 1.21 p.u. During the day, the voltage is primarily determined by charging modes, with median values between 1.08 and 1.14 p.u. In contrast, at night or on cloudy days, the battery's voltages partially or wholly establish it, with median values between 0.97 and 0.99 p.u. The four community households surveyed had overwhelming positive views of the microgrid. These outcomes show the potential of this DC microgrid design to support the off-grid energy transition.