Island Power System Operation with Single-Wire Earth Return (SWER), Solar PV and Diesel Generator Systems – Case Study of Marinduque, Philippines

Abstract

Single-wire earth return system (SWER) is a cost-effective solution to rural electrification. Developed in New Zealand in the 1920s, sparse remote areas utilized as farmlands were electrified using this system. Aging system and with capacity constraints, however, are factors that have been considered as main conundrums of distribution utilities operating with SWER system. SWER systems operate by drawing power from the grid to supply the end load. With the increasing solar PV system penetration in the consumer side, this study looked in the possibility of bi-directional operation of SWER system during surplus generation at the load side. A MatLab model of the system consisting of the grid, a SWER system, a solar PV system, and a diesel generator was created to test the possibility of bi-directional operation. Results showed that the system can operate in reverse, thus sending power back to the grid. It can also be inferred based on the resulting voltage measurements across the load that the system voltage can be improved using additional generating facilities at the load side. A case study that will offset a 2MW capacity via rooftop solar PV was done for Marinduque, Philippines. Using a sample household demand, a 1.34 kWp rooftop solar PV capacity was designed. In order to offset a 2MW-capacity from the grid, the number of household that needs to be installed with this system is 1600 at a total cost of PHP 430 357 158 or NZD 12 295 918.80. Also conducted was a case study that will energize five out of the remaining 20 unenergized sitios in the province of Marinduque. These sitios will be energized using SWER system. The system was designed based on the connected loads per sitio. Line impedances were calculated using Carson's mathematical model of a SWER system while the load flow analysis on the newly designed system integrated with solar PV system and diesel generator was done using DIgSILENT. The additional 2MW capacity and the designed SWER system were integrated with the existing power system of Marinduque, Philippines. The existing power system was modelled in DIgSILENT using the power systems data given by the Technical Services Department of Marinduque Electric Cooperative (MARELCO). Several cases were made with the model. To maximize the benefit of the integrated system and the additional 2MW-capacity, additional generation plants must be connected to the towns of Gasan and Santa Cruz with the interconnection switch between Buenavista and Torrijos closed. This thesis was able to prove that bi-directional operation using SWER system is possible and was also able to provide a theoretical solution to further improve the current power system of the province of Marinduque, Philippines.