Application of United Nations Framework Classification for Resources (UNFC) in Ulumbu Geothermal Field, East Nusa Tenggara, Indonesia

Abstract

The Ulumbu Geothermal Field, located in East Nusa Tenggara and operated by PT PLN (Persero), is strategically supporting Indonesia’s renewable energy goals. Ulumbu Geothermal Power Plant currently operates at a total capacity of 10 MW (4 × 2.5 MW) and has an estimated additional potential of at least 40 MW for future development. Although the field has been in operation for several years, PLN has not yet implemented an internationally recognized classification framework such as the United Nations Framework Classification for Resources (UNFC) to manage its geothermal assets. This paper explores the application of the UNFC to the Ulumbu Geothermal Field by assessing its geothermal resources through three fundamental criteria of environmental-socio-economic viability (E-axis), technical feasibility (F-axis), and degree of confidence in the estimate (G-axis). Utilizing publicly available data and internal reports, the study evaluates how the field’s current status aligns with each UNFC axis. The results provide classification of the Ulumbu geothermal resources according to UNFC and highlight the challenges and opportunities of adopting such a system in PLN. The findings suggest that applying UNFC can enhance project transparency, optimize decision-making, and support more sustainable geothermal development in Indonesia.