Seasonal Water-Flow Risk and Business Sustainability in a Mini-Scale Hydropower Enterprise: Evidence from Central Java, Indonesia

Fixed-tariff power purchase agreements (PPAs) give small-scale mini-hydropower plant (MHP) entrepreneurs in Indonesia price certainty, but not certainty over the volume of electricity they can sell. This study assesses the production and revenue vulnerability of an MHP enterprise to streamflow variability through a case study of the Pageruyung-1 MHP (2 MW, run-of-river) in Kendal Regency, Central Java. Recorded daily discharge for May 2023–August 2026 was used to estimate power output, simulate energy and the effective capacity factor (CF), and construct a monthly indicative revenue index; debt service capacity was analysed as a scenario. The lowest monthly mean discharge (431 L/s, October 2023) was only about one-third of the design discharge (1,311 L/s). Simulated annual CF ranged from 43% (May–December 2023) to 88% (2025), while monthly CF fell to as low as 33% in the dry season, below the 60% regulatory benchmark. In 2024, the revenue index of the lowest month was only 44% of that of the highest month (a 56% decline), with a coefficient of variation of 32%, compared with 18% in the wetter year of 2025. Under a level repayment scenario sized at an annual debt service coverage ratio (DSCR) of 1.3, the monthly DSCR in 2024 fell below 1.0 for six consecutive months (minimum 0.58); a repayment schedule sculpted to the seasonal pattern reduced this to four months. These findings indicate that the production and revenue vulnerability of MHPs should be assessed on the basis of the monthly distribution rather than annual averages, as a foundation for liquidity and financing planning by small-scale renewable energy entrepreneurs.