Trade-offs between economic and environmental performance of an autonomous hybrid energy system using micro hydro

Abstract

This paper evaluates the trade-offs between economic and environmental performance of an autonomous energy system utilising an existing Micro hydro power plant while improving its future reliability. The analysis primarily focuses on developing sustainable alternative to excessive reliance on Diesel Gensets in fulfilling the increasing seasonal shortfall in electricity supply from standalone Micro hydros. First, a preliminary assessment is conducted using hypothetical future shortfall in electricity supply from a Micro hydro of 10%, 20% and 30%, compared to a baseline of 2% shortfall, which shows drastic increase in the environmental costs (combined human health and ecological) by as much as 400%, 900%, 1400% respectively from continued use of conventional Diesel Genset. In the next step, a ‘Micro hydro sustainability indicator’ is formulated as the ratio of environmental costs to net present costs of different hybrid options. This is estimated through a mixed assessment framework, which combines consumer engagement for understanding the current and the projected future diurnal and the seasonal electrical loads along with quantitative evaluation of the corresponding costs. Finally, a demonstration case study implements this framework at the Khun Pang micro hydropower project in Si Lanna National Park within Chiang Mai province, northern Thailand for two scenarios – Scenario 1 (circa 2016–17, annual shortfall of 4% i.e. 571 kW h); Scenario 2 (circa 2025, projected future annual shortfall of 12.5% i.e. 3904 kW h).For smaller unmet load of up to 4% in Scenario 1, Diesel Genset turns out to be the most preferred hybrid option, irrespective of whether the environmental costs were included alongside the net present costs or not. However, for an increased future load of 12.5% in Scenario 2, including the environmental costs makes the hybrid Micro hydro-PV-Diesel-Battery system cost-competitive to the Diesel only option. Considering a 25-year project lifespan, it becomes the most sustainable solution for retrofitting micro hydro facilities in ecologically sensitive locations in order to meet future shortfall in electricity supply, with improved renewable penetration of up to 97.5%.