Prefeasibility Study of Piedras Negras Hydropower Plant

Piedras Negras hydropower plant, found in the high altitudes of the Andes mountain range, specifically on the San José river in the Libertador O'Higgins region of Chile, will have a design flow of 10 m³/s, a gross head 281.5 m, 23 MW of installed capacity and 62.3 GWh/year of energy production. A third of the area of the catchment, from which the flow that will feed the power plant is going to be derived, is covered by the Universidad glacier, which controls the hydrological regime of the San José river, imposing a challenge for the hydrological study which was satisfactorily overcome using the HBV model, a hydrological model popular in the Scandinavian countries. The hydrological study produced a series of 39 years of runoff data with a mean annual discharge of 4.0 m³/s for the San José river at the intake point. For the design of the hydropower plant itself, three layouts alternatives were analyzed and evaluated from a hydraulic, energy production and costs point of view. All the alternatives considered a flow conduction using pressure pipes and a powerhouse with two Pelton units of varied sizes. Financially speaking, the most attractive alternative was quoted in 71.3 million of USD with a unit price of energy production of 1,145 USD/MWh. Although the presence of the glacier in the intake catchment makes this area especially susceptible to the impact of climate change, the results of this evaluation for the lifetime of the power plant showed that under the RCP4.5 scenario, the energy production would increase by 15% while for the most extreme scenario, RCP8.5, this increment would reach 22%. This shows that the installed capacity could be increased to take advantage of the future effects of climate change. Finally, and due to the characteristics of the project, a detailed analysis of the transient phenomenon in the system is recommended at a future engineering stage as well as a sediment management plan with the goal of extending the lifetime of the electro-mechanical equipment of the power plant, and thus, keeping the operational costs as low as possible