Geothermal and Hydropower Flashcards

A project developer is evaluating a high-head, low-flow water resource for a new hydropower plant. Which type of turbine would be most suitable and efficient for this application?

Answer: Pelton turbine

A Pelton turbine is an impulse-type turbine that is most efficient for high-head (significant vertical drop) and low-flow-rate applications. [2, 4, 8, 9] Jets of water strike buckets on the turbine wheel, making it ideal for these conditions. Francis turbines are suited for medium heads, and Kaplan/Propeller turbines are used for low-head, high-flow scenarios. [2, 8]

Which of the following geothermal power plant types is best suited for resources with lower water temperatures (107-182°C) and utilizes a secondary fluid with a low boiling point to drive the turbine?

Answer: Binary cycle plant

Binary cycle power plants are designed to work with lower-temperature geothermal resources. They use the heat from the geothermal water to boil a separate working fluid (like isobutane) that has a lower boiling point than water. [15, 17, 19, 23] This vaporized secondary fluid then drives the turbine. Dry steam and flash steam plants require higher temperature resources to produce steam directly. [15, 17, 23]

A major concern during the operational phase of a hydrothermal geothermal power plant is the potential for land subsidence. What is the primary engineering practice used to mitigate this risk?

Answer: Reinjecting cooled geothermal fluids back into the reservoir

Land subsidence in geothermal fields is primarily caused by the reduction of pressure in the underground reservoir as fluids are extracted. The most effective mitigation strategy is to reinject the cooled geothermal water back into the reservoir, which helps to maintain pressure and support the overlying rock structure. [29]

A renewable energy consultant is assessing a potential site for a pumped-storage hydropower facility. What is the primary function of this type of plant in an electrical grid?

Answer: To serve as a large-scale energy storage solution for grid stability

Pumped-storage hydropower (PSH) facilities act like large batteries for the electrical grid. They use surplus electricity (often from renewables during periods of low demand) to pump water from a lower reservoir to an upper one. [3, 5, 21] When demand is high, the water is released back down through turbines to generate electricity. This provides critical grid stabilization and energy storage services, not continuous baseload power. PSH is a net consumer of energy but provides value by time-shifting generation. [3, 5]

During the initial exploration phase for a geothermal resource, which of the following methods would be used to analyze the chemical composition of fluids from hot springs to estimate subsurface temperatures?

Answer: Geochemical analysis

Geochemical analysis involves studying the chemistry of fluids and gases from surface features like hot springs and fumaroles. The concentrations of certain dissolved elements and gases (geothermometers) can be used to estimate the temperature of the deep underground reservoir from which they originated. [6, 7, 10]

Which of the following is a significant socio-environmental impact that must be carefully managed when developing large-scale reservoir hydropower projects?

Answer: Displacement of communities and habitat fragmentation

The creation of large reservoirs for hydropower dams often requires flooding vast areas of land. This can lead to the displacement of local communities, loss of agricultural land, and significant disruption to terrestrial and aquatic ecosystems through habitat fragmentation. [11, 12, 18, 25] While hydropower is a low-carbon energy source, these social and environmental impacts are major considerations in its development. [11]