Question

Pumped-hydraulic storage power plants use relatively inexpensive off-peak baseload electricity to pump water from a lower reservoir to a higher reservoir. During periods of peak demand, electricity is produced by discharging water from the upper to the lower reservoir through a hydraulic turbinegenerator. A single device normally plays the role of the pump during upper-reservoir charging and the turbine-generator during discharging. The ratio of the power developed during discharging to the power required for charging is typically much less than \(100 \%\). Write a report describing the features of the pump-turbines used for such applications and their size and cost. Include in your report a discussion of the economic feasibility of pumped-hydraulic storage power plants,

Short answer

Pumped-hydraulic storage power plants use off-peak electricity to pump water to a higher reservoir and generate electricity during peak demand. Pump-turbines play dual roles, with efficiency ratios typically less than 100%. These plants are economically feasible due to long-term benefits and grid reliability.

Step-by-step solution

Introduction to Pumped-Hydraulic Storage

Begin by explaining what pumped-hydraulic storage power plants are. These plants use off-peak electricity to pump water to a higher reservoir and release it to generate electricity during peak demand. This helps balance the electricity grid.

Function of Pump-Turbines

Describe how pump-turbines operate. When charging, the device functions as a pump to move water to the upper reservoir. During discharging, it acts as a turbine-generator to produce electricity.

Efficiency Ratio

Discuss the efficiency ratio of power developed during discharging to the power required for charging. Typically, this ratio is less than 100%, indicating that some energy is lost in the process.

Size and Cost of Pump-Turbines

Provide information on the size and cost of pump-turbines used in these storage plants. Mention the varying sizes depending on the plant capacity and the capital cost involved, usually high but justified in the long-term.

Economic Feasibility

Analyze the economic feasibility of pumped-hydraulic storage. Discuss factors such as initial costs, benefits of energy storage, grid reliability, and return on investment over time.

Conclusion

Summarize the key points: the functionality, economic impact, and benefits of pumped-hydraulic storage power plants in aiding grid stability and efficient energy use.

Key concepts

pump-turbines efficiency

Pumped-hydraulic storage power plants play a crucial role in balancing electricity supply and demand. However, they're not perfectly efficient. The efficiency ratio of power developed during discharging to the power needed for charging is generally less than 100%. This means that some energy is lost in the process. Several factors contribute to this inefficiency:
• Losses due to friction and turbulence in the water channels
• Conversion losses in the pump-turbine motor-mechanism
• Electrical losses due to resistance in wiring and transformers
Typical efficiency rates are around 70-85%. It's essential to consider these factors when evaluating the overall performance of a storage plant.

grid stability

The role of pumped-hydraulic storage in maintaining grid stability cannot be overstated. Modern electricity grids require a stable and consistent supply to match fluctuating demand.
• During off-peak hours, excess electricity is used to pump water to a higher reservoir, effectively storing potential energy.
• During peak demand periods, this stored energy is released to generate electricity, ensuring a continuous supply.
By quickly responding to changes in electricity demand, pumped-hydraulic storage plants help prevent blackouts and stabilize voltage levels across the grid.
This rapid response capability is especially important as more renewable energy sources, like wind and solar, are integrated into the power system. Their intermittent nature can destabilize the grid without reliable storage solutions.

economic feasibility

Assessing the economic feasibility of pumped-hydraulic storage plants involves multiple factors. Initial capital costs can be high due to the need for precise engineering and construction of large-scale reservoirs and turbines. However, the long-term benefits often justify these initial expenses.
Key considerations include:
• Initial capital investment versus operational and maintenance costs
• Lifetime of the plant, typically spanning several decades
• Savings from utilizing off-peak electricity to pump water, which is cheaper
• Revenue generation during peak demand periods
Additionally, pumped-hydraulic storage can delay or eliminate the need for new power plants, which would require even higher investments. Thus, despite the substantial initial costs, the long-term economic benefits and grid reliability can make these plants economically viable.

energy storage benefits

Energy storage through pumped-hydraulic systems offers several significant benefits:
• Smoothes out fluctuations in supply and demand, providing a more reliable electricity grid.
• Optimizes the use of renewable energy sources by storing excess energy generated during peak production times and releasing it during low production periods.
• Reduces greenhouse gas emissions by minimizing the need for fossil fuel-based peaking power plants.
• Provides ancillary services like voltage support and frequency regulation, which are essential for stable grid operation.
These benefits contribute not only to a more robust and flexible electricity grid but also to broader environmental and economic goals.