6-28 The demand for electric power is usually much higher during the day than it is at night, and utility companies often sell power at night at much lower prices to encour- age consumers to use the available power generation capacity and to avoid building new, expensive power plants that will be used only a short time during peak periods. Utilities are also willing to purchase power produced during the day from private par- ties at a high price. Suppose a utility company is selling electric power for $0.05/kWh at night and is will- ing to pay $0.12/kWh for power produced during the day. To take advantage of this opportunity, an entrepreneur is considering building a large reservoir 40 m above the lake level, pumping water from the lake to the reservoir at night using cheap power, and letting the water flow from the reservoir back to the lake during the day, produc- ing power as the pump-motor operates as a turbine-generator during reverse flow. Preliminary analysis shows that a water flow rate of 2 m³/s can be used in either di- rection. The combined pump-motor and turbine-generator efficiencies are expected to be 75 percent each. Disregarding the frictional losses in piping and assuming the sys- tem operates for 10 h each in the pump and turbine modes during a typical day, deter- mine the potential revenue this pump-turbine system can generate per year.

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**Figure P6-28 Explanation**

This diagram represents a pumped-storage hydropower system, illustrating a water cycle between a reservoir and a lake. Here's a detailed breakdown:

1. **Reservoir**: Located at a higher elevation, the reservoir stores water that can be released to flow downward as needed.

2. **Pump-Turbine**: Positioned between the reservoir and the lake, this device acts both as a pump and a turbine. 
    - As a turbine, it generates electricity when water flows down from the reservoir due to gravitational force.
    - As a pump, it moves water back up to the reservoir from the lake during periods of low electricity demand, storing energy for future use.

3. **Height Difference**: The vertical distance between the reservoir and the lake is marked as 40 meters, indicating the potential energy available for power generation.

4. **Flow Arrows**: Arrows indicate the bidirectional flow of water, signifying that water can either flow from the reservoir to the lake or be pumped up from the lake to the reservoir.

This system exemplifies how energy is stored and generated in a sustainable manner, leveraging gravitational forces and electricity demand cycles.
Transcribed Image Text:**Figure P6-28 Explanation** This diagram represents a pumped-storage hydropower system, illustrating a water cycle between a reservoir and a lake. Here's a detailed breakdown: 1. **Reservoir**: Located at a higher elevation, the reservoir stores water that can be released to flow downward as needed. 2. **Pump-Turbine**: Positioned between the reservoir and the lake, this device acts both as a pump and a turbine. - As a turbine, it generates electricity when water flows down from the reservoir due to gravitational force. - As a pump, it moves water back up to the reservoir from the lake during periods of low electricity demand, storing energy for future use. 3. **Height Difference**: The vertical distance between the reservoir and the lake is marked as 40 meters, indicating the potential energy available for power generation. 4. **Flow Arrows**: Arrows indicate the bidirectional flow of water, signifying that water can either flow from the reservoir to the lake or be pumped up from the lake to the reservoir. This system exemplifies how energy is stored and generated in a sustainable manner, leveraging gravitational forces and electricity demand cycles.
**Understanding Power Demand and a Pump-Turbine System**

The demand for electric power is usually much higher during the day than it is at night. Utility companies often sell power at night at much lower prices to encourage consumers to use the available power generation capacity and to avoid building new, expensive power plants that will be used only a short time during peak periods. Utilities are also willing to purchase power produced during the day from private parties at a high price.

**Potential Business Opportunity:**

A utility company sells electric power for $0.05/kWh at night and is willing to pay $0.12/kWh for power produced during the day. To take advantage of this opportunity, an entrepreneur is considering building a large reservoir 40 m above the lake level. The plan involves pumping water from the lake to the reservoir at night using cheap power, and letting the water flow from the reservoir back to the lake during the day. This reverse flow operates as a turbine-generator.

**System Analysis:**

- **Water Flow Rate:** 2 m³/s in either direction.
- **Efficiencies:** 
  - Pump-motor: 75%
  - Turbine-generator: 75%

Assuming the system operates for 10 hours each in the pump and turbine modes during a typical day, and disregarding the frictional losses in piping, the goal is to determine the potential revenue this pump-turbine system can generate per year. 

This setup aims to leverage the cost differences in day and night power pricing for profit, effectively storing and generating energy through water flow.
Transcribed Image Text:**Understanding Power Demand and a Pump-Turbine System** The demand for electric power is usually much higher during the day than it is at night. Utility companies often sell power at night at much lower prices to encourage consumers to use the available power generation capacity and to avoid building new, expensive power plants that will be used only a short time during peak periods. Utilities are also willing to purchase power produced during the day from private parties at a high price. **Potential Business Opportunity:** A utility company sells electric power for $0.05/kWh at night and is willing to pay $0.12/kWh for power produced during the day. To take advantage of this opportunity, an entrepreneur is considering building a large reservoir 40 m above the lake level. The plan involves pumping water from the lake to the reservoir at night using cheap power, and letting the water flow from the reservoir back to the lake during the day. This reverse flow operates as a turbine-generator. **System Analysis:** - **Water Flow Rate:** 2 m³/s in either direction. - **Efficiencies:** - Pump-motor: 75% - Turbine-generator: 75% Assuming the system operates for 10 hours each in the pump and turbine modes during a typical day, and disregarding the frictional losses in piping, the goal is to determine the potential revenue this pump-turbine system can generate per year. This setup aims to leverage the cost differences in day and night power pricing for profit, effectively storing and generating energy through water flow.
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