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.
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.
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter8: Natural Convection
Section: Chapter Questions
Problem 8.46P
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Transcribed Image Text:Figure P6-28
Reservoir
Pump-
turbine
40 m
Lake
Transcribed Image Text: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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