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2.1 Power, discharge, head relationship

Historical hydropower development in the U.S.

In the early days of large dam construction in the US, hydropower was considered a byproduct of water development. However, the need for hydropower soared as energy demands increased during World War II. The 1944 Flood Control Act empowered the USACE to sell the power produced at federal projects, leading the way for a multipurpose approach to dams. In the early 20th century, hydropower represented about 75 percent of all the electricity consumed in the West and Pacific Northwest, and about one third of the total United States' electrical energy.

Power, discharge, head relationship

Hydropower generation curves for different reservoir elevations and hydropower releases provide a useful resource for hydropower planning. Recall the simplified equation for hydropower generation:

 P = (η QH) / (1.181 * 10^4)

where, P is power (MW), η  is turbine efficiency (%), Q is discharge (ft3/s), and H is head (ft). For this example let us assume (incorrectly) that the efficiency factor is constant, while discharge and head vary over the course of a day, yielding different power output. The following activity allows you to explore how energy output varies with hydraulic head and discharge.

Folsom powerplant power, discharge head relationship (historic)

As mentioned previously, Folsom Dam was initially authorized for flood management objectives and reauthorized in 1949 for power production, after construction began. The plant provides peaking power to first meet the requirements of the project facilities (including power to pump residential supply) and then the remaining energy is marketed to northern California power customers.

 

 

The flood control objectives dictated the height of Folsom Dam at 340 ft. Planners tried to maximize the head available for power production and place the turbines at base of the dam (134 ft. elevation) such that at the gross pool elevation (466 ft) minus the head equals 332 ft (= 466 - 134 ft). Let ε = 0.85, signifying an 85% efficiency rating, typical of an older powerplant. Use this information to write an equation for the relationship between energy and discharge when the reservoir is full.

P= ( Q  x   x   ) / (   x 10^  )

As mentioned previously, Folsom Dam was initially authorized for flood management objectives and reauthorized in 1949 for power production, after construction began. The plant provides peaking power to first meet the requirements of the project facilities (including power to pump residential supply) and then the remaining energy is marketed to northern California power customers.

However, during the flood season, the operators manual for Folsom dam requires the reservoir to remain at the flood conservation elevation of 426 ft during non-emergencies. Try again assuming the reservoir is at the flood conservation pool elevation, rather than the maximum pool elevation. Remember, the turbines are located at 134ft, so the head is the difference between the pool and turbine elevations.

P= ( Q  x   x   ) / (   x 10^  )

Now try to enter some reservoir elevations at intermediate stages to get a better idea of the relationship between power, discharge and head. 

P= ( Q  x   x   ) / (   x 10^  )

Present day

Today, hydropower accounts for about seven percent of US energy consumption, although it still plays a major role in some basins.

As a result of increased power demand, Folsom's three generators were upgraded in 1972 from a nameplate capacity of 162 MW to 198 MW of power. In addition, current construction will raise the dam approximately 7 ft, providing more head for power supply.

 

 

 

 

References

http://www.calwater.ca.gov/Admin_Record/C-073130.pdf

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