Green Manufacturer - November/December 2011

Transmission Voltage (kV)

Cost per
Mile
($/mile)

Capacity (MW)

Cost per Unit of Capacity ($/MW-mile)

230

$2.077 million 500 $5,460

345

$2.539 million 967 $2,850

500

$4.328 million 2,040 $1,450

765

$6.578 million 5,000 $1,320

you’re going 500 miles, then you’ve got significantly lower power losses on the line. This makes DC a more cost-effective investment,” Detweiler said.

345 kV
Six Single-
Circuit Towers
(900-ft. Right-of-Way)

765 kV
One Single-
Circuit Tower
(200-ft. Right-
of-Way)

345 kV
Three Double-
Circuit Towers
(450-ft. Right-
of-Way)

Figure 5

A 765-kV line has 10 times the capacity of a 230-kV line and about one-fourth its cost per unit of capacity. Image courtesy of Edison Foundation, AEP.

Note: Approximate relationship based on surge impedance loading (i.e., reactive power balance point)

Resolving Wind Power’s
Variable Loads

One of the major differences between wind power generation and other forms of energy generation is that wind power is variable. This challenge can be well-managed via an extensive and robust transmission line network, Detweiler maintains.

“One of the advantages of a DC system is that you get a lot of control as a result of converting back and forth from AC to DC,” Detweiler said. “So, big picture, with wind and solar energy resources’ variability, the best way to integrate large volumes of renewables is

Transmission Lines in Progress

The Obama administration says it will speed approval for seven transmission projects in 12 states in an effort to connect renewable energy to load centers, spur infrastructure building, and modernize the U.S. grid.

Together, the projects will cost more than $8.5 billion, according to a Bloomberg report. At least five of them will transport renewable energy.

•;A;$3;billion,;600-kV,;725-mile-long;transmission;line called TransWest Express is being developed by billionaire Philip Anschutz that would connect energy from a 2,500- MW wind farm his company is building in south-central Wyoming to Southern California, Nevada, Arizona, Colorado, and Utah.

•;The;$450;million,;500-kV,;300-mile;Boardman-Heming- way transmission line, part of the Idaho Power transmission line, would ship hydropower and wind power, as well as electricity generated from coal and natural gas-fired power, between Boardman, Ore., and Melba, Idaho.

• The $825 million, 500-kV, 210-mile-long Cascade
Crossing project being developed by Portland General Elec-
tric Co. would ship power to populated areas in western Or-
egon from wind farms in the eastern part of the state and
from gas-fired power plants that might be built to replace
power from the Boardman coal plant, which Portland General
plans to shut down in 2020.