Environmental Engineering Reference
In-Depth Information
Figure 13.1
Role of Transmission System
Transmission Lines
Carry Electricity
Long Distances
Power Plant
Generates Electricity
Distribution Lines
Carry Electricity
To Houses
Transformer
Steps Up Voltage
For Transmission
Neighborhood
Transformer
Steps Down Voltage
Transformers On Poles Step
Down Electricity Before It
Enters Houses
Source:
USEIA 2011d.
Most of the energy fuel technologies currently in use, to the extent that they rely upon central-
station generation, also rely on high-voltage transmission of electric power to remote locations or
lower-voltage distribution to consumers. Only electricity used at the location where it is generated,
and energy fuels that require no transmission (e.g., fuel in cars and trucks), avoid these costs. The
role of transmission and distribution lines is illustrated in
Figure 13.1.
Because large quantities of electricity cannot be stored effectively, it must be produced at the
same time it is used. High-voltage transmission lines are used to carry electricity from power-
generating stations to places it is needed. Before arriving at the point of use, high-voltage electric-
ity must be stepped down to a lower voltage using transformers so it can be used safely (USEIA
2011a), as illustrated in
Figure 13.1.
In 2010, 3.889 trillion megawatt-hours (MWh) of electricity
(USEIA 2011b, Table 7.2) were consumed by residential, commercial, and industrial customers
in the United States. Most of this electricity was transported over high-voltage transmission lines
(NERC 2011c). Alternating current transmitted at high-voltage loses some of its energy to heat
due to resistance of the conductor (Brown and Sedano 2004, 35). Thus, less energy is received
than the amount transmitted, and the difference is described as transmission losses. The higher
the voltage of transmission lines, the more efficient they are at transmitting electricity, resulting
in lower transmission losses. At the national level, transmission losses are generally estimated
as the difference between what was produced and what was consumed. Total transmission losses
in the United States were about 5.7 percent in 2010, or 236,013 MWh (calculated from USEIA
2011b, Table ES1). Revenues lost due to transmission loses were worth $1.6 to $2.7 billion in
2010, depending on whether the electricity would have been sold to residential or industrial con-
sumers at average retail prices (calculated from USEIA 2011b, Table ES1). These revenues might
not have been lost if the electricity had been generated nearer to consumers and did not require
long-distance, high-voltage transmission to get to markets.
The portion of net electric generating capacity available from each fuel source in the United States
during summer 2010 is illustrated in
Figure 13.2.
Summer is when maximum simultaneous demand
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