U.S. Energy Information Administration - EIA - Independent Statistics and Analysis
Energy in Brief
What is the electric power grid and what are some challenges it faces?
Last Updated: December 22, 2015
The U.S. power grid is the electrical system that connects electricity producers and consumers by transmission and distribution lines and related facilities. The U.S. power grid has evolved into three large interconnected systems that move electricity around the country. Mandatory reliability standards have been developed by the electric power industry and have been approved by the Federal Energy Regulatory Commission (FERC) to ensure coordinated electric system operations. FERC is an independent federal agency that regulates the interstate transmission of natural gas, oil, and electricity.
The process of transporting electricity
To ensure the stability of the entire power grid, electricity must be produced at the same time it is used as large quantities of electrical power cannot be stored effectively.
High-voltage transmission lines, which are often seen hanging between tall metal towers, are used to carry electricity from power generating stations to the places where electricity is needed. When electricity flows through these transmission lines, some of it is lost. High-voltage transmission lines have a high carrying capacity, which makes them more efficient at transmitting electricity. This carrying capacity results in lower losses of electricity. Transformers at substations then reduce the strength of the high-voltage electricity coming from power plants through the stepped-down process, which lowers the voltage levels so the electricity can be used safely in homes and businesses.
History of the electric power grid
At the beginning of the 20th century, there were more than 4,000 individual electric utilities. Each utility operated in isolation from one another. Almost all of the electric utilities used low-voltage, direct current connections to transport electricity over distribution lines to their customers. This changed when the power industry adopted alternating current (AC) technology, which transmits electricity over longer distances than direct current. Widespread use of AC technology throughout the electric industry enabled utilities to build larger power plants located father away from their customers.
As the demand for electricity grew, particularly in the post-World War II era, electric utilities found it more efficient to interconnect their transmission systems. This enabled utilities to share the benefits of building larger and often jointly-owned electric generating units to serve their combined electricity demand at the lowest possible cost. Interconnection also reduced the amount of extra capacity that each utility had to hold to ensure reliable service. Over time, three large interconnected systems evolved in the United States. Today, these three large interconnected systems separately serve Texas and the eastern and western halves of the United States.
U.S. electrical systems are now interconnected
Today, electric transmission and distribution lines owned by an individual utility are no longer used only by that utility. Electrical systems have been expanded and interconnected.
Close coordination of operations among the three power grids is needed to keep the various components connected. The interconnected systems now include about 2,000 electric distribution utilities, more than 300,000 miles of transmission and distribution lines, millions of customers, and more than 7,200 power plants and generating facilities that each has at least 1 megawatt of generating capacity.
Electric utilities are responsible for maintaining the safety of their systems and for planning the future power needs of their customers. Initially, voluntary standards were developed by the electric power industry to ensure coordination for linked interconnection operations. These voluntary standards were instituted after the historic power blackout in 1965 that left much of the northeastern United States (including New York City) and parts of Canada in the dark.
Today, there are mandatory reliability standards for planning and operating power systems and for addressing security concerns at critical electrical infrastructure. These standards are developed and enforced by the country's designated electricity reliability organization, the North American Electric Reliability Corporation (NERC). NERC's activities are regulated and overseen by FERC.
The national power grid
Challenges facing the power grid
Investments in U.S. electricity infrastructure began in the early 1900s and were driven by the increased use of new transmission technology, by central station generating plants, and by growing electricity demand following World War II. Given the age of the national electric grid, some existing transmission and distribution lines must be replaced or upgraded. New lines will also need to be constructed to maintain the electrical system's overall reliability.
There are several challenges to improving the infrastructure of the electric power grid:
- Siting new transmission lines (getting approval of new routes and obtaining rights to the necessary land)
- Determining an equitable approach for recovering the construction costs of a transmission line being built in one state when the new line provides benefits to out-of-state customers
- Ensuring that the network of long-distance transmission lines reaches renewable energy generation sites where high-quality wind and solar resources are located, which are often far from areas where electricity demand is concentrated
- Addressing the uncertainty in federal regulations regarding who is responsible for paying for new transmission lines; this uncertainty affects the private sector's ability to raise money to build transmission lines
- Protecting the grid from physical and cybersecurity attacks
Did you know?
There is no national power grid. There are actually three power grids operating in the 48 contiguous states: (1) the Eastern Interconnection (generally for states east of the Rocky Mountains), (2) the Western Interconnection (from the Pacific Ocean to the Rocky Mountain states), and (3) the Texas Interconnected System. These systems operate independently of each other for the most part, although there are limited links between them. Major areas in Canada are interconnected with the U.S. western and eastern power grids, while parts of Mexico have limited connections to the Texas and the western power grids. In Alaska and Hawaii, several electrical systems cover areas smaller than the states, such as the interconnections serving Anchorage, Fairbanks, and the Kenai Peninsula in Alaska and the individual islands in Hawaii.
The smart grid
The smart grid incorporates digital technology into the traditional electrical system, which enables utilities and customers to receive information from and communicate with the grid. A smarter grid makes the electrical system more reliable and efficient by helping utilities reduce electricity losses and to detect and fix problems more quickly. The smart grid can help consumers conserve energy, especially at times when demand reaches significantly high levels or when an energy demand reduction is needed to support system reliability.
Smart devices in homes, offices, and factories can inform consumers and their energy management systems of times when an appliance is using relatively higher-priced electricity. This helps consumers or their intelligent systems to optimally adjust settings to lower their energy bills. Smart devices on transmission and distribution lines and at substations allow a utility to more easily find out where an outage, or other problem, is on the system. Smart grids can sometimes even remotely correct problems in the electrical distribution system by sending digital instructions.