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The Flow of Energy on the Grid


Current Grid Fuel ChartTwo posts ago, I introduced you to the national energy grid. Last post I described how The Grid is organized. This post I will describe some of the major energy flows along The Grid.

The chart at right shows the major sources of electricity flowing along The Grid. The largest portion is generated by burning natural gas, the next largest portion by burning coal. Nuclear, hydro, and renewables are the three sources that do not emit carbon dioxide by burning fossil fuel, so they are desirable from a climate change perspective. Together, they account for only 24% of the energy transmitted over the grid.

(Click on chart for larger view.)

I described NERC, the North American Electric Reliability Corporation, in the last post. NERC attempts to estimate changes in grid capacity into the future. The second chart at right shows the current situation, planned changes through 2023, and planned & conceived changes through 2023. 2023 Grid Sources ChartThe chart shows that a significant decrease in energy from coal is being planned and discussed, while significant increases in energy from natural gas, hydro, and renewables are being planned and discussed. If all of the changes being planned and discussed are actually accomplished, by 2023 the portion generated by nuclear, hydro, and renewables will increase from 24% to 34%.

(Click on chart for larger view.)

Most electricity is generated within the NERC region where it is consumed. The flow between NERC regions is a small, but important, percentage of total electricity consumption. It flows in sometimes surprising directions. The direction is determined by many factors, including the availability of transmission lines with unused capacity, historical patterns of energy consumption, and the cost of the electricity. Inexpensive electricity generated at a distance is sometimes substituted for more expensive electricity generated locally.

RegionalPowerFlowsThe flow of energy over The Grid is shown in the map at right. The map is from 2010. The regions shown in it differ slightly from current NERC regions, and they use different names. However, it was the best representation I could find. On this map, “Midwest” = the MISO Region, “Central” = the SPP Region, “TVA” = the SERC-N Region, and “Mid-Atlantic” is roughly the PJM Interconnection Region. Let’s look a bit more closely at the map.

(Click on map for larger view.)

A region in Northern Illinois served by Commonwealth Edison belongs to the Mid-Atlantic Region, but is physically separated from it. The largest power flow in the nation occurs from this region to the rest of the Mid-Atlantic Region. This represents power that is generated by highly efficient coal and nuclear generating stations operated by Commonwealth Edison. They can’t be cycled on and off easily, so during periods of slack demand (at night) they export large amounts of power at low prices.

The second largest flow occurs from the Southwest into California. As a single state, California imports more electricity than any other.

The Midwest Region is a net exporter of power. It receives power from Manitoba and Commonwealth Edison, but it distributes even more to the TVA and Central Regions. In doing this, it participates in a counterclockwise flow from Manitoba, through the Midwest and the South to the Mid-Atlantic Region.

The Central region is a net importer of electricity. It receives inflows from the Midwest, keeps some of it, and distributes less than it receives to Texas and the Gulf.

The amount of energy available to any region, therefore, depends mostly on the generating capacity within the region, but also on the amount it receives from other regions. The transmission of energy between regions depends not only on the need for it, but also on price and the availability of transmission capacity.


North American Electric Reliability Corporation. 2013. 2013 Long-Term Reliability Assessment. http://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/2013_LTRA_FINAL.pdf.

Source: “Electricity tends to flow south in North America.” Today in Energy. EIA, http://www.eia.gov/todayinenergy/detail.cfm?id=4270.

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