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Long-Term Reliability of the National Electrical Grid


The previous 5 posts have described the national electrical grid, how electricity flows on The Grid, how it is organized, Missouri’s portion of The Grid, and the complex balancing act that operators of The Grid face every day. Finally we’re in a position to look at the 2017 Long-Term Reliability Assessment. This is an annual report published by NERC, the North American Electric Reliability Corporation. The assessment identifies several main threats to long-term reliability:

  1. The increasing mix of variable generation may present operational and planning challenges. Let me explain. We saw in the previous post that operating The Grid is a complex balancing act: enough electricity has to be delivered to meet demand, but operators have to be careful not to damage The Grid by flowing either too much or too little electricity through any one part of it. In this balancing act, generating stations that supply ever-changing amounts of electricity complicate the balancing act. It is like a high wire aerialist: if there is a constant wind that is not too strong, he might be able to compensate for it. But if the wind starts gusting strongly, he is in real trouble!
    Yet, that is precisely what wind and solar energy do – the amount of energy they deliver varies with the wind and with the clouds. We need these kinds of power sources to reduce GHG emissions, and they represent an ever-increasing portion of the energy supplied to The Grid. But the challenge of managing these constant fluctuations poses a threat to Grid reliability that will have to be managed. Specifically, operators need flexible generating sources that can increase or decrease the amount of electricity they generate quickly. As California derives a larger percentage of its electricity from intermittent sources than other areas of the country, this need is largest there, and it is increasing faster than previously predicted,
  2. The Grid was designed around large central-station power plants as the primary source of electricity. Wind and solar power plants tend not to be as large. There are more of them, and they are more widely distributed. Integrating a lot of power plants is harder than integrating fewer. Accommodating them will require additions and changes to the distribution system.
  3. Resource adequacy in two reporting regions will fall below reserve margin targets. Let me explain. NERC believes that each operating region needs to maintain a generating and transmission capacity that is larger than the largest anticipated demand in order to ensure reliability. When a problem arises, the reserve is needed to make up for it. How large the reserve margin needs to be depends on the energy mix in a given region. Regions with higher intermittent energy sources require larger reserve margins. In the TRE-ERCOT region (most of Texas), generating capacity will fall below the target level by 2018. In the SERC-E region (Virginia and the Carolinas), it will fall below the target level by 2020. Neither of these regions include Missouri. Without additional generating resources, an increased likelihood of “load shedding” in these regions is possible. “Load shedding” means that they turn off electrical service to some customers or some regions in order to avoid having the whole system collapse.
  4. The growth of demand over the whole system is expected to be the slowest on record. Environmentally, this is good news. From a reliability perspective, the implications are primarily economic, and need to be managed appropriately.
  5. A transition from coal-fired power plants to natural gas-fired ones has been occurring. It will continue. The change is partial good news environmentally. Natural gas power plants produce fewer emissions than do coal-burning ones. However, as natural gas becomes a larger and larger portion of the energy mix on The Grid, the potential for interruptions in energy supply becomes more important. While current supplies seem adequate, power stations are long-term assets that last 40 years or more. For instance, Ameren’s Meramec Energy Center began operations 64 years ago, and KCP&L’s Hawthorn Power Plant began operations 65 years ago. Both are still going strong. The future supply of natural gas so far into the future is less well known than is the coal supply. This may be most important during very cold weather, when demand for natural gas for heating will be high. It may compete with demand for electrical generation, causing supply interruptions.

So, NERC works hard to identify and anticipate future stability threats to The Grid. Are they succeeding? Are outages on The Grid less common than before? That is not an easy question to answer, actually. You have to separate outages that occur on the high voltage bulk power distribution grid from those that occur on local distribution grids. And you have to factor in severe weather. It only stands to reason that years with high numbers of severe weather events will have more outages. No grid will stand up to hurricanes or tornadoes. You don’t want your grid going down every time there is wind or ice, but the 2017 Long-Term Reliability Report does not address weather-related outages.

Figure 1. Data source: Inside Energy 2014.

I found a database prepared by the Inside Energy Project. It is not a peer-reviewed source, so I have no way of assessing their methods, and it is not comprehensive, as small electricity distributors are not required to report outages. With that said, between 2000 and 2014 the database lists 1,652 outage events, affecting anywhere from 0 to 4.6 million customers. The data do not show whether the outages happened on local grids or bulk power grids. As a rough proxy, Figure 1 shows the number of outages affecting 100,000 or more customers by year. You can see that they peaked in 2011, which, amazingly, was not the year of either Hurricane Katrina or Superstorm Sandy (2008 and 2012, respectively). It was, however, the year of Hurricane Irene, a year of many tornado outbreaks, and a year of severe winter blizzards in the Northeast.

While the data is distorted by yearly weather events, there does not appear to be any strong trend toward fewer grid outages. Inside Energy actually argues that they are becoming more common, due to the factors I have discussed above, but also due to increased demand and aging infrastructure.

In the next post in this series, I will look at what NERC has to say about future grid reliability in Missouri.


Ameren Missouri. 2018. Fact Sheet. Viewed online 5/2/2018 at https://www.ameren.com/-/media/missouri-site/files/aboutus/amerenmissourifactsheet.pdf.

Gottscho-Schleisner, Inc., photographer. Hawthorn Power Plant, Kansas City Light and Power, Kansas City, Missouri. View from north I. Viewed online 5/4/2018 at the Library of Congress website, https://www.loc.gov/item/gsc1994027605/PP.

Inside Energy. 2014. Grid Disruption_00_14_Standardized. A Google Spreadsheet downloaded 5/9/2018 from https://docs.google.com/spreadsheets/d/1AdxhulfM9jeqviIZihuODqk7HoS1kRUlM_afIKXAjXQ/edit#gid=595041757. Cited in Inside Energy. 7/18/2014. Data: Explore 15 Years of Power Outages. Viewed online 5/9/2018 at http://insideenergy.org/2014/08/18/data-explore-15-years-of-power-outages.

North American Electric Reliability Corporation. 2017. 2017 Long-Term Reliability Assessment. http://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/2013_LTRA_FINAL.pdf.

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