Reliability and Resilience: Different Concepts, Common Goals


Common Goals of Reliability and Resilience

  • Keep the power on.
  • Minimize the risk of outages.
  • Withstand disruptions and minimize the impact of outages.
  • Quickly and efficiently restore the system.
  • Incentivize reliability.

By Andy Ott, President and CEO

As operator of the nation’s largest electrical grid, it is PJM Interconnection’s job to keep the power flowing to 65 million people in 13 states and District of Columbia, and I am proud to say that our system is both reliable today and will be into the future.

But what does that mean? And what is the difference between reliability and resilience, a term that you will hear increasingly applied to the electric system?

Today we offer our latest contribution to answering those questions with the publication of our full Fuel Security Analysis (PDF), a summary of which was released last month. We believe this paper will help give substance to the elusive concept of resilience and its relation to reliability.


Reliability is PJM’s most important job, and has been since we started in 1927. Reliability is about designing, running and maintaining electricity supply to provide an adequate, safe and stable flow of electricity. In your everyday life, that means the lights come on when you get home, the refrigerator is working and businesses continue to hum around the clock.

Traditional threats to reliability have included the loss of generation, loss of transmission or loss of customer demand – a generator breaks down, a substation trips off, or a fallen tree knocks out power in your neighborhood. Equipment failure and extreme weather are common threats to reliability.

Reliability is also well defined within the electricity industry, and we are accountable to many federal and industry standards that ensure we maintain reliable operations. I can safely say that the grid is more reliable that it has ever been, as underscored by our fuel security study (PDF), which found that the grid will continue to perform under a number of stressed conditions.

But are we properly preparing for changes and disruptions for which there are no standards? Can we withstand and recover quickly from major catastrophes, coordinated attacks or some combination of events we have never experienced? That’s where resilience comes in.


There are many dimensions to resilience and no standard fits them all.

Resilience is directly linked to the concept of reliability; you cannot be resilient if you are not first reliable. Resilience encompasses additional concepts – preparing for, operating through and recovering from significant disruptions, no matter what the cause. It is about our ability to withstand extreme or prolonged events.

While some of these risks are considered in traditional reliability planning, threats evolve quickly and reliability standards – and the related regulatory requirements — may not be able to keep pace.

Determining how best to invest in resilience is essential for PJM and our stakeholders. Costs must be balanced with both the likelihood of an event and the societal impact of the loss of electricity for an extended period.

Striking the right balance of risk and cost requires ongoing discussion with our stakeholders, regulators, legislators, consumer advocates and the electricity industry at large.

Common Objectives of Reliability and Resilience

The core functions of planning and operating the grid are rooted in the following objectives shared by both reliability and resilience:

Keep the Power On

We work around the clock to balance supply and demand and keep the electricity flowing. We plan and coordinate the dispatch of power plants and the operation of high-voltage equipment that transports electricity over long distances.

Minimize the Risk of Outages

We plan far ahead for a robust system that can provide a reliable and efficient flow of electricity and minimize the risk of interruptions.

Withstand Disruptions and Minimize the Impacts of Outages

We work to monitor and adjust the power grid so it can withstand disruptions. The more robust the grid is, the lower the impact of outages is on customers.

Quickly and Efficiently Restore the System

We must be prepared to quickly and efficiently restore the electric system after an outage.

Incentivize Reliability

Competitive markets offer incentives that help maintain a reliable system and also be designed to enhance resilience.

Grid operators like PJM can anticipate and prepare for certain threats, but we cannot foresee everything, especially as the world becomes more interconnected and different threats emerge. That is why the grid must be not only reliable but also resilient. The fuel security analysis looks closely at one aspect of resilience, the supply of fuel that powers the generators that power the grid.

As we continue to push forward studying resilience and incorporating its attributes into our operations, planning and markets, we are committed to ensuring that any solutions remain cost-effective for the customers who live and work in the region we serve.

Know More

You can read more in our fact sheet “Reliability and Resilience: Working Toward Common Goals” (PDF) as well as our study “Fuel Security Analysis: A Resilience Initiative.” (PDF)