A Reliable Grid is not a Resilient Grid

With three major hurricanes wreaking havoc on the United States’ power sector in 2017

2560px-Katia,_Irma,_Jose_2017-09-08_1745Z–1935Z
Katia, Irma and Jose…After Harvey and before Irma…                 Hurricane Season 2017

there has been a growing discussion on how to make the grid more resilient. Due to climate change, it is anticipated that storms are likely to become more intense and possibly more frequent, placing growing pressure on the ability of the power system to keep the lights on. We are already finding that climate-induced extreme weather events are already resulting in more frequent and longer duration outage events in the United States.

Defining Resilience 

With this growing threat, a resilient power system sounds like a good thing. Unfortunately, it appears that there is some difficulty in defining what we mean by a resilient power system. From many of my recent conversations, I find there is confusion by what we mean by resilience. For example, I see in some cases, reliability and resilience are used interchangeably. To be clear, reliability is not resilience. According to a recent National Academies of Science Report “Enhancing the Resilience of the Nation’s Electricity Grid,” reliability deals with ensuring there is an adequate amount of power supplied to meet demand, even in times of expected and “reasonably” unexpected outages. Resilience differs in that the expectation is that a resilient system can adapt and lessen the likelihood that an outage will occur and if one does occur to manage the event, lessen impacts, recover as quickly as possible and learn how to deal with future outages.

Valuing Resilience 

IceStormPowerLinesBeyond defining resilience another issue we face is that much of the decision making and cost/benefit calculations are based on economic efficiency calculations that value the benefits of a reliable grid, not a resilient grid.  The focus is on short-term cost-benefit optimization that is detrimental to resilience improvements. In other words, the calculation looks at what keeps the lights on now in our current environment, not what investment would limit the large-area, long-duration outages that may occur due to severe weather activity or other cyber or physical attacks. To overcome this issue requires that there is a better understanding of how to value resilience. To do this requires that we have a better idea as to the probability and intensity of future events that may impact the grid. These known unknowns and unknown unknowns are not easy to value which is problematic when putting together a rate case to fund this investment. Fortunately, steps are being taken to quantify metrics tied to what would be considered a resilient power system. With the development of better metrics to measure performance, it will be more likely we can make more resilient appropriate investments.

Resilient Components – Weighing the Costs

As we get better at improving our ability to define, measure and value a more resilient power system, what would be some strategies that we could pursue? There are a variety of ways to make the transmission and distribution system more robust. All of them may add significant upfront costs to the system but are likely to also provide long-term benefits as the power system is more able to withstand more severe weather events. Following is a very high-level overview of some options that could be considered.

Put the wires underground, sometimes…Undergrounding power lines is an option that I hear a lot. The problem with “undergrounding” is that it is significantly more expensive than hanging the wires on poles. So, we must weigh the cost and benefit of such an approach. In an area that is susceptible to high winds, ice storms and tornadoes, placing the wires underground may be worth the cost. The question we must ask is whether we anticipate there will be an increasing number of these events that would justify burying these cables? At this time, we know that things are going to get a bit hairier, but we are uncertain as to how hairy and when. That makes it difficult to pull the trigger.

Also, we must remember that an approach that would make a power system more resilient in one location may not be as successful in other. For example, if an area is susceptible to flooding, burying wires may be a bit more problematic. Although protections can be put in place to protect against flooding of underground lines, that adds additional cost and it may still not prevent a disruption. Further, any disruption, due to damage to an underground cable, will likely take longer to fix and be more costly than repairing above-ground wires. We must ask are we preparing for floods, high winds or both?

Elevate substations…Not only are the wires susceptible to water, substations can be, as Underwater_substation,_Cedar_Rapids,_June_12_2008well. This was demonstrated by Hurricane Harvey flooding which ruined multiple substations. This damage can be limited by elevating the platform for where these components sit. Levees and dikes can also be built to protect these systems. This is easier done for new infrastructure development, however moving or elevating legacy systems can be cost prohibitive if the proper valuation of this benefit is not properly accounted for.

Strengthen wires and poles...Additionally, for the transmission system, there are methods that can make it more robust, particularly to ice storms and strong wind events. This would include reinforcing poles and towers or constructing wind-resistant concrete and/or steel poles. There could also be more frequent deadends placed along the system. At present, the practice is to place a dead end every ten miles. Placing these deadends more closely together will reduce the likelihood of a domino effect if one of the standard designed poles are compromised.

A smarter gridFor distribution systems, improving resilience requires moving from a radial design to a more networked design. A networked design has more than one supply feed that limits outages if one of the lines go down. The network designs should be coupled with more advanced communication infrastructure that allows systems damage to be isolated and to reroute power when a component is damaged. These smarter grid systems have been deployed in a patchwork across the United States. CenterPoint, in the Houston-Galveston region, does have some smart grid components deployed which allowed for more rapid recovery during Hurricane Harvey.

Conclusion

The bottom line is that solutions exist. I presented a short list of options that may be considered. I didn’t even touch on the fast-approaching opportunities that come with decreasing cost of battery storage. The problem with pursuing many of these strategies is the added expense. Our decision-making frameworks for utility investment are not set-up for resilience investment, they are set up to ensure a reliable grid. Fortunately, with better climate modeling and resilience metrics, we are getting closer to properly valuing the short and long-term benefits of the resilient investment and are moving in the right direction. In the meantime, we will just keep trimming the trees.

 

 

 

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