Electric Reliability Planning for Extreme Weather and System Conditions

The New York State Reliability Council (NYSRC) Executive Committee approved the Extreme Conditions Whitepaper on July 8, 2022.  The white paper evaluates the potential need for revised New York

resource adequacy and transmission planning design rules for planning the system to meet “extreme weather and other extreme system conditions.”  This post provides background information on the disconnect between weather and climate prevalent in most of the electrical planning reports, identifies resource adequacy requirements, and describes the identified problems in the whitepaper

Everyone wants to do right by the environment to the extent that efforts will make a positive impact at an affordable level.  I have written extensively on implementation of New York’s Climate Leadership and Community Protection Act (Climate Act) because I believe the ambitions for a zero-emissions economy embodied in the Climate Act outstrip available renewable technology such that it will do more harm than good.  This post also addresses the mis-conception of many on the Climate Action Council that an electric system with zero-emissions is without risk.  The opinions expressed in this post are based on my extensive meteorological education and background and do not reflect the position of any of my previous employers or any other company I have been associated with, these comments are mine alone.

Weather and Climate

The difference between weather and climate is constantly mistaken by politicians, media, and, as far as I can tell, most electric system planners.  According to the National Oceanic and Atmospheric Administration’s National Ocean Service “Weather reflects short-term conditions of the atmosphere while climate is the average daily weather for an extended period of time at a certain location.”  The referenced article goes on to explain “Climate is what you expect, weather is what you get.”  Also keep in mind that the standard climatological average is 30 years.  In order to think about a change in today’s climate averages you really should at least compare the current 30 years against the previous 30 years. 

In my experience the common perception that there are observable changes in frequency and intensity of extreme weather events does not withstand close scrutiny.  Furthermore, Dr. Cliff Mass has coined the golden rule of climate extremes that says “The more extreme a climate or weather record is, the greater the contribution of natural variability”.  I believe that any trends in weather events due to climate change are tweaks not wholesale changes.  The best way to evaluate weather trend impacts is to use as long a data set as possible.  On the face of it that might seem easy but the reality is that the conditions for a representative trend are difficult to achieve.  Ideally you need to use the same instruments, the same methodology, and keep the conditions around the observing location the same.  That is almost never the case.

One final point.  We are just starting to understand natural variability of ocean temperature and circulations.  Many people have heard of the El Niño and La Niña weather patterns.  El Niño and La Niña are two opposing weather patterns that make up the El Niño-Southern Oscillation (ENSO) cycle. El Niño and La Niña regimes typically last nine to 12 months, but can sometimes last for up to seven years on average. Over longer periods, the Atlantic Multi-decadal Oscillation (AMO) has been “identified as a coherent mode of natural sea surface temperature variability occurring in the North Atlantic Ocean with an estimated period of 60-80 years”. In the Northern Pacific the Pacific Decadal Oscillation (PDO) is a similar sea surface temperature source of decadal natural variability.  These patterns and oscillations all affect our weather but it is not clear exactly how, especially when the combined effects are considered.   If we cannot explain how these naturally variable systems affect our weather then it is unlikely that the climate change weather event perturbation imposed by the greenhouse effect can be described.

Resource Adequacy Modeling for a High Renewable Future

The National Regulatory Research Institute (NRRI) report  “Resource Adequacy Modeling for a High Renewable Future“ gives an excellent overview of electric resource adequacy planning as performed today and describes what they think will be needed in the future.  I did a post on this report that can be used to provide more detailed background information on resource planning standards.

In this article I am only going mention the resource adequacy metrics described in the article.  The report describes traditional resource adequacy planning:

Electric utilities have used the resource planning process for decades to develop long-term, least-cost generation supply plans to serve expected customer demand. Resource adequacy planning ensures that a system has enough energy generation throughout the year to serve demand with an acceptably low chance of shortfalls.  Resource adequacy is measured by the metrics described in Figure 1.  Reliability metrics provide an indication of the probability of a shortfall of generation to meet load (LOLP), the frequency of shortfalls (LOLE and LOLH), and the severity of the shortfalls (EUE and MW Short).

The industry has traditionally framed resource adequacy in terms of procuring enough resources (primarily generation) to meet the seasonal peak load forecast, plus some contingency reserves to address generation and transmission failures and/or derates in the system.  This approach and the metric used to define it is called the “reserve margin.”  Planners establish a reserve margin target based on load forecast uncertainty and the probability of generation outages. Required reserve margins vary by system and jurisdiction, but planners frequently target a reserve margin of 15 percent to 18 percent to maintain resource adequacy.

New York resource planning analyses use the “one day in ten years,” criteria (LOLE), meaning that load does not exceed supply more than 24 hours in a 10-year period, or its equivalent metric of 2.4 hours loss of load hours (LOLH) per year. This analysis is performed at the “bal­ancing authority” (BA) level. In the past New York BAs were vertically integrated utilities with defined service terri­tories. After deregulation this responsibility passed to the state’s independent system operator (ISO).  The region covered now includes many utility service territories.  More importantly the New York Independent System Operator (NYISO) has to develop market or compliance-based rules to main­tain sufficient system capacity which adds another layer of complexity.  The NYISO does their resource adequacy planning using resources within its geographic region or have firm transmission deliverability into the New York Control Area (NYCA).  There is another complication in the state.  New York City has limited transmission connectivity so there are specific reliability requirements for the amount of in-city generation that has to be operating and other rules to prevent blackouts in the City.

The NRRI report concludes:

The electric grid is transitioning quickly from a system of large, dispatchable generators to a system reliant on high levels of variable renewable energy, energy storage, and bi-directional flow. Against this backdrop, analytical tools used for decision making regarding resource adequacy are more important than ever and those tools need to evolve to meet the modern grid challenges outlined in this paper. Models based in realistic weather-driven simulations more accurately capture the risk of load shedding due to inadequate generation. Simulations derived from historical data ensure models include load and generation patterns as well as correlations among resources and the ability to adjust to future climate conditions. Models that do not account for these factors may lead to decisions that underinvest in resources or invest in the wrong re­sources. Recent events in California and Texas indicate the importance of getting these projections right to keep the grid reliable.

To model resource adequacy in future power systems with high penetration of renewables, we recommend several enhancements in modeling tools and tech­niques. Modeling tools should simulate key structural variables and allow for validation of the simulations by benchmarking against the historical data used to create the simulations. While maintaining statistical properties derived from historical data, simulations should also include future expectations of load growth along with changes in seasonal and daily load shapes. Genera­tion-forced outage simulations should include the possibility of correlated outages from extreme weather. Finally, climate change will drive more weather events in the power system and this risk should be accounted for in the models, at least in the form of sensitivity cases or stress tests.

New York State Reliability Council

In addition to the NYISO the New York State Reliability Council has reliability planning mandates.  According to their webpage:

The New York State Reliability Council, L.L.C. (“NYSRC”) is a not-for-profit entity, organized as a Delaware limited liability company, whose mission is to promote and preserve the reliability of electric service on the New York State Power System by developing, maintaining, and, from time-to-time, updating the Reliability Rules which shall be complied with by the New York Independent System Operator (“NYISO”) and all entities engaging in electric transmission, ancillary services, energy and power transactions on the New York State Power System. The NYSRC shall carry out its mission with no intent to advantage or disadvantage any Market Participant’s commercial interests.

The NYSRC’s mission also includes monitoring compliance with the Reliability Rules by working in consultation with the NYISO to assure compliance, including when necessary, seeking compliance through the dispute resolution procedure contained in the ISO/NYSRC Agreement, and taking such other actions which may be necessary to carry out the purpose of the NYSRC Agreement.

Extreme Conditions Whitepaper

New York’s Climate Act mandates that the state’s electric system is supposed to be 100% zero emissions by 2040. The authors of the Climate Act envisioned that this transition would use new wind and solar resources without any new nuclear generation.  The NYSRC Extreme Conditions Whitepaper reflects the need to address the issues raised in the NRRI report:

A NYSRC 2022 goal for the NYSRC Reliability Rules Subcommittee (RRS) to: “identify actions to preserve NYCA reliability for extreme weather events and other extreme system conditions” and its corresponding action plan to: “evaluate the potential need for new resource adequacy and transmission planning design rules for planning the system to meet extreme weather and other extreme system conditions.” Accordingly, this paper presents Extreme Weather Resilience Plan recommendations which are designed to ensure that the NYS electric system continues to deliver reliable performance in the face of a changing climate.

Two extreme system conditions were explicitly considered: extreme weather events and loss of natural gas supply.  Extreme weather events are considered low-probability widespread weather events

or climate conditions occurring within a limited period, with the potential of having a very severe impact on the reliability of the bulk power system.  The majority of loss of natural gas supply to generating facilitates are due to operational or scheduling or market deficiency issues. Natural gas pipeline failures account for a relatively minor fraction of loss of gas supply events.  I am only going to address the extreme weather aspects in this article.

The section on extreme weather events starts:

Climate change has led to an increase in the frequency and intensity of extreme weather events, raising concerns about the resilience of the electric grid and its ability to successfully address such hazards.

As explained above I don’t subscribe to the increase in the frequency and intensity claim.  This sentence includes a reference to an Oak Ridge National Laboratory  report “Extreme Weather and Climate Vulnerabilities of the Electric Grid: A Summary of Environmental Sensitivity Quantification Methods” that provides more details on the weather events that cause blackouts.  It also repeats the claim that extreme weather is changing due to climate change.  It is almost as if they think that they don’t need to document the claim because “everybody” knows it is the case.

The Whitepaper goes on to say:

All components of electricity supply and demand are potentially vulnerable to such events, including electric power generation and transmission. Further, the changing resource mix with higher penetrations of solar and wind generation adds to the vulnerability of the system to extreme weather. Extreme weather events, such as prolonged cold and hot weather spells, wind lulls, hurricanes and storms, are considered one of the main causes of wide area electrical disturbances worldwide. In the United States, 96% percent of power outages in 2020 were caused by severe weather or natural disasters.

The whitepaper lists the types of extreme weather that impact the NYCA. 

The whitepaper explains an important consideration:

It should be noted that extreme weather events, by their nature, infrequent but have a large impact on system reliability such as widespread blackouts. This is in contrast to normal or design events such as generator or transmission outage events. Normal events are predictable in a probabilistic sense in terms of, for example, expected forced outage rates for generators, and generally do not result in wide-spread blackouts. In terms of a statistical frequency distribution, normal events occur around the mean of the distribution while extreme weather events occur at the tails of the distribution. This means that a different form of analysis, reliability criteria, and system loading condition may be appropriate for extreme weather events when compared to normal events.

The whitepaper concludes its discussion on the need for new planning rules by looking at recent blackouts in California and Texas:

The risk profiles in Table 2 below depict the reliability impacts of recent extreme weather events in California and Texas10. As a way of comparison, unserved energy or EUE resulting from the California event exceeded the average annual expected unserved energy in the NYSRC 2021 and 2022 IRM Study base cases by a factor of 12, while the unserved energy from the Texas event exceeded these IRM study base case EUEs by a factor of 4400!

The report explains that the NYISO has conducted a “wind lull” study as part of its 2021 Reliability Planning Process to determine the effects of an extreme situation of low wind resource availability. The study evaluated several scenarios for which there is no wind generation output for an extended period of time, i.e., one week.  According to the report:

Table 3 below shows the results of one of these scenarios.12 In this scenario each base case LOL event resulted in a loss of energy of 857 MWhr compared to 1,276 MWhr for the wind lull scenario. The NYISO study also calculated the compensatory MW (perfect capacity MW available every hour of the study year) required to bring NYCA back to the LOLE criterion for each of 18 scenarios examined. For these scenarios compensatory MW requirements ranged from 0 to 400 MW in Zones J or K.

One important NYISO lull study conclusion was that using compensatory MW to bring the NYCA LOLE back to criterion level increases the Expected Unserved Energy (EUE) metric over the base case level. This is because non-extreme weather events are mitigated by the compensatory MW, but the wind lull events themselves create a larger energy deficit than in the base case during the week of the extreme weather.

Resource Adequacy Modeling for a High Renewable Future

Based on these analyses the report concludes that there are changes to weather impacts that need to be addressed and new reliability rules need to be developed.  In my opinion, the most important weather concern is that changing the resource mix to one relying upon weather-dependent wind and solar generation is the critical vulnerability that has to be addressed.  As noted above I think that the trend of extreme weather events due to greenhouse gas concentrations in the atmosphere is much smaller than natural variability.  Therefore, using a long record of data for evaluation will cover most of the potential variability.  Unfortunately, recent major blackouts due to extreme weather in California and Texas suggest that we haven’t even been able to plan for the past.  So far, New York has avoided such a blackout either due to more stringent standards and better policy development or luck.  When New York’s resource mix changes due to the Climate Act there is a need for new reliability rules to maintain current levels of reliability.

Whitepaper Recommendations

In order to address the future electric grid requirements, the NYSRC Reliability Rules Subcommittee (RRS) recommends that:

Accordingly, RRS recommends that the NYSRC should adopt an “extreme weather resource adequacy criterion” — such as the 1-in-10-year LOLE criterion or a new criterion (One example of a new criterion could be use of a dual LOLE/EUE criterion) – for mitigating loss of load impacts of extreme weather events. Development of an “extreme weather resource adequacy criterion” shall include the use of the results of probabilistic resource adequacy assessments of the reliability impacts of a range of types of extreme weather events, to be conducted by the NYISO staff.

RRS recognizes that the NYISO and ICS will need adequate time to develop more detailed probabilistic models for extreme weather analyses and that the RRS will need sufficient time to develop and adopt an appropriate extreme weather resource adequacy criterion. Included in these modeling efforts the NYISO and ICS should identify the types of extreme weather events to be considered and modeled, including an estimate of the relative likelihood of occurrence. The NYISO staff and ICS should also discuss and coordinate the development of procedures for using appropriate extreme natural event assumptions and data for NYCA resource adequacy and IRM assessments.

Prior to adopting an extreme weather resource adequacy criterion, RRS recommends that initial rules should be adopted requiring the NYISO to periodically conduct probabilistic resource adequacy assessments of the reliability impacts (LOLE, LOLH, and EUE metrics) of a range of types of extreme weather events similar to the “Wind Lull” analysis reported in Appendix E of the NYISO 2021-30 CRP report. In addition, it is recommended that the NYISO develop extreme weather scenarios based on appropriate system conditions as well as analytical methods with which to test system performance under extreme weather events. These initial assessments should utilize existing NYISO extreme weather probabilistic models which should improve over the near term.


I endorse the recommendations for additional extreme weather criteria proposed in the Whitepaper. However, based on my background in meteorology, I believe that natural weather variability is a much bigger driver of the magnitude of extreme weather events than climate change.  As a result, the necessary changes to reliability rules should focus on the observed variability of extreme weather more than any projection of future changes due to climate change.  To date no one in the state has done a satisfactory job evaluating observed weather event variability using a sufficiently long data record.  In my Draft Scoping Plan comments on renewable energy resource availability I explained that there is a viable approach that could robustly quantify the worst-case renewable energy resources and provide the information necessary for adequate planning. 

Author: rogercaiazza

I am a meteorologist (BS and MS degrees), was certified as a consulting meteorologist and have worked in the air quality industry for over 40 years. I author two blogs. Environmental staff in any industry have to be pragmatic balancing risks and benefits and (https://pragmaticenvironmentalistofnewyork.blog/) reflects that outlook. The second blog addresses the New York State Reforming the Energy Vision initiative (https://reformingtheenergyvisioninconvenienttruths.wordpress.com). Any of my comments on the web or posts on my blogs are my opinion only. In no way do they reflect the position of any of my past employers or any company I was associated with.

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