Reliability Goal of a Renewable-Dependent Electricity System

In early September 2021 I wrote an article, “Reliability Challenges in Meeting New York’s Climate Act Requirements”, that described a presentation made by the New York State Reliability Council (NYSRC) to the New York Climate Action Council.  In this post I describe a recent paper that analyzes synoptic-scale extreme reductions in wind and solar power energy resources that I think raises an important reliability question: when New York relies on fragile intermittent wind and solar energy resources is the current New York reliability goal to prevent a loss of load event due to resource adequacy of no more than once per ten years still appropriate.

I have written extensively on implementation of the CLCPA because I believe the solutions proposed will adversely affect reliability and affordability, will have worse impacts on the environment than the purported effects of climate change, and cannot measurably affect global warming when implemented.   The opinions expressed in this post 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.


In my reliability challenge article, I explained that there is consensus that the future worst-case situation in New York will be a multi-day winter time wind lull when both wind and solar availabilities are low.  Coupled with increased electricity load in order to reduce emissions from transportation and heating, any analysis of future renewable energy resources that adequately addresses the worst-case renewable energy resource availability shows the required amounts of wind, solar and energy storage will have to be enormous.  Importantly, the NYSRC analysis indicates that in order to ensure reliability the installed reserve margin will have to be increase substantially above current levels to satisfy anticipated load and the intermittent nature of wind and solar resources.  The NYSRC presentation concludes that the state of New York appears to be headed down a transition path which will require reliance on technologies that do not currently exist in less than ten years.

Wind and Solar Droughts

Dr. Patrick Brown’s blog post describes his recent paper co-authored with David J. Farnham and Ken Caldeira entitled “Meteorology and climatology of historical weekly wind and solar power resource droughts over western North America in ERA5” (Brown et al., 2021).  His post explains that as wind and solar become more indispensable for providing electricity it is important that we understand the intensity, frequency, and duration of droughts of their availability.  In Brown et al., 2021 they use a meteorological database that covers 71 years from 1950 to 2020.  They compared estimated weekly solar and wind availability against cooling and heating degree days as a proxy for electrical load over that entire period. 

The following plot of the weekly values is of special interest.  The plot explanation states:

All weekly values from 1950 to 2020 (average over the western North America domain, Fig. 1) for power supplied by wind and solar resources (x and y axes respectively) and a proxy for power demanded via cooling degree days (color of dots). The mean seasonal cycle in wind and solar power is shown by the black loop (52 black dots for each week of the year). Drought weeks are indicated with black edge colors with wind droughts represented as circles, solar droughts represented as squares and compound wind and solar droughts represented as diamonds.

Of particular concern is the lower left quadrant which represents weeks where both wind and solar resources are lower than the annual mean of long-term availability.  Note that this quadrant is “mostly astronomical autumn. The mean wind & solar power given a wind + solar drought label shows that during a drought you can only expect around 40% of the solar resource and 65% of the wind resource.

There is an animation showing the degree to which there is persistence in time.  In the video each week is sequentially plotted since 1979 over a plot of the seasonal cycle.  As you watch the video keep in mind that you are watching the seasonal progression of plots.  While the majority of weeks with both wind and solar droughts are in autumn there are periods at the start of each year that appear to me to be among the most intense.  That is consistent with New York analyses that define the ultimate problem

that must be resolved to ensure reliability: firm capacity is needed to meet a multi-day period of low solar and wind resource availability during the winter. 

In their presentation to the Power Generation Advisory Panel on September 16, 2020 E3 included a slide titled Electricity Supply – Firm Capacity that states: “The need for dispatchable resources is most pronounced during winter periods of high demand for electrified heating and transportation and lower wind and solar output”.  The slide goes on to say: “As the share of intermittent resources like wind and solar grows substantially, some studies suggest that complementing with firm, zero emission resources, such as bioenergy, synthesized fuels such as hydrogen, hydropower, carbon capture and sequestration, and nuclear generation could provide a number of benefits.  Of particular interest is the graph of electric load and renewable generation because it shows that this problem may extend over multiple days.

Brown et al., 2021 is a promising approach for evaluating the long-term frequency of wind and solar droughts.  However, there are some limitations.  Obviously, the work has to be done for a New York centric domain.  In addition, because previous New York analyses by Energy + Environmental Economics  and The Analysis Group both identified problems on a multi-day basis it would be more appropriate to evaluate New York’s droughts on a daily basis. I strongly recommend that New York sponsor this analysis to determine the frequency and duration of renewable resource droughts. 

Because wind and solar are naturally intermittent the amount of energy storage needed to balance output must be determined.  The Brown et al., 2021 technique can also be used to identify periods that should be evaluated in more detail to determine the intensity of the droughts so that energy storage requirements can be determined.  This is important not only for grid planning but also for distributed energy resources (DER).  In theory DER can “generate smaller amounts of clean electricity closer to end-users, to increase energy efficiency, reduce carbon pollution, improve grid resiliency, and potentially curtail the need for costly transmission investments”.  However, unless they incorporate sufficient energy storage these resources won’t work when the system is stressed the most, so they may not be the panacea that advocates claim.

Reliability Planning

New York’s electric system is de-regulated so reliability planning is provided by the New York Independent System Operator, various state agencies and the NYSRC.  The NYSRC presentation describes the NYSRC and the Installed Reserve Margin (IRM) parameter.  The IRM is defined as the “minimum installed capacity margin above the estimated peak load to meet the Northeast Power Coordinating Council (NPCC) requirement that the probability of shedding load is not greater than one day in ten years”.   Load shedding occurs when the demand for electricity exceeds supply and grid operators have to turn power off for groups of customers in order to prevent the whole system from collapsing. 

To this point, reliability planning has been primarily focused on an electric system powered by conventional dispatchable generating resources. In that context resource obtainability is not particularly concerned with long-term availability of the resource because the resources are not intermittent.  That changes when the system becomes dependent upon wind and solar because there are short-term and long-term availability concerns.  It is in this context that the results from Brown et al., 2021 climatology becomes important and raises the question whether planning based on a ten-year metric is still appropriate in the future.  Using this approach, we can determine the frequency and duration of the expected worst case over ten years consistent with current IRM planning.  However, because we can consider a longer period, we can also consider the frequency and duration of droughts over the whole 70 years and get expected worst cases over other time periods.  If there is a marked difference over say the 30-year time period, it may be appropriate to expand the IRM planning period in order to prevent the probability of shedding load due to more severe drought.

Black Swan Events

To this point in this article, I have only addressed normal weather variability effects. During the preparation of this post, I came to believe that there is another reliability concern related to renewable resource adequacy that has to be addressed.  What happens to the electric system when unprecedented extreme weather cripples the relatively fragile renewable generating and transmission system?  These statistical outliers are described as a “black swan event”.

A Black Swan event is an event in human history that was unprecedented and unexpected at the point in time it occurred. However, after evaluating the surrounding context, domain experts (and in some cases even laymen) can usually conclude: “it was bound to happen”. Even though some parameters may differ (such as the event’s time, location, or specific type), it is likely that similar incidences have had similar effects in the past.

In this context the conclusion that “it was bound to happen” has to be discussed.  At an Our Energy Policy (OEP) panel discussion on New York State’s emerging offshore wind market, someone asked an off-shore wind industry expert whether wind turbines in New York would be able to withstand a Category 5 storm.  Clint Plummer the head of market strategies and new projects for Ørsted, the world’s largest owner, developer, and operator of offshore wind responded: “wind turbines are designed to withstand a Category 3 hurricane, and they have built into their permit applications an insurance fund that can pay for repairs in cases of catastrophic loss from a storm more severe”. He said “a Category 5 hurricane has a return period in excess of 100 years, while the design life of a wind farm is 30-35 years, so wind turbines are not designed to withstand a Category 5 storm because they are not expected to experience one”. “Anything less than that up to a certain speed is just a really good day for producing a lot of wind power,” he said.

In the October 1, 2021 Climate Action Council meeting presentation Carl Mas described the initial results of the integration analysis that will be used to develop the plan to implement changes to New York’s energy system to meet the CLCPA targets.  Four scenarios have been developed with different renewable resource, load reduction and sequestration strategies.  The new findings indicate that 20 GW of offshore wind resources will be necessary.  Assuming that New York builds the latest generation offshore wind turbine, e.g. the GE Haliade-X 12 MW turbine, that equates to over 1,600 turbines with 220 m or 722 foot rotors. 

However, hurricanes likely exceeding the threshold described by Ørsted expert Plummer have occurred in the area New York plans to build its offshore wind facilities.  In 1635 the “Great Colonial” Hurricane hit New York and New England and the “Great Storm of 1693” devastated Long Island. There were other hurricanes that made landfall in the Tri-State area – 1788 (left the Battery in ruins), 1821, 1893 (the second hurricane that year, different from the one that hit Halifax, Nova Scotia), 1944 (“Great Atlantic” hurricane), 1954 (Carol), and 1991 (Bob). The 1938 “Long Island Express” made landfall in Long Island as a Category 3 hurricane with sustained winds of 125 mph and wind gusts up to 150 mph bringing waves surging to 35 feet.  Given that part of the rationale for the CLCPA is that extreme weather events such as hurricanes are becoming more frequent and severe there should be no question that a contingency plan is necessary for the time that a hurricane inevitably affects, if not destroys, the New York offshore wind resource.  Moreover, should that not be a part of the reliability planning process?

Unfortunately, that is not the only extreme weather event that can have extreme consequences on a more fragile wind and solar electricity network.  I am particularly worried about ice storms.  On a local level it is not clear how the public will be able to survive a multi-day power outage caused by an ice storm when the CLCPA mandates electric heat and electric vehicles but the bigger reliability concern is that fact that ice storms can take out transmission lines.  For example, consider, the January 1998 North American ice storm:

The North American Ice Storm of 1998 (also known as Great Ice Storm of 1998) was a massive combination of five smaller successive ice storms in January 1998 that struck a relatively narrow swath of land from eastern Ontario to southern QuebecNew Brunswick and Nova Scotia in Canada, and bordering areas from northern New York to central Maine in the United States. It caused massive damage to trees and electrical infrastructure all over the area, leading to widespread long-term power outages. Millions were left in the dark for periods varying from days to several weeks, and in some instances, months. It led to 34 fatalities, a shutdown of activities in large cities like Montreal and Ottawa, and an unprecedented effort in reconstruction of the power grid. The ice storm led to the largest deployment of Canadian military personnel since the Korean War, with over 16,000 Canadian Forces personnel deployed, 12,000 in Quebec and 4,000 in Ontario at the height of the crisis.

New York Governor Kathy Hochul recently announced “two major green energy infrastructure projects to power New York City with wind, solar and hydropower projects from upstate New York and Canada”.  The press release claims that the combined project will deliver 18 million megawatt-hours of upstate and Canadian renewable energy per year.  Clean Power New York plans on over 20 wind and solar generation projects – all located in New York State – and a new 174-mile, underground transmission line. Champlain Hudson Power Express is a 338-mile underground power line from Quebec hydroelectric facilities to New York City.  The problem is that not all the associated infrastructure in these projects is underground and immune from ice storms.

Photo from 1TAC Survival Blog


The requirements for New York reliability planning will have to change for a future grid that relies on intermittent and diffuse wind and solar.  Current planning for the electric system is based on decades-long experience with a system powered primarily by sources that are dispatchable and includes sources that have on-site storage.  The potential for lack of source availability over days, weeks, and even months is not a serious concern today because the New York system has been diverse, redundant, and resilient to the vagaries of weather.

The CLCPA requirement for a zero-emissions electric system that relies on wind and solar energy resources changes the reliability planning requirements.  Previous analysis has highlighted the need to address multi-day wind lulls in the winter as a particular problem.  Brown et al., 2021 have developed a technique that can be used to determine the climatological frequency and duration of those periods of low wind and solar resource availability that clearly should be included in New York reliability planning.  Their analysis technique can also be used to identify the worst-case periods of wind and solar droughts so that more detailed resource availability analyses can estimate how much energy storage is needed not only for the electric grid but also the distributed energy resources proposed for the CLCPA.  This analysis is needed to prevent the kind of Texas February 2021 disaster from happening in New York.

The existing New York system has evolved over years of trial-and-error experience to the point where it is relatively resilient to extreme weather events.  While there have been exceptions, the possibility of widespread, weeks-long outages is extremely low.  However, because wind and solar resources are more fragile to wind and ice crippling damage than existing generating sources, the likelihood of the conditions that cause that level of damage should be determined.  Brown et al., 2021 can determine the occurrence of events over a 71-year period.  If, for example, their analysis suggests that the return period of a crippling event is one in thirty years, then should New York reliability planning incorporate a longer time horizon for its planning?

At this time, the off-shore wind strategy calls for 20 GW of development.  The ramifications of a Category 4 or greater hurricane destroying or significantly damaging those facilities should be at least be considered.  Repairing them will take months if not years and the ramifications if insufficient resources are available are immense. If nothing else the statements claiming that the future wind and solar dependent electric system will be more resilient should be toned down.

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 ( reflects that outlook. The second blog addresses the New York State Reforming the Energy Vision initiative ( 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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