Sunday, June 16, 2024

Renewable Energy Gap Characterization – Watts Up With That?

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Roger Caiazza

Advocates for the net-zero transition of the energy system frequently argue that existing wind, water, and solar technology can provide 100% of the energy needed.  The legislation that created New York’s Climate Leadership & Community Protection Act (Climate Act) relied on that presumption as rationale for its mandate for 100% zero-emissions electricity by 2040 and I believe that is a commen presumption in other energy transition initiatives.  However, a session at the New York Department of Public Service (DPS) Proceeding 15-E-0302 technical conference Zero Emissions by 2040 titled Gap Characterization  shows that a new category of generating resources called Dispatchable Emissions-Free Resources (DEFR) is necessary to keep the lights on during periods of extended low wind and solar resource availability.  This post highlights the findings of this technical session.

Gap Characterization Session

The first session (video)

of the conference was titled Characterizing the Potential “Gap”.  It addressed resource adequacy, transmission security, and grid stability arising from shuttering fossil fuel-fired resources and increased loads due to the Climate Act electrification strategies.  It was moderated by Schuyler Matteson from DPS.  There were four panelists and I have included links to the location in the video with their introductions: 

  • Deidre Altobell, Chief Transmission Planning Engineer Consolidated Edison.  She represented the concerns of the New York City electric system provider.  New York City has unique issues within the New York State electric power market that are a particular challenge for a transition to a system dependent upon renewables.
  • Prof. C. Lindsay Anderson, Chair of Department of Biological and Environmental Engineering Cornell.  Professor Anderson provided an independent check on the work of other electric system planning analysts because her group has modeled resources necessary for the New York electric system transition.
  • Zach Smith, VP System Resource Planning, New York Independent System Operator (NYISO).  NYISO is “responsible for operating wholesale power markets that trade electricity, capacity, transmission congestion contracts, and related products, in addition to administering auctions for the sale of capacity.”  As part of those responsibilities NYISO has done extensive modeling resource projections of the net-zero transition.
  • Kevin Steinberger, Director, Energy and Environmental Economics (E3).  As part of the New York Climate Act transition plan an Integration Analysis was performed that included an assessment of the electric system net-zero transition resources.  E3 provided the quantitative analysis for that effort.

Issues Identified

After the introductions the moderator asked a series of questions.  This section lists the questions with a link to that location in the video.  I highlight some of my concerns and points made by the panelists

The first questions was: “How do we know if there is a gap?”  Professor Anderson described an analysis her group did.  They made projections for expected loads and potential resources then used 22 years of hourly historical data to model the system.  Without considering cost constraints they assessed system vulnerabilities to evaluate periods where there was insufficient generation to meet projected loads.  Even with optimistic projections they found there will be periods during the coldest and hottest periods where there will be insufficient generation from wind, solar, and energy storage resources.  Steinberger also responded that their modeling consistently showed the need for a new resource that is firm, dispatchable, and has no emissions that can power the system for days without significant recharge from wind and solar resources.  He stressed the importance of considering actual historical meteorological conditions because renewable energy production is dependent on weather conditions.

Zachary Smith gave an overview summary presentation of the DEFR issue that was the focus of an earlier post of mine.  In his first slide (shown below) he gave an overview of the generating resource outlook to make the point that a large amount of new generating resources needs to be developed.  The estimates shown are from the 2021-2040 System & Resource Outlook and represent two plausible load projections.  He noted that there are “a lot of attributes that fossil fuel resources provide today that wind, solar, and energy storage simply cannot provide”.  He also made the point that the DEFR replacements do not have to be a single technology but could be several technologies that in aggregate can replace the fossil generation.

The ultimate problem for reliability in an electric system that depends on wind and solar is illustrated in the following slide from Smith’s presentation.  It highlights a 7-day wind lull when the wind, solar, and energy storage are insufficient to meet demand.  The replacement resources must be able to ramp up quickly, stay online for a long period, and provide ancillary services to support the transmission system.  The sum of the grey area under the curve during that period is the amount of energy (MWh) that must be provided by DEFR sources based on an analysis of historical weather data. If there are insufficient resources during a wind lull, then the load cannot be met.  One final point, the analyses performed by all panelists show that adding more of each technology is not going to solve the gap problem.  There is a limit to over-building as a solution because the wind lulls are rare

To meet this need for dispatchable resources Smith explained that dispatchable emission-free resources (DEFRs) must be developed and deployed throughout New York:

  • As resources shift from fossil generators to zero emission resources, essential grid services, such as operating reserves, ramping, regulation, voltage support, and black start, must be available to provide New Yorkers with a reliable and predictable electric system that consumers require.
  • DEFRs will be required to provide both energy and capacity over long durations, as well as the reliability attributes of retiring synchronous generation. The attributes do not need to be encapsulated in a singular technology, but in aggregate the system needs a sufficient collection of these services to be reliable.

The NYISO must toe the political correctness line, so Smith downplays the enormity of the challenge to bring DEFR online in the timeframe necessary to meet the arbitrary Climate Act schedule.  I have no such restrictions so I will note that I think that anyone who thinks that this can be done on the schedule proposed is crazy.  Smith lists the attributes needed by DEFR in his presentation.  In the following I offer my comments on his list of attributes.

Smith’s first attribute for DEFR is that it must have “dependable fuel sources that are carbon free and allow these resources to be brought online when required”.  Clearly intermittent wind and solar do not meet this fundamental requirement. 

The second DEFR attribute is that it must be “non-energy limited and capable of providing energy for multiple hours and days regardless of weather, storage, or fuel constraints”.  This is a particular concern of mine.  Wind and solar resources correlate in time and space.  In other words, when the wind is light at one wind farm in New York it is very likely that all the wind farms in the state are experiencing light winds.  The seven-day wind lull example in the dispatchable resources needed figure illustrates the problem.  If there are insufficient resources during that wind lull, then the load cannot be met.  My concern is that we do not know what the worst case low renewable resource availability period is.  Until there has been more analysis done then I believe that planning to prevent reliability issues is inadequate.

The NYISO operators balance generation with load constantly.  Smith describes several attributes necessary for this requirement.  DEFR must be able to “to follow instructions to increase or decrease output on a minute-to-minute basis”.  There must be “flexibility to be dispatched through a wide operating range with a low minimum output”. Finally, DEFR must be “fast ramping to inject or reduce the energy based on changes to net load which may be driven by changes to load or intermittent generation output”. 

In addition to the attributes needed when units are operating, there are startup attributes.  DEFR must be “quick start to come online within 15 minutes” and capable of “multiple starts so resources can be brought online or switched off multiple times through the day as required based on changes to the generation profile and load”.  Smith explains that a range or DEFR generation will likely be required.  Not every DEFR must be capable of every attribute for matching load but sufficient amounts each attribute for the system requirement will be required.

In addition to the generating requirements that cannot be supplied by wind and solar, there are ancillary support services for the transmission system.  Smith describes three transmission support DEFR attributes:

  • Inertial Response and frequency control to maintain power system stability and arrest frequency decline post-fault;
  • Dynamic Reactive Control to support grid voltage; and
  • High Short Circuit Current contribution to ensure appropriate fault detection and clearance.

Smith’s presentation lists the attributes of twelve sample technologies in the following slide.  This represents the NYISO opinion of the capability of different technologies to meet the attributes necessary to maintain a reliable system.  In the future grid the insistence that all fossil fired units must be shut down means that numerous technologies that meet some of the necessary attributes will be required.  The added complexity of these technologies does not increase resiliency because wind, solar, battery and demand response are all energy limited.  In other words, their dependency on the vagaries of weather means the available energy is constrained and must be backed up.  Ancillary support services will be a major consideration because wind, solar and battery do not provide those services.  Just from this overview, it is clear that affordability and reliability will be challenges.

Attributes of Sample DEFR Technologies

The moderator asked for Altobell’s reaction relative to the situation in New York City.  She noted that Con Ed agrees with NYISO analyses and that their work has shown similar results.  She made the point that there is a minimum amount of generation that must be on-line in New York City to provide reactive support.   She explained that the location of that generation is important.  Importantly, she noted that we cannot let any more fossil retire until replacement services are provided.

Altobell also described some of the reliability standards that electric system operators are required to address.  For example, the reliability standard N-1-1 addresses the loss of the two largest components on the system and the ability to recover from the loss of those two components.  This criterion is considered on a daily and on a long-term basis.  Currently the system relies on quick start units to get the system back to normal after the loss of large components but the peaking turbines that have historically been used for this are being retired which complicates compliance with the requirement.

In another example of a hidden cost of the net-zero transition Altobell explained that the New York City transmission system needs to be modified to eliminate load pockets.  Historically Con Ed has relied on generating resources that were located to serve those load pockets.  To replace those resources, the load pockets must be eliminated to open up the system.  This is complicated by the fact that there isn’t much room available for infrastructure like substations.

I was interested in her comments on inverter-based resources relative to a dispatchable resources.   She noted that 1,000 MW of offshore wind is equivalent to 100 MW of dispatchable resources in transmission security analyses.  That means to replace the 2,000 MW of dispatchable Indian Point nuclear power that the State shut down a couple of years ago, 20,000 MW of offshore wind must be deployed.  Note that the Climate Act mandates 9,000 MW of offshore wind which is far less than what is needed to simply replace Indian Point.

The next question from the moderator addressed the quantity of resources necessary to address the gap.  Specifically, he asked can wind, solar, short-duration energy storage, and improvements to the transmission system eliminate the gap.  Professor Anderson explained that her team’s work found that adding more of each technology is not going to solve the gap problem.  It is not just that we need more, we need it in the right places. 

The moderator reflected the consensus of the panelists when he noted the New York gaps cannot be solved using existing technology because of the physical characteristics of the grid and the location of load in the state.  He followed up by asking Steinburg when the gap will show up, how quickly do we need to react, and what is the magnitude of the resources necessary to respond.  Steinburg said the work his group did for the Integration Analysis showed that the timing of the gap problem depends on the rate of electrification and retirements of existing fossil resources.  The problem will be worse in the winter once the load peak shifts to account for electric heating and electric vehicles.  Smith noted that the NYISO expects that New York will be a winter peaking system in the ”early to mid- 2030’s”.

Schyler Matteson, the moderator, pointed out that before the DEFR resources can be deployed a long period of planning, permitting, construction, and inter-connection is required.  He stated that this could be on the order of seven years.  He followed up with a question to Smith about how planning for the system reserve margins and the local transmission security issues most prevalent in New York City will affect the process to develop DEFR to replace existing fossil.  Smith emphasized the point that this is a challenge that will require extensive collaboration between agencies.  In order to address the retirement issues NYISO has instituted a quarterly “short-term assessment of reliability” process.  While this reactively addresses generator deactivation notices, NYISO is also trying to consider longer-term issues.  In particular, the Department of Environmental Conservation has a rule promulgated to retire old peaking combustion turbines.  In that process, NYISO requested a temporary delay for the retirement dates until reliability solutions could be deployed.  Smith emphasized that a similar process needs to be incorporated as part of the Climate Act net-zero transition.  Smith went on to point out that some of the DEFR required is not yet commercially available so there is even more lead time than required to simply deploy the resources.  Altobell explained that there is another consideration – outage scheduling.  The existing system still has to operate and the outages when changes can be made without threatening reliability are getting smaller and smaller.

The moderator gave his summary of the panel discussion and asked for comments.  He said a gap “definitely exists”, that the gap is flexible based on the future load characteristics, the generation mix, load profiles, and transmission constraints.  The gap will start to show up around 2035 and is definitely an issue by 2040.  DEFR needs to be commercially available during the deployment planning period.  Three different analyses showed that at least 20 to 30 GW of capacity is needed.  Gaps of four maybe five days occur as much as every few years.  Smith pointed out that future planning also must address extreme events and the need for resilience.

The session ended by discussing a question raised in the chat.  The question raised was how do we characterize what the maximum DEFR need is?  Smith replied that more analysis is needed.  He mentioned that the New York State Reliability Council is charged with addressing this issue.  It is necessary to define the worst-case conditions and then decide how to design the system to deal with it.  Altobell supported his comments and pointed out that the Reliability Council has an Extreme Weather Working Group that is looking at gap characteristics.  They are also addressing the reliability rules that will be needed when the projected amounts of inverter-based resources (wind, solar, and energy storage) are deployed. 


This technical conference session is a good description of one aspect of the electric system net-zero transition that is ignored by proponents.  The experts all agree that new technology is needed and there are implementation issues.  The analyses performed by all panelists show that adding more renewables is not going to solve the gap problem.  There is a limit to over-building as a solution because wind lulls are rare.  If the goal is to ensure adequate availability for the one in ten-year worst case low wind and solar availability period, then there will be resources that are only used once in ten years. 

Designing a wind and solar dependent electric system has a major challenge unacknowledged by renewable advocates.  The worst-case low availability period will be in the winter when days are short reducing solar availability and a massive high-pressure system lowers wind speeds over large areas.  Proponents argue that the wind is always blowing somewhere but the enormity of the high-pressure systems means that the extraordinary amounts of over-building of both wind and solar but also transmission would be needed for rare events in the absence of DEFR. An overarching issue is that these periods are also accompanied by the coldest weather and thus the highest loads.  If the system is dependent upon renewables and is designed for a one in ten-year worst case what happens when there is a one in fifteen-year worst case?  The DEFR technologies must be flexible enough to handle any worst case or the energy available will not be adequate and the electric grid will not be able to supply the necessary electricity when society needs it the most.

There are two implementation issues. The first concern is that there are DEFR candidate technologies that are not commercially available.  There is a long road between theory and lab prototype tests and having a technology available that can be deployed to maintain reliability.  It is likely that many of the candidate technologies will fail this test.  Secondly, even if the technologies are viable there are issues related to deployment time and costs.  The Climate Act net-zero transition includes an ambitious schedule and there are affordability concerns.  Neither issue can be addressed at this time, but the transition mandates do not reflect these uncertainties.

A more immediate New York concern is the push to retire existing fossil-fired resources as soon as possible.  The simplest definition of DEFR is a fossil-fired peaking resource without any emissions.  This panel discussion showed that the activist belief that wind, solar, and energy storage are resources that can just be plugged into the New York City electric system to replace peaking power plants is dangerous.  Those existing facilities provide much more than electric energy and wind, solar, and energy storage don’t provide other necessary services.  The session made the point that location matters and that there are spatial limitations in New York City that could very well preclude development of alternative technology even if it is viable because of different footprint requirements. 


New York’s vocal proponents of the Climate Act believe that New York can “rapidly move away from fossil fuels and instead be fueled completely by the power of the wind, the sun, and hydro” and that  “it could be done completely with technologies available”.  The position that “it could be done completely with technologies available at that time” had an out-sized influence on the Climate Action Council decision to approve the Scoping Plan that guides the net-zero transition.  After all, if there are no technological barriers then it is simply a matter of political will. 

This session proves this belief is wrong.  The work of  Prof. C. Lindsay Anderson, Chair of Department of Biological and Environmental Engineering Cornell; Zach Smith, VP System Resource Planning, New York Independent System Operator; and Kevin Steinberger, Director, Energy and Environmental Economics all found that a new resource that has all the attributes of fossil-fired peaking units but without any emissions is needed.   At some point, New York State is going to have to confront the fact that the naïve implementation plan based on rhetoric and not facts must be changed.  Hopefully, the confrontation will occur before there is a catastrophic blackout.

Roger Caiazza blogs on New York energy and environmental issues at Pragmatic Environmentalist of New York.  More details on the Climate Leadership & Community Protection Act are available here and an inventory of over 400 articles about the Climate Act is also available.   This represents his opinion and not the opinion of any of his previous employers or any other company with which he has been associated.

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