Lesson 13 Overview

In our last Lesson, we touched on the challenges of the integration of intermittent generating resources into the power grid. We will continue the discussion of these challenges, add some more concepts, and discuss some real world examples of the types of issues we now confront and some of those we will confront in the future. The lesson is pretty heavy on readings from research and academia this week. This is to be expected, as we are dealing with major transitions, here. One thing you can be sure of - the readings will be foundational, but also out of date fairly shortly. Certain problems will persist, while others will be solved. The motivation for the inclusion of these papers is to show the current state of affairs while also allowing you to place the best thinking about these problems in context.

Learning Outcomes

By the end of this lesson, you should be able to:

• Define energy storage and its many forms
• Explain why transmission of energy is such an important topic
• Suggest ways that ancillary services could be provided to the grid and by what assets
• Explain the Duck Curve
• Explain the Falcon Curve
• Discuss how storage, transmission, and the evolving grid fit into your project

Reading Materials

There are a lot of good resources

• N.A. (2022). 3 Key Takeaways from New Study on Building Electrification - Introducing the Falcon Curve [1]. Harvard T.H. Chan School of Public Health.
• Buonocore, J., Salimifard, P., Zeyneg, M., and Allen, J. (2022). Inefficent Building Electrification Will Require Massive Buildout of Renewable Energy and Seasonal Energy Storage [2]. Nature.com/Scientific Reports.
• Jones-Albertus, B. (2017). Confronting the Duck Curve: How to Address Over-Generation of Solar Energy [3]. Office of Energy Efficiency & Renewable Energy.
• N.A. (2023). Flattening the Duck Curve with Vertical Solar Panels [3]. Sunzaun Verticle Solar Systems.
• Pitra, G., and Musti, K. (2022). Impact Analysis of Duck Curve Phenomena with Renewable Energies and Storage Technologies [4]. Journal of Engineering Research and Sciences.
• US Energy Information Administration (2023). As Solar Capacity Grows, Duck Curves Are Getting Deeper in California [5]. Eia.gov website.
• Seel, J., Millstein, D., Milles, A. et al. (2021). Plentiful Electricity Turns Wholesale Prices Negative [6]. Lawrence Berkeley National Laboratory.
• N.A. (2023). Types of Energy Storage [7]. New York State Energy Research and Development Authority.
• N. A. (2023). Tackling High Costs and Long Delays for Clean Energy Interconnection [8]. Office of Energy Efficiency & Renewable Energy.
• N.A. (2022). Solar-Plus-Storage: 3 Reasons Why They're Better Together [9]. UtilityDive.
• Please watch the following interview with Ben Kroposki. If this video is slow to load here on this page, you can always access it and all course videos in the Media Gallery in Canvas.
  To access the transcript, once the video begins to play, choose the transcript icon, next to the magnifying class icon in the upper right corner of the video. 

Video: Interview with Ben Kroposki (26:43)

• Please watch the following Solar Podcast video: Grid Interactive Buildings with Mark Kleinginna and Jared Rodriguez. If this video is slow to load here on this page, you can always access it and all course videos in the Media Gallery in Canvas.

Video: Solar Podcast: Grid Interactive Building with Mark Kleinginna and Jared Rodriguez (57:47)

What is due for Lesson 13?

This lesson will take us one week to complete. Please refer to the Course Calendar for specific due dates. Specific directions for the assignment below can be found within this lesson.

• Complete all assigned readings and viewings for Lesson 13
• Complete Quiz 10
• Project work: No deliverables this week

Questions?

If you have any questions, please post them to our Questions? discussion forum (not email). I will not be reviewing these. I encourage you to work as a cohort in that space. If you do require assistance, please reach out to me directly after you have worked with your cohort --- I am always happy to get on a one-on-one call, or even better, with a group of you.

Energy Storage

The notion of energy storage is fairly straight forward and simple from a business context. In business we would call it “inventory.” This is the notion that we should have enough supply in stock to meet demand on a timely basis. In the context of a supermarket, the grocer would have a certain number of cartons of eggs, for instance, so that throughout the day as customers showed up, there would be eggs available to be bought. Energy as a good is slightly different from eggs, though. Certain forms of energy can be stockpiled or inventoried like gasoline in your car’s tank or natural gas in a storage reservoir. Other forms of energy must be produced at exactly the same time as they are consumed. This is mainly true for electricity, which must be balanced on any hourly basis. Natural gas loads are balanced with supply on an hourly basis as the commodity can be stored and pressures can fluctuate to allow for peaks and troughs in delivery. The storage of energy allows us to match supply with demand on a timely basis (instantaneously, hourly, daily, seasonally, annually).

In the case of natural gas we have a storage network by state that looks like this in the US:

Figure 13.1 US Design working natural gas capacity by state

Click here for a detailed description of Figure 13.1.

The image is a map of the United States showing the design working natural gas capacity by state as of November 2021. The states are color-coded based on their capacity, measured in billion cubic feet, into five categories: 0, 1-150, 151-300, 301-450, and over 450. Darker shades of green represent greater capacities.

Design working natural gas capacity by state, 2021

Billion Cubic Feet	States
0	NV, ID, AZ, ND, SD, WI, ME, VT, NH, MA, RI, CT, NJ, NC, SC, GA, FL
1-150	WA, OR, WY, UT, CO, NM, NE, KS, MN, IA, MO, AR, IN, KY, TN, AL, VA, NY
151-300	MT, OK, MS, OH, WV
301-450	CA, IL, PA
>450	TX, LA, MI

Credit: US Energy Information Administration (EIA), Monthly Underground Natural Gas Storage Report [10]

Check out the US Energy Information Administration site's Natural Gas page [10] for some interesting discussion about natural gas storage.

In terms of the types of storage and the locations, please see the map below (Figure 13.2).

Figure 13.2 US Natural Gas storage types and locations

Click here for a detailed description of Figure 13.2.

This US map shows active UGS wells by region, active UGS wells by facility and type, and UGS facility counts by state and type. Most active UGS wells are in the Eastern, Midwestern, and South Central regions of the US. Active UGS wells include aquifers, depleted oil/gas wells (PA, MI, and TX have most), and salt dome wells. Most aquifers are located in the Midwest (IL has most), most depleted oil/gas wells are concentrated in the Mid-Atlantic region, and most salt dome wells are in the Gulf region (TX, LA, and MI have most). 

Credit: Michanowicz, D., Buonocore, J., Rowland, S., Konschnik, K. (2017) A National Assessment of Underground Natural Gas Sotrage: Identifying Wells with Desigbns Likely Vulnerable to a Single-poin-of-failure [11]. in Environmental Research Letters 12(6):064004. Material is licensed under CC BY 3.0 [12].

Natural gas can be stored in underground caverns for release on a seasonal, monthly, daily and intra-day basis. The need to balance the system is not necessarily instantaneous, but there does need to be gas available to meet sudden increases in demand (usually due to cold weather).

The electricity grid, though, must be able to meet increases and decreases in demand on an instantaneous basis. This means that until recently, almost all fluctuations in electricity demand were met by ramping a power plant up or down. With the advent of intermittency on the generation side, the value of the ability to meet less predictable fluctuations has increased the interest in electricity storage. Please see the diagram below for insight into the technologies being considered as we transition to a more flexible energy delivery system. The diagram shows how various technologies are positioned to provide services to the electricity grid. On the x-axis is depicted the scale in terms of the capacity of the resource in Ws. On the y-axis, we see the temporal ability of the resource in terms of seconds, minutes, and hours. The selected technology then appears at an intersection of those two variables (capacity and size). For instance, a nickel-cadmium battery can provide up to 200 kW in the second-to-minute range, making it a good resource to provide Uninterrupted Power Supply (UPS) or Power Quality services.

Figure 13.3: Positioning of Energy Storage Technologies

Credit: Akhil et al. (2013). Review of Energy Storage Services, Applications, Limitations, and Benefits [13]. Energy Reports 6(5). Licensed under CC BY 4.0 [14]

Energy Transmission and Interconnection

One of the most important issues in the renewable energy transition is that posed by the ability of the grid to accept the great quantity of renewable resources required for decarbonization. The issues can be broken down into two major categories. The first is location. We have discussed transportation basis differential in previous lessons, and it plays an important role in the integration of renewable resources as well. It is simply a fact that the renewable resources are not necessarily located near the energy loads. Supply and demand are separated by space. (Much of the electric load in the US is located near the coasts, while much of the wind resource is located in the Mid-Continent or off-shore. There is a great solar resource in the desert of Arizona without a really significant load there.) Consequently, the interstate electric transmission grid will need to be built out to a significant degree for the loads intended to be met with electricity to be served. This is not always an easy process as transmission paths can be disputed and new transmission is expensive to build.

The second issue is variability. Intermittent renewable resources like wind and solar do not respond to grid dispatch commands the way that on-demand combustion and steam turbines do. Since most renewable resources are not currently dispatchable and actually may become available in large quantities at inconvenient times, there comes a place for increased levels of ancillary services provided by the transmission grid. These services take the form of frequency response, spinning and non-spinning reserve. Sometimes these services can be supplied by shifting loads, electric and thermal storage, but very often by dispatchable gas or diesel fired combustion turbines. These combustion turbines are often very carbon intensive, and if we are to reduce the carbon footprint of the electric grid, it becomes essential to try to move to supplying these ancillary services from other sources. This is one of the reasons we are starting to see greater deployment of battery storage with solar and wind.

Current Integration Issues

The Duck Curve

The Duck Curve is a classic example of having a lot of something when you might not need it as much as you used to. In California, electricity loads peak in the mid-day when commercial and residential air conditioning peaks as a result of warm weather. This mid- to late-afternoon peak coincides quite nicely with the fact that the solar resource is also at its greatest when the sun is high in the sky. The electricity generation eco-system in California responded by building a lot of roof-top, commercial and utility scale solar to capture this resource as well as meet environmental energy generation targets. This led to a significant proliferation of solar generation, which provided huge amounts of energy in the middle of the day, thereby depressing the mid-day peak and moving it to the late afternoon with a significant ramp. Please see the figure below, which shows the net loads on the CAISO during the March-May time frame. Kind of looks like a duck, no?

Figure 13.4: California's Duck Curve is Getting Deeper

Click here for a text description of Figure 13.4.

This graph shows, in gigawatts, CAISO's lowest net load day each spring for March through May from 2015 - 2023. The x-axis shows time of day and the y-axis shows gigawatts from 0 to 25 in increments of 5. The general form of the lines on the graph (one for the trend for each year, 2015 - 2023) takes the form of a duck's silhouette (raised tail, low belly, high head and beak - it looks like a wide letter U). The data shows that the lowest loads always occur at mid day, and that the curve has been getting steadily deeper since the spring of 2015. The lowest gigawatt measure in the spring of 2015 was about 15 (at around 2 pm) but has continually dipped and hit 0 gigawatts at around 1 pm in the spring of 2023.

Credit: Energy Information Administration [5] (EIA.gov)

This phenomenon poses two significant problems for the energy market. First, grid stress - the system has to be able to meet that ramp in net usage from HE1600-HE1900 which is very steep. Second, economics - how does the market price a resource for which there may be zero demand, as is shown above?

The Falcon Curve is a potential problem that we could face as we start to electrify heating and domestic hot water in the cold climates around the world. A significant portion of the energy consumed in the northern states and in Canada goes to provide heating in cold climates. One very simple decarbonization strategy for the decarbonization of heating is the installation of air source heat pumps. This strategy appears attractive currently because the electric system is built to provide enough electricity for a currently high summer peak. So currently, there is enough electric system transmission and distribution capacity to meet demand for the addition of a certain level of air source heat pumps. Unfortunately, these air source heat pumps do not operate as well when temperatures get lower. As we approach a greater saturation rate with air source heat pumps, virtually all systems will become winter peaking, which will cause the annual energy demand to be much higher than it currently is in the winter months. This phenomenon was actually experienced in Texas in February 2021 during Winter Storm Uri when electric heating demand skyrocketed when temperatures plummeted. If there had not been blackouts, it is entirely possible that the Texas grid would have posted an all-time peak in the winter even in a climate as usually warm as Texas is. The curve below kind of looks like a Falcon, eh?

Figure 13.5: The Falcon Curve

Click here for a text description of Figure 13.5.

The Falcon Curve, the silhouette of which (sort of) resembles a bird in flight -- lifted wings on either side of a head - shows that if we electrify, then during coldest months (Jan, Feb, March, Nov, December), our energy usage will become much greater than it currently is in the summer/warmest months (May, June, July, Aug, Sept). Consequently, when we graph this useage on an annual basis, it etches out a silhouette resembling a falcon (coldest months graph as lifted wings and warmest months graph as bird's head and shoulders).

Credit: N.A. (2022). 3 Key Takeaways from New Study on Building Electrification - Introducing the Falcon Curve [15]. Harvard T.H. Chan School of Public Health.

The challenges of renewable energy integration are many, but these examples provide a look at how people are thinking about them. I challenge you as a student of EME 801 to begin to use some of the tools we developed in class and during the project to think about challenges you face and how you might meet them. Enjoy.

Lesson 13 Summary and Final Tasks

Summary

In this lesson, we have presented a few of the problems with the integration and development of renewables as they exist in the current environment. As the energy transition continues, some of these will be solved, some will be exacerbated and others will emerge. The skills developed and honed in this course will allow you to think critically about them and help to solve them.

Reminder - Complete all of the Lesson 13 tasks!

You have reached the end of Lesson 13! Double check the What is Due for Lesson 13? section of the Lesson 13 Course Overview page. Complete the quiz and remember and rejoice - there is no deliverable due for Lesson 13.... but please continue to work on your project!