Win-Win for all: Replacing Peaker Power Plants by Discarded EV batteries

Introduction

Peaker Plants are those power plants which run only when the demand for electricity crosses a certain base load[1]. As these power plants are used occasionally, the cost of operating them is much higher than the normal power plants, which are operated continuously. The time of operation of peaker plants depends on the location of the plant. In case the plant is located in a region of lower temperatures, the peak might occur during early hours of the morning. However, if the temperatures are considerable high, the peak could occur in later evenings. Thus, operating periods of these peaker plants have a spatial variability and do not have a standard period of operation.

Traditionally, peaking power plants are run on non-renewable sources such as coal or natural gas. Apart from fossil fuels, hydropower could also be integrated into the power generation system[2]. Although these plants serve a noble purpose of providing a supporting hand to mainstream power plants in cases of high demand, the feasibility of operating such a power plant has more negatives to it than its positives.

This project aims to bring focus to the problem of operating and constructing newer peaking power plants, and explores alternatives to the using peaker plants, mainly through stationary ESS (Energy Storage Systems). The focus of the implementation is directed towards using Second Use Batteries from PEVs (Plug-in Electric Vehicles) and hybrid electric vehicles as energy storage to address the problem of peak load demand.

Shortcomings of Peaker Plants

Operating a peaker plant is very expensive, let alone being profitable. There are more than 1000 peaker plants which are currently operating in the United States, with the top 10 metropolitan regions accounting to around 20% of the total number of plants accounting to 60 gigawatt source of emissions[4]. As peaking plants operate occasionally, they lead to a multi-fold higher price per kWh, which causes a burden to the tax payers. Based on the high operating cost of such plants, construction of new peaker plants cannot be justified, from an economic point of view. For instance, the peaker plants in New York cost more than 1300% than the average cost of electricity[5].

Apart from the economic disadvantages, the peaker plants also contribute to the emissions in the environment closer to their location. These plants emit harmful pollutants such as fine particulate matter, nitrogen oxides and sulfur dioxide leading to health problems for the surrounding communities, especially those of low income neighborhoods[6].

It is thus imperative to look out for alternative options to tackle these problems. Stationary energy storage comes up as a good solution to integrate it with renewable sources of energy. Moreover, the rising demand for electric vehicles could provide impetus to using the retired electric vehicle batteries, integrated to the microgrid, thereby helping save a mammoth amount of costs and also proving beneficial to the environment.

Analysis of Use Cases in USA

Replacement of peaker plants would involve bringing in a new type of energy source in place. Stationary Energy Storage Systems seem to be the best option, which provides a cheaper and modular solution. As per the reports of PSE [6], nine states in the USA were identified as use-cases which could provide good opportunities for primary candidates as peaker plant replacements.

A common point of inference from the use-cases of these 9 states is that most states are looking forward to curb carbon and greenhouse emissions, while also promoting stationary energy storage.

Batteries prove to be the best alternative for peaker plants with the primary advantage being it’s cheaper cost of installation and operation. In addition to that, batteries provide a cleaner alternative in terms of reduced environmental harm and could also help reduce the cost of transmission by installing it near high demand areas[7]. As the batteries could be charged using renewable energy sources of energy, it could also help in achieving goals set by the state policies. Further improvements to reduce costs and utilize available resources could be through second-use batteries, procured from early discharge of PEVs (Plug-in electric vehicles) or hybrid electric vehicles. Using second-use batteries as an alternative could further incentivize electric vehicles by lowering its operating costs. An increase in such modes of transport would lead to a substantial decrease in standard vehicular emissions.

Modeling of Second Use Batteries to Mimic Peaker Plant Behavior

This section puts forth a modeling approach to estimate the amount of second-use batteries required in a grid to mimic peaker plant behavior. There are certain assumptions to the approach such as:

1. All second use batteries are assumed to be identical in nature and of similar capacity

2. The batteries in use are compatible with the energy grid installed

3. All batteries are retired at a fixed interval, that is when the battery performs at a certain capacity since its production

Modeling Second-use battery equivalents for New York city

As per Clean Energy Group’s report[8], New York’s peaker plants generate one of the most polluted and expensive electricity during peak load. Thus, the use case under consideration was that of NYC (New York City). As per the data obtained from NYISO[9], electricity load data for January 2020 to July 2020(Current date as of analysis) was extracted and used for modeling. The data was averaged for the entire duration of the month, amounting to a single value every hour for every month for New York City.

The base demand for New York City was varied from 14000 to 20000 MWh (assumed units) and any load above that was assumed to be excess. Additional parameters for equation (2) were fixed as follows:

Using Equation (4), number of second-use battery equivalents for every month and every period of the day were estimated.

It can be observed that, as the base load demand increases, lesser number of battery equivalents are required. This comes from intuition that as the capacity of normal power plants to cater the demand increases, lower will be the peak requirement. Using this methodology, the maximum amount of batteries required per month of the year (2020) was evaluated, and tabulated.

It can be further observed that the trend for number of second-use batteries which could mimic the peaker plant capacity at more than base demand depends on the month (season plays an important role) and hour of the day.

A similar trend is followed in case of the three lines. As the base load is increased, peak demand is required on a lower number of instances and thus, overall, lesser number of second use batteries are required. The trend indicates that for the month of July 2020, a greater number of second-use battery equivalents were required as opposed to the lowest during the period of April and May 2020. Seasonal fluctuations in the demand for electricity, thus influences the number of second use batteries which could replicate the same.

Further, this methodology can be replicated to multiple areas, if more data is available. The code for the entire modeling is made available publicly [10].

Choosing Optimal Replacement Strategy

In order to determine optimal energy storage system design, two aspects defining a battery have been taken into account. Choosing the correct architecture and chemistry is an important step before assessing the safety of the site. This section, thus, takes into account the selection of architecture by multiple criteria and battery chemistry through analysis.

· Battery Cell Architecture

Two options were identified for the cell architecture, Prismatic and Pouch cells, both of which are used in hybrid vehicles and could act as a replacement for traditional peaker plants through a second-use application.

The two architectures were judged on the basis of 10 criteria and were allotted a binary score. A score of 1 meant the option was superior, 0 meant inferior and 0.5 was attributed in cases were there wasn’t a striking difference.

Size:

- Prismatic cells: They have large capacity and prismatic shape which makes it easy to connect multiple cells together and create a larger battery pack.

- Pouch cells: Generally not used in larger electric storage system. However, recently, GM have announced that they plan to use large pouch cell battery for their EVs. Thus, this could be a major source of second use batteries [11].

- Packing efficiency:

- Prismatic cells: They have a good space utilization, although it is lower than pouch cells.

- Pouch cells: They have a 90–95% packaging efficiency, comparatively higher than prismatic cells, implying better space utilization [12].

Capacity:

- Prismatic cells have a general capacity of 20–50 Ah per cell [13] whereas pouch cells have a capacity of 30 Ah per cell [14]. Capacity for both these cells could be considered of similar magnitude and thus, doesn’t contribute to be a major factor in deciding the architecture.

Electrode structure:

- Prismatic cells consist of a solid, metal housing with a cubic form, where electrodes and separators are stacked onto each other [15] whereas in case of pouch cells, conductive foil tabs are welded to the electrodes.

Manufacturing costs:

- For the same capacity, prismatic cells have a higher manufacturing cost than pouch cells [16].

Thermal management:

- Prismatic cells are lesser efficient in thermal management as compared to pouch cells [16].

Life cycle:

- Prismatic cells have a higher capacity at 0.2C charge (40–275 Ah) whereas pouch cells have a lower capacity at 0.2C charge (2.5–8) for a life cycle of 2000 cycles [17].

Charge & Weight:

- Prismatic cells have a much higher charge/g whereas pouch cells have a lower charge/g.

- (Prismatic Cells: 46.511 Ah/g to 52.88 Ah/g, Pouch Cells: 0.033 Ah/g)

- Thus, for a lower weight, much higher charge is possible for prismatic cells. Thus, a lower weight will be required for prismatic cells to mimic peaker plants.

Based on this, pros and cons of using the two architecture types have been tabulated.

Based on the analysis, it is evident that Prismatic cells have better size optimization coupled with better lifecycle and provides higher charge at a weight equivalent to pouch cells. However, Pouch cells have a better packing efficiency and space utilization coupled with lower manufacturing costs and efficient thermal management. Moreover, pouch cells are currently being used in large scale PEVs and hybrid vehicles.

Replacement of peaker plant would require addressing certain pain points, as identified:

- Maintenance of peaker plants and its operation is a very costly affair. To tackle this pain point, we are looking forward for a solution which has comparatively lower manufacturing costs.

- Space optimization need not be a major cause of concern here as coal-fired or natural-gas fired peaker plants occupy a large space for its operations. However, stationary storage need not require such a large space and choosing the architecture with better space utilization need not be a major selection criteria.

- The chosen architecture must be thermally efficient, ready to operate, even at higher temperatures and drastic atmospheric conditions.

- Also, as the final idea is to replace the peaker plants with second-use batteries rather than first use batteries, life cycle would play a major part. An architecture which provides for higher life cycle would always be a better candidate for the same.

Based on the following criteria, Prismatic cells would seem to cater more to the problem we are trying to solve as it has a better charge/weight ratio and also has a higher lifecycle. Although it has a higher manufacturing cost and requires additional cost for increasing the thermal efficiency, the total cost for setting up the system would be marginally higher than the pouch cells, but much lower than the cost of operation of a peaker plant.

· Battery Cell Chemistry

There are certain aspects to be considered while choosing optimal chemistry for EV batteries, which can then be used for second use as peaker plant replacement. Certain criteria to choose optimum EVs are rechargeability, energy and power density, cost and safety amongst others. Although Lithium-ion batteries emerge to be the best option for EV batteries, which can then be used as second use, there are other options which can be explored. At the initial stage of the replacement plan, different battery chemistries can be compared to then scale-up the same for higher capacity.

A possible alternative to Li-ion batteries can be Mg-ion batteries, which has the capacity to offer a higher potential energy boost as compared to the Li-ion. An Mg-ion battery, half the size of a Li-ion battery can provide the same amount of power for the energy grid. Development of such a battery is still a challenge and thus cannot be used until the prototype is successfully implemented [18].

Ni-MH (Nickel Metal Hydride) batteries can also be used as a replacement for Li-ion batteries. The major advantage of using such a battery type is that they can have double the specific energy compared to Li-ion batteries. The drawback of using Ni-MH batteries is its rapid discharge rate at higher temperatures. As peaker plants might be located at even extreme sites, using this battery type need not be a viable option as the rapid discharging might lead to shortage of power during peak times.

Based on the analysis, Optimum combination was chosen as: ‘Li-ion battery with a prismatic cell architecture’.

Health, Safety & Environment Review

There are multiple aspects to be considered while replacing the existing power plants with stationary energy storage system. Based on the analysis to choose optimum cell configuration, ‘Li-ion battery with Prismatic cell architecture’ was considered as the best option, considering the current scenario. In order to mitigate the risks associated with using stationary storage, the review consists of three aspects:

1. Identifying potential risks associated with peaker plants (power plants in general)

2. Identifying potential risks associated with stationary energy storage

3. Eliminating existing risks posed by power plants with the emerging risks due to energy storage in order to encourage replacement

· Peaker Plants Safety Review

The most critical point of consideration is that a power plant (coal-fired or natural-gas fired) poses risks to the workers through multiple modes, the most striking being through electric short circuits, fires, gas leakage or spilling of hazardous materials [19].

Based on the SDG-HAZOP method proposed by Zhang et al [20], the study of power plants is carried out using a combination of using a network graph (SDG) and HAZOP (Hazard and Operability Studies). The method plans to lower the complexity of the multiple units of plants by defining a hierarchal structure of different equipment used in the unit. Upon defining the structure, pain points for safety at each individual location in the network graph is identified and then acted upon. As shown in the Figure 1, the graph follows a descending structure in terms of composition of a power plant. For a standard coal/natural gas operated power plant, major units such as the boiler unit, turbine unit, electrical unit, etc. are considered in depth with a focus on multiple sub-units used in the operation.

Based on the same structure, this section aims to follow a similar approach for the replacement of power plants with stationary storage. The entire renewable energy operated power plant will be assessed for potential areas of risk, broken down into sub-domains and eliminating instances of sufficient doubt, by defining proper safety measures

· Stationary Energy Storage Systems (EES) Review

In this case, the Li-ion battery has been chosen to be used, which is an electro-chemical source of energy. This energy storage is planned to be operated at moderate temperatures with additional structuring in case of extreme conditions.

Certain key pain points have been identified with their proposed solutions:

Conclusion

As the world is slowly moving towards cleaner technologies for energy and most ruling bodies are pushing for reduction in emissions, getting away with the polluting peaker plants seem to be a viable solution and replacing it with a stationary storage system serves the purpose. To cater to the growing energy demand, USA needs to add around 20 GW of peaking capacity to its grid over the next 10 years, with around 60% of it to be installed between 2023 and 2027 (Newbery, 2018). The high operating cost and much higher cost of electricity produced would serve as deterrents to building new peaking power plants. Thus, in order to cater to the rising demand, building robust ESS using batteries would work in favor, both economically and from an environmental standpoint. Also, using second use batteries serves as a viable purpose in lowering the cost of electric and hybrid vehicles, which in-turn help further towards lesser emissions. The optimum cell configuration (Li-ion Prismatic cells), is often used in electric vehicles and could thus, be used in energy storage systems upon retirement from its first use.

Overall, second use batteries showcase a great potential in being a key player to replace peaker plants and also as an alternative to new peaker plants being set up. Upon successful implementation of second use batteries in energy storage systems as a prototype for providing supply for peak load, similar implementations could be followed for generalizing the storage systems. Additional avenues into using second use batteries for electricity can also be explored through setting up such systems in regions with low income (around the world), promoting cheaper alternatives to first use batteries and cleaner alternatives to fossil fuel energy.

References

[1] Wikipedia: Peaking Power Plants

[2] Wijesuriya, S. (2020). The “Peakers”: The role of peaking power plants and their relevance today. Retrieved from SciencePolicy circle: https://www.sciencepolicycircle.org/38-the-peakers-the-role-of-peaking-power-plants-and-their-relevance-today

[3] Phase out Peakers. Retrieved from CleanEnergy Group: https://www.cleanegroup.org/ceg-projects/phase-out-peakers/

[4] Phase out Peakers. Retrieved from CleanEnergy Group: https://www.cleanegroup.org/ceg-projects/phase-out-peakers/

[5] Ramirez, R. (2020, 05 19). The Drive to Replace Summer-Only ‘Peaker’ Power Plants. Retrieved from Wired: https://www.wired.com/story/the-drive-to-replace-summer-only-peaker-power-plants/

[6] PSE. (2020). Energy Storage Peaker Plant Replacement Project. Retrieved from PSE: https://www.psehealthyenergy.org/our-work/energy-storage-peaker-plant-replacement-project

[7] Newbery, C. (2018, 10 01). Energy Storage Poses a Growing Threat to Peaker Plants. Retrieved from Transform: https://www.ge.com/power/transform/article.transform.articles.2018.oct.storage-threat-to-peaker-plants

[8] Phase out Peakers. Retrieved from CleanEnergy Group: https://www.cleanegroup.org/ceg-projects/phase-out-peakers/

[9] NYISO (New York Independent System Operator). Retrieved from Energy Online: http://www.energyonline.com/Data/GenericData.aspx?DataId=13

[10] Code repository: https://github.com/yashgokhale/Miscellaneous/tree/master/battery_modeling

[11]Flaherty, N. (2020, 03 16). Large pouch cell battery tech at heart of GM EV strategy. Retrieved from eeNews Power Management: https://www.eenewspower.com/news/large-pouch-cell-battery-tech-heart-gm-ev-strategy

[12]Lam, M. (2019, 11 09). Advantages of pouch cell battery, trend and opportunities. Retrieved from Medium: https://medium.com/battery-lab/advantages-of-pouch-cell-battery-trend-and-opportunities-d08a5f0c6804

[13]Battery University. (2019, 04 24). BU-301a: Types of Battery Cells. Retrieved from Battery University: https://batteryuniversity.com/learn/article/types_of_battery_cells

[14]Bestgo battery. (2019). Li-ion Pouch cells. Retrieved from Bestgo battery: https://www.bestgobattery.com/pouch-cells.html

[15]TWAICE. (2019, 08 26). BATTERIES EXPLAINED — FROM CELL FORMATS TO CHEMISTRIES. Retrieved from TWAICE: https://twaice.com/articles-battery-technology/#:~:text=Prismatic%20cells%20consist%20of%20a,onto%20each%20other%20in%20layers.&text=The%20large%20surface%20area%20specific,be%20stacked%20to%20save%20space.

[16]Battery University. (2019, 04 24). BU-301a: Types of Battery Cells. Retrieved from Battery University: https://batteryuniversity.com/learn/article/types_of_battery_cells

[17]epec. (n.d.). PRISMATIC & POUCH BATTERY PACKS. Retrieved from epec Engineered Technologies: https://www.epectec.com/batteries/prismatic-pouch-packs.html

[18]FutureBridge. (n.d.). Alternative Chemistries to Li-ion for E-mobility. Retrieved from FutureBridge: https://www.futurebridge.com/industry/perspectives-mobility/alternative-chemistries-to-li-ion-for-e-mobility/

[19]PowerGen International. (2005, 06 01). Power plant safety. Retrieved from Power Engineering: https://www.power-eng.com/2005/06/01/power-plant-safety/#gref

[20]Zhang, C., Zhang, P., Yang, Z., & Song, L. (2009). Safety Assessment Modeling for Thermal Power Plants Using Hierarchical SDG-HAZOP Method. 2009 IEEE International Conference on Intelligent Computing and Intelligent Systems. IEEE.

[21]Ma, S., Jiang, M., Tao, P., Song, C., Wu, J., Wang, J., . . . Shang, W. (2018, 12). Temperature effect and thermal impact in lithium-ion batteries: A review. Progress in Natural Science: Materials International, 28(6), 653–666. doi:https://doi.org/10.1016/j.pnsc.2018.11.002

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