Critical Analysis of Battery Technology for Utility Level Storage
Research paper from science research program in high school
Mentored by Dr. Devendra Sadana at IBM TJ Watson Research Center
Abstract:
This paper analyzes batteries for utility level storage and the efforts of Tesla to bring this technology to consumers. Tesla’s vision for utility level storage as well as their home utility level storage technology are discussed. Three individual cells similar to the 21700 Li-ion cells that will be used by Tesla were tested for charge/discharge capacity over time at a charge/discharge rate of 1C and for their reaction to discharge rates from 1-5C. The capacity data was analyzed to see if these batteries, which are similar to the ones that will be used by Tesla, are cost effective by calculating their levelized energy cost. The tests performed at different discharge rates determine if these batteries will be able to handle the variable load they might encounter in a utility level storage application. It was found that these batteries and the battery proposed by Tesla are not yet cost effective in utility level storage applications. However, high volume production and research of Li-ion batteries are expected to reduce the overall cost in the near future. The future vision of this paper discusses the use of all solid state batteries and the performance characteristics of the ideal battery for utility level storage.
Notes and reflection on the content presented in this paper:
My main concern with the content presented in this paper now having more experience in engineering design, the performance characterization and life expectancy goals set in this paper are not very accurate. The main design assumption driving these numbers is that these batteries will undergo a full charge discharge cycle in a day and given average cycle lives will only last 3 years. This assumption is short sighted because it assumes the consumer electronic model where battery size is optimized for size and wait and cycle lives of around 3 years coincide with typical upgrade patterns. In many industrial and automotive applications, where the product life cycle is 15 years or even beyond, the focus is more on robustness and reliability. It is not as important that your home utility level storage solution fits in your pocket. taking this into account I don't believe there is enough information in this paper to make predictions about home utility level storage system sizing, and the LCOE metric doesn't take into account overall cell life cycle in terms of time, I think these new assumptions may have an affect on the cell performance. Given the extended timeline and the usage of utility level storage as an economic tool and energy saver, I think it fair to apply some coefficients to the current LCOE numbers to move closer to the actual result. From a cell longevity perspective, it would not be too bold to assume that under the conditions of a pack lasting 15-20 years and operating at fairly low charge/discharge rates (<0.5C) cell degradation will be reduced and cycle life increased. In addition taking measures to not reach peak DoD have also been shown to have a positive cycle life impact. It might also be feasible to tolerate extra SOH degradation than is normally acceptable in consumer electronics since the utility level storage acts as an auxiliary to the grid instead of a home's only power source. Considering the magnitude of this purchase for a homeowner as well it is not unlikely that cycle lives will be pushed in order to get the best economic use out of the product, similar to how cars will stay in the hands of a single owner, or continue to be sold on the used market for long after their designed life. With the following coefficients, cycle life * 4, DoD * 0.75, efficiency * 0.95, the new LCOE for the 3 cells presented in the paper become $0.34 / kWh for the Lithium Iron Phosphate cell, $0.35 / kWh for the LiNiMnCo cell, and $1.08 / kWh for the generic Li-ion cell from Panasonic. Leveling this cost to the current estimated price of Telsa Cells ($114), a cost of $0.16 / kWh (it would be $0.24 per kWh when this paper was written so still questionable). Depending on where you live and how long you use your utility level storage device, and contrary to the previously stated position of this paper. It would be currently economically viable to purchase a Utility level storage device for your home. Notwithstanding current trends in V2X and other home energy advancements, home utility level storage is finally viable to the average consumer.
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