Comparative Life Cycle Assessment of Pumped Hydroelectric and Lithium-Ion Battery Storage

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The CA government proposes to convert to 100% dependence on renewable energy. However, energy produced by renewable sources cannot always be created at the point of demand. Furthermore, solar energy cannot be created after sunset, when the demand may be at its peak. Energy storage that is clean and economical must be utilized in order to fully transition to renewable sources of energy.I was part of a group that compared two promising, utility-scale storage solutions for the power grid in Los Angeles and propose a solution that has a lower environmental impact per Functional Unit (FU) of electricity supplied to the grid.

Problem Statement:

Locally, renewable energy is increasing in scale. 32% of California’s electricity came from renewable sources in 2017, the objective is to make this figure 100% by 2045. However, the risks that come with this conversion are mainly two:-

  • Overgeneration at low demand but high solar supply
  • Power outage if peak demand surpasses generation at low supply

This can be graphically represented by the 'duck-shaped' curve (Fig 1) that displays how 'out-of-phase' the generation of renewable resources is (Fig 2) w.r.t the energy demand across a typical day in a CA household. 

Thus, storage technologies to tap these renewable sources of energy for utilization at a later time are imperative. What is even more important is to analyze the environmental impact per Functional Unit - which we decided to consider as 'impact per MWh of energy supplied to the grid' - expected from building and maintaining these technologies over the next 50 years.

     Fig 1: The duck-shaped curve to represent energy demand

 

Fig 2: Distribution of renewable energy across a typical day in CA

Possible solutions:-

In order to maximize the opportunity to tap sources of renewable energy for exploitation at a different time, we need storage technologies. In our research, we identified two viable storage technologies that may help achieve the CA Government's vision of converting to wholly renewable dependence on energy:-

a. Pumped hydropower storage at the Hoover Dam 

Pumped storage entails an energy storage system where excess renewable energy is used to pump water from a downhill to an uphill basin, and released at times of high demand in order to generate electricity through a hydropower plant. The technology is reliable and in wide use today. Energy is stored as gravitational energy potential of the pumped water, however the pumping process does result in energy losses and the plant comprises a net consumer of energy. 

b. Tesla-style battery storage powerpack facility

Battery storage is a relatively new and fast-evolving field. The technology is based on an electrochemical cell converting stored chemical energy to electricity; the battery can be recharged by reversing the chemical reaction with the use of electrical energy. Lithium-ion battery technologies are commonly analyzed as a potential near-future solution to the energy storage issue in utility-scale context due to their high energy density, relatively long life span, and high charge/discharge efficiency.

Assumptions:-

Owing to lack of relevant data and to maintain a certain complexity level, our team outlined a handful of pre-analytical assumptions. While these assumptions may not provide a 100% reflection of our predictions for these technologies, we also ensured that the target of this research was not being overly compromised:-

a. Dam storage

  • The impacts from Design, engineering, and commissioning were considered equivalent to Tesla Powerpack facility.
  • Impact from Power Generation Costs were excluded
  • Methane/CO2 Releases from the Reservoir were also taken off the chart.
  • Routine Maintenance impacts were assumed to be infinitesimal

b. Tesla powerpack

  • System Life: 50 years, Battery Life: 10 years - 5 warranty replacements
  • Energy production to each Powerpack system is same - exempted from LCA analysis
  • Transmission impacts are negligible per functional unit to the grid
  • Labour and their transport costs and impacts were also taken out of the equation

Analysis:-

To perform an LCA analysis, we needed to choose major impact categories that could be quantitatively measured w.r.t the FU. 

Impact categories for this analysis were chosen based on available outputs form the EIO-LCA tool to try to show the overall impact across several areas with just a few key indicators. Classification and characterization of outputs is largely done by the EIO-LCA tool developed by CMU and a comparison between total results and results based on functional unit. It should be noted that the 1997 Purchaser price model does not output water use as some other EIO-LCA models do, and in future studies this impact should be included for completeness, since several processes, including battery materials extraction and production, and cement / concrete production, are very water-intensive. The selected impact categories are listed below:

  • Particulate Matter 10 Micron (PM10) - has the potential to cause heart and lung health effects when inhaled; used as a basic human health indicator for production, especially since many construction / production activities happen in US.
  • Global Warming Potential (GWP, Tonnes CO2 Equiv.) - since these systems are designed to work with green energy, it is worth looking at the impacts from production of each system to see the potential for unintended consequences of “green” updates to the power grid.
  • Total Energy Use (TJ) - this is a useful comparative measure for the total effect of each system as energy use and water are two of the main inputs, other than materials, to any process.
  • Total Releases Transfers of Toxic Substances (Toxics, kg) - this impact is important for comparison in the systems because of the metals and other toxic substances resulting from both batteries production and steel turbine manufacturing. 

Comparative analysis between the two technologies per MWh (functional unit) show that, across all impact categories that the battery system has higher impacts (Fig 3). When looking at the battery system with replacements incorporated, the impacts are nearly three times as large as those for the battery system without replacements, and many times those associated with the dam system per MWh.

 Fig 3: Comparison of systems' impact per functional unit

Conclusions:-

  • Total impact score of Hoover Dam Storage is multi-fold times lesser than that of Tesla utility scale battery
  • Tesla powerpack system has a higher impact score despite smaller in scale and more readily deployable
  • At similar costs, capacity of pumped storage is higher, though this may be offset by utilizing existing transmission and generation facilities at Hoover Dam

Challenges and future scope for research:

a. Hoover Dam

  • Lack of data regarding actual pumped-storage facility plans and scale 
  • Practical implementation of battery facility is uncertain.
  • Impact on local species that thrive in the river.
  • Effect of altering water levels at Lake Mead need to be accounted for - evaporative losses, emissions due to algae.
  • Flow pattern of the river must be analyzed
  • Possible refurbishment costs over the 50 year timespan 

b. Tesla Powerpack

  • EOL of battery - vastly increases environmental impacts, recycling rates are understood but there is disagreement in how to apply
  • Potential for improved battery technology, battery lifetimes in future
  • Investigations into Tesla Gigafactory improvements for comparative LCA

Please feel free to reach out to me at shuvamsinha1995@gmail.com in case you have any clarifications regarding the sources of the data we mined to measure impacts from various sectors that contribute to building each storage technology - I can't make them public on this blog due to an NDA but we can certainly discuss them in detail in case anyone's interested!

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