Solar Energy Storage

Happy Friday! In this week's education issue, we will be wrapping up our focus on solar energy with a discussion on energy storage! While renewable energy is a great source of clean power, it is ultimately dependent on local weather patterns that determine when and how much energy these systems can produce. The Office of Energy Efficiency & Renewable Energy notes that, “solar energy production can be affected by season, time of day, clouds, dust, haze, or obstructions like shadows, rain, snow, and dirt.” (“Solar Integration”). By storing energy, typically through lithium-ion batteries, solar can continue to be relied upon and better integrated into the energy sector.


Lithium Ion batteries are the most common form of battery used for energy storage today and can be found in energy products, electric vehicles and your everyday electronics. These rechargeable batteries are made up of a few main parts; an anode, a cathode, a separator and two current collectors (one positive and one negative). Both the anode and the cathode store Lithium, while the separator keeps them apart. The separator is designed so that no electrons can flow through it, but Lithium Ions can. (“How Does a Lithium-Ion Battery Work?”)



Figure 1. Lithium Ion Battery with five distinct sections; from left to right they are the positive current collector, Cathode, Separator, Anode and negative current collector. Here, the Lithium Ions are flowing from left to right from the Cathode to Anode through the Separator. The electrons however are forced to move through the circuit, creating a current. This direction (positive to negative) corresponds to a charging battery. Image courtesy of Sarah Harmon and Charles Joyner, US Department of Energy.




This is where the battery chemistry takes over. When a battery is charging, these positively charged Lithium Ions flow through the separator from the cathode to the anode, creating a potential between the two collectors. Electrons always want to flow so that there is equilibrium, or zero potential. Therefore, this created potential will cause electrons to also flow from the cathode to the anode side of the battery, but since they cannot move through the collector, they are forced to travel outside the battery through the circuit in order to reach its equilibrium state on the other side of the battery. (“How Does a Lithium-Ion Battery Work?”)


Keep in mind that there is no point to a battery if it is not connected to a circuit! Just imagine all those unused AA batteries sitting in your kitchen drawer. These will not lose their stored power because there is no circuit (aka your tv remote, or if you’re like me, your calculator) attached to it to use up the battery’s energy. These are not rechargeable batteries, but the same is true for our Lithium Ion batteries. It is also important to note that this constant movement of Lithium Ions and electrons is fairly taxing on batteries and they are only rated for a certain number of ‘cycles’. This is why your iPhone or laptop battery will tend to get worse overtime as it gets old.


Battery Science Overview:

  1. As a battery charges or discharges, positively charged lithium ions flow from one side of the battery to the other through the separator. This creates an electric potential.

  2. This electric potential will cause the movement of electrons in the same direction as the lithium ions. Since the electrons cannot move through the separator, they are forced to travel through the circuit in order to reach equilibrium at the other side of the battery.

  3. This movement of electrons through the circuit creates a current that is either flowing in a direction to charge the battery if it’s in charging mode or discharge the battery for use if it’s in discharging mode.

Now that we understand a bit about how energy storage through a battery works physically, we can begin to comprehend how these systems are integrated with renewable energy sources!


While wind and solar power are both great examples of highly efficient and clean energy generators, they can only do it under ideal conditions, such as sunny days or windy nights. Unfortunately, these unpredictable production patterns conflict with our current energy grid set up in which power is produced when and where we need it using fossil fuel power plants. Therefore, everytime we get an extra windy night in an area with wind power production, much of this energy is ‘spilled,’ or wasted, since there is no energy demand for it. (“Grid Integration”)


The solution then lies in our ability to capture this often spilled energy and store it until a time when it is needed. This is where our Lithium Ion batteries come into play. By increasing the electrical grids available battery storage capacity in conjunction with renewable energy projects, it becomes much more feasible to shut down fossil fuel burning power plants. While battery costs remain very high, research and development has resulted in the ongoing construction of battery storage systems of the magnitude of 400 plus MW (The Race to Build the World’s Largest Solar-Storage Plant Is On - Bloomberg). Additionally, academic studies have found various ways to reduce the stress on a fully renewable energy grid by drawing power from larger regions (think of if Texas had access to power from other states during their massive power outages back in February), finding an optimum mix of wind vs solar power and producing more power than we actually need. (“Grid Integration”)




Figure 2. The popular Tesla Powerwall shown here in a completed installation for a residential solar project. Image courtesy of Mass Renewables.


Led by tech companies such as Tesla, batteries are often viewed as a dazzling, fun technology that is slated to transform our cars and homes. However, storage technologies such as Lithium Ion Batteries are perhaps the most crucial tool we have to fully eradicate fossil field burning power plants. With the ability to store vast amounts of energy potential to the grid, we could seamlessly transition and integrate renewable energy into our everyday lives. The bottom line is that many renewable energy methods will remain unreliable and unrealistic unless we can store the energy they generate for when it is needed most, with battery technology being the most likely candidate.



 

Bibliography


“How Does a Lithium-Ion Battery Work?” Energy.Gov, https://www.energy.gov/eere/articles/how-does-lithium-ion-battery-work. Accessed 13 July 2021.

“Solar Integration: Solar Energy and Storage Basics.” Energy.Gov, https://www.energy.gov/eere/solar/solar-integration-solar-energy-and-storage-basics. Accessed 10 July 2021.


The Race to Build the World’s Largest Solar-Storage Plant Is On - Bloomberg. https://www.bloomberg.com/news/articles/2019-03-28/the-race-to-build-the-world-s-largest-solar-storage-plant-is-on. Accessed 14 July 2021.



Moore, Nicholas (2020) "Large Scale Grid Integration of Wind and Solar Power with Storage," Macalester Journal of Physics and Astronomy: Vol. 8 : Iss. 1 , Article 13. Available at: https://digitalcommons.macalester.edu/mjpa/vol8/iss1/13


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