Energy Storage Technologies Lecture Notes

Instructor: Annokka Santa Salouarnjian, Assistant Professor, School of Engineering, Aalto University
This lecture serves as an introductory overview of energy storage technologies.
Target Audience: Particularly designed for those not majoring in Advanced Energy Solutions Master's programme or those who haven't taken the obligatory course "Introduction to Advanced Energy Systems".
Purpose: Introduce technical aspects of various energy storage technologies.

Discovery Learning Approach:
- Emphasizes active engagement through prior knowledge.
- Students are encouraged to create a mind map of energy storage technologies known to them.
- Can be completed individually or collaboratively using tools like StudyMate.
Objective: To connect new information with existing knowledge.

Energy storage can primarily be categorized into the following types:
- Mechanical Energy Storage:
- Pumped Hydro Storage:
  - Most common form of energy storage.
  - Uses potential energy by pumping water upstream.
- Compressed Air Energy Storage (CAES):
  - Efficiency: 75-80%.
  - Low-cost solution but not widely adopted; usually requires geological formations like caverns or old mines.
- Flywheels:
  - Store energy in kinetical form.
  - Efficiency of around 90%, becomes more effective with materials minimizing friction.
- Electrochemical Storage:
- Includes various types of batteries and their chemistries.
- Batteries: Two electrode systems subject to electrochemical reactions (redox).
  - Primary Batteries: Non-rechargeable, e.g., used in flashlights.
  - Secondary Batteries: Rechargeable batteries used for energy storage.
- Flow Batteries: Different from traditional batteries; utilize flow of liquids containing electrolytes.
Superconductors:
- Focus on superconductive magnetic energy storage.
- Conduct energy with negligible resistance.
Chemical Storage:
- Power to X Concepts:
- Refers to converting electricity into different chemical forms (e.g., hydrogen, fuels, gases).
- Example Highlight: Power to Hydrogen through electrolysis which involves splitting water molecules.
- Green hydrogen production: a significant future energy source.

Utilizes potential energy by lifting water to a higher elevation and releasing it to generate electricity when needed.

Works by using electricity to compress air, storing it in caverns, and releasing it to drive turbines.
Efficiency ranges between 75-80% but requires specific geological formations.

Batteries Function:
- Made of two electrodes - anode (negative) and cathode (positive).
- Electrochemical reactions create voltages that power devices.
- Various battery chemistries exist due to different materials used for electrodes, e.g., lithium-ion vs. lead-acid batteries.

Lithium-Ion Battery:
- Consists of a negative electrode (anode), a positive electrode (cathode), and an electrolyte for ion conduction.
- Anode often contains carbon sheets with lithium ions moving between them.
- Cathode commonly made from structured metal oxides that stabilize during charging.
Lead-Acid Battery:
- Utilizes lead oxide in the positive electrode and metallic lead in the negative electrode, with a capacitor reaction forming lead sulfate, yielding lower voltages.

Features separate tanks for vanadium solutions.
Reaction involves moving liquids through a cell, providing scalable energy storage capacity and safety advantages.

Designed for high-speed energy discharge and are often used in conjunction with batteries.
Types of supercapacitors:
- Electrochemical Double Layer Capacitors (EDLC):
- Utilize carbon material such as graphene.
Pseudocapacitors:
- Employ electrochemical reactions inside cells, using transition metal oxides.
Hybrid Capacitors:
- Combine features from both batteries and supercapacitors.

Electrolysis Process:
- ** alkaline electrolyzer:** An older, commercially available technology but with lower efficiency.
- PEM (Polymer Electrolyte Membrane) Electrolyzer: Offers higher efficiency and flexibility, sustained at 80-120 degrees Celsius.
- Solid Oxide Electrolyzer: Operates at higher temperatures (600-800 degrees Celsius) and uses solid electrolytes.

Chemical Storage: Creates and stores usable products (H2 and O2).
Electrochemical Storage: Stores energy through ionic movement; focused on efficiency and capacity limitations.

Function of Fuel Cells: Convert stored chemical energy (like hydrogen) back into electricity.
Process overview: Hydrogen is fed into the anode where it splits into protons and electrons; on the cathode side, this combination creates water as a byproduct.
Definition: Fuel cells do not store energy but convert it, differentiating them from traditional storage systems.

Summary of various energy storage modalities discussed.
Encouragement towards further exploration through suggested readings and course materials.
## Takeaway:** Students encouraged to reflect on what they learned and document insights in their notes or lecture journal.