Energy Storage Systems - Hydrogen

Energy Storage Systems

• Energy storage using hydrogen is a promising technology due to its high energy density (33 kWh/kg). It is a good candidate for mid and long-term storage, especially for seasonal storage in renewable energy sources (RES).
• Hydrogen has significantly higher energy content than diesel (3 times more) and natural gas (2.5 times more).
• Hydrogen can be produced from electricity using electrolyzers and converted back into electricity using fuel cells.
• Storing hydrogen is challenging due to its low weight density, requiring a large storage volume (11 m³ for 1 kg).
• Hydrogen is typically compressed at high pressure (350-700 bar).
• Hydrogen is suitable for long-distance transmission.
• Hydrogen is considered a clean fuel, producing zero emissions during use (except for water vapor), if generated by renewable sources. However, current production methods are not always sustainable, often relying on fossil fuels. A future approach uses water electrolysis powered by RES.
• Current hydrogen production is significantly more expensive compared to fossil fuels.

Energy Densities

• The presentation includes a figure showing energy densities of various energy carriers, including hydrogen, natural gas, propane, diesel, and ethanol.
• A typical lithium-ion battery has a much lower energy density (only 0.15 kWh/kg).

Hydrogen Storage Methods

• Three main ways to store hydrogen to reduce its volume:
  • Compressed gas (350-700 bar)
  • Liquid phase (-253°C)
  • Solid form (metallic hydride) or chemical form (e.g., MgH₂)
• Compressing hydrogen to high pressure requires energy which accounts for 10-15% of its energy content.
• Liquid hydrogen requires significant energy to bring it to the low temperatures for storage.
• Metal hydrides are common storage methods, capable of high storage densities exceeding liquid hydrogen, but require higher temperatures and pressures.

Hydrogen Production Methods and Sources

• A diagram shows that various renewable energy sources (wind, solar PV, hydro, geothermal, and biomass) can power hydrogen production via electrolysis.
• Fossil fuels (oil, gas, coal) are also involved in hydrogen production through reformation/gasification methods.

Global Hydrogen Production

• A table presents global hydrogen production by different sources and categorized with their shares, advantages, and disadvantages.
• Natural gas is the leading producer with around 48%.
• Oil, coal, and electrolysis are the other sources.
• Main sources have low production cost but may have environmental impacts (e.g., greenhouse gas emissions).
• Electrolysis can be a sustainable technology with low emissions.

Hydrogen Applications

• Hydrogen is used in various applications, including ammonia production, oil refining, and methanol production.
• The graph illustrates the increase in H₂ demand from 1950 to 2020.

Hydrogen Color

• Different colors representing different categories of hydrogen production:
  • Grey: Polluting process (fossil fuel based)
  • Blue: Partially fossil fuel based with carbon capture and storage
  • Green: Using renewable energy sources.

Power-to-Power Storage System

• A figure illustrates a hydrogen-based power-to-power storage system involving an electrolyzer, hydrogen storage, and a fuel cell.
• Intermediate processes (such as hydrogen and oxygen conditioning) are necessary to improve energy density.
• Both hydrogen and oxygen storage reservoirs are shown.

Electrolysis of Water

• Around 50% of hydrogen is produced from fossil fuel reformation.
• Electrolysis is a more expensive process for hydrogen production, but it is becoming increasingly important.
• Electrolysis involves water decomposition into hydrogen and oxygen through the use of an electric current.
• Different technologies exist, each with varying efficiency and temperature requirements, including Alkaline Electrolysis (AE), Proton Exchange Membrane (PEM), and Solid Oxide Electrolysis.

Types of Water Electrolyzers

• Alkaline Electrolysis (AE): Well-established with 70-80% efficiency and moderate temperatures.
• Proton Exchange Membrane (PEM): High production rate and high purity, efficiency of 80-90% with lower operating temperatures.
• Solid Oxide Electrolysis (SOE): High energy efficiency (90-100%) but operates at high temperatures, 500-850° C, consuming 3.2 kWh/m³ of hydrogen.

Fuel Cell Generation

• The figure illustrates how a fuel cell operates, converting hydrogen and oxygen into water, electricity, and heat.