Regan Brown
Hydrogen fuel cells are an exciting alternative to fossil fuels, with the potential to power vehicles and ships. Hydrogen burns cleanly, emitting only water vapour, and is the most abundant element on Earth. The amount of hydrogen required by a fuel cell depends on several factors, including the efficiency of the fuel cell, environmental and driving conditions, and the availability of hydrogen refuelling stations. Hydrogen storage is a key challenge, with physical storage requiring high-pressure tanks or cryogenic temperatures. Despite these challenges, advancements in hydrogen storage systems and refuelling infrastructure are being pursued to meet performance expectations and enable the broader application of hydrogen fuel cells.
| Characteristics | Values |
|---|---|
| Hydrogen consumption | Depends on the efficiency of the fuel cell |
| Fuel cell efficiency (BOL) | 51% |
| Fuel cell efficiency (EOL) | 45% |
| Lower heating value (LHV) of hydrogen | 120,000 kJ/kg |
| Hydrogen consumption formula | (Total energy required x time) / (Efficiency x LHV of hydrogen) = Total hydrogen required |
| Hydrogen consumption for a 200 kW fuel cell for 8 hours | (200 kW x 8 hours x 3600 s) / (51% x 120,000 kJ/kg) = 94 kg of hydrogen |
| Hydrogen consumption for a 1 kW fuel cell | 1.666 kWh of chemical energy to generate 1 kWh of electrical energy |
| Hydrogen storage | Stored physically as gas or liquid |
| Hydrogen storage as gas | Requires high-pressure tanks (350-700 bar, 5000-10000 psi tank pressure) |
| Hydrogen storage as liquid | Requires cryogenic temperatures (boiling point of hydrogen at one atmosphere pressure is -252.8°C) |
| Hydrogen vehicle consumption | 0.05-0.1 kg of hydrogen per kilometer (50-100 km/kg) |
| Hydrogen vehicle range | 500-800 kilometers per full tank (5-8 kg of hydrogen) |
| Hydrogen vehicle efficiency | Conversion efficiency of hydrogen into electricity can exceed 60% |
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What You'll Learn
Hydrogen fuel cell vehicles
The amount of hydrogen a fuel cell vehicle requires depends on several factors, including the efficiency of the fuel cell and the vehicle's electric motor design. Modern hydrogen engines are quite efficient, with a conversion rate of chemical energy into electrical energy that can exceed 60%. This is significantly higher than traditional internal combustion engines. The efficiency of the fuel cell is higher at the beginning of its life, at approximately 51%, and lower at the end of its life, at around 45%.
On average, a hydrogen vehicle consumes about 0.05 to 0.1 kg of hydrogen per kilometre, resulting in a range of about 50 to 100 kilometres per kilogram of hydrogen. The range of a hydrogen vehicle depends on the amount of hydrogen it can store in its tank, which is typically between 5 and 8 kg of high-pressure compressed hydrogen. This results in a range of approximately 500 to 800 kilometres per tank. Additionally, the availability of hydrogen refuelling stations plays a role in the practicality of hydrogen vehicles.
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Hydrogen's high energy per mass
Hydrogen has one of the highest energy density values per mass. Its energy density is between 120 and 142 megajoules per kilogram (MJ/kg). To put this in context, for every kilogram of hydrogen, it contains an energy value of 120-142 MJ. This is nearly three times the energy content of gasoline, which has 44 MJ/kg.
This high energy per mass makes hydrogen an attractive fuel option, particularly for transport applications. Hydrogen-powered fuel cells are being explored for use in vehicles, with the aim of providing a driving range of over 300 miles and easy, quick refuelling. Hydrogen is also used in power applications, with the US hydrogen industry producing nine million tons per year for electrical applications, among other uses.
However, hydrogen storage is a challenge, particularly for transport applications. Hydrogen can be stored as a high-pressure gas or low-temperature liquid, but both options present difficulties. Gas storage requires large-volume, high-pressure tanks, which are less of an issue for stationary applications but can be problematic for vehicles where space is limited. Liquid storage can achieve greater densities but is more energy-intensive and requires extremely low temperatures.
Research and development are underway to advance hydrogen storage systems and meet onboard light-duty vehicle requirements. This includes exploring novel storage materials and methods to improve vehicle performance, range, and refuelling time.
Overall, hydrogen's high energy per mass makes it a promising energy carrier, but storage technology advancements are needed to fully realize its potential, particularly in the transportation sector.
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Fuel cell efficiency
The efficiency of a fuel cell is influenced by various factors, such as the morphology and structure of the carbon used in electrode synthesis. The efficiency can also be impacted by the management of water within the cell, as the rate of evaporation affects the performance and longevity of the fuel cell. Additionally, the efficiency of a fuel cell is higher at the beginning of its life (BOL) compared to the end of its life (EOL). For example, a 200 kW fuel cell with a BOL of 51% and an EOL of 45% would require 94 kg of hydrogen to run for 8 hours.
The conversion efficiency of a fuel cell improves when the external load is decreased, and careful design is required to handle variable power requirements while maintaining high efficiency. Fuel cells have higher efficiency than combustion engines as they directly convert chemical energy into electrical energy, skipping intermediate steps that result in energy losses. This direct conversion also contributes to lower fuel consumption, reduced operating costs, and lower emissions.
Overall, fuel cell efficiency is a critical factor in determining the operating cost and fuel storage requirements, especially in mobile applications where fuel efficiency directly impacts the range and performance.
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Hydrogen storage
For automotive applications, hydrogen is typically stored onboard in high-pressure tanks (350–700 bar [5,000–10,000 psi] tank pressure). These tanks are often made of composite materials to reduce weight. The storage of hydrogen as a gas allows for a driving range of more than 300 miles, meeting cost, safety, and performance requirements. However, the large volume of these systems remains a challenge for light-duty vehicles.
Liquid hydrogen storage requires cryogenic temperatures, as the boiling point of hydrogen at one atmosphere pressure is −252.8°C. This method is less commonly used due to the technical challenges and high costs associated with maintaining cryogenic temperatures.
Metal hydride (MH) systems offer an alternative storage solution. These systems consist of metal alloys that form weak bonds with hydrogen at relatively low pressures (10–40 bar). MH systems can be used for fuel cell hydrogen storage in submarines and have the advantage of reversibility. However, issues of thermal integration and system durability need to be addressed.
Research and development activities are ongoing to improve hydrogen storage systems and develop novel storage materials. The goal is to enhance storage capacity, reduce weight, and improve safety to meet the performance expectations of customers and the requirements of various applications, including automotive, aerospace, and marine.
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Hydrogen's renewability
Hydrogen is a clean fuel with a diverse range of production methods, making it highly versatile. Hydrogen can be produced from renewable sources, such as solar, wind, geothermal, biomass, and nuclear power. This renewability is a key factor in the growing interest in hydrogen as an energy source.
Solar energy, for instance, can be used in multiple ways to produce hydrogen. Sunlight can directly or indirectly provide the energy required to generate hydrogen. Solar-driven processes include photobiological, photoelectrochemical, and solar thermochemical methods. Photobiological processes harness the natural photosynthetic activity of bacteria and green algae to produce hydrogen. Photoelectrochemical processes, on the other hand, use specialized semiconductors to separate water into hydrogen and oxygen. Solar thermochemical production employs concentrated solar power to drive water-splitting reactions.
Biological processes also play a role in hydrogen production. Microbial biomass conversion utilizes microbes such as bacteria and microalgae to produce hydrogen through biological reactions. These microbes break down organic matter, such as biomass or wastewater, to generate hydrogen. Additionally, wind-generated electricity can be used to power water electrolysis to produce hydrogen, which can then be used in fuel cells or to fuel vehicles.
Hydrogen's ability to store and transport energy is another significant advantage. It can be used to store energy from renewable sources, such as solar photovoltaics (PV) and wind, and transport it over long distances. This versatility enables regions with abundant renewable resources to supply energy to distant cities. Furthermore, hydrogen can be transformed into electricity and methane, powering homes and industries, and even fuelling vehicles, ships, and planes.
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Frequently asked questions
The amount of hydrogen needed by a hydrogen fuel cell vehicle depends on several factors, including the vehicle's efficiency, environmental and driving conditions, engine efficiency, consumption per kilometer, desired range, and available refueling infrastructure. An average hydrogen vehicle consumes approximately 0.05 to 0.1 kg of hydrogen per kilometer, resulting in a consumption rate of about 50 to 100 km/kg.
The efficiency of a fuel cell vehicle's engine plays a critical role in determining its hydrogen consumption. Modern hydrogen engines are quite efficient, with conversion rates exceeding 60%, which is significantly higher than traditional internal combustion engines. A more efficient engine will require less hydrogen to produce the same amount of energy.
The range of a hydrogen fuel cell vehicle is directly related to the amount of hydrogen it can store in its fuel tank. Hydrogen vehicles typically have tanks that can hold 5 to 8 kg of high-pressure compressed hydrogen, resulting in a range of approximately 500 to 800 kilometers per full tank. Therefore, a vehicle with a longer range will require more hydrogen to fill its tank.
