Rajan Wilcox
Hydrogen fuel cells are an exciting prospect for the future of energy. Hydrogen is classed as an energy carrier, and can be used to fuel internal combustion engines and fuel cell vehicles. 1kg of hydrogen contains approximately the same energy as a gallon of diesel, and can be used to power an electric motor. Hydrogen can be produced with zero environmental impact, and can be stored in mega watt utility-scale energy. This paragraph will explore the energy content of 1kg of hydrogen fuel cell, and its potential as a future energy source.
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What You'll Learn
- Energy density: 1 kg of hydrogen has an energy density of 120 MJ/kg
- Electrical energy: This is equal to 33.6 kWh of usable energy
- Comparison to gasoline: 1 kg of hydrogen is equal to 1 gallon of gasoline
- Electrolysis: Electrolysis of water converts electrical energy to chemical energy
- Efficiency: A fuel cell's efficiency is, on average, about 55%
Energy density: 1 kg of hydrogen has an energy density of 120 MJ/kg
Hydrogen is a highly efficient energy carrier, with 1 kg of hydrogen containing approximately 120 megajoules (MJ) of energy. This is almost three times the energy density of diesel or gasoline, which have energy densities of 45.5 and 45.8 MJ/kg, respectively. In electrical terms, 1 kg of hydrogen contains 33.6 kilowatt-hours (kWh) of usable energy, compared to diesel's 12-14 kWh per kg. This means that 1 kg of hydrogen used in a fuel cell has a similar energy output to 1 gallon of diesel.
The high energy density of hydrogen makes it an attractive alternative fuel, particularly for heavy transport. Hydrogen fuel cells offer high torque, similar to battery-electric vehicles, but at a lower weight. For example, the hydrogen fuel cell truck Nikola One has a range of 500-750 miles with a 250-kWh battery pack, which is estimated to weigh around 2.5-3 tons. In comparison, the battery-electric Lion 8 with a 480-kWh battery pack and a 250-mile range weighs 2-5 tons.
The energy density of hydrogen also has implications for energy storage and transportation. Hydrogen can be used to store megawatt-scale energy and can enable the development of smart microgrids when combined with batteries and renewables. However, one of the challenges with hydrogen is its storage and transportation, as it needs to be stored under pressure or liquified, both of which require additional energy.
The production of hydrogen through electrolysis also impacts its energy density. The efficiency of electrolysis varies depending on the type of electrolyzer used, with solid oxide electrolysers offering 80% conversion of electricity to hydrogen, while alkaline and PEM electrolysers currently offer around 67% efficiency. The round-trip efficiency of converting electricity to hydrogen through electrolysis, purifying and compressing it, and then converting it back to electricity in a fuel cell is approximately 35%.
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Electrical energy: This is equal to 33.6 kWh of usable energy
Hydrogen is a versatile energy carrier that can be used for various applications, including fuelling internal combustion engines, cooking, heating, and storing megawatt-scale energy. One of its critical advantages is its high energy density, which is approximately 120 MJ/kg—significantly higher than diesel or gasoline.
When considering electrical energy, 1 kg of hydrogen is equivalent to 33.6 kWh of usable energy. This value is derived from the energy density of hydrogen and provides a direct comparison to other energy sources. For example, diesel fuel typically holds about 12-14 kWh per kg, showcasing hydrogen's superior energy density.
The process of converting electrical energy into hydrogen involves electrolysis, where electricity is used to separate water into gaseous hydrogen and oxygen. This conversion process typically yields an efficiency of around 67% for Alkaline and PEM electrolysers, resulting in an energy output of 33.3 kWh for every 50 kWh of electrical energy input.
Solid Oxide electrolysers offer even higher efficiency, achieving up to 80% conversion of electricity to hydrogen. However, they require substantial external heat sources. The round-trip efficiency, which includes converting electricity to hydrogen, purifying and compressing it, and then converting it back to electricity in a fuel cell, is approximately 35%.
The efficiency of a fuel cell also plays a role in determining the usable electrical energy obtained from hydrogen. A new fuel cell has a higher efficiency of around 51% (beginning of life, BOL), while a fuel cell at the end of its life (end of life, EOL) has a lower efficiency of approximately 45%. These factors are essential in calculating the exact amount of usable electrical energy extracted from 1 kg of hydrogen fuel cell.
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Comparison to gasoline: 1 kg of hydrogen is equal to 1 gallon of gasoline
Hydrogen is a low-carbon, low-cost, and low-weight alternative to gasoline, diesel, and natural gas. It can be produced and consumed with zero environmental impact when made using renewable energy sources. In terms of energy density, hydrogen outperforms gasoline and diesel. While gasoline has an energy density of 45.8 MJ/kg, hydrogen has an energy density of approximately 120 MJ/kg, almost three times more. This means that 1 kg of hydrogen contains roughly the same energy as 1 gallon of gasoline or diesel.
In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, compared to diesel, which holds about 12-14 kWh per kg. This higher energy density of hydrogen allows a fuel cell car to go 2.8 times farther on a kilogram of hydrogen than an internal combustion engine (ICE) car on a gallon of gasoline.
The production of hydrogen through electrolysis, however, comes with its own set of challenges. Hydrogen is produced in gaseous form and requires additional energy for storage, either by pressurization or liquefaction. The round-trip efficiency of converting electricity to hydrogen through electrolysis, purifying and compressing it, and then converting it back to electricity in a fuel cell is approximately 35%.
Despite these challenges, hydrogen has advantages over gasoline and diesel in terms of weight and refuelling speed. FCEVs (Fuel Cell Electric Vehicles) offer similar high torque to battery-electric vehicles but at a lower weight. Additionally, hydrogen trucks can be refuelled in less than 15 minutes, similar to diesel trucks.
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Electrolysis: Electrolysis of water converts electrical energy to chemical energy
Electrolysis is a process that uses electricity to split water into hydrogen and oxygen, converting electrical energy to chemical energy. This process can be used to produce hydrogen fuel, which has a much higher energy density than diesel or gasoline.
The energy density of hydrogen is approximately 120 MJ/kg, compared to 45.5 MJ/kg for diesel and 45.8 MJ/kg for gasoline. In electrical terms, this equates to 33.6 kWh of usable energy per kg of hydrogen, compared to 12-14 kWh per kg for diesel. This means that 1 kg of hydrogen contains about the same energy as 1 gallon of diesel.
The process of electrolysis involves passing an electric current through water, which breaks the water molecules (H2O) into their constituent atoms, forming gaseous hydrogen (H2) and oxygen (O2). This is a method of producing what is known as green hydrogen, or renewable hydrogen, as it can be produced using electricity from renewable sources.
The efficiency of the electrolysis process depends on the type of electrolyser used. Alkaline and PEM electrolysers currently have an efficiency of around 67% (50 kWh of electricity in, 33.3 kWh of hydrogen energy out), while Solid Oxide electrolysers offer 80% efficiency but require substantial external heat. The efficiency of the process is expected to improve, with Alkaline and PEM electrolysers projected to reach 75% efficiency within five years.
The round-trip efficiency, which includes the process of converting electricity to hydrogen, purifying and compressing it, and then converting the hydrogen back to electricity in a fuel cell, is approximately 35%. This means that there is a 35% increase in available energy when using hydrogen fuel cells, rather than a 65% loss as some may assume.
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Efficiency: A fuel cell's efficiency is, on average, about 55%
Hydrogen fuel cells are a clean and reliable energy source with an average efficiency of about 55%. This means that a fuel cell can convert approximately 55% of the chemical energy stored in hydrogen fuel into electricity.
Fuel cells have a higher efficiency than combustion engines, which must first convert the fuel's chemical energy into heat, then into mechanical work, and finally into electricity. Each additional step causes the overall efficiency to drop. In contrast, fuel cells directly convert chemical energy into electricity, skipping the intermediate steps that result in energy losses.
The efficiency of fuel cells varies depending on their type and operating temperature. Low-temperature fuel cells, such as proton-exchange membrane fuel cells (PEMFCs), have an energy efficiency of between 40% and 60%. High-temperature fuel cells, such as carbonate fuel cells, can reach efficiencies of more than 60% and outperform similar-sized conventional energy sources. Phosphoric acid fuel cells (PAFCs), which operate at temperatures of 150 to 200 °C, can achieve efficiencies of 40 to 50%. However, if the waste heat from these fuel cells is captured and used in cogeneration systems, their efficiency can increase to about 80%.
The round-trip efficiency of converting electricity into hydrogen through electrolysis, purifying and compressing it, and then converting the hydrogen back into electricity in a fuel cell, is approximately 35%.
The high efficiency of fuel cells results in lower fuel consumption and reduced operating costs. Less fuel consumption also leads to decreased carbon dioxide emissions if the fuel is non-renewable.
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Frequently asked questions
1 kg of hydrogen has an energy density of 120 megajoules per kilogram (MJ/kg) or 33.6 kilowatt-hours (kWh) of usable energy.
Hydrogen has an energy density almost three times that of diesel or gasoline. 1 kg of hydrogen is equivalent to 1 gallon of gasoline.
Approximately 48-50 kilowatt-hours (kWh) of electricity is required to produce 1 kg of hydrogen through electrolysis.
The efficiency of a hydrogen fuel cell is approximately 55%. The beginning-of-life (BOL) efficiency of a fuel cell is around 51%, while the end-of-life (EOL) efficiency is about 45%.
The cost of producing hydrogen is expected to decrease over time. Currently, green hydrogen costs around $1.50 per kilogram, and it may reach as low as $1.40 per kilogram in the coming decade.
