Introduction: The Energy Balance
When we talk about producing green hydrogen, the conversation eventually turns to a single critical question: How much energy do we lose along the way? No machine is perfectly efficient, and electrolyzers are no exception.
The “efficiency” of an electrolyzer refers to the ratio between the energy content of the hydrogen produced and the electrical energy consumed to produce it. In the world of green hydrogen, efficiency isn’t just a technical metric—it is the primary driver of production costs.
1. The Efficiency Benchmark: What Is “State-of-the-Art”?
Current commercial electrolyzers generally operate with an electrical efficiency between 55% and 80%. This means that for every 100 units of electricity you put into the machine, you get 55 to 80 units of energy out in the form of hydrogen gas.
| Technology | Typical Efficiency Range | Maturity |
| Alkaline (ALK) | 60% – 70% | Commercial Standard |
| PEM | 55% – 75% | Commercial/Rapid Growth |
| Solid Oxide (SOEC) | 80% – 90%+ | Early Stage/Pilot |
Standard Energy Consumption: On average, it takes approximately 50–55 kWh of electricity to produce 1 kilogram of hydrogen. Since 1 kg of hydrogen contains about 39.4 kWh of energy (based on its Higher Heating Value), this translates to an efficiency of roughly 71–79%.
2. Where Does the Energy Go? (The Losses)
If an electrolyzer is 70% efficient, where is the other 30%? Most of the “lost” energy is converted into heat. This happens due to several factors:
Electrical Resistance: Known as Ohmic losses, energy is lost as heat as electricity moves through the cell’s components.
Bubble Formation: Gas bubbles on the electrodes block the active area, causing “bubble overpotential” and reducing efficiency.
Activation Losses: The extra energy required to actually trigger the chemical reaction at the electrode surfaces.
3. The SOEC “Heat Hack”
The most efficient technology today is the Solid Oxide Electrolyzer (SOEC), which can reach efficiencies of 90% or higher.
How? Unlike ALK or PEM systems that run at low temperatures, SOEC runs at extremely high temperatures (up to 800°C–1,000°C). Because it uses heat as part of its energy input, it requires significantly less electricity to split the water molecules.
4. Why Efficiency Isn’t the Only Metric
While higher efficiency is always better, it isn’t the only factor in the Levelized Cost of Hydrogen (LCoH).
Capital Cost (CAPEX): High-efficiency systems like SOEC are currently much more expensive to build than standard Alkaline systems.
Operating Hours: If a plant only runs during peak renewable generation, a cheaper, slightly less efficient machine might be more profitable than an expensive, highly efficient one.
Conclusion
Improving efficiency is a primary focus for reaching global climate goals. Every percentage point gained reduces the amount of wind and solar power needed, making the green hydrogen economy more affordable.
Next Up: We’ve mentioned them briefly, but what makes them tick? In Article 6, we take a deep dive into the machines themselves: What are the types of electrolyzers used in hydrogen production?
