Hydrogen is often touted
as a “fuel of the future,” but a technical examination reveals that it
functions primarily as an energy carrier rather than a primary fuel. Recent
introduction of hydrogen-powered trains by the Indian Railways has brought the discussion on hydrogen
to public mind-space in India and must trigger a reasoned debate.
By definition, a fuel provides more energy than is required for its extraction or production. Examples include fossil fuels (coal, petroleum, natural gas) and nuclear fuels (enriched uranium or plutonium). Hydrogen, however, requires substantial energy input for production, storage, and distribution, making it analogous to a battery in its role as an energy storage medium, only less efficiently.
Thermodynamic Analysis
1. Electrolysis Efficiency:
State-of-the-art electrolysers operate at a maximum efficiency of approximately 65%, constrained by thermodynamic limits. For every unit of energy input, only 65% is converted into usable hydrogen energy. This process will not see dramatic improvements due to the inherent energy losses governed by the second law of thermodynamics.
2. Fuel Cell Efficiency:
Hydrogen is typically used in fuel cells to convert chemical energy back into electricity. The most advanced proton exchange membrane (PEM) fuel cells achieve an efficiency of around 65%, with a theoretical maximum close to 70%.
3. Roundtrip Efficiency:
Combining electrolysis
and fuel-cell efficiencies, the roundtrip efficiency of hydrogen energy systems
is further adversely affected by:
Additional energy losses
occur in hydrogen compression (to 800 bar), liquefaction (-253°C), and
transportation, which consume another 7–10% of the energy. This reduces the
effective efficiency to approximately 35%, or lower.
4. Comparison with Batteries:
In contrast, lithium-ion batteries have a charging efficiency of about 90% and a discharging efficiency of roughly the same. The practical roundtrip efficiency for batteries is 80+%.
Batteries thus offer more
than twice the efficiency of hydrogen systems for energy storage and retrieval.
Hydrogen in Internal Combustion Engines (ICEs)
When used in ICEs, hydrogen’s efficiency drops dramatically. ICEs have a peak thermodynamic efficiency of around 35%. Combining this with electrolysis efficiency of 65%, and after accounting for compression, storage, and transportation losses, the effective efficiency falls to a mere 16%. This makes hydrogen a poor choice for ICE applications.
Infrastructure Challenges
1. Storage and Transportation:
Hydrogen has a very low
volumetric energy density, requiring compression to 800 bar or liquefaction at
-253°C. Both processes are energy-intensive, with compression consuming 10–15%
of the energy content and liquefaction consuming up to 30%. Hydrogen is also
prone to leakage due to its small molecular size, which causes embrittlement in
storage and transport materials, a serious technical challenge.
2. Electrolyser and Fuel Cell Costs:
The capital costs of electrolyser systems and fuel cells remain high, with significant maintenance and replacement costs over time. Furthermore, large-scale hydrogen storage infrastructure (pipelines, cryogenic tanks) is underdeveloped, requiring significant investment.
3. Energy Source Dependency:
Hydrogen’s environmental benefits depend heavily on the energy source used for electrolysis.
• Green
Hydrogen:
Produced from renewable electricity, it is sustainable but expensive. Even
considering that renewal energy is available in plenty and in surplus amounts,
use of battery to store and deliver that energy beats the hydrogen cycle again.
• Grey/Blue
Hydrogen:
Derived from methane or coal, it undermines the environmental benefits due to
CO₂ emissions and methane leakage.
Potential Niche
Applications
While hydrogen struggles as a general-purpose energy carrier, it holds promise in specific high-value applications, such as:
1. Industrial Feedstock:
• Green
Steelmaking:
Hydrogen can replace coke as a reducing agent in iron ore processing. Since
hydrogen is consumed chemically, only the electrolysis efficiency (65–70%)
matters. Tata Steel and other major players are investing heavily in green
steel production. Besides, high pressure or cryogenic storage may be dispensed
with.
• Ammonia
Production:
Hydrogen is essential for synthesizing ammonia, a critical component of
fertilizers.
2. Hard-to-Decarbonize Sectors:
• Long-haul
aviation, where batteries are impractical due to weight constraints though
hydrogen tanks pose a challenge here too.
• Maritime
shipping, using hydrogen-derived fuels like ammonia or methanol.
• Seasonal
energy storage for grid balancing in regions with high renewable penetration.
Hydrogen vs. Batteries:
The Practical Reality
Hydrogen systems currently lag behind batteries in terms of efficiency, cost, and infrastructure readiness. Batteries dominate in applications where high roundtrip efficiency and scalability are crucial, such as electric vehicles and grid-scale energy storage.
The enthusiasm for hydrogen often appears to be driven by economic interests rather than scientific principles. Equipment manufacturers and infrastructure developers stand to benefit from hydrogen’s adoption, regardless of its inefficiency. This recalls the gold rush era, where the blacksmiths profited more than the miners themselves.
Policy Recommendations
Policymakers must approach hydrogen with a nuanced understanding:
- Prioritize hydrogen development for niche applications where it offers unique advantages (e.g., green steelmaking, aviation).
- Avoid over-subsidizing hydrogen for areas where batteries or other technologies are more efficient.
- Invest in renewable energy expansion to ensure hydrogen production (via electrolysis) is sustainable.
- Support research into reducing the costs of electrolysers, fuel cells, and hydrogen storage systems.
Conclusion
Hydrogen’s role in the energy transition should be realistic and targeted. While it has potential in industrial processes and hard-to-decarbonize sectors, its inefficiency and infrastructure challenges preclude it from becoming a universal energy solution. Discussions around hydrogen must be grounded in thermodynamic principles, economic feasibility, and practical considerations, rather than being swayed by hype or vested interests.
By focusing on where hydrogen truly adds value, we can avoid misallocating resources and accelerate the transition to a sustainable energy future. If the launch of hydrogen-trains by Indian Railways leads to intelligent and techno-commercial debate in the country, such a venture would have served a far bigger purpose than simply being a technology demonstrator or people-carrier.
