Below some concise exercices, for different sectors, designed to help students understand how hydrogen can be integrated into transport, industry, and energy storage. Each includes a practical scenario and guiding questions.
-----------------------------------------------------------------------------------------------------------
1) Transport: Hydrogen Fuel Cell Vehicles
Scenario:
A city plans to replace 100 diesel buses with hydrogen-powered buses using Hydrogen Fuel Cells.
Exercise: Each bus consumes 8 kg of hydrogen per day. Hydrogen has an energy content of ~33 kWh/kg.
Questions:
1. Calculate the total daily hydrogen demand for the fleet.
2. Estimate the total daily energy consumption (in kWh).
3. Compare this with diesel: if 1 diesel bus uses 40 liters/day (~10 kWh/liter), which system uses more energy?
4. Discuss two advantages and two challenges of switching to hydrogen in public transport.
Correction:
Step 1: Total hydrogen demand
Each bus uses 8 kg/day
Fleet = 100 buses
Total H₂=100×8=800 kg/day
Step 2: Total energy consumption
Hydrogen energy content = 33 kWh/kg
Energy=800×33=26,400 kWh/day
Step 3: Diesel comparison
Each diesel bus uses:
40 L/day × 10 kWh/L = 400 kWh/day
Fleet: 100×400=40,000 kWh/day
Step 4: Interpretation
Hydrogen fleet: 26,400 kWh/day
Diesel fleet: 40,000 kWh/day
--> Hydrogen appears to use less energy overall
BUT:
-Fuel cells are more efficient than combustion engines
-Diesel engines waste a lot of energy as heat
Step 5: Advantages vs challenges
Advantages:
-Zero tailpipe emissions (no CO₂, only water vapor)
-Higher efficiency than diesel engines
-Quiet operation and better air quality
Challenges:
- Hydrogen production is energy-intensive
- Lack of refueling infrastructure
- Storage and transport of hydrogen is complex
-----------------------------------------------------------------------------------------------------------
2) Industry: Green Steel Production
Scenario:
A steel plant wants to replace coal with hydrogen in the Direct Reduction of Iron process.
Exercise:
To produce 1 ton of steel, about 50 kg of hydrogen is required.
Questions:
-How much hydrogen is needed to produce 1 million tons of steel annually?
-If hydrogen is produced via Electrolysis requiring ~50 kWh/kg, estimate total electricity demand.
-Compare CO₂ emissions between coal-based and hydrogen-based production.
-Identify one economic and one technical barrier to adopting hydrogen in steelmaking.
Step 1: Hydrogen requirement
1 ton steel → 50 kg H₂
1 million tons → 1,000,000×50=50,000,000 kg H₂/year
--> 50 million kg (50,000 tons) of hydrogen per year
Step 2: Electricity demand for hydrogen
Electrolysis requires 50 kWh/kg
50,000,000×50=2,500,000,000 kWh --> 2.5 TWh/year
Step 3: CO₂ emissions comparison
Coal-based steel:
~1.8–2.0 tons CO₂ per ton steel
1,000,000×1.9≈1.9 million tons CO₂/year
Hydrogen-based steel:
Near 0 CO₂ (if hydrogen is green)
--> Emissions reduction ≈ ~1.9 million tons CO₂/year
Step 4: Interpretation
This is a massive decarbonization impact, but requires:
- Huge electricity supply (2.5 TWh = large power plant output)
- Renewable energy to truly be “green”
Step 5: Barriers
-Economic: Green hydrogen is still expensive compared to coal
-Technical: Scaling electrolyzers and hydrogen infrastructure; Retrofitting existing steel plants
-----------------------------------------------------------------------------------------------------------
3) Energy Storage: Power-to-Hydrogen-to-Power
Scenario:
A solar farm produces excess electricity that is stored as hydrogen and later converted back to electricity.
Exercise:
The system uses Power-to-Gas with:
-Electrolysis efficiency: 70%
-Fuel cell efficiency: 50%
Questions:
-If 1,000 kWh of solar electricity is used, how much energy is stored in hydrogen?
-How much electricity is recovered after conversion back?
-Calculate the round-trip efficiency.
-Discuss why hydrogen storage might still be useful despite efficiency losses.
Step 1: Energy stored as hydrogen
-Input electricity = 1,000 kWh
-Electrolysis efficiency = 70%
Stored energy=1000×0.7=700 kWh
Step 2: Energy recovered
Fuel cell efficiency = 50%
Recovered energy=700×0.5=350 kWh
Step 3: Round-trip efficiency
Efficiency = 35/1000 = 35%
Step 4: Interpretation
--> Only 35% of the original energy is recovered
--> 65% is lost in conversion steps
This is much lower than batteries (~80–90%)
Step 5: Why hydrogen storage still matters
Despite low efficiency, hydrogen is valuable because:
1. Long-term storage
-Batteries are better for hours/days
-Hydrogen works for weeks or seasons
2. Large-scale storage
Can store massive energy quantities (underground, tanks)
3. Grid balancing
Useful for intermittent renewables like solar and wind
4. Multi-sector use
Stored hydrogen can also be used in: Transport, Industry