- Classify energy sources as renewable or non-renewable and explain how each converts energy.
- Explain the production, storage and uses of green hydrogen and the colour classification of hydrogen.
- Describe carbon capture, utilisation and storage and nature-based carbon sinks.
- State Egypt’s national measures for mitigation and adaptation in energy, coasts and water.
🌳 Concept tree
Renewable Energy and the Hydrogen Economy
├── Mitigation and the energy transition
│ ├── Reduce demand → efficiency
│ ├── Change the supply → renewables and nuclear
│ └── Remove the emission → capture and sinks
├── Renewable sources│ ├── SolarPV (photovoltaic) and CSP (concentrated)
│ ├── Windkinetic energy of air → turbine → generator
│ ├── Hydropotential energy of water
│ ├── Geothermal, tidal, wave and biomass
│ └── Limits→intermittency, storage, grid and land use
├── Green hydrogen
| Comparison aspect | Main idea | Keywords |
|---|
| • | │ ├── Electrolysis of water with renewable electricity | Electrolysiswaterrenewableelectricity |
| │ ├── Colours | - grey (fossil
- no capture) · blue (fossil + CCUS) · green (renewable)
| greyfossilcaptureblue |
| │ ├── Storage | - compressed
- liquid (−253 °C)
- or as ammonia/methanol
| compressedliquidammoniamethanol |
| │ └── Uses | - industry
- heavy transport
- shipping
- seasonal storage
- export
| industryheavytransportshipping |
| • | - ├── Carbon capture
- utilisation and storage (CCUS)
| Carboncaptureutilisationstorage |
| ├── Nature-based solutions | - forests
- wetlands
- mangroves
- soils
| forestswetlandsmangrovessoils |
└── Egypt’s adaptation plan
- ├── Benngir solar park · New and Renewable Energy Authority
- ├── Hydrogen strategy and the Suez Canal economic zone
├── Delta shoreline protection and canal lining
└── Desalination and re-use of treated sewage
| Comparison aspect | Main idea | Example | Keywords |
|---|
| Renewable energy | - energy from sources that are naturally replenished on a human time scale — sun
- wind
- water
- heat of the Earth and living biomass
| — | sourcesnaturallyreplenishedhuman |
| Non-renewable energy | - fossil fuels (coal
- oil
- natural gas) and nuclear fuels
| | fossilfuelscoalnatural |
| Photovoltaic cell | a p–n junction semiconductor that converts light directly into electricity by the photoelectric effect | — | junctionsemiconductorconvertslight |
| Concentrated solar power (CSP) | mirrors focus sunlight on a fluid to make steam that drives a turbine | — | mirrorsfocussunlightfluid |
| Capacity factor | - the actual output of a plant divided by its output if it ran full power all year
- solar about 20–25%
- wind 30–40%
- thermal 80%+
| — | actualoutputplantdivided |
| Electrolysis | passing direct current through water (with an electrolyte) to decompose it: 2H₂O → 2H₂ + O₂ | — | passingdirectcurrentthrough |
| Fuel cell | an electrochemical device that combines hydrogen and oxygen to give electricity and water — the reverse of electrolysis | — | electrochemicaldevicecombineshydrogen |
| Energy density | - energy per unit mass
- hydrogen is the highest of all fuels (about 120 MJ/kg) but has the lowest per unit volume unless compressed or liquefied
| — | unitmasshydrogenhighest |
| CCUS | - carbon capture
- utilisation and storage — separating CO₂ from flue gas or air
- using it (fuels
- chemicals
- concrete) or injecting it into deep saline aquifers or depleted reservoirs
| — | carboncaptureutilisationstorage |
| Comparison aspect | Main idea | Keywords |
|---|
| Power of the wind | - P = ½ ρ A v3 — doubling the wind speed multiplies the power by eight
- which explains why wind farms are sited on coasts and ridges
| doublingspeedmultiplieseight |
| Hydropower | - P = ρ g Q h
- a flow of 10 m3/s falling 50 m gives about 4.9 MW
| flowfallinggives |
| Solar input | - about 1
- 361 W/m2 above the atmosphere and roughly 1
- 000 W/m2 at the ground on a clear day
- a 20% efficient panel of 1 m2 gives about 200 W
| aboveatmosphereroughlyground |
| Electrolysis energy | - thermodynamic minimum 39.4 kWh/kg H₂ (1.23 V)
- practically 48–55 kWh/kg at industrial cell voltages of 1.8–2.0 V
| thermodynamicminimumpracticallyindustrial |
| Efficiency chain | - renewable electricity → hydrogen (about 70–80%) → compression or liquefaction (loss up to 30% if liquid) → fuel cell (about 50–60%)
- direct electrification is therefore always more efficient when it is possible
| renewableelectricityhydrogencompression |
| Egypt’s potential | - 9–11 kWh/m2/day of global horizontal irradiation
- wind of 8–10 m/s along the Gulf of Suez
- and more than 1
- 000 km of coastline on two seas for ports and export
| globalhorizontalirradiationwind |
| Comparison aspect | Main idea | Keywords |
|---|
| Reduce demand | - insulation
- LED lighting
- efficient motors and appliances
- public transport
- and industry heat recovery — the cheapest “source” is the unit of energy not used
| insulationlightingefficientmotors |
| Change the supply | - replace coal and oil with solar
- wind
- hydro
- geothermal and
- where accepted
- nuclear
- retire the least efficient thermal units
- interconnect grids so that surplus renewable power is exported instead of curtailed
| replacecoalsolarwind |
| Remove what is left | - CCUS on cement and steel plants
- direct air capture
- and biological sinks (afforestation
- wetlands
- soil carbon)
| CCUScementsteelplants |
| Targets | - the Paris Agreement aims to keep the warming well below 2 °C and to pursue 1.5 °C
- which requires net-zero CO₂ emissions around 2050 and net-negative emissions afterwards
| ParisAgreementaimskeep |
| Energy justice | - developing countries ask for finance and technology transfer
- because their per-capita emissions are small — Egypt emits about 0.6 t CO₂ per person against more than 7 t in high-income countries
| developingcountriesfinancetechnology |
How it is made
- Renewable electricity drives an electrolyser that splits water: at the cathode 2H₂O + 2e− → H₂ + 2OH−, at the anode 4OH− → O₂ + 2H₂O + 4e− (alkaline cell). Types: alkaline (AEL), proton-exchange membrane (PEM), solid oxide (SOEC) at high temperature and higher efficiency.
- The only emission of using hydrogen is water; in a fuel cell the same chemistry runs backwards and produces electricity directly, without combustion and therefore without NOx from air nitrogen at flame temperature.
Colours of hydrogen — classified by source and impact
| Comparison aspect | Main idea | Keywords |
|---|
| Grey | - from natural gas by steam reforming (CH₄ + H₂O → CO + 3H₂)
- CO₂ released — about 9–10 kg CO₂ per kg H₂
| naturalsteamreformingreleased |
| Brown / black | - from coal or gasification
- the highest emissions
| coalgasificationhighestemissions |
| Blue | the same fossil route but with carbon capture and storage | samefossilroutecarbon |
| Green | electrolysis with renewable electricity — near-zero emissions | electrolysisrenewableelectricitynear |
| Turquoise / pink | - methane pyrolysis to solid carbon
- or electrolysis with nuclear power
| methanepyrolysissolidcarbon |
Storage, transport and uses
- Hydrogen is stored as a compressed gas at 350–700 bar, as a cryogenic liquid at −253 °C, or chemically bound as ammonia (NH₃) or liquid organic carriers, which are easier to ship.
- Hard-to-electrify sectors are its market steel (direct reduction of iron ore with hydrogen instead of coke), fertiliser (Haber–Bosch ammonia), refineries, shipping and aviation through synthetic e-fuels, long-haul road transport, and seasonal storage of surplus summer solar energy for winter.
- Egypt’s national hydrogen strategy positions the country as an exporter, with projects in the Suez Canal economic zone using the Benngir solar park and the wind farms of Gabal El-Zeit and Ras Ghareb.
Carbon capture, nature-based solutions and other sinks
Carbon capture, nature-based solutions and other sinks
| Comparison aspect | Main idea | Keywords |
|---|
| Post-combustion capture | - flue gas is bubbled through an amine solution that chemically binds CO₂
- the solvent is then regenerated by heating and the CO₂ is compressed
| fluebubbledthroughamine |
| Oxy-fuel combustion | - burning in pure oxygen gives a flue gas of almost only CO₂ and water
- easy to condense and capture
| burningpureoxygengives |
| Pre-combustion | the fuel is gasified first and the CO is shifted to CO₂ before combustion — used with IGCC plants and hydrogen production | fuelgasifiedfirstshifted |
| Direct air capture | - solid sorbents or alkaline solutions take CO₂ straight from ambient air
- expensive because the CO₂ is only about 0.04% of the air
| solidsorbentsalkalinesolutions |
| Mineralisation and utilisation | - CO₂ into carbonated aggregates
- urea
- methanol or plastics
- permanent storage in deep saline aquifers under an impermeable cap rock
- monitored for leakage
| carbonatedaggregatesureamethanol |
| Nature-based solutions | - mangroves
- seagrass and salt marshes store blue carbon in their waterlogged soils at rates far above terrestrial forest
- soils
- peatlands and forests are the other major sinks. Protecting what exists is cheaper than rebuilding it
| mangrovesseagrasssaltmarshes |
| Comparison aspect | Main idea | Keywords |
|---|
| Energy | - the strategy aims at about 42% renewable electricity by 2035
- the Benngir solar park is one of the largest in the world (over 1.6 GW)
- and the Gulf of Suez is among the best wind sites on Earth
| strategyaimsrenewableelectricity |
| Coastal protection | - sea walls
- breakwaters and nourishment of the Delta beaches
- because a rise of half a metre threatens the most fertile land and the freshwater aquifer by salt-water intrusion
| wallsbreakwatersnourishmentDelta |
| Water security | - lining of canals to stop seepage
- replacement of flood irrigation with drip and sprinkler systems
- re-use of treated agricultural drainage
- large desalination plants on both coasts
- and the New Delta project on treated water
| liningcanalsstopseepage |
| Agriculture | - early-maturing and salt- and heat-tolerant varieties
- changed sowing dates
- and water-efficient crop patterns
| earlymaturingsaltheat |
| Cities and people | upgrading informal areas, green roofs and urban forests, heat-warning systems, and the loss-and-damage fund agreed at COP27 in Sharm El-Sheikh. | upgradinginformalareasgreen |
| Transport | - the electric rail and monorail
- a national bus rapid transit network
- and the conversion of cars to run on natural gas and
- in the next step
- on hydrogen blends
| electricrailmonorailnational |
- A wind turbine has blades 40 m long and the wind speed is 10 m/s; ρ = 1.225 kg/m3. Estimate the power in the wind. — A = π(40)2 = 5,027 m2; P = ½(1.225)(5027)(103) ≈ 30.8 MW, and the Betz limit gives at most 59% = 18 MW.
- How much electricity does a 500 MW electrolyser consume in a day, and how much hydrogen does it make at 50 kWh/kg? — 500 × 24 = 12,000 MWh; 12,000,000/50 = 240 t of hydrogen.
- A household solar water heater of 2 m2 with 50% efficiency in 800 W/m2 insolation heats 150 L. Find the temperature rise in 5 h. — Energy = 2 × 800 × 0.5 × 5 × 3600 = 14.4 MJ; ΔT = 14.4×106/(150 × 4184) ≈ 23 °C.
- Compare the CO₂ of 1 kg of green hydrogen with 1 kg of grey hydrogen. — Green: about 0.5 kg CO₂ (only manufacturing and electricity losses) against 9–10 kg for grey, a reduction of roughly 95%.
- Why is hydrogen liquid at −253 °C and why is that a problem? — Its boiling point is 20 K because H₂ is a light non-polar molecule with only weak dispersion forces; cryogenic losses make transport expensive, which is why ammonia is preferred for shipping.
| Comparison aspect | Main idea | Keywords |
|---|
| Hydrogen is an energy carrier, not a source. | It must be made from something else — the exam expects exactly that wording | mustmadesomethingelse |
| Colour depends on the source of the energy, not on the molecule. | - H₂ from natural gas with capture is blue
- without capture it is grey
| naturalcapturebluewithout |
| Wind power varies with the cube of speed | not the square | square |
| A fuel cell is not a battery | it keeps producing as long as fuel is supplied and is not “recharged” | keepsproducinglongsupplied |
| Solar PV converts light, CSP converts heat | do not merge their mechanisms | mergemechanisms |
| Biomass is renewable but not automatically carbon-free | - burning it releases the carbon recently fixed
- so it is counted as near-neutral only when the feedstock is regrown
| burningreleasesrecentlyfixed |
| Green hydrogen costs fall with the price of electricity | so the answer about feasibility is always tied to cheap renewable power and capacity factor | answerfeasibilityalwaystied |
