Renewable Energy Sources, Green Hydrogen and Climate Adaptation

• Renewable energy: energy from sources that are naturally replenished on a human time scale — sun, wind, water, heat of the Earth and living biomass.
• Non-renewable energy: fossil fuels (coal, oil, natural gas) and nuclear fuels such as uranium, which are finite.
• Photovoltaic cell: a p–n junction semiconductor that converts light directly into electricity by the photoelectric effect.
• Concentrated solar power (CSP): mirrors focus sunlight on a fluid to make steam that drives a turbine.
• 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%+.
• Electrolysis: passing direct current through water (with an electrolyte) to decompose it: 2H₂O → 2H₂ + O₂.
• Fuel cell: an electrochemical device that combines hydrogen and oxygen to give electricity and water — the reverse of electrolysis.
• 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.
• 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.

• 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.
• Hydropower: P = ρ g Q h; a flow of 10 m³/s falling 50 m gives about 4.9 MW.
• 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.
• 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.
• 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.
• 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.

• 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.
• 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.
• Remove what is left: CCUS on cement and steel plants, direct air capture, and biological sinks (afforestation, wetlands, soil carbon).
• 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.
• 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.

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 NO_x from air nitrogen at flame temperature.

Colours of hydrogen — classified by source and impact

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.

• 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.
• Oxy-fuel combustion: burning in pure oxygen gives a flue gas of almost only CO₂ and water, easy to condense and capture.
• Pre-combustion: the fuel is gasified first and the CO is shifted to CO₂ before combustion — used with IGCC plants and hydrogen production.
• 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.
• 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.
• 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.

1. 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.
2. 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.
3. 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.
4. 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%.
5. 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.