Power Plants — Types, How They Work, Global Capacity & Emissions

Coal Power Plants

A coal-fired power plant burns pulverised coal in a boiler to produce steam at high pressure and temperature, which drives a steam turbine connected to an electrical generator. The Rankine cycle describes the thermodynamic process.

Evolution of coal plant technology:

• Subcritical (pre-1990s dominant): steam below 221 bar / 374°C critical point; efficiency 33–37%; most old plants worldwide
• Supercritical (1990s+): steam above critical point, 540°C; efficiency 38–42%; most new coal plants built in 2000s
• Ultra-supercritical (USC) (2010s+): 600°C / 250+ bar; efficiency 43–47%; China leads with >100 USC units operating
• Advanced USC (A-USC) (emerging): 700°C+ using nickel superalloys; target efficiency >50%; still developmental
• Integrated Gasification Combined Cycle (IGCC): coal gasified to syngas, then burned in gas turbine; cleaner but expensive; limited commercial deployment

Emissions control systems on modern coal plants include selective catalytic reduction (SCR) for NOₓ, flue gas desulfurisation (FGD/"wet scrubbers") for SO₂, electrostatic precipitators (ESP) or fabric filters for particulate matter, and mercury control systems. These add 10–20% to capital cost but are mandatory in EU, US, and increasingly China.

Natural Gas Power Plants

Natural gas power is now the most widely used thermal generation technology in the US and many OECD countries due to lower emissions than coal, fast ramp rates, and the shale gas revolution's impact on gas prices.

Gas turbine (OCGT — Open Cycle Gas Turbine):

• Compressed air + gas combustion drives turbine (similar to aircraft jet engine)
• Start time: 5–10 minutes; ideal for peaking
• Efficiency: 33–42%
• Exhaust gas exits at ~600°C — most heat wasted in OCGT

Combined Cycle Gas Turbine (CCGT):

• Gas turbine exhaust heat generates steam for a second steam turbine
• Two turbines on the same shaft or separate generators
• Efficiency: 55–63% (highest of any commercial thermal plant)
• Start time: 30–60 minutes cold; 10–20 min warm
• Best for mid-merit and baseload operation; too slow for pure peaking

How Nuclear Power Plants Work

Nuclear power plants generate heat through nuclear fission — the splitting of heavy atomic nuclei (typically uranium-235 or plutonium-239) when struck by neutrons. Each fission event releases ~200 million electron-volts of energy, and in a chain reaction, released neutrons trigger further fissions. The heat produced is used — like any thermal plant — to make steam and drive a turbine.

Key components of a typical PWR (Pressurised Water Reactor):

• Fuel assemblies — uranium dioxide (UO₂) pellets stacked in zircaloy-clad rods; bundles form the reactor core
• Control rods — neutron-absorbing materials (boron, hafnium) that can be inserted to slow or stop the chain reaction
• Primary coolant loop — pressurised water (155 bar) circulates through the core, heated to ~325°C without boiling
• Steam generator — primary loop heats secondary loop water to steam; the two loops never mix (limits radioactive contamination)
• Containment structure — reinforced concrete dome enclosing reactor; designed to contain a loss-of-coolant accident
• Cooling towers — reject waste heat to atmosphere; the iconic large hyperbolic concrete structures are the condenser cooling system, not radioactive

Reactor Types Worldwide

Hydroelectric Power

Hydroelectricity converts the potential energy of water at height into kinetic energy via penstock (pressure pipe), then into rotational energy via a turbine, and finally into electricity via generator. It is the world's largest renewable source and the most flexible: output can be increased or decreased in seconds by opening or closing water flow.

Three main turbine types:

• Pelton turbine — high head (100–1,800 m), low flow; water jets hit spoon-shaped buckets on a wheel; used in mountain regions
• Francis turbine — medium head (10–600 m), medium flow; most common worldwide; used in Three Gorges Dam
• Kaplan turbine — low head (2–40 m), very high flow; adjustable-pitch propeller blades; used in run-of-river and tidal plants

Pumped storage hydro (PSH) is currently the world's dominant form of grid energy storage (~170 GW globally): use cheap overnight power to pump water uphill; release water during peak demand to generate power. Round-trip efficiency 75–82%.

Wind Power — Onshore & Offshore

Wind turbines convert kinetic energy of moving air to rotational energy. Modern utility-scale turbines use three-bladed horizontal-axis designs (HAWT) with variable-pitch blades and variable-speed generators optimised across a wide range of wind speeds.

Key turbine parameters:

Solar PV — Utility Scale

Photovoltaic cells generate electricity when photons from sunlight knock electrons into a higher energy state in a semiconductor (typically silicon). No moving parts; no combustion; no water consumption (unlike all thermal plants).

Cell technology evolution:

• Monocrystalline silicon (mono-Si): 22–24% efficiency; highest performing; dominant in utility-scale
• Polycrystalline silicon (poly-Si): 16–18%; cheaper; declining market share vs. mono
• PERC (Passivated Emitter and Rear Cell): improved mono-Si; industry standard as of 2020s; 22–24%
• TOPCon (Tunnel Oxide Passivated Contact): next-gen; 24–26%; rapidly gaining market share 2023+
• HJT (Heterojunction): 24–26%; low temperature coefficient; works better in heat
• Perovskite (emerging): tandem cells achieving 33%+ in lab; durability at scale still being solved; commercial deployment ~2026–2030

Utility-scale solar (10 MW–5 GW+) uses fixed-tilt or single-axis tracking panels, central or string inverters, and grid-scale transformers. Bifacial panels absorb reflected ground irradiance on the rear surface, adding 5–15% yield.

Geothermal Power

Geothermal plants tap the Earth's internal heat — from radioactive decay in the mantle and residual formation heat. They require high-temperature geothermal resources, found primarily along tectonic plate boundaries and volcanic regions.

Three main technology types:

• Dry steam (oldest; The Geysers, CA): steam directly from reservoir drives turbine
• Flash steam (most common): high-pressure hot water "flashes" to steam when pressure drops in separator
• Binary cycle: moderate-temperature water heats a low-boiling-point working fluid (isobutane, isopentane) in a heat exchanger; fluid vaporises and drives turbine; zero water emissions; can use 80–150°C resources

Enhanced Geothermal Systems (EGS) — the next frontier: drill into hot dry rock anywhere on Earth, inject water, fracture rock, extract steam. If EGS scales, geothermal could become available globally rather than only at volcanic hotspots. Fervo Energy (Utah) and Project InnerSpace are leading commercial EGS development.

Technology Comparison Matrix

CO₂ Emissions Intensity by Source

Global Electricity Capacity Additions by Source (GW/year)

Coal Power — The Slow Phase-Out

Coal remains the single largest source of electricity globally despite being the most carbon-intensive option. The global coal fleet situation as of 2025:

• US: From ~50% of generation in 2005 to ~16% in 2024; 120+ GW retired since 2010; remaining plants largely 30–50 years old
• EU: Germany closed last coal plant by 2038 target; UK ended coal generation in 2024; Poland still ~70% coal-dependent
• China: Operates ~1,100 GW of coal capacity — more than the rest of the world combined — and approved new plants in 2022–2023 after power shortages; also the world's largest builder of new renewables
• India: ~200 GW of coal; still growing; coal needed for development, but solar capacity additions now exceed coal additions annually
• Just Transition: GFANZ and MDB financing packages ($8.5B Just Energy Transition Partnerships for South Africa, Indonesia, Vietnam, etc.) aim to accelerate coal retirement in developing countries