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Making electricity: thermal, nuclear, hydro, wind and solar: Key terms, quiz and sources

Understanding Energy / Module 7: Making electricity: thermal, nuclear, hydro, wind and solar Wrap-up

Making electricity: thermal, nuclear, hydro, wind and solar: review

Key terms

Rankine cycle
The steam cycle of pumping, boiling, expanding through a turbine and condensing that underlies most thermal power plants.
Condenser
The heat exchanger that turns spent steam back into water, rejecting about half of a coal plant's fuel energy as low-temperature heat.
Supercritical steam
Steam above about 22 MPa, where water changes to vapour without boiling, allowing plant efficiencies of 42-47%.
Combined cycle (CCGT)
A plant in which a gas turbine's hot exhaust raises steam for a second turbine, reaching about 60% efficiency.
Cogeneration
Producing electricity and useful heat from the same fuel, also called combined heat and power, with total efficiency of 80-90%.
Dispatchable
Able to raise or lower output on command at any hour, as thermal, hydro and storage plants can.
Gas turbine
An engine that compresses air, burns fuel in it continuously and expands the hot gas through a turbine to make thrust or shaft power.
Compression ignition
The diesel principle of compressing air until it is hot enough to ignite injected fuel without a spark.
Fission
The splitting of a heavy nucleus such as uranium-235 by a neutron, releasing energy and more neutrons.
Enrichment
Raising the share of uranium-235 from the natural 0.7% to the 3-5% used in most reactors.
Fast breeder reactor
A reactor designed to create more fissile fuel than it consumes; promised for decades but never commercial.
Capacity factor
Actual annual output divided by the output if the plant ran at full power all year.
Head
The vertical height through which water falls in a hydro plant; power is proportional to head times flow.
Cube law
The rule that wind power rises with the cube of wind speed, so doubling speed gives eight times the power.
Betz limit
The theoretical maximum of about 59% of the wind's power that any turbine can capture.
Photovoltaic effect
The release of electrons by light in a semiconductor, producing direct current with no moving parts.
Levelised cost of electricity (LCOE)
A plant's lifetime costs divided by its lifetime output, in money per MWh.
Duck curve
The dip in net electricity demand at midday and steep rise at sunset on grids with much solar power.

Try it in the table

  • Open the 'Steam turbines and thermal power plants' tile and find its efficiency range. Compare it with 'Gas turbines and combined cycle' and work out how much less fuel a combined-cycle plant needs per kWh.
  • In the 'Nuclear fission reactors' tile, look at the fuel needed per year. Then open the 'Uranium' commodity tile and estimate how many tonnes of natural uranium a 1,000 MW reactor requires.
  • Compare 'Onshore wind' and 'Offshore wind': note the capacity factor and cost for each, and check whether the higher capacity factor offshore makes up for its higher cost.
  • Open 'Solar photovoltaics' and 'Solar heat collectors' side by side. Compare the share of sunlight each turns into useful energy and think about which suits an Indian hospital's hot-water needs.
  • In 'Hydropower dams', find the largest plants listed and their capacity. Then open 'Pumped hydro storage' and see how the same physics is used to store electricity.
  • Open 'Internal combustion engines and gensets' and look at the cost of genset electricity. Compare it with 'Lithium iron phosphate batteries' to see why rooftop solar plus batteries is replacing diesel backup.

Final quiz

Of 100 units of coal energy entering a subcritical power plant, roughly how many leave as electricity?

About 35-38 units become electricity. About 10 leave in the flue gas and about half at the condenser.

Why do nuclear plants need more cooling water per kWh than modern coal plants?

At about 33% efficiency, two thirds of a reactor's heat must be rejected, more than a 45% efficient coal plant rejects per kWh.

Which machine has the lowest mass per unit of power?

Large jet engines need under 0.1 g per watt, far less than any piston engine or steam plant.

One cubic metre of water per second falls 100 metres through a turbine. About how much power results?

Density times gravity times flow times height gives about 0.98 MW; a 90% efficient turbine delivers about 0.9 MW.

IRENA's global weighted-average LCOE for onshore wind commissioned in 2025 was about:

About USD 33 per MWh, the lowest of any technology. USD 78 is offshore wind and USD 115 is concentrated solar.

Which share of world electricity did renewables reach in 2025, according to Ember?

33.8%, slightly above coal at 33.0%. Wind and solar alone were about 17%.

A 1,000 MW reactor runs at a 90% capacity factor. How much solar capacity at a 20% capacity factor would produce the same annual energy?

1,000 x 0.9 / 0.2 = 4,500 MW. Capacity in megawatts says little without the capacity factor.

What is Smil's point when he says you need fossil fuels to get electricity from wind?

Coke for steel, kilns for cement and hydrocarbon resins for blades all depend on fossil energy, although a turbine repays its embodied energy quickly.
Next module: Power density: why land and space matter →

Sources for this module

  • Smil, Energy: A Beginner's Guide (2006) · via Smil Mastery Course, M7 'How thermal power plants work', 'Solar electricity'
  • Jaffe and Taylor, The Physics of Energy (2018) · via Smil Mastery Course, M7 'How thermal power plants work', 'Nuclear electricity: an unfulfilled promise'
  • Smil, Energy at the Crossroads: Global Perspectives and Uncertainties (2003) · via Smil Mastery Course, M7 'How thermal power plants work', 'Hydro and wind electricity'
  • Smil, Power Density: A Key to Understanding Energy Sources and Uses (2015) · via Smil Mastery Course, M7 'How thermal power plants work', 'Hydro and wind electricity', 'Solar electricity'
  • Smil, Two Prime Movers of Globalization: The History and Impact of Diesel Engines and Gas Turbines (2010) · via Smil Mastery Course, M7 'Gas turbines: power for flight and grids', 'Diesel engines: the movers of global trade'
  • Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020) · via Smil Mastery Course, M7 'Gas turbines: power for flight and grids', 'Nuclear electricity: an unfulfilled promise', 'Hydro and wind electricity', 'Solar electricity'
  • Smil, How the World Really Works: A Scientist's Guide to Our Past, Present and Future (2022) · via Smil Mastery Course, M7 'Diesel engines: the movers of global trade', 'Hydro and wind electricity', 'Grids, storage and the real cost of electricity'
  • Smil, Energy Myths and Realities: Bringing Science to the Energy Policy Debate (2010) · via Smil Mastery Course, M7 'Nuclear electricity: an unfulfilled promise'
  • Smil, Invention and Innovation: A Brief History of Hype and Failure (2023) · via Smil Mastery Course, M7 'Nuclear electricity: an unfulfilled promise'
  • Smil, Energy Transitions: History, Requirements, Prospects (2010; 2nd ed. 2017) · via Smil Mastery Course, M7 'Hydro and wind electricity'
  • Ember, Global Electricity Review 2026 (April 2026) · 2025 world shares and growth, India section: https://ember-energy.org/latest-insights/global-electricity-review-2026/2025-in-review/ and https://ember-energy.org/countries-and-regions/world/
  • IRENA, Renewable Power Generation Costs in 2025 (Abu Dhabi, July 2026) · LCOE by technology, installed costs, battery costs, regional values: https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2026/Jul/IRENA_TEC_RPGC_in_2025_2026.pdf (all LCOE values, India 35 and China 36 for PV, China 27 for onshore wind, battery USD 140/kWh, firm solar-plus-storage below USD 85/MWh, CCGT comparison and installed costs checked against the report's executive summary)
  • IEA, Electricity 2026: Analysis and Forecast to 2030 (Paris, February 2026) · demand growth, electricity share of final energy, coal share 2025 and 2030, India, nuclear record and China's share of nuclear growth: https://www.iea.org/reports/electricity-2026 (figures checked in the report's executive summary)
  • PIB, SHANTI Bill backgrounder (December 2025) · web
  • Department of Atomic Energy, PFBR first criticality (April 2026) · web
  • PIB, PM Surya Ghar: Muft Bijli Yojana factsheet (December 2024) · web
  • Deccan Herald (Bloomberg), India shrinks its gas fleet (May 2025) · web
  • CP24/AP, Finland grants licence for world's first nuclear waste repository (October 2026) · web
  • Ember, India country page (2026) · web