# Energy, power and the units that measure them: Electricity and the nucleus Source page: https://www.materialinsights.org/learn/energy/energy-power-units/p5/ [Understanding Energy](https://www.materialinsights.org/learn/energy/) / [Module 1: Energy, power and the units that measure them](https://www.materialinsights.org/learn/energy/energy-power-units/) Part 5 of 5 ## Electricity and the nucleus Electricity is the most flexible form of energy, able to run a motor, a light, a computer or a furnace with little fuss. Nuclear energy is the most concentrated, packing millions of times more energy per kilogram than any chemical fuel. Both rest on a few physical principles, and those principles explain the shape of modern power systems. ### 5.1 Electricity is a carrier, and high voltage keeps losses down Electricity is a flow of electric charge, usually electrons moving through a metal wire. It is not a primary source of energy like coal or sunlight. It is a carrier, made from those sources and delivered to wherever it is needed, almost instantly and with few moving parts. Two quantities describe the flow. Voltage, measured in volts, is the push that drives charge. Current, measured in amperes, is the rate at which charge flows. Power is the product of the two: power = voltage x current. A 230 volt Indian socket supplying 10 amperes delivers 2,300 W. Wires resist the flow, and that resistance turns some electrical energy into heat. The loss grows with the square of the current. Double the current and the loss quadruples. This simple fact shapes every grid in the world. To send a large amount of power a long way, engineers raise the voltage so that the same power travels with a small current. India's main transmission lines run at 400,000 and 765,000 volts, and its long-distance direct current links at up to 800,000 volts. Raising voltage tenfold cuts the current tenfold and the resistive losses a hundredfold for the same wire. This is why electricity is generated at moderate voltage, stepped up for transmission, and stepped down in stages before reaching homes. Even so, losses are real. Well-run grids lose about 5 to 8% of electricity in transmission and distribution. Indian distribution companies have lost far more: the Ministry of Power puts their aggregate technical and commercial (AT&C) losses at about 22.6% in 2013-14 and about 15% in 2024-25. A large share of that is commercial loss, meaning theft, unbilled supply and unpaid bills, rather than physics. Electricity's flexibility is its great virtue. It can be turned into motion at over 90% efficiency, into light, into heat at nearly 100%, and it powers every digital device. That is why the share of energy reaching users as electricity keeps rising. Worked example #### Why the lines hum at 765 kV Suppose a line must carry 1,000 MW. On a three-phase line at 765 kV the current in each conductor is about 750 amperes (calculated as power divided by 1.73 times the voltage). At 76.5 kV it would be about 7,500 amperes, and the resistive losses in the same conductor would be a hundred times larger. To keep losses tolerable at the lower voltage you would need conductors many times thicker, with far heavier towers. High voltage is the cheapest way to move bulk power, which is why it pays to build tall towers, large insulators and wide corridors. - Smil, Energy: A Beginner's Guide (2006) · via Smil Mastery Course, M1 'Electricity and the nucleus' - Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020) · via Smil Mastery Course, M1 'Electricity and the nucleus' - Outlook Business (PTI), 'Discoms post Rs 2,701 cr profit in FY25 after years of losses', citing Ministry of Power, January 2026 · AT&C losses 22.62% in FY 2013-14 and 15.04% in FY 2024-25. https://www.outlookbusiness.com/corporate/discoms-post-2701-cr-profit-in-fy25-after-years-of-losses - GE Vernova, 'Champa 800 kV HVDC: delivering efficient energy highways in India' (case study) · Champa-Kurukshetra +/-800 kV, 3,000 MW, 1,365 km; India's 765 kV substations. https://www.gevernova.com/electrification/sites/default/files/case_studies_pdfs/case-study-champa-800-kv-hvdc-delivering-efficient-energy-highways-in-india.pdf ### 5.2 Induction, transformers and alternating current built the grid Nearly all the world's electricity comes from one discovery. In 1831 Michael Faraday showed that moving a conductor through a magnetic field induces a current in it. Spin a coil of wire inside a magnetic field, or spin a magnet inside a coil, and you have a generator. Coal, gas, nuclear, hydro and wind plants differ only in what turns the shaft. Solar photovoltaics are the main exception, turning light directly into current without moving parts. Run induction backwards and you get a motor: feed current into a coil in a magnetic field and it turns. Motors are the great consumers of electricity. Smil points out that electric motors, from tiny phone vibrators to factory compressors and locomotive drives, use roughly half of all the electricity produced in the world. Pumps, fans and compressors are among the largest users in Indian industry and agriculture alike. The transformer is the third pillar. It is a pair of coils wound on an iron core, with no moving parts, that steps voltage up or down with efficiencies above 99% in large units. Smil calls transformers unsung, silent devices without which large grids could not exist. Transformers only work with alternating current, which reverses direction many times a second, 50 times in India and Europe and 60 times in the US. That is why alternating current beat Thomas Edison's direct current in the 1890s: AC voltage could be changed cheaply, so power could be sent far at high voltage and used safely at low voltage. Direct current has returned for very long and undersea links, because modern power electronics can now convert it efficiently and DC lines lose less over great distances. Process flowchart From coal to light in an Indian home Inputs **Thermal coal**1 kg at about 15 MJ (Indian grade) Process steps 1 **Boiler and steam turbine** chemical energy → steam → rotation, about 34-38% efficient 2 **Generator** rotation → electricity by induction, about 98% 3 **Transformers, lines and distribution** about 85-92% of electricity reaches the meter 4 **LED lamp** electricity → visible light, roughly 30-40% Outputs **Visible light**about 1.3-2 MJ (calculated) **Heat at the plant, lines and lamp**about 13 MJ With an old incandescent bulb (about 2-5% to light) the same kilogram of coal would yield only about 0.1-0.25 MJ of light. Source: Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020), via Smil Mastery Course, M1 'Electricity and the nucleus' In the data #### Smil's 1867 to 1914 Smil argues that the decades between 1867 and 1914 created the technical basis of the twentieth century, and electricity is the clearest example. Within about thirty years came practical dynamos, incandescent lamps, central power stations, steam turbines, transformers, AC motors and long-distance transmission. Most of the components of a modern grid would be recognisable to an engineer of 1910. What has changed is scale, materials and control, not the basic principles. - Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020) · via Smil Mastery Course, M1 'Electricity and the nucleus' - Smil, Creating the Twentieth Century: Technical Innovations of 1867-1914 and Their Lasting Impact (2005) · via Smil Mastery Course, M1 'Electricity and the nucleus' ### 5.3 Nuclear energy is a million times more concentrated than chemical fuel Chemical reactions rearrange the outer electrons of atoms. Nuclear reactions rearrange the protons and neutrons in their cores, which are bound together far more tightly. The energy involved is roughly a million times larger per reaction, and that ratio is the whole story of nuclear power's concentration. Fission splits heavy nuclei such as uranium-235 or plutonium-239. When a neutron strikes a uranium-235 nucleus, it splits into two lighter fragments, releases a large burst of energy and frees two or three more neutrons, which can split further nuclei. A reactor controls this chain reaction so that, on average, exactly one neutron from each split causes another. Fissioning one kilogram of uranium-235 completely releases about 80 TJ, roughly what burning 3,000 tonnes of good coal provides. Reactors use fuel enriched to only 3 to 5% uranium-235 and burn only part of it, but a kilogram of natural uranium used once through a typical reactor still yields something like 15,000 to 20,000 times more heat than a kilogram of coal (calculated). The energy comes from mass. The fission fragments weigh very slightly less than the original nucleus and neutron, and the missing mass appears as energy according to Einstein's E = mc2. Because c, the speed of light, is so large, a tiny mass yields a vast energy: converting one gram of mass entirely into energy would release 9 x 10^13 J, about the energy in 2,100 tonnes of crude oil. Fusion joins light nuclei, such as the hydrogen isotopes deuterium and tritium, into helium. It powers the Sun and releases even more energy per kilogram than fission, but it needs temperatures of over 100 million degrees to start on Earth. Smil counts controlled fusion for electricity among the inventions we keep waiting for: decades of steady scientific progress, but still no plant selling power to a grid. Value chain Where nuclear energy comes from - **Nuclear binding energy** about a million times larger per reaction than chemical bond energy - **Fission: split heavy nuclei** - **Uranium-235** about 0.7% of natural uranium; enriched to 3-5% for most reactors - **Plutonium-239** bred from uranium-238 inside reactors - **Uranium-233 from thorium** the basis of India's long-term three-stage programme - **Fusion: join light nuclei** - **Deuterium + tritium** easiest fusion reaction; tritium bred from lithium - **In the Sun: hydrogen → helium** the original source of sunlight, wind and fossil fuels Source: Smil, Energy: A Beginner's Guide (2006), via Smil Mastery Course, M1 'Electricity and the nucleus' Case #### Fuel for a year A 1 GW coal plant running at 80% capacity factor and 37% efficiency burns roughly 3 million tonnes of good bituminous coal a year, or closer to 4.5 million tonnes of Indian grade coal, which means several long coal trains every day. A 1 GW pressurised water reactor at a 90% capacity factor uses about 20 to 25 tonnes of enriched uranium fuel a year, which fits in a few trucks. The tiny fuel mass is why nuclear fuel costs are a small part of nuclear electricity's price, and why most of the cost and controversy lies in building the plant and managing spent fuel. - Smil, Energy: A Beginner's Guide (2006) · via Smil Mastery Course, M1 'Electricity and the nucleus' - Smil, Numbers Don't Lie: 71 Stories to Help Us Understand the Modern World (2020) · via Smil Mastery Course, M1 'Electricity and the nucleus' ### See it in the table [H₂O Water](https://www.materialinsights.org/commodities/water/)[Oil Crude oil](https://www.materialinsights.org/energy/crude_oil/)[U Uranium](https://www.materialinsights.org/energy/uranium/)[He Helium](https://www.materialinsights.org/commodities/helium/)[H2 Hydrogen](https://www.materialinsights.org/chemicals/hydrogen/)[PV Solar photovoltaics](https://www.materialinsights.org/energy/e_pv/) ### Check your understanding If a line's voltage is doubled while carrying the same power, what happens to its resistive losses? Doubling voltage halves the current. Losses scale with the square of the current, so they fall to one quarter. Why did alternating current win over direct current for early grids? Transformers let AC be sent at high voltage and used at low voltage. DC returned later for long links once power electronics matured. Why is nuclear fuel so much more concentrated than coal? Fission rearranges protons and neutrons in the nucleus, which are bound about a million times more tightly than the electrons involved in combustion. [← Part 4: Energy in matter: fuels and energy density](https://www.materialinsights.org/learn/energy/energy-power-units/p4/)[Mark read · Wrap-up →](https://www.materialinsights.org/learn/energy/energy-power-units/review/) ## Other sections - [Module overview](https://www.materialinsights.org/learn/energy/energy-power-units/index.md) - [What energy is](https://www.materialinsights.org/learn/energy/energy-power-units/p1/index.md) - [Units and orders of magnitude](https://www.materialinsights.org/learn/energy/energy-power-units/p2/index.md) - [Energy versus power](https://www.materialinsights.org/learn/energy/energy-power-units/p3/index.md) - [Energy in matter: fuels and energy density](https://www.materialinsights.org/learn/energy/energy-power-units/p4/index.md) - [Key terms, quiz and sources](https://www.materialinsights.org/learn/energy/energy-power-units/review/index.md)