# Using energy: food, materials, mobility and buildings: Key terms, quiz and sources Source page: https://www.materialinsights.org/learn/energy/using-energy/review/ [Understanding Energy](https://www.materialinsights.org/learn/energy/) / [Module 11: Using energy: food, materials, mobility and buildings](https://www.materialinsights.org/learn/energy/using-energy/) Wrap-up ## Using energy: food, materials, mobility and buildings: review ### Key terms **Primary energy** : Energy as taken from nature, such as coal, crude oil, gas, uranium, wind or sunlight, before any conversion. **Final energy** : Energy delivered to users, such as electricity, petrol or gas, after power plants and refineries have taken their losses. **Useful energy** : The heat, motion or light a user's machine actually delivers from final energy. **Non-energy use** : Fossil fuels used as raw materials, such as gas for ammonia or oil for plastics, rather than burned for energy. **Nitrogen fixation** : Turning inert air nitrogen (N2) into forms plants can use, such as ammonium or nitrate. **Haber-Bosch process** : The industrial synthesis of ammonia from nitrogen and hydrogen at high pressure and temperature over an iron catalyst. **Steam reforming** : Reacting methane with steam at high temperature to make hydrogen, releasing CO2. **Urea** : A solid nitrogen fertiliser, 46% nitrogen, made from ammonia and CO2. **Blast furnace** : A tall furnace where coke supplies heat and strips oxygen from iron ore to make molten iron. **Electric arc furnace** : A furnace that melts scrap steel or reduced iron using electric arcs, needing far less energy than the ore route. **Calcination** : Heating limestone to drive off CO2 and make lime, the chemical step that gives cement its process emissions. **Hall-Heroult process** : The electrolytic process that splits alumina into aluminium metal using large electric currents. **Weight-to-payload ratio** : The mass of a vehicle divided by the mass of what it carries; a simple measure of transport efficiency. **Energy density (gravimetric)** : Energy stored per kilogram of fuel or battery, such as about 43 MJ/kg for jet kerosene. **Tonne-kilometre** : One tonne of freight moved one kilometre; the standard unit for comparing freight energy use. **Coefficient of performance** : Units of heat moved by a heat pump or air conditioner per unit of electricity used. **Conversion chain** : A sequence of energy conversions whose overall efficiency is the product of each step's efficiency. ### Try it in the table - Open the Energy in farming tile and find how much of farming's energy is indirect, through fertiliser, rather than diesel on the farm. Then open the [Ammonia](https://www.materialinsights.org/chemicals/ammonia/) chemical tile and compare its energy per tonne with the 28 to 40 GJ range here. - In the Energy-intensive industry tile, look at the split between [steel](https://www.materialinsights.org/commodities/steel/), [cement](https://www.materialinsights.org/commodities/cement/), chemicals and [aluminium](https://www.materialinsights.org/commodities/aluminum/). Check which uses electricity and which still relies on coal or gas for high-temperature heat. - Compare the Combustion road vehicles and Electric and hybrid vehicles tiles. Look for the drivetrain efficiency figures and see whether they match the 20 to 30% and 80 to 90% used here. - Open the Aviation propulsion and Ship propulsion tiles and note which fuels they list as low-carbon options. Then check the [Ammonia](https://www.materialinsights.org/chemicals/ammonia/), [methanol](https://www.materialinsights.org/chemicals/methanol/) and e-fuels tile for their energy density per kilogram. - In the Heat pumps, air conditioning and refrigeration tile, find the typical coefficient of performance and compare it with an air conditioner's 3 to 5. Then look at the Energy in buildings tile for the share of building energy used for cooling. - Open the Lighting and displays tile and trace the coal-to-light chain using the efficiencies given there. How many times more light does an LED give than an incandescent bulb? ### Final quiz In the UN's world energy statistics for 2023, which sector used the most final energy? 'Other', dominated by homes and services, used about 139 EJ, against about 134 EJ for industry and 101 EJ for transport. Once feedstocks are added, industry becomes the largest at a little over two-fifths. Smil calls ammonia synthesis the most important invention of the twentieth century because: Without synthetic nitrogen, Smil estimates 40 to 50% of today's population could not be fed. The other options are side effects or are wrong. Roughly how much fossil energy goes into a one-kilogram sourdough loaf, from field to oven? Smil estimates at least 250 mL of diesel equivalent for growing, milling and baking a kilogram of bread. A litre is closer to seafood; ten litres to wild shrimp. Why does steelmaking from iron ore release CO2 even if the furnace heat could be supplied cleanly? In a blast furnace, carbon is the chemical reducing agent as well as the fuel. Replacing it requires another reductant, such as hydrogen in direct reduction. Recycled aluminium needs about what share of the energy of primary aluminium? Remelting scrap avoids the electrolysis that frees aluminium from oxygen, so it needs only about a twentieth of the energy. A lone 70 kg driver in an 1,800 kg SUV has a weight-to-payload ratio of about: 1,800 divided by 70 is about 26. A bicycle is about 0.1, which is Smil's point about how much of a car's energy moves the car rather than the person. Which statement about electric vehicles in 2025 matches the IEA's Global EV Outlook 2026? Over 20 million were sold, about one in four new cars, but fleets turn over slowly. China was near 55%, India about 4%, and electric trucks reached about 9% of truck sales. Why are heat pumps a natural fit for heating buildings? Rooms and hot water need heat below about 60 degrees. Burning fuel at over 1,000 degrees for that wastes its potential, while a heat pump moves heat that already exists. [Next module: Efficiency, waste heat and recovery →](https://www.materialinsights.org/learn/energy/efficiency-and-recovery/) ### Sources for this module - Smil, Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (2001) · via Smil Mastery Course, M10 'Nitrogen: the nutrient that limits harvests' and 'Haber and Bosch: the most important invention' - Smil, How the World Really Works (2022) · via Smil Mastery Course, M10 'Eating fossil fuels: energy in modern farming'; M11 'The material foundations of modern life', 'Plastics, aluminium, silicon and transition materials' - Smil, Making the Modern World (2014) / Materials and Dematerialization (2nd ed., 2023) · via Smil Mastery Course, M11 'The material foundations of modern life', 'Cement and concrete', 'Plastics, aluminium, silicon and transition materials' - Smil, Still the Iron Age: Iron and Steel in the Modern World (2016) · via Smil Mastery Course, M11 'Steel today: energy, stocks and the future' - Smil, Numbers Don't Lie (2020) · via Smil Mastery Course, M11 'Cement and concrete'; M14 'Moving people: cars, jets and flight safety' - Smil, Two Prime Movers of Globalization: The History and Impact of Diesel Engines and Gas Turbines (2010) · via Smil Mastery Course, M14 'Moving people: cars, jets and flight safety' - Smil, Energy: A Beginner's Guide (2006) · via Smil Mastery Course, M1 'Conservation and efficiency' - Smil, Energy Myths and Realities (2010) · via Smil Mastery Course, M9 'Energy myths and realities' - [United Nations Statistics Division, Energy Statistics Yearbook 2023, Table 3: Total final consumption and its components (2023 data)](https://unstats.un.org/unsd/energystats/pubs/yearbook/2023/t03.pdf (world 2023: total final consumption 418,723 PJ; industry 134,055; transport 100,542; other 139,235; non-energy use 44,891; international bunkers not included)) · web - Energy Institute, Statistical Review of World Energy 2025 (2024 data) [web ↗](https://www.energyinst.org/statistical-review) · web - [IEA, World Energy Outlook 2025, International Energy Agency, 2025](https://www.iea.org/reports/world-energy-outlook-2025 (electricity's share of final consumption and its rise)) · web - [IEA, Global EV Outlook 2026: Executive summary, International Energy Agency, 2026](https://www.iea.org/reports/global-ev-outlook-2026/executive-summary) · web - [IEA, Global EV Outlook 2026: Trends in electric cars, International Energy Agency, 2026](https://iea.org/reports/global-ev-outlook-2026/trends-in-electric-cars) · web - [IEA, Energy Efficiency 2025: Executive summary, International Energy Agency, 2025](https://www.iea.org/reports/energy-efficiency-2025/executive-summary) · web - [IEA, World Energy Outlook 2025, International Energy Agency, 2025, as reported by POWER magazine](https://www.powermag.com/the-age-of-electricity-and-5-other-forces-reshaping-the-global-energy-outlook/ (electricity 'roughly 20% of global final energy use')) · web - [IEA, Ammonia Technology Roadmap: Towards More Sustainable Nitrogen Fertiliser Production, International Energy Agency, 2021](https://www.fertilizer.org/wp-content/uploads/2023/03/2021_IEA_Ammonia-Technology-Roadmap.pdf (185 Mt in 2020; about 2% or 8.6 EJ of final energy; 28 GJ/t best gas, 36 GJ/t best coal, about 41 GJ/t world average; 1.8, 3.2 and 2.4 t CO2/t)) · web - [worldsteel, 'December 2025 crude steel production and 2025 global crude steel production totals', World Steel Association, 23 January 2026](https://worldsteel.org/media/press-releases/2026/december-2025-crude-steel-production-2025-global-crude-steel-production/ (1,849.4 Mt in 2025; 1,886.8 Mt in 2024)) · web - US Geological Survey, Mineral Commodity Summaries 2026: Cement [web ↗](https://pubs.usgs.gov/publication/mcs2026) · web - [Plastics Europe, Plastics: the Fast Facts 2025, as reported by Polimerica](https://polymeric.polimerica.it/articolo.asp?id=498 (world output up 4.1% in 2024; on the 413.8 Mt reported for 2023 this gives about 431 Mt, calculated)) · web - [International Aluminium Institute primary aluminium production statistics, as reported by Mysteel, January 2026](https://www.mysteel.net/news/5111608-iai-global-primary-aluminum-output-exceeds-73-million-t-in-2025 (over 73 Mt in 2025)) · web - [International Aluminium Institute, factsheet 'Aluminium recycling saves 95% of the energy needed for primary aluminium production', via Australian Aluminium Council, 2024](https://aluminium.org.au/news/iai-factsheet-claim-2-aluminium-recycling-saves-95-of-the-energy-needed-for-primary-aluminium-production/ (186 GJ/t primary, 8.3 GJ/t recycled, 2019 global data)) · web - [Global Efficiency Intelligence, 'Global cement industry's GHG emissions', 2021](https://www.globalefficiencyintel.com/new-blog/2021/global-cement-industry-ghg-emissions (calcination about 60% of cement CO2; cement about 7% of global CO2, 2019)) · web - [Krammer, P. et al., 'Energy intensity of freight transport modes', npj Sustainable Mobility and Transport (2025), Table 1](https://discovery.ucl.ac.uk/10206729/1/Krammer_et_al-2025-npj_Sustainable_Mobility_and_Transport.pdf (sample means: ocean vessels 0.136, railways 0.241, trucks 2.19, freighter aircraft 16.4 MJ per tonne-km)) · web ## Other sections - [Module overview](https://www.materialinsights.org/learn/energy/using-energy/index.md) - [Where final energy goes](https://www.materialinsights.org/learn/energy/using-energy/p1/index.md) - [Food: nitrogen, ammonia and fossil-fuelled farms](https://www.materialinsights.org/learn/energy/using-energy/p2/index.md) - [Materials: steel, cement, plastics and aluminium](https://www.materialinsights.org/learn/energy/using-energy/p3/index.md) - [Moving people and goods](https://www.materialinsights.org/learn/energy/using-energy/p4/index.md) - [Buildings and appliances](https://www.materialinsights.org/learn/energy/using-energy/p5/index.md)