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Using energy: food, materials, mobility and buildings: Key terms, quiz and sources

Understanding Energy / Module 11: Using energy: food, materials, mobility and buildings 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 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, cement, chemicals and aluminium. 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, 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 →

Sources for this module