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Moving energy: wires, pipes and ships: Key terms, quiz and sources

Understanding Energy / Module 9: Moving energy: wires, pipes and ships Wrap-up

Moving energy: wires, pipes and ships: review

Key terms

Resistive (I^2R) loss
Energy turned into heat in a conductor, equal to the current squared times the resistance.
Transformer
A device with two coils on an iron core that raises or lowers the voltage of alternating current.
Alternating current (AC)
Current that reverses direction many times a second, 50 in India and Europe and 60 in North America.
High-voltage direct current (HVDC)
Bulk transmission using direct current, with converter stations at each end.
Converter station
The plant at each end of an HVDC link that changes AC to DC or back, losing about 0.7 to 1% of the power.
Reactive power
Energy that sloshes back and forth in AC lines each cycle, doing no useful work but taking up capacity.
Grid frequency
The rate at which AC alternates; it falls when demand exceeds supply and rises when supply exceeds demand.
Inertia
Energy stored in the spinning mass of generators, which slows frequency changes for a few seconds.
AT&C losses
India's measure of aggregate technical and commercial losses: energy lost to physics, theft, metering and unpaid bills.
Mini-grid
A small local network with its own generation, often solar and batteries, serving a village or site.
Line pack
Gas held in a pipeline under pressure, drawn down and refilled daily as short-term storage.
Compressor station
A plant along a gas pipeline that restores the pressure lost to friction, usually burning some of the gas.
Liquefied natural gas (LNG)
Natural gas cooled to about minus 162 C so that it shrinks about 600 times for shipping.
Boil-off
LNG or liquid hydrogen that evaporates as heat leaks into the tanks during storage and shipping.
Very large crude carrier (VLCC)
A tanker of about 300,000 tonnes carrying roughly 2 million barrels of crude.
Hydrogen carrier
A substance such as ammonia, methanol or an organic liquid that holds hydrogen in a denser, easier-to-ship form.
District heating network
Insulated pipes carrying hot water or steam from central plants to many buildings.
Chokepoint
A narrow strait, canal or single pipeline through which a large share of energy trade must pass.
Utilisation
The share of its capacity that a line, pipe or ship actually uses over a year, which sets its cost per unit moved.

Try it in the table

  • Open the "AC transmission" tile and compare the losses quoted for 765 kV and 345 kV lines carrying the same 5,000 MW. Does the ratio fit what the I^2R rule predicts?
  • In "HVDC links", find the converter losses per station and the line losses per 1,000 km. Work out the distance at which the line losses equal the losses in the two converters.
  • Open "Distribution grids, mini-grids and interconnectors" and compare India's AT&C losses with US network losses. How much of the gap is theft and billing rather than physics?
  • In the "LNG chain" tile, add up liquefaction, boil-off and regasification. Then open "Gas pipelines and city gas" and find how far a pipeline could carry gas before its compressors burned the same share.
  • Open "Tankers, barges and fuel trucks" and "Oil and product pipelines" and note how freight and bypass flows changed in 2026. Then check the "Crude oil" commodity tile for that year's price peak.
  • In "Hydrogen and hydrogen carriers", compare the energy cost of liquefaction with the ammonia route, then open the "Ammonia" chemical tile to see where ammonia is already made and used.

Final quiz

A utility raises transmission voltage from 220 kV to 440 kV while carrying the same power on the same conductors. Resistive losses fall to roughly what share of their former level?

Current halves when voltage doubles, and loss goes with the square of current, so it falls to a quarter.

Which of these is NOT an advantage of HVDC over AC?

HVDC needs converters at both ends; they are its main cost and source of fixed losses.

What is grid inertia?

Rotating masses release or absorb energy as frequency moves, buying a few seconds for controls to act.

Roughly what share of electricity is lost in US transmission and distribution?

The EIA puts it at about 5% on average for 2018 to 2022, most of it at lower voltages.

Why is moving gas as LNG more expensive in energy terms than moving it a similar distance by pipeline over land?

Liquefaction consumes roughly 9 to 15% of the energy, whereas compressors burn about 2 to 3% per 1,000 km.

About what share of world oil supply moved by sea in the first half of 2025?

Seaborne trade was about 80 million barrels a day, roughly 76% of supply.

Why were many large coal power stations built at the mine mouth?

Coal is a low-value bulk fuel; moving the electricity instead of the coal can avoid heavy rail costs.

World LNG regasification capacity is about 1,100 million tonnes a year against trade of 437 million tonnes. What does the gap mainly reflect?

Spare terminals let buyers switch suppliers quickly when a source is cut, as in 2022 and 2026.
Next module: Storing energy: from fuel stocks to batteries →

Sources for this module