Learn & Understand

The Lightest Fuel: The Promise and Problem of Hydrogen

Hydrogen is often hailed as a clean fuel of the future — burn it or run it through a fuel cell, and the only exhaust is water. But hydrogen is not an energy source so much as an energy carrier, and its wonderful cleanliness comes tangled with stubborn challenges of storage, production, and the very lightness that defines it.

A Carrier, Not a Source

Unlike coal or oil, hydrogen is not dug from the ground — it must be manufactured, which takes energy. It is therefore an energy carrier: a way to store and move energy produced elsewhere, much like a battery. This is crucial to understanding hydrogen. Its environmental value depends entirely on how the energy to make it was generated in the first place.

Green Versus Grey

How hydrogen is made determines whether it is clean. “Green” hydrogen, split from water using renewable electricity, is genuinely low-carbon. But most hydrogen today is “grey,” made from natural gas in a process that releases carbon dioxide — so the fuel is only as clean as its production. The dream of clean hydrogen hinges on producing it without emissions.

The Storage Headache

Hydrogen's greatest practical obstacle is its lightness. As the lightest element, it holds little energy per unit of volume, so storing a useful amount takes enormous compression or extreme cold. Fuel-cell vehicles pack hydrogen at very high pressure just to fit a practical range into a reasonable tank. Containing this slippery, diffuse gas is a persistent engineering challenge.

Measured by Mass

Because hydrogen is so light and voluminous, it is fueled and measured by mass — kilograms — rather than volume, which would be unwieldy. A fuel-cell car's efficiency is rated in distance per kilogram of hydrogen. Whether hydrogen becomes a pillar of clean energy depends on solving its production and storage puzzles, but its allure — a fuel whose exhaust is water — endures.

Estimating Hydrogen Use

To convert distance into hydrogen needed, use the Hydrogen Fuel Consumption Calculator. Compare with other alternative fuels via the Ethanol Fuel Consumption Calculator and the CNG Consumption Calculator.