Hydrogen is a useful gas in the race against climate change. It is energy-dense and releases no greenhouse gases when used. It's a suitable fuel and feedstock for a range of energy applications that currently have no viable alternative to fossil fuels.
It is also a colourless gas... so how can it be ''blue''?
There is a veritable rainbow of hydrogen ''colours'' that have been appearing in public recently.
They have nothing to do with traits of the gas itself, but refer to how it is made.
Currently, hydrogen is made from high temperature processing of fossil fuels, mainly natural gas, but also coal and other heavy hydrocarbons.
Large volumes of hydrogen are made this way (~70 million tonnes in 2019), for making fertiliser, refining petrochemicals and other industrial applications.
In the process, a lot of carbon dioxide is released, accounting for about 2 per cent of global emissions.
In the colour scheme, black or brown hydrogen are made from coal, while grey hydrogen is made from natural gas.
At the other end of the scale, green hydrogen is made from electrolysis using renewable energy. No greenhouse gases are released during production.
Similarly, there is pink hydrogen, which is produced by electrolysis and powered by nuclear energy.
As with grey hydrogen, blue hydrogen is made from natural gas, but with carbon capture and storage (CCS).
Carbon capture is a suit of technologies that removes carbon dioxide from gas waste streams (think factory chimneys).
Once captured, the carbon dioxide can be compressed and pumped underground to be stored permanently in suitable geological rock formations.
The International Energy Agency has calculated that 52-89 per cent of the carbon dioxide emissions from the hydrogen production from gas can be avoided using CCS, depending on the technology used.
However, despite significant investment, the economics of CCS are challenging.
Our recent analysis compared green and blue hydrogen production and found that the total costs for CCS are often underestimated, making it likely that green hydrogen would become cheaper than blue hydrogen in the near future.
A more pressing problem is that methane is a far more potent greenhouse gas than carbon dioxide.
One kilogram of methane has the same warming potential as 86 kilograms of carbon dioxide over a 20-year period.
The IPCC estimates that 0.8 to 2.6 per cent of methane is lost due to leakage during natural gas extraction.
Recent studies measuring atmospheric methane show that the percentage can be much higher in some gas fields, especially those that use unconventional methods such as fracking.
Given that the use of unconventional methods is growing more common, fugitive emission rates will continue to grow.
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