What is hydrogen and how green is it?

African business and political leaders are betting big on hydrogen to fuel the continent's "green industrial revolution," as Namibia holds a major summit hyping the gas that many believe will play a key role in shifting away from polluting fossil fuels.

The three-day summit in Windhoek will bring together investors and project developers from across Africa and the world, all attempting to boost investment in the gas. Europe, in particular, is eyeing up the continent's production potential.

But how does hydrogen really stack up as a climate solution?

What is hydrogen?

Hydrogen, the universe's most abundant element, is a colorless, odorless and nontoxic gas. It's light, flammable and has a high energy density — but it's also highly explosive. So much so that the name Hindenburg — referencing the hydrogen-filled airship — became synonymous with disaster after the 1937 accident.

Despite the notoriety, hydrogen has been used for decades in the petrochemical industry. It's used to refine oil, produce ammonia for fertilizers, to make plastics and steel and generate methanol.

Hydrogen is a potent carrier of energy. One kilogram (about 2.2 pounds) of hydrogen has 2.4 times more usable energy than the same amount of natural gas, nearly three times more than a kilo of gasoline and roughly four times more than a kilo of coal.

Is hydrogen a clean energy?

By itself — used in a fuel cell to generate electricity for some cars, for example — hydrogen doesn't produce any direct greenhouse gas emissions. It only creates water, electricity and heat.

But hydrogen isn't as easy to source as fossil fuels, which can just be dug up and burned directly. In nature, hydrogen is most commonly found in water. It's the H in H2O. But isolating and storing the gas requires time and energy.

There are many ways to separate hydrogen from water. But today, more often than not, these processes are polluting. Hydrogen production contributes around 2.2% of global greenhouse gas emissions, even if the hydrogen fuel at the end burns clean.

Gray, blue green, pink — how is hydrogen produced?

Hydrogen may be a colorless gas, but the industry has come up with a veritable rainbow of colors to describe the different production methods.

Today, most of what we produce is known as gray hydrogen. It uses a process called "steam reforming" which is powered by natural gas or methane. Every ton of gray hydrogen produced releases about 10 tons of CO2 emissions into the atmosphere.

Black and brown hydrogen is even more detrimental. It's made by transforming black or brown coal into gas at high temperatures and separating out the hydrogen. It pollutes the atmosphere with both planet-heating CO2 and poisonous carbon monoxide.

Gray, black and brown hydrogen are commonly used in oil refining and to produce fertilizers, and today make up around 95% of the hydrogen produced worldwide.

Blue hydrogen is more promising, but only marginally. This process captures the CO2 generated during the steam reforming process and stores it underground, rather than letting it escape. Though it's sometimes considered to be carbon neutral, some 10-20% of the carbon emissions can't be captured.

Pink hydrogen, meanwhile, is generated using nuclear power. No emissions, but you're still left with radioactive waste. And it's difficult to use on a global scale, with nuclear not readily available everywhere.

Turquoise, an experimental process which leaves behind solid carbon, and yellow — using either solar power or a mix of renewable and fossil fuel energies — also exist, but don't factor much into global production.

Neither does green hydrogen, the only method that doesn't emit CO2 during production. It's made using electrolysis — splitting water into oxygen and hydrogen — using renewable energy.

Green hydrogen produces no CO2 emissions, but it only makes up less than 1% of global hydrogen production.

What's holding green hydrogen back?

A few things: cost, proper infrastructure and the lack of renewable energy.

Today, green hydrogen costs more than twice as much to produce as gray. And to build up the wider hydrogen sector to supply 15-20% of the world's energy demand, we would need to invest $15 trillion (€13.5 trillion) by 2050, according to the Energy Transitions Commission, an international think tank.

But in its 2023 report on hydrogen, the International Energy Agency said the expansion of renewable energy where sun and wind are plentiful — places like India, the Middle East and Africa — could significantly increase the share of green hydrogen. And that would bring down costs, though some critics have said it would be more efficient to just use renewable energy directly.

That gas also needs to be delivered to clients around the world, and hydrogen is notoriously difficult to transport in large quantities. It has to be stored in special pressurized containers, or liquefied (at minus 253 degrees Celsius/minus 423 Fahrenheit) and transported in pipelines, trucks or ships. It can also be moved in the form of ammonia, which is easier to ship as a liquid.

Before all that, the world would need to build up the necessary infrastructure. Germany and other countries aim to massively invest and scale up in this area over the next decade, in a bid to make hydrogen a viable alternative to fossil fuels.

Edited by: Jennifer Collins