Green is the only hydrogen that's truly “clean”

Green is the only hydrogen that's truly “clean”

We talk about green, blue or gray hydrogen. About burning it or using it in cells to generate electricity. About distributing it through gas pipelines or large hubs. Nicola Armaroli, a scientist with CNR, explains which are the right choices from a sustainability perspective, as we head towards a zero emission future. This is an approach that Enel, as a “Renewables Super Major,” fully shares.



The world needs to get back on its feet and energy will be one of the key factors in doing so. This is underlined by the UN through one of its Sustainable Development Goals, SDG 7 (“Affordable and Clean Energy”), which aims for a fair and sustainable distribution of this invaluable resource. Many countries have also endorsed this approach and are now developing their own plans to get their economies going again following the pandemic. Among them is Italy, which in its Recovery Plan focuses on the process of energy transition, and in particular on hydrogen, for an emission-free future with more efficient buildings, industry and transport.


A molecule that doesn't exist in nature

However, on the subject of hydrogen, and which one to use, opinions are mixed. To try to clarify the situation we spoke to Nicola Armaroli, scientist, writer and research director – Istituto ISOF – Consiglio Nazionale delle Ricerche, PHEEL Unit. "First of all,” he explains, "when we talk about hydrogen as an energy carrier, we mean its molecular form, H2, which doesn't exist in nature and, therefore, must be produced."


Colors that have meaning

Yes, but how? Today the central theme is precisely this, the technologies used to obtain molecular hydrogen; these technologies differ and scientists have begun to differentiate between them using colors. "Gray hydrogen,” explains Armaroli, "is that which is obtained from methane, while brown is derived from coal. Green hydrogen is produced from water with the help of renewable electricity, which is used to power electrolyzers in which the H20 molecule is split into oxygen and hydrogen. And then there's blue hydrogen, which is obtained from methane, like gray hydrogen, but then capturing the carbon dioxide that derives from the process and storing it underground."


Blue hydrogen? It isn't a viable option

And this is where the confusion starts for anyone who’s looking for an answer and is hearing lots of different opinions. Which hydrogen is truly sustainable, the one that's obtained without generating emissions? "It can only be green hydrogen,” says Armaroli, "and I'll explain why. CO2 is the by-product of the production process from methane. But humanity already has a problem in that it produces too much of this gas; a gas which alters the thermoregulation of the planet. Those who advocate the blue hydrogen approach, claiming that the CO2 issue can be solved by locking it away underground, fail to explain that carbon capture technologies are still a long way from being ready to enable such a solution. Every major carbon capture project that has been launched, for example in Texas and Australia, has failed; they've proved to be extremely expensive, difficult to implement and, even if the approach does eventually prove to be feasible, it won't be a zero-emissions technology. In essence, as things stand at the moment, producing blue hydrogen isn't a genuinely viable prospect."


Electrolyzer technology

How far advanced is the technological development of green hydrogen? "It's based on the use of electrolyzers," reaffirms Armaroli, "for which there are still problems to be solved, for example regarding the intermittency of the power supply from renewable sources, but they have already reached a good level of reliability. Electrolyzer technology is far more advanced than that of CO2 capture and, within a decade, it could certainly be sufficiently advanced to enable the creation of several large green hydrogen production and distribution hubs in Europe. Here in Europe we are very advanced in terms of the development of electrolyzer technology. We have a technological advantage in this area, and we need to exploit it."


Green hydrogen: how to make the best use of it

Once hydrogen is produced, green hydrogen that is, strategic decisions need to be taken regarding how to make the best use of it.

"The smartest thing we can do with hydrogen," explains Armaroli, "is to use it where better alternatives aren't available. For example, it wouldn't make much sense to use it in fuel cells for cars and light transport vehicles, because battery electric motors have already proved themselves to be highly efficient and there isn't an extensive hydrogen distribution network in place. But for heavy means of transport, for example long-distance haulage trucks, aircraft or ships, using hydrogen in fuel cells would be ideal, because for large vehicles electric charging is very complicated, if not practically impossible.” Another intelligent use of hydrogen is in heavy industry, to make the so-called "hard-to-abate" sectors sustainable. "For example,” Armaroli specifies, "in the steel industry, where green hydrogen can replace coal to reduce metal oxides and to separate out the oxygen in order to make cast iron, iron and steel."


Don't burn, electrify

However, it would make no sense whatsoever to use hydrogen as a fuel, to burn it. "For this purpose," continues Armaroli, "we already have methane, which is naturally available. It would be wasteful to replace methane with hydrogen, which has been obtained through expensive and complex means. But actually, what we really need to do in this regard, is to abandon our combustion mentality. Thermal systems, in contrast to electrical systems, are largely inefficient and are characterized by significant levels of waste." For use in vehicles, for example, or even for heating, the best solution from an efficiency standpoint would be to electrify, not to burn.


Produce close to where it's consumed

Producing green hydrogen would also enable us to improve on the predominant energy model, which is based on importing the required sources of energy. The optimal model is to locate the electrolyzers close to the renewable facilities, which are themselves close to where the hydrogen is consumed. Solar and wind power are widely available and are increasingly becoming low-cost technologies. "However, for this to happen," explains Armaroli, "more renewable energy facilities need to be built. To meet Italy's hydrogen needs for heavy industry, for example, we would have to at least triple the number of photovoltaic systems in the country. Naturally, these are political decisions, but if those decisions are made quickly, it could feasibly be done in a decade or so."


What do we have to do for the future?

So what do we still need in order to build a true hydrogen economy? "To produce green hydrogen," Armaroli concludes, "we need to invest in renewable energy facilities, particularly photovoltaics. And then we need to focus on what we already know how to do: renewables, electrification, improving efficiency, electrolyzers. Time is running out. Europe has an objective to cut emissions by 55 % by 2030, compared to 1990 levels. This means we have to up our game and work much faster in the coming decade than we have in the last 30 years."

The bottom line is: making the right choices today has never been more critical.