Cars, fuels and a raft of other products contain an invisible ingredient: heat. Furnaces reaching 1,500 degrees Celsius (2,700 Fahrenheit) or more are commonly needed in manufacturing. But producing those ultra-high temperatures requires burning something, usually coal, oil or natural gas. That’s why the heat used by industry is responsible for about 10% of global carbon dioxide emissions, more than the fuel burned by all the world’s cars and aircraft combined. Under mounting pressure from protesters and climate-conscious investors, major industrial companies and governments are experimenting with what’s called green hydrogen.

1. Why hydrogen?

Hydrogen flames hot and clean. When it burns, it only leaves water vapor instead of the greenhouse gases that come from fossil fuels. And its value as a fuel is proven. Since it’s lighter than any other element, airships used it to keep aloft in the last century, albeit not without incidents such as the Hindenburg disaster in 1937. It also powers rocket engines that need to work where there’s no oxygen.

2. Where does it come from?

There’s plenty of hydrogen in the atmosphere around us, but harnessing it for industrial purposes is a different matter. Most of the hydrogen used as fuel is derived by splitting it off from molecules of natural gas. But that requires a good deal of energy and also produces carbon dioxide at the same time, making the process decidedly unclean. What’s changing is that some of Europe’s most important names in energy and industry are racing to develop ways to make the gas without those emissions. That’s what’s meant by green hydrogen.

3. How’s that done?

By electrolysis -- sending an electric current through water to split hydrogen atoms from oxygen. It’s the reverse of the process used in fuel cells, in which hydrogen and oxygen are combined to make water and electricity. Producing hydrogen by electrolysis eliminates the carbon dioxide released by splitting natural gas molecules. And if the electricity comes from renewables, the hydrogen is made without any emissions. The industrial gas maker Air Liquide SA, steelmaker ThyssenKrupp AG and the oil major Royal Dutch Shell Plc have some of the highest profile demonstration projects. Efforts to make the technology a commercial reality are furthest advanced in Europe, where policy makers are quickly tightening the screws on industry to scale back pollution.

4. How would it be used?

Green hydrogen has hundreds if not thousands of uses in helping industry cut emissions. Glass and cement makers need ultra-high heat to drive their processes, as do oil and chemical refineries. It’s most useful for steelmakers, who need a way of coaxing carbon atoms out of iron ore. Hydrogen could replace coal in that process -- both as an purifying agent and to fire the furnaces that melt metal and stone.

5. What companies are doing this?

The Russian pipeline company Gazprom PJSC is experimenting with mixing in green hydrogen with its natural gas to make a cleaner fuel. At the moment, there’s a limit to how much hydrogen can be mixed in pipelines with gas, but if the technical issues involved are overcome those systems could in theory become 100% green hydrogen for homes and industry. Even adding a little bit of hydrogen to the existing gas grid could reduce the carbon footprint of all those industries and utilities using the gas. And the reversible nature of electrolysis means that green hydrogen could act as a kind of battery: excess electricity generated by renewables sources could be converted into hydrogen, stored and used in a fuel cell to produce electricity when it’s needed. The German utility Uniper SE is doing just that with BP Plc, linking a wind farm to electrolizers that could generate 100 megawatts of energy, the equivalent of a small power plant.

6. What’s the catch?

Cost. While the companies involved are all confident the technology will work, question marks remain over whether hydrogen can ever be profitable. Green hydrogen costs between $2.50 and $6.80 a kilogram to make, due to the relatively high costs of renewable-powered electrolysis, according to an analysis from BloombergNEF. That would need to fall below $2 dollars in order to make renewable hydrogen competitive with coal, and to around 60 cents to beat the cheapest natural gas-based production, according to BNEF. The other issue is that making huge amounts of green hydrogen may strain electricity grids that are already facing a big challenge in preparing for a broad societal shift to powering more things with electricity rather than fossil fuels, most notably electric cars.

7. When will hydrogen technology go mainstream?

Green hydrogen could become economical in the 2030s, according to BloombergNEF. That assumes policy makers provide incentives to support it. Costs are expected to tumble as electrolysis technology becomes more efficient and production is scaled up. Moves by European governments to increase the cost of carbon dioxide emissions could further tilt the economics of the market in favor of hydrogen. The chief competitor for making clean industrial heat is carbon capture and storage technology, which may be even more expensive. In Germany, Chancellor Angela Merkel’s climate cabinet said in September green hydrogen would play a central role in “rebuilding” Germany’s industrial base as it moves to zero emissions by 2050.

To contact the reporters on this story: William Wilkes in Frankfurt at wwilkes1@bloomberg.net;Vanessa Dezem in Frankfurt at vdezem@bloomberg.net;Anna Shiryaevskaya in London at ashiryaevska@bloomberg.net

To contact the editors responsible for this story: Reed Landberg at landberg@bloomberg.net, John O’Neil

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