Hydrogen’s True Colors: A Key to Defining Carbon Intensity

Here’s a riddle for you: What’s colorless but most often referred to by its colors?

The answer: hydrogen. Often referred to as a “clean-burning” fuel, because it generates near-zero carbon greenhouse gas emissions at the tailpipe, hydrogen is the most abundant chemical substance in the universe. It’s also colorless, odorless, and burns with a near-invisible flame. So why does nearly every Google search or news story about hydrogen turn up terms like “green,” “blue,” and even “pink”?

A rainbow of production processes

Hydrogen as a fuel source isn’t found freely in nature. It must be extracted from naturally occurring compounds, typically through energy-intensive processes. And though there are multiple ways to make hydrogen fuel — all resulting in the same molecular hydrogen — the lifecycle greenhouse gas intensity of each production method varies. Energy experts and engineers started labeling these processes by color to make it easier for the rest of us to understand the differences.

Whether this color designation makes it simpler is up for debate. There’s no universal standard for hydrogen color labeling, and different organizations and countries sometimes use different definitions. Still, if you’re considering hydrogen as a potential fuel source for your electric power needs, it’s good to have at least a basic understanding of the terminology. So, here’s a quick look at the most common “colors of hydrogen” and their meanings.

The cleanest H₂: green hydrogen

Not surprisingly, green is the color chosen for the hydrogen production method, resulting in zero net greenhouse gas emissions. Green hydrogen is made by using electricity from renewable sources, like solar or wind power, to electrolyze water. Electrolysis is a chemical reaction that separates water molecules into their two components — hydrogen and oxygen — and nothing more. This type of production is costly, so only a small percentage of hydrogen is made this way.

The rest of the hydrogen spectrum

• When natural gas and steam react through a process called steam methane reforming, they create hydrogen — along with carbon dioxide. If that carbon dioxide is captured and sequestered, resulting in a significantly reduced amount of greenhouse gases reaching the atmosphere, the result is blue hydrogen. If those carbon gases are unabated, it’s called gray hydrogen instead.
• Another method to create hydrogen starts with coal instead of natural gas. This process, called gasification, also releases carbon dioxide into the atmosphere. That’s known as brown hydrogen (sometimes called “black”).
• Methane pyrolysis splits natural gas or biomethane into hydrogen and a solid form of carbon. If the thermal process used for pyrolysis comes from renewable sources — and the solid carbon byproduct is stored permanently — then you get turquoise hydrogen. Sometimes referred to as “cyan,” it can be considered a low-carbon or carbon-neutral fuel source.
• Two other production methods involve electrolysis (see green hydrogen above). When hydrogen is created directly from an electrolyzer that is powered from the grid and therefore has greenhouse gas intensity equivalent to the greenhouse gas intensity of the grid energy mix, it’s called yellow hydrogen. When it’s generated by nuclear power, it’s dubbed pink, red, or purple hydrogen. No carbon is produced in the latter process, but nuclear waste is a byproduct.

No black-and-white solution

Clear as mud? Don’t worry about remembering exactly what each color means. The key takeaway is that not all hydrogen is created equal, especially when looking at it from a carbon footprint and sustainability perspective. More companies are turning to sustainable solutions to help lower their carbon footprint. Renewable hydrogen and hydrogen blends are among several alternative fuels customers consider to achieve their sustainability goals. In fact, we already offer generator sets capable of operating on 100% hydrogen — including fully renewable green hydrogen. Here’s a look at our 35-plus years of hydrogen experience, products with hydrogen-blending capabilities, and other hydrogen-related projects currently underway.