Tag: life-cycle emissions of hydrogen

This article is part 2 of a 4-part series on hydrogen in Alberta. See part 1 here.

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In a world rapidly shifting toward decarbonization, hydrogen has generated excitement as a potential zero-emission fuel. But how clean is it, really?

In this post, we’ll explore how the life-cycle emissions of hydrogen vary depending on how it’s produced, and what that means when we use hydrogen to power vehicles, generate electricity, or heat our homes.

TL;DR: Not all hydrogen is created equal. Life-cycle emissions depend heavily on the production method – and that has major implications for Alberta’s clean energy future.

Hydrogen Production Pathways

Hydrogen is produced through several methods, commonly identified by color codes. The two most discussed pathways are ‘blue’ and ‘green’ hydrogen.

Green hydrogen is produced through electrolysis, where electricity splits water into hydrogen and oxygen. When that electricity comes from renewable sources like wind or solar, the result is hydrogen with very low associated emissions. Electrolysis efficiency typically ranges from 70-80%, with technological innovations pushing toward 90-95%. The majority of emissions from green hydrogen come from the construction and manufacturing of the renewable energy infrastructure.

Blue hydrogen refers to hydrogen made from natural gas using steam methane reforming (SMR) or auto-thermal reforming (ATR), coupled with carbon capture and storage (CCS). These processes convert methane into hydrogen and carbon products, and capture the CO₂ instead of releasing it into the atmosphere. Larger centralized production plants can make carbon capture more viable through economies of scale.

Grey hydrogen is simply blue hydrogen without carbon capture, making it significantly more carbon-intensive.

Due to their respective production methods, green hydrogen is generally the cleanest option, with blue hydrogen’s footprint depending heavily on carbon capture efficiency (see a 2021 systematic review for more information).

Life-Cycle Emissions of Hydrogen

If hydrogen doesn’t release carbon emissions upon use, how do we characterize its carbon impact?

To understand the full climate impact of hydrogen, we use a life-cycle analysis (LCA) method, which accounts for all emissions from production to end-use.

Blue Hydrogen	Green Hydrogen
Natural gas extraction, transportation, reforming, electricity usage, and hydrogen transportation.	Construction of renewable energy infrastructure and transportation of hydrogen.

Quantifying Hydrogen’s Carbon Footprint

To estimate emissions specific to Alberta, we used a Pembina Institute report that provided a carbon intensity (CI_Blue) model for blue hydrogen based on the carbon capture efficiency (eff_CCS):

At 100% CCS efficiency, blue hydrogen still has a baseline emission of 2.84 kg CO₂/kg H₂ due to upstream methane and electricity emissions.

For green hydrogen, the formula is:

Where CIₑ is the carbon intensity of the electricity used, HHV_H2 is hydrogen’s higher heating value (39.4 kWh/kg), and electrolyzer efficiency (eff_elec) is typically ~75%.

Using the equations above, we can map the carbon intensity of different hydrogen production mixes. To meet the CertifHy threshold (an international standard for carbon emissions in hydrogen production), SMR (blue hydrogen) must have a CCS efficiency of at least 78%.

Comparing Hydrogen Production Scenarios

Since the carbon intensity of hydrogen production is highly dependent on the chosen technique, it’s helpful to set up some different scenarios:

1. Current: Alberta’s current hydrogen production mix, with 81% grey and 19% blue hydrogen.
2. All Blue: Considering a shift to 100% blue hydrogen.
3. Blue/Green: Assuming a mix of 70% blue and 30% green hydrogen.
4. All Mix: Assuming some of each color, with 60% blue, 20% grey, and 20% green.
5. All Green: 100% green hydrogen.

Using these scenarios, we can build a map of each scenario’s carbon intensity:

As expected, the pathway with the most grey hydrogen has the highest carbon emissions, while the pathway with the most green hydrogen has the lowest carbon emissions.

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Emissions from Hydrogen End-Uses

Let’s explore how these upstream emissions translate to real-world use in transportation, electricity generation, and heating.

Fuel Cell Electric Vehicles (FCEVs)

FCEVs are vehicles that convert hydrogen into electricity directly through a thermochemical process. According to NRCAN, a typical FCEV consumes 0.94 kg of hydrogen per 100 km. In contrast, an average petrol vehicle emits 20.24 kg CO₂ per 100 km (NRCAN).

All hydrogen production scenarios yield lower emissions than gasoline vehicles. Even today’s hydrogen mix results in a 56% reduction in driving emissions. All scenarios also outperform EVs charged from Alberta’s grid.

Hydrogen FCEVs already offer major emissions reductions in Alberta, especially when clean hydrogen is used.

Electricity Generation

There are three key pathways for electricity generation using hydrogen:

• Burning hydrogen in a gas turbine (H₂ turbine)
• A 5% H₂ / 95% natural gas blend in conventional turbines
• Hydrogen fuel cells

Replacing hydrogen completely in a gas turbine eliminates end-use emissions, making the life-cycle emissions dependent mainly on the production technique. Blending hydrogen with natural gas offers only marginal improvements, with a thermodynamic limit of around 1.5% due to hydrogen’s lower energy density. Fuel cells, while more expensive and with lower capacity, convert hydrogen more efficiently and release zero emissions at the point of use, making them the cleanest electricity generation option.

This plot yields three key observations:

• The current hydrogen mix is too carbon-intensive for combustion.
• Blending hydrogen into natural gas offers a maximum emissions reduction of just ~1.5%.
• Fuel cells have significantly lower emissions and higher efficiency than gas turbines, but at higher capital costs and lower generation capacity.

Home Heating

In cold climates like Alberta, heating is a major source of emissions. Hydrogen offers a combustion-based alternative to natural gas which can be used in furnaces.

Assuming a 92% efficient furnace heating a 1200 sq. ft. home at 50,000 BTU/hr, a furnace would require 1.1 kg of natural gas or 0.4 kg of hydrogen per hour to sustain this heat rate. Using this, we can compare the emission intensities per hour at a heat output rate of 50,000 BTU/hr:

While the current mix is not viable at a 40% emissions increase, all other scenarios decrease the heating-related carbon emissions, with green hydrogen leading at a 70% emissions reduction. However, logistical challenges such as volume density, infrastructure retrofitting, and flame characteristics remain engineering challenges for H₂ heating, despite the emissions upside.

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Key Takeaways

Hydrogen holds tremendous promise as a low-emission energy carrier, but as we’ve seen, not all hydrogen is created equal. The life-cycle emissions of hydrogen are highly dependent on how it’s produced.

In Alberta, the most significant determinant of hydrogen’s climate impact is the production mix. Current reliance on grey hydrogen undermines its potential, leading to emissions that can even exceed those of the fossil fuels it seeks to replace. However, as carbon capture efficiencies improve and renewable electricity sources expand, a shift to blue and green hydrogen can deliver substantial reductions in life-cycle emissions.

Across all end-use cases – transportation, electricity, and heating – green hydrogen consistently offers the lowest emissions. Even a modest integration of green hydrogen into existing blue hydrogen infrastructure can push us meaningfully closer to decarbonization targets. In contrast, strategies like blending hydrogen with natural gas offer only marginal gains.

Ultimately, hydrogen can play a valuable role in Alberta’s energy future, but only if we get the production side right.

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In the next part, we’ll investigate the economics surrounding hydrogen production and usage. Stay tuned for the next installment of this series!