Unveiling hydrogen’s true colours — how clean is it really?
In the ongoing effort to decarbonize emissions, hydrogen has recently gained unprecedented momentum as an alternative clean energy source. However, amid the growing hype, a continuous stream of studies keeps highlighting the ongoing controversy surrounding reported emissions. Our science team took a closer look at how clean these technologies actually are.
The prospects of hydrogen
Hydrogen is an essential building block of today’s economy and will gain even more importance in the future. Today, hydrogen is consumed by three primary industries, i.e. the production of ammonia (55%), crude oil refining (25%), and methanol production (10%) (WHA International, Inc).
The problem: in 2022, 6.6 EJ of hydrogen was produced of which more than 99% was produced using fossil fuels like natural gas and coal and less than 1% from clean sources (IEA 2022, IEA 2023). The future demand for hydrogen is predicted to increase substantially due to the decarbonization efforts undertaken in many sectors.
On top of that, future demands for hydrogen will arise from the use of hydrogen as a reaction agent for directly reducing iron ore in steel manufacturing, its use to produce synthetic fuels, and its use as an energy carrier. Different studies estimate a total hydrogen demand of 14 to 55 EJ in 2050 (Fraunhofer ISI & IEG 2022).
The increase in demand and decarbonization efforts present a huge opportunity for startups to develop alternative cleaner production methods. There are numerous methods for producing hydrogen, each with its own set of advantages and disadvantages, and striking a balance between cost-effectiveness and environmental sustainability is typically a challenge for startups. Many technologies now promise that they can achieve competitive prices with minimal impact, however, the lack of transparent data raises several concerns and questions.
The colours of hydrogen
First things first — before we move on to explore the mentioned concerns, let’s take a look at where hydrogen comes from. The production tends to be labelled with different colours depending on the energy sources they use, for differentiation purposes. Figure 1 below summarizes the main colours of hydrogen production.
- Brown and Grey hydrogen represent the majority of production due to their low cost and maturity, however, at the expense of high GHG emissions.
- Blue hydrogen is gaining increased momentum as it is produced in the same way as Brown and Grey hydrogen, however with the addition of capturing the carbon emitted in the process.
- Turquoise hydrogen uses pyrolysis of natural gas and converts carbon into a solid form called carbon black, thus reducing GHG emissions. However, GHG emissions still occur, especially earlier in the supply chain.
- Green hydrogen uses electricity from renewable sources to electrolyze water and produce hydrogen achieving low life cycle emissions. However, its high cost of production and dependence on the supply of intermittent renewables limit its scalability.
- Pink hydrogen uses electricity from nuclear power plants to electrolyze water and produce hydrogen, achieving very low emissions. However nuclear waste is a major concern of using electricity from nuclear power plants.
The promise of Blue and Turquoise hydrogen
Everyone’s been particularly excited about two kinds of hydrogen: Blue and Turquoise. Since they rely on more mature technologies like steam methane reforming, gasification, and pyrolysis, it might allow them to reach competitive costs at scale. Both technologies convert natural gas (or biomethane) to hydrogen. While the production of blue hydrogen seeks to capture arising CO₂ emissions, turquoise hydrogen production converts emissions into a solid form.
Both options are widely discussed because they eliminate a bottleneck of many other means of hydrogen production: availability and transport. Blue and Turquoise hydrogen can be readily produced wherever natural gas is delivered, 24/7. This is a very convenient solution, but is it a sustainable one?
Peaks and leaks — debunking Blue and Turquoise hydrogen
So, as you can see, while Blue and Turquoise hydrogen pathways show promising potential, the amount of pollution they cause is worth shedding some light on. In an effort to explore the true impact, we conducted a detailed literature review of the natural gas supply chain of hydrogen and more specifically the production of Blue and Turquoise hydrogen (see Figure 2 below).
Natural gas supply chain emissions
Emissions in the natural gas supply chain are caused by several actions and are primarily carbon dioxide (CO₂) and methane (CH₄). Carbon dioxide emissions that represent around 40% of total emissions are caused by unavoidable operations like flaring, which is used to regulate the pressure and flow of pipelines.
Methane emissions, however, which represent more than 60% of total emissions, occur due to fugitive gas/leaks. Fugitive gas is defined as unintentionally released gas that occurs due to accidents or leaks (Balcombe et al. 2015, this source provides an excellent overview of the GHG intensity of natural gas production and transportation).
The main sources of those leaks tend to be compressors, valves, flanges, and pipes that are improperly maintained, leading to rust, corrosion, and unsecured issues. For this reason, natural gas pipelines that are found in developing countries tend to have higher leaks than those in developed countries like Norway. A combination of a lack of established legislation, negligence, and safety issues are all likely part of the problem (IEA 2023).
Natural gas leakages
There has been a large range of reported leakage emissions. However, when comparing official leakage data like the US EPA at 2–3%, it differs significantly from data from robust studies reporting leakages closer to 10% (Omara 2022, et al.). Current measurement techniques are mainly based on two approaches.
→ Measuring the leakage over a period of time at one specific location, but failing to cover many sites.
→ Measuring a larger area via aerial techniques but only in a specific period of time.
Both approaches have drawbacks regarding the number of locations and the time period, resulting in lower leakage measurements than in reality.
Transportation
Some hydrogen production sites might lack a robust natural gas pipeline and require the need to import natural gas from overseas. Between January and November 2022, Europe imported more than 25% of natural gas from overseas via LNG (European Council 2023).
To transport natural gas, it must be compressed and liquefied due to its low density and then stored in specially designed vessels as Liquefied Natural Gas (LNG). Once reaching the destination of consumption, it must be gasified to reach a suitable state. These processes require energy and emit GHG emissions at different stages. The additional conversion to LNG substantially increases GHG emissions (Balcombe et al. 2015).
Hydrogen production emissions
After reviewing both the leakages of the natural gas supply chain and the transportation emissions, we were able to derive a graph summarising the emission ranges for each colour of hydrogen in Figure 3 below.
Mean and median values for Blue and Turquoise hydrogen indicate that both technologies perform worse than Green hydrogen. Nevertheless, it is true that under better conditions like using a natural gas pipeline with lower leaks, those technologies could potentially achieve lower emissions than Green hydrogen produced, for instance, with solar PV.
Hydrogen leakages
Another factor to take into account when discussing hydrogen is the leakage of hydrogen itself. Due to its smaller molecules compared to methane, leaks occur much more easily than with natural gas. This can cause leakage rates up to 1.3 to 3 times higher than technologies using or converting methane (Ocko et al. 2022).
What happens when hydrogen is leaked into the atmosphere? Hydrogen potentially impacts the climate by affecting atmospheric chemistry. Atmospheric hydrogen triggers a complex chain of chemical reactions that could influence climate change. In simplified terms, atmospheric methane reacts with hydroxide radicals (a compound containing oxygen and hydrogen, OH), leading to methane decomposition, a potent GHG. Hydrogen (H₂), when released, disturbs this process by reacting with these OH radicals, producing water vapour and atomic hydrogen (H). The result of this reaction is threefold:
→ First, fewer OH radicals are available to remove atmospheric methane.
→ Second, atomic hydrogen is highly reactive and could lead to increased tropospheric ozone through intermediate reactions.
→ Third, stratospheric water vapour levels rise. All of these aspects contribute to more heat being trapped in the Earth’s atmosphere.
Figure 4 below illustrates how the GHG intensity of Green hydrogen is affected when accounting for this effect. Note: the impact remains consistent regardless of the origin (colour) of hydrogen and needs to be added to the GHG emissions and other impacts of hydrogen production. Most current studies do not consider such leakages. More details and quantification of the climate impact of hydrogen leaks can be found in Ocko et al. 2022.
Our take
Our analysis indicates that leakages of natural gas and hydrogen are the main sources of emissions. There are three alternatives regarding whether these leaks are preventable or not:
- Technology is there but it is physically unavoidable.
- Technology is there but there is no significant incentive to prevent leaks.
- Technology is not there or is poorly implemented and requires further innovation.
Alternative 3 is the most likely problem and opportunity for venture capital investments.
After delving into this analysis, here are our key takeaways:
- Blue and Turquoise hydrogen can achieve emissions as low as Green hydrogen, but only if a clean natural gas pipeline is used and production occurs at the location of consumption.
- Replacing natural gas as a feedstock with alternative energy sources like biogas and converting the outputs of the chemical reaction into valuable materials will reduce lifecycle emissions and improve costs.
- Implementing better measurement processes and reducing leakages from “dirty” natural gas pipelines will reduce GHG emissions of Blue and Turquoise hydrogen.
- Overseas transportation of natural gas leads to more leaks and emissions. It is better to use local pipelines to minimize this effect.
- Hydrogen has small molecules and can easily leak through a pipeline. Once released into the atmosphere, its effects are worse compared to leaked methane.
- Producing hydrogen at the point of consumption can avoid losses along the conversion chain.
- Green hydrogen remains the leading technology when looking at the environmental impact side. While some electrolyzer technologies have reached maturity, others lag behind. Directing investment toward low TRL electrolyzers could eventually bring costs down and transform Green hydrogen into a cost-competitive technology.
- Alternative hydrogen colours are coming into play, like yellow hydrogen which involves the direct solar photoelectrolysis of water and orange hydrogen which utilizes natural H2 deposits.
- Taking into account the time taken for clean technologies to reach commercial scalability, alternatives that are better impact-performing than Brown and Grey hydrogen but at price parity could still work as a short-term solution
📚Interesting reads :
- Methane and CO2 emissions from the natural gas supply chain
- Natural gas emission intensities at different countries
- Methane emissions of natural gas well sites
- Hydrogen chemical reactions when released in the atmosphere
- Green hydrogen electrolysers
Authors: Dimitrios Rizos and Benedikt Buchspies
