Hydrogen has long been touted as the key to decarbonising shipping, with a growing number of orders for vessels capable of running on H2 derivatives such as ammonia and methanol.

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Ammonia, when burned, produces zero carbon emissions, while combusting methanol produced with captured carbon dioxide could be carbon-neutral, with no more CO2 emitted than used to make it.

If the hydrogen used to make these chemicals is green, then the maritime sector could reach net zero emissions if it switches to these cleaner fuels.

But given that the global fleet of ships already uses hundreds of millions of tonnes of fossil fuels every year, how much hydrogen would need to be produced to decarbonise shipping? And how many gigawatts of renewables would need to be installed to power that scale of production?

How many tonnes of hydrogen?

According to the International Energy Agency's 2050 net-zero scenario, shipping will have to annually consume 233 million tonnes of clean ammonia, 13 million tonnes of methanol, and 15 million tonnes of hydrogen directly used as a fuel. In total, this would mean around 59.5 million tonnes of H2 would be consumed annually by that year to produce fuels or for direct use, Hydrogen Insight calculates.

The International Renewable Energy Agency (Irena) predicts a similar scale of hydrogen feedstock in its own model for the world to reach net zero, estimating around 60 million tonnes of green H2 a year will be needed as a feedstock for shipping fuels by mid-century.

However, making a dent in shipping emissions in the short term is also expected to require vast volumes of hydrogen — with less time to build out infrastructure.

The IEA calculates in a recent report, The Role of E-Fuels in Decarbonising Transport, that around 70 million tonnes of either ammonia or methanol — requiring between 12.6 million and 14 million tonnes of H2 — would be required to make up a 10% share of fuels in the maritime sector by 2030, 3.5-times the current traded volume of ammonia or twice the traded volume of methanol.

Maritime certification agency DNV expects an even smaller share of green fuels by 2030.

In its latest maritime forecast up to 2050, it estimates a demand of 17 million tonnes oil-equivalent for carbon-neutral fuels — ie, those made using clean H2 and captured CO2 — by 2030, although this is only 6% of the 280 million tonnes oil-equivalent of fuels consumed by shipping today.

Since one tonne of fuel oil has the same energy as 2.2-2.3 tonnes of methanol or ammonia, Hydrogen Insight calculates at least 6.7 million tonnes of hydrogen feedstock would be needed for these fuels.

However, Eirik Ovrum, DNV’s principal consultant in maritime environmental technology, notes that the 17 million tonnes oil-equivalent figure represents an upper bound “but it could potentially be much less”.

“We cannot give a uniform answer to how much e-fuels we believe will be in use in shipping in 2030, the uncertainties are simply too large,” he tells Hydrogen Insight.

What does that mean for upstream renewable electricity?

The IEA estimated in a recent report that for a 10% share of green fuels in shipping by 2030, an extra 600TWh of renewable electricity would be needed to power hydrogen production.

The agency estimates that this, combined with the 1,500TWh for e-fuels to make up a 10% share of aviation fuel, would be equivalent to 23% of the scale of clean electricity capacity it predicts to be installed between 2022 and 2030 in its STEPS (ie, business as usual) scenario.

Ovrum estimates that producing 17 million tonnes oil-equivalent of green hydrogen-based fuels would require around 500TWh of electricity, which in turn would need 230GW of installed wind and solar capacity, saying “Norway produces about 140TWh per year, for comparison.”

So does this mean the build-out of upstream wind and solar assets could present a potential bottleneck for reducing ship emissions?

“Renewable electricity is a sought-after commodity by other sectors than shipping, electricity production needs to be scaled up in many different countries,” Ovrum warns. “This could both lead to less supply than demand, or perhaps higher prices in the short term, resulting in reduced demand.”

However, Irena’s head of innovation and end-use applications, Francisco Boshell, is more optimistic, noting that 1,200GW of renewable energy capacity to power electrolysers by 2050 would require 46GW of new wind and solar built every year until then.

“This is certainly ambitious but a feasible effort, considering that 2023 alone saw more than 500GW additions of solar PV and wind capacity deployed, and this annual rate is expected to grow, thanks to the pledges to triple renewables made at COP28,” he tells Hydrogen Insight.

“Renewable energy deployment is not a bottleneck for the energy transition. We know that renewable potentials are more than enough to satisfy this demand, and the same can be said for the materials needed to build this infrastructure.”

However, Boshell cautions that there will still be challenges around “rapidly creating the enabling frameworks to build up the renewable electricity capacity, source the carbon for the e-fuels [ie, methanol], and build the infrastructure to manage and trade those e-fuels”.

“We need the timely mobilisation of finance, growing and diversified supply chains — including sourcing materials, refining, manufacturing capacity and skills among others — and developing the necessary infrastructure for these fuels to thrive.”

What about electrolysers?

While different analysts are split on whether renewables will present a bottleneck, they agree that hundreds of gigawatts of electrolysers will need to be installed.

The IEA estimates that 130GW of electrolyser capacity would be needed to produce enough H2 for ammonia to make up 10% of maritime fuels, although this rises to 150GW for green methanol.

The agency estimates there are are 175GW of sufficiently-advanced electrolyser projects planned by 2030, although many of these will also have to feed into large-scale demand not only to displace grey hydrogen in existing sectors, but to produce e-fuels for the aviation industry. However, if early-stage concepts are counted, the pipeline rises to 420GW.

DNV, meanwhile, says that there are more than 2,200 existing and planned projects producing carbon-neutral fuels — albeit without specifying how many are using green hydrogen or biofuels, or how many depend on carbon capture for clean H2 — which it forecasts could supply between 45 million to 63 million tonnes of oil-equivalent to the market by 2030.

However, most of these tracked projects have not reached a final investment decision or started construction. The Norwegian firm cautions in its 2050 forecast that lead times for green hydrogen projects with more than 1GW of electrolysis capacity can range from six to ten years, meaning “only a few projects that are not already announced will be operational before 2030”.

Additionally, many of these projects are not specifically dedicated to supplying the maritime sector.

While DNV notes that “if all the produced carbon-neutral fuels in 2030 end up being available to the shipping industry, the supply would cover the demand with a margin”, it also calculates that existing industries such as fertilisers and chemicals already consume around 120 million tonnes oil-equivalent per year, or 40% of the energy demand in the shipping sector.

“This methanol and ammonia are currently produced from fossil sources with GHG [greenhouse gas] emissions, and these industries will most likely compete for the same carbon-neutral methanol and ammonia towards 2030,” DNV warns.

Meanwhile, Irena anticipates that around 600GW of electrolysers would need to be installed to produce its projected 60 million tonnes of green hydrogen for shipping fuels by 2050.

IMO and EU targets for clean shipping fuels

Far less green hydrogen will likely be needed for shipping to comply with current targets and regulations to reduce greenhouse gas emissions.

The International Maritime Organization (IMO), the UN agency that regulates global shipping, has set out a target for net-zero emissions “close to” 2050, with a 40% reduction in carbon intensity across global shipping by 2030.

This strategy also includes a target for the uptake of “zero or near-zero GHG emission technologies, fuels and/or energy sources” to account for at least 5% and “striving for 10%” of final energy consumption by 2030, which would suggest a scale of green hydrogen production somewhere between the DNV and IEA scenarios would be needed.

However, this does not refer purely to hydrogen-based fuels, with battery-powered or hybrid-electric propulsion systems explicitly included in the IMO definition, and biofuels likely to count too.

Last September, the EU signed its FuelEU package into law, setting out legally binding targets for ships operating in European waters to reduce their emissions.

All ships with a gross tonnage above 5,000, regardless of what flag they fly, will have to cut greenhouse gas emissions by 2% from the start of 2025 against a reference emissions intensity of 91.16 grams of CO2 equivalent per MJ of energy used. This progressively rises to 6% from 2030, 14.5% from 2035, 31% from 2040, 62% from 2045, and finally 80% from 2050.

However, in the calculations of greenhouse gas intensity, vessels will be rewarded for using hydrogen or its derivatives — known in EU parlance as renewable fuels of non-biological origin (RFNBOs) — between the start of 2025 and the end of 2033, by allowing the double-counting of their emissions savings from using these fuels.

If the share of RFNBOs in maritime fuels used in the EU is less than 1% in 2031, the EU will set a binding target for ships to use 2% of these fuels in annual on-board energy consumption by the beginning of 2034.