Welcome to Part II of this three-part series on unpacking the green hydrogen economy for the layperson. This is focused on unpacking why forecasters are predicting the green hydrogen economy to be multiples (3-8x) larger than today’s grey hydrogen economy (albeit with a high degree of forecasting variance) by 2050. More specifically, this edition explores some key chemical and thermodynamic characteristics of hydrogen that have a big impact on the potential for hydrogen to be a cost effective energy source in the transitioning energy markets.
This is an extension to Part I (Solving today’s grey problem and prioritising the expensive green) in this series where I explored the current market for hydrogen today as a molecular feedstock into oil refining and various chemical process. It concluded that given how much green energy is required to decarbonise where fossil-based hydrogen is already polluting today, a cautious and prioritised approach is required to exploring green hydrogen’s broader application – particularly if heavily subsidised by public money.
While in theory hydrogen can be used in many applications, it won’t magically happen in sectors that don’t currently use it today – just because it is green. Hydrogen is going to have to win, use-case by use-case, and it will not be easy. Not only does it have to beat the incumbent technology, it also has to beat every other zero-carbon option for that use-case. This is where green hydrogen’s potential really meets electrification reality.
So to explore hydrogen’s broader application, let’s again start by digging deeper into my high school science memory bank. As it turns out, isolating the hydrogen molecule through electrolysis powered by low-cost renewable energy is just the start of where chemistry and thermodynamics play an important role in understanding green hydrogen’s potential.
Hydrogen’s low volumetric density makes it challenging and expensive to store and move
Matching hydrogen’s attractive high energy density is its more problematic low volumetric density – that is, it needs a high level of compression to store hydrogen efficiently. You guessed it, compression is an energy intensive process. Hydrogen’s most dense form is as a liquid, however, liquefaction only occurs under high pressures (180 psi) and at temperatures of negative 253 degrees. These pressures and temperatures pose significant challenges for materials used in containment and transportation – rendering most of the existing storage and distribution capital stock around the globe unsuitable for hydrogen. In response to these challenges, much enquiry is focused on exploring more ‘friendly’ hydrogen storage and transport ‘vectors’ such as converting hydrogen to ammonia or methocyclohexane (MCH). Yep again you guessed it, more energy and cost to combine and separate these alternative chemical transporters in order to put green hydrogen to work.
Low cycle efficiency
Adding to storage and distribution challenges is hydrogen’s low cycle-efficiency. Cycle efficiency is effectively the amount of energy that is retained from a starting green electron (from renewables) after the process of converting this electron to a hydrogen molecule (through electrolysis) and then storing and shifting it around before returning it to provide end-use energy as an electron (through a fuel cell).
Let me put cycle efficiency into context with some numbers. Say we start with 100kWh of renewable energy. By putting this renewable energy through a hydrogen electrolyser, it suffers an immediate 22% energy loss and with transport, storage and distribution (compression) we lose about the same energy again. This means out of the 100kWh of renewable energy put into a hydrogen electrolyser, only around 60kWh of useable energy will remain at the point of sale/end-use application. This is before a further 50% conversion losses associated with processing hydrogen through a fuel cell to put green hydrogen to work. By contrast, transport, storage, and distribution of pure electricity results in only 5-10% energy losses, meaning that an initial 100kWh of energy would result in 90-95kWh of useable energy at the same point of sale. Almost all this available electrical energy is transferred to working energy through an electric motor.
This leads to an important conclusion – putting the green electron to work directly is far more energy efficient (and thereby cost competitive) than converting the green electron to a green hydrogen molecule.
This conclusion is important when unpacking the potential applications of green hydrogen in; storing our precious wind and sun energy for when and where we most need it, heating our living rooms, and powering our mobility.
Hydrogen’s is not the most efficient form of storing energy
These thermodynamic characteristics of low volume density and low cycle efficiency are the biggest barriers to exploiting hydrogen’s potential as an efficient carrier and store of energy – particularly where other distribution and storage alternatives exist. In short, when green hydrogen is in direct competition with electricity, it has an immediate cycle efficiency disadvantage and costs a great deal more. So why not save a fortune and an awful lot of hassle by using the electricity directly, rather than converting it into hydrogen gas?
Heat pumps are already a much more efficient application for residential heating
Equally, the extension of green hydrogen into residential and industrial heating applications is not straightforward. First and foremost, there are no residential hydrogen boilers in existence today and there are much more efficient electrical residential heating alternatives. Electrical heat pumps today are 2-4 times more efficient than a potential hydrogen boiler, meaning to get the same heating output would require setting aside 2-4x the land mass to host even more renewable energy to achieve the same heating application as today’s heat pumps. This is all before getting into the valid debate around safety, regulation, and social acceptance of hydrogen in the home.
But what about blending hydrogen (10-20% of the feed) into the gas distribution networks – isn’t this a beneficial transition path and wouldn’t it help to underpin a transitioning hydrogen economy? It’s understandable to expect that blending 20% of green hydrogen into the natural gas grid would save 20% of greenhouse gas emissions. However, a 20% mixture of hydrogen with natural gas in a pipeline has only 86% of the energy content of pure natural gas. Therefore, you’d have to burn 14% more of the blended mix to create the same heat energy. This means the savings in greenhouse gas emissions are nowhere near 20% — they’re closer to 7%.
A smooth transition between natural gas and hydrogen in our current natural gas pipeline infrastructure isn’t possible. Once blending limits are maximised (circa 10-20% hydrogen blend), full replacement of the existing natural gas infrastructure is required. Given how valuable hydrogen is, blending it into the existing gas grid does not make sense as a transition plan due to its high cost and its limited impact on emissions savings.
Even in high temperature (>800 degrees) industrial heating, a targeted application for green hydrogen, more cost-effective electrical options are available including resistance furnaces, infrared heaters, induction furnaces, plasma heating, and electric arc furnaces.
Mobility and transport applications
In light vehicles, the game in most geographies is all but lost for hydrogen fuel cells. A comparison of cycle efficiency shows battery vehicles 3 times more energy efficient than hydrogen fuel cell cars. Electrification is simply too easy, prevalent, cheap, and effective.
But what about long-distance haulage, doesn’t hydrogen carry significantly more energy than the equivalent weight of batteries? Or commercial vehicles where recharge/refuelling times have a more direct impact on the financial bottom line? While hydrogen retains some appeal in these segments, end-use applications may be narrower than first thought with around 80 percent of the daily driving distance being less than 400km, well within the range of existing battery technology. Additionally, research continues into more efficient batteries, such as solid state or lithium sulphur, which would extend the current advantage of battery electric trucks and buses, further shrinking the case for hydrogen. Add on top of this sparse and high-cost refuelling infrastructure, low market demand impacting heavy vehicle supply, limited track record on full life cycle costs of hydrogen vehicles, no second-hand market for hydrogen vehicles, and varying regulatory standards – hydrogen’s penetration into land transport is likely to be slow.
That only leaves long-haul shipping and long-haul aviation as areas where green hydrogen might have a play. However, in these applications, liquid fuels have many advantages over hydrogen, most significantly improved energy density and power-to-liquid; making for a stronger fuel than pure hydrogen. In addition, to put the green hydrogen generating challenge into perspective, to power all European air traffic with green hydrogen, Europe would need a land mass larger than the size of Hungary to operate 119,800 large wind turbines. As such, low-carbon biofuels are likely to be a more attractive solution in these applications.
Stay tuned for the next instalment of this green hydrogen series where I unpack the relative merits of directing green hydrogen to decarbonise the global steel industry, the potential for export industries, and the social and political implications of hydrogen.