Sinot Yacht Architecture & Design made headlines in February when they released a design for the €500M superyacht “Aqua”. While the (false) rumor that Aqua had already been purchased by Bill Gates captured the public’s attention, it was the Aqua’s use of a hydrogen fuel cell electric powertrain that caught mine.
I started working with hydrogen fuel cell technology over 20 years ago. And the first applied project I did was examining their feasibility to power boats. From 2014 until today, I have been focused on the maritime application of hydrogen fuel cells first with research at the US Department of Energy’s Sandia National Laboratories where I established the nation’s only Zero Emission Maritime program, and now with Golden Gate Zero Emission Marine, a company I co-founded in 2017 to commercialize packaged hydrogen fuel cell marine powertrains.
In the transportation world, if you want to achieve zero emissions there are really only two choices: batteries or hydrogen fuel cells. On the maritime side, because of the high duty cycles, power requirements, and – what’s really key – high energy consumption, batteries are not technically possible to support the vast majority of vessel types and voyages. It takes a lot of weight and volume to store the enormous amount of energy required, using even the best projections for known battery technologies. This leaves hydrogen fuel cells as the only solution. However, even hydrogen fuel cells have a difficult time meeting the demands of some types of vessels.
To understand why, it is important to take a quick look at the fundamentals behind the technology. Hydrogen is a flammable gas and has properties remarkably similar to natural gas. This makes sense because the main constituent of natural gas is methane, or CH4, which means 80% of the atoms in methane are hydrogen. But there are a few differences. While natural gas liquefies at -162 C (making LNG), hydrogen will not liquefy until -253 C – just 20 degrees above absolute zero. Handling liquid hydrogen (LH2) is industry standard today, but the colder temperature means more energy is needed to make LH2 and there are some different handling procedures.
Made simply of a single proton and an electron, hydrogen is also the lightest gas in the universe. This is good and bad. The good side of this is that if hydrogen leaks it immediately goes straight up into the air at about 70 km/hr – that’s enough to clear an 8 story building in 5 seconds – and is so light that it escapes the earth’s atmosphere and leaks into space. What this means is that while flammable, in open air it is extremely difficult to build up to the concentrations needed to ignite. However, this benefit comes with a price. Hydrogen is so diffuse that storing it takes up a lot of space. In the automotive world, where Toyota, Honda, and Hyundai have retail hydrogen fuel cell vehicles, the hydrogen is stored in thick carbon fiber tanks at 70 MPa pressure. Even then, the volume of the tank is about 8-times larger than a tank of diesel containing the same amount of energy. And pressurized gas tanks do not scale well – to contain hydrogen for a vessel, a pressurized tank array would have a volume 12-15 times that of the equivalent diesel tank.
Liquefying the hydrogen reduces the volume far more than pressurization. A tank of LH2 is still about twice the volume of LNG and 4-times the volume of diesel, but much more manageable than pressurized gas. (Interestingly, hydrogen is much lighter than diesel on an energy basis, which means that even though the tank will be larger, it won’t add as much weight to the vessel as the diesel tank. Displacement-limited vessels can benefit from this characteristic.)
Today’s commercially-available fuel cells – which are needed to convert the hydrogen to electricity to power the on-board electric powertrain – are larger and heavier than their diesel engine counterparts. Throw in the electronics needed to manage the high power flows for the powertrain, and this part of the system adds even more volume.
The key takeaway here is that hydrogen fuel cell systems are larger than their diesel engine counterparts. Small, high-powered catamarans have a difficult time squeezing all of that volume into their slender hulls. Conversely, large monohulls typically have plenty of space available belowdecks. In the commercial sector vessels typically get larger as range increases, and are able to more easily accommodate the larger equipment.
Large luxury yachts are in a different class though, because their specifications often call for moderate speeds and long ranges that are similar to a commercial cargo vessel, but in a smaller package. Two conventionally-powered yachts of similar size to the 112 m Aqua, the 115 m Luna and the 107 m Andromeda can be compared to as off-the-cuff examples. The Luna has about 11 MW installed power for a 22.5 knot top speed, with a 1 million liter fuel tank allowing a stated range of 9,000 nm. The Andromeda has 4.4 MW for a 16 knot top speed with enough fuel for a 8,500 nm range. Commercial cargo vessels with these power and range numbers would typically be in the 150 m – 200 m size class, and some of that added volume could be used to accommodate the larger hydrogen fuel cell powertrain. In a yacht there is simply less space to work with, making packaging a challenge for today’s hydrogen fuel cell systems.
The overall effect of this challenge in the case of the Aqua can be seen in her resulting performance specifications: 4 MW installed power for a 17 knot top speed and a 3,750 nm range. In other words, she has a similarly-sized powerplant to the Andromeda but less than half the range. The volume issue appears to have affected more than the range, however. A look at the deck plans and capacities also reveals compromises, with fewer decks, accommodations, and excursion toys than the two comparison vessels. Indeed, the entire “lower” deck of the Aqua appears dedicated to the propulsion and hotel load system, while in conventional yachts this is able to be confined to just a portion of a single deck. Adding this all up, the specifications of the Aqua on paper are more similar to a class of vessels in the 80 m range. Indeed, it is perhaps unfair to compare the Aqua to her 110 m class cousins and instead to think of her as an 80 m yacht that has been masterfully “stretched” to accommodate the larger powerplant.
In general, the Aqua’s hydrogen fuel cell powertrain design is a great example of how this technology would be typically implemented on a vessel. She hosts a full-electric system where the power is primarily generated by 4 MW of fuel cells. There are two Voith Schneider Propellers (VSPs) powered by electric motors each rated for 550 kW, and two conventional propellers turned by electric motors, 1 MW each. This gives a total 3.1 MW of propulsive power. A diesel-electric system would not look much different, with just diesel generators producing the power instead of fuel cells.
The proton exchange membrane (PEM) fuel cells are arranged in four 1 MW blocks, and from the publicly-released 3D image of the Aqua each block appears to be about 16.8 m3. (This exactly matches the predicted volume for this amount of power in a report I co-authored from my time at Sandia, so this is either a happy coincidence or a result of that work. Either way, the Aqua designers appear to have accurately estimated the volume required for this system.) The selection of a PEM-type fuel cell, which is the kind used all over the world in vehicles, trucks, backup power systems, equipment, and more, means the designers understand that these are the lightest, quietest, most responsive, and most mature of all types of fuel cells today.
Power electronics are an important part of the system, because this equipment converts the fluctuating DC voltage output of the fuel cells into the regulated AC and DC power needed by the propulsion equipment and house loads. They are located in the stern near the fuel cells, likely intended to handle the full fuel cell output, and are shown as four blocks each about 8.4 m3. In other words, the designers assumed the power electronics are about half the size of a fuel cell on a per-MW basis. With so much variety of power electronics from different vendors today, this is a good approximation. In both cases (the fuel cell and the power electronics) the volume estimates are conservative. By the time this vessel is commissioned, it is likely that both technologies will be smaller than as shown today and this savings can either free up volume for other uses, or pack more power into the same envelope.
The cryogenic hydrogen fuel is stored in cylindrical tanks located amidships. To keep the fuel as a cold liquid, LH2 tanks have an inner tank surrounded by a vacuum space, superinsulation, and an outer tank. The inner tank, which holds the LH2, is typically only 50-70% of the overall volume of the assembly. I estimate the outer volume of the tanks on the Aqua is about 350 m3 each, and for this size tank I suppose the inner tank to be around 200 m3. This gives a rough hydrogen-carrying capacity of 14 tons per tank, or about 28 tons total. In terms of stored energy, this is equivalent to about 930 MWh. The stated range of the Aqua is 3,750 nm and the cruise speed is stated as 10-12 knots. Using very rough approximations, at 12 knots the Aqua might consume about 22 tons of fuel to reach maximum range. This would leave about 20% margin in the tanks, which is reasonable. Unlike diesel or fuel oils, contamination build-up is not an issue for LH2 tanks so while 20% is a conventional and comfortable margin a case could be made to decrease this margin in order to reduce tank size or allow a longer range.
Every major component on the Aqua’s powertrain consists of multiple redundant blocks. This not only allows flexibility in placement, it also provides inherent resiliency. If there’s an issue with any part of the fuel cell or hydrogen supply system the vessel will continue to have power to propel itself and support the house loads. The fuel cells themselves provide another layer of redundancy, because each 1 MW block is itself comprised of smaller units anywhere from 30 kW to 100 kW each depending on the manufacturer. If a single fuel cell “fails” the power output of the block is barely affected. Crew can isolate the failed unit and replace it with a backup from the ship stores in a matter of hours with no noticeable effect on operations. Back in port, the failed unit can be sent back to the manufacturer for refurbishment and returned in like-new condition to maintain replacement stock. Over time, as fuel cells naturally degrade, all units will eventually be replaced in this manner. There is never a need to take the vessel out of service for an extended overhaul or repower. This is just one of the ways maintenance is drastically reduced with the use of a fuel cell-based, solid-state power system.
A curious aspect of the Aqua’s power system design is the inclusion of a 1.5 MWh Li-ion battery pack. Battery packs are typically required with diesel electric powertrains to allow the diesel engines to operate at peak efficiency and lowest emissions. With fuel cells, the need for batteries is different. PEM fuel cells provide electrical power faster than diesel engines, so there is no need for batteries to provide power in case of demand spikes. Fuel cells are also instantly load following, which means that they only produce the power that is needed and there is no need to absorb extra power during demand changes. Being zero emission themselves, and having similar efficiency across the load range removes the need for batteries to optimize emissions or efficiency. As noted above, the multiple redundancy nature of a fuel cell powertrain also precludes the need for a battery pack for backup power, although the battery could be thought of as a second redundancy measure.
For some fuel cell vessels, batteries make sense to provide additional power for intermittent peak demands such as high-speed sprints (ferries), high-power maneuvering (tugs), or specialized on-board equipment requiring large house loads (work boats). Although Li-ion batteries are the lightest and smallest large-scale batteries on the market, their ability to hold energy pales in comparison to LH2, which is just 1/10th the size and over 100-times lighter for the same amount of energy. On-board Li-ion batteries also bring additional safety considerations because of the potential for thermal runaway. Unless needed for one of the special cases mentioned above, minimizing the amount of on-board batteries to reduce added weight and volume and to enable the use of conventional technologies (e.g. lead acid) is often desirable. I can only assume that Aqua’s designers included this large pack for either added redundancy or a special use-case of which I am unaware.
The mechanics of fueling Aqua would be based on well-established practices for handling and transferring LH2 on land, with modifications to meet maritime regulations. Because of the similarity between LNG and LH2 many of the existing regulations can be used with only minor modifications. However, the logistics of obtaining 28 tons – about 8-10 truckloads – of LH2 would be challenging outside of North America, which has nearly 90% of the world’s LH2 generation capacity today at close to 300 tons per day. Today’s total generation capacity in the EU is just 26 tons per day, Japan at about 35 tons per day, and a smattering of small plants in a few other locations around the globe. This is changing rapidly though, with multiple projects in the EU, Japan, and other places focused on increasing LH2 production and import/export terminals to support the coming global hydrogen economy. A vessel of this magnitude will single-handedly encourage this development, in some cases directly, for the benefit of the entire globe.
The Sinot design team appears to have thoroughly and accurately depicted the hydrogen fuel cell powertrain on the Aqua, and to have incorporated it in a deliberate and thoughtful way to take advantage of its benefits. The design theme of water is appropriate, for the only emission from the fuel cells is ultra-pure water. Passengers will enjoy the silent, vibration free powerplant with no possibility of smoke, diesel fumes, or diesel fuel spills whether moored offshore or cruising. Combined with the on-board design elements, passengers will feel an uninterrupted deep connection to the sea that is unprecedented.
Aqua’s eventual impact cannot be overstated. Far beyond decreasing the pollution by a single vessel, or increasing the cachet of an owner looking to showcase the latest trend, the Aqua will impact an entire industry. It will support awareness, be responsible for building infrastructure, and chart a new path that others can more easily follow. Although a magnificent vessel, the action of commissioning the Aqua will not be a self-indulgent one. The owner who does this will be responsible for enabling the elimination of all maritime pollution.
A couple weeks ago a friend called me and said, essentially: “Hi Joe, hope you’re safe and happy, no corona and all of that. Hey, quick question for you: my father's brother's nephew's cousin's former roommate has made a ton in Nikola, and you know something about hydrogen, do you think I should invest too?”
]]>A couple weeks ago a friend called me and said, essentially: “Hi Joe, hope you’re safe and happy, no corona and all of that. Hey, quick question for you: my father's brother's nephew's cousin's former roommate has made a ton in Nikola, and you know something about hydrogen, do you think I should invest too?”
When Nikola’s valuation hit $20 billion in June plenty of people took notice and many articles were written that debate the current and future prospects of the company. I’m not going to evaluate Nikola in this article, nor am I going to pontificate on the (dis)connection between a corporation’s technology and its market value.
Instead I’m going to describe a simple way to determine the validity of a hydrogen technology company’s claims with respect to its core technology and its market assumptions. Because while hype can drive share prices high in the short term, I still believe that long term viability of a technology company depends on the viability of the technology itself. Whether you use this guide as a way to figure out into which company you will invest in the first place, or to decide when to exit investment in a hype-driven company, the principles are exactly the same.
Let’s start with the market. The key driver of market viability of any hydrogen related business is the cost and price of hydrogen itself. And the cost to make hydrogen is tied directly to the cost of the “feedstock”, i.e., the energy source used to make it. Today, hydrogen can be produced from natural gas (methane) in large scale reformers for around $2/kg, and the cost is directly related to the cost of natural gas. Hydrogen can also be made by splitting water using electricity in electrolyzers, in which case the cost is directly tied to the cost of electricity. At larger scales, the cost of retail electricity today leads to a hydrogen cost of around $7/kg this way.
If you’re seeing assumptions on hydrogen cost or price that are significantly lower than either of these markers, then some questions about the process and the technology are in order. There are a few ways to legitimately reduce the feedstock cost. For the reformer-production route, that can be done by capturing methane from landfills or digesters or producing it by some more exotic methods like partial oxidation of coal and crude oil. If any of these methods are used, potentially the cost can be lower so it warrants checking the cost of the captured methane or the cost of the extraction technology is needed.
For the electrolysis-production route, the most common way to achieve lower hydrogen cost is through negotiation with the electricity generator for (very) favorable rates. To reach $2/kg, however, the cost of electricity would need to be around $0.04/kWh, about 2-5 times less than retail rates. Fortunately, the dropping prices of wind and solar electricity make this viable today, but the hydrogen production company would need to either have their own solar or wind farm, or have a long-term power purchase agreement with an existing one. If this is the claim, then check: What is the status of power purchase agreements, what is the electricity rate, or what is the electricity cost from a company’s own facility?
Production cost numbers are helpful to do a first-cut evaluation of companies in the hydrogen production business, but hydrogen cost numbers are also extremely important to companies that are using the hydrogen or producing technology that uses hydrogen. Just don’t make the mistake of assuming the price point for the consumer is the same as the producer, even neglecting margin. The consumer company would only get this price if it were located next door to the production facility, could tap into their pipeline at marginal cost, and use it at its (relatively low) production pressure. Any other scenario adds cost. For example, for hydrogen dispensing stations that fuel vehicles, the cost of transporting the hydrogen to the dispensing station and compressing it to the pressure needed for these vehicles will roughly increase the cost of the hydrogen produced at the plant anywhere from double to 10x. So be wary if a consumer company, or company selling hydrogen-consuming technology, is claiming a hydrogen purchase price less than $6/kg. They would either have to (a) be located next door to the production facility and able to use the hydrogen directly at low pressure, or (b) have a way to reduce the feedstock cost at the production side. In which case questions need to be asked about exactly how they are doing this.
Which leads to the second part of this article, assessing the core technology. Inevitably, a company claiming a much lower hydrogen cost will have a unique “innovation” enabling this advantage. Over the 20+ years since I started work in hydrogen years I’ve been subjected to all kinds of pitches and claims about “new” and “innovative” ways to make cheap hydrogen and have yet to see any of them come to fruition. The most common claim revolves around drastically reducing or eliminating the feedstock cost. The second is a convenient or ignorant neglect of some of the processes and/or process costs to produce and distribute the hydrogen. How can we separate truth from fiction?
Hydrogen is a form of energy, so from a technology analysis point of view it makes sense to start with an energy balance. This is simply an accounting of the energy needed to make the hydrogen, which has to equal the energy of the hydrogen that was made. It’s sort of like adding up expenses and income on a balance sheet, and making sure they match. We can do this with energy because energy can never be created or destroyed, it can only change forms. So if we have 100 energy units of natural gas coming in, we’d better have 100 energy units of hydrogen (and/or something else) going out.
Let’s apply this to an example. I recently saw news about a company that is “creating free hydrogen” from underground for “less than $0.65/kg.” I became suspicious, as always. Did someone discover a reservoir of hydrogen underground – never known to occur naturally on earth? Because besides that, the hydrogen has to be made from something. In other words, we have 100 energy units of hydrogen coming out but where are the 100 energy units going in? More details from the company describe how they inject oxygen-enhanced air into an underground reservoir containing hydrocarbon “gases, coke, and heavier hydrocarbons” which are then oxidized via in-situ combustion. The byproduct of this combustion is reacted with water and produces hydrogen and heat in a similar way to a conventional natural gas reforming process. Aha! The feedstock here is actually the hydrocarbon fuels below the earth, and the energy equation makes sense: 100 energy units of fossil fuels goes to 100 energy units of hydrogen and heat. Pricing-wise, $0.65/kg is 33% of our $2.00/kg rule of thumb, so presumably the company has access to the fuel for around 33% of the cost of natural gas. Although I don’t quite agree with the marketing jargon “free hydrogen” and “completely clean and green”, it appears the technology is legitimate. The cost of the injection and extraction infrastructure and the cost of the fossil fuel resource just needs to be checked to make sure this is not Hype.
A different hydrogen production company claims (according to their materials) to harness the powerful forces observed in nature to produce hydrogen anywhere from water on-demand without the use of chemicals or electrolysis, at cost-competitive prices. Sounds exciting, so let’s check the energy balance: 100 energy units of “powerful forces” goes to 100 energy units of hydrogen. With no additional details given on the source of energy, we don’t have enough information to evaluate either the technical claims nor the market viability. Verdict: Hype – I’ll pass and re-evaluate if more information becomes available.
There are many more nuances to assessing a market opportunity besides hydrogen cost, and other tools to evaluate technology than an energy balance. But hopefully, with a few benchmark numbers and a quick way to check the most common claim of technological innovation, you can wade through the Hype and find some targets worth spending time getting to know further. For anything deeper, shoot me a note and I’ll give you my take!
]]>Consider that for a minute. You can take a clean, non-toxic substance and convert it to pure water, and in the process get electricity. Or in reverse, you can take pure water, add electricity, and make pure hydrogen. You can do this at home – or, actually anywhere – and create a fuel that you can use where you don’t have electricity, like in your car. It seems too good to be true. Why are we not using it more?
There are two issues with hydrogen. The first is it has a profound image problem. In the public’s mind, hydrogen is associated with spectacular displays of “energy gone wild” such as in the Hindenberg disaster and with fusion bombs (commonly misnamed “hydrogen bombs” even though they do not contain hydrogen, only hydrogen isotopes). Another day I’ll address this in more detail along with other safety considerations on this fuel.
The second issue, and the one we’re going to look at today, is that hydrogen is very difficult to contain in small spaces. From a safety perspective this is a good thing, because once it reaches free air it immediately zooms upward as fast as possible, leaving no traces around to (literally) flare up into problems. But to store hydrogen to use later, such as in a car, this means it takes up a LOT of space. To put this into perspective, let’s say we wanted to store hydrogen in a basketball, which is normally inflated to 8 psi. And let’s say we want to store the amount of hydrogen that equals the same amount of energy in 1 gallon of gasoline. To do so, our hydrogen-filled basketball would need to be over 8 feet in diameter! This is clearly a problem for any kind of transportation application such as a car, truck, ship, or airplane.
Why is hydrogen so darn big the first place? At the atomic level, hydrogen the molecule is made up of two hydrogen atoms, which is why we write “H2” instead of just H, and it contains two protons and two electrons. The shape of the molecule is simple, just like a dumbbell where the ends are the protons. More complex molecules have different shapes, like the open-triangle of H2O, or the tetrahedral of methane (CH4). When you start adding different elements and shapes, the molecules can become “polarized” like a magnet, and also get tangled up easier. But hydrogen is so simple that it is not polarized and it cannot get tangled. In short, it does not like being next to its neighbors. And like kids at a 7th grade dance, it needs a lot of external help to overcome its repulsion.
Over the years, many creative ideas have been used to solve this problem. These include a good DJ, dim lighting, and… oh wait I was talking about hydrogen. To reduce the size of hydrogen, one way is to increase the pressure in our theoretical hydrogen basketball. For example, today’s hydrogen fuel cell cars store hydrogen in thick carbon fiber tanks at 10,000 psi. If we had a magic basketball that could hold 10,000 psi without bursting, it would end up being about 15 inches in diameter. Not bad! But this comes at a large cost because instead of a magic basketball we would need a highly-engineered thick carbon fiber tank (making our basketball more like 19 inches in diameter), and it also takes quite a bit of energy and machinery to get the hydrogen up to 10,000 psi.
Another solution is to turn hydrogen into a liquid. Chemistry magic happens when substances turn into liquids. The molecules lose so much energy during this process that they slow way down and end up getting much closer together. Going back to the previous example basketball, if we could fill the basketball with the same amount of hydrogen as before, only now it’s a liquid, it would be just over 12 inches in diameter, about half the volume as before, without any added pressure.
However, liquifying hydrogen is an even more intense process than pressurizing it to 10,000 psi. Hydrogen doesn’t become a liquid until it is cooled down to -423 °F, just 36 ° above absolute zero. And unlike propane, it will not automatically liquify when pressurized. Once it becomes a liquid, adding just a little heat will cause it to boil into a gas again, so the tank needs to be insulated with a vacuum and layers of so-called “super-insulation”. This is even more complex than a high-pressure carbon fiber tank, but with similar cost and volume penalty. Liquifying hydrogen requires special turbomachinery to get it so cold, and this uses a lot of energy: the energy required to liquefy hydrogen is 1.5 to 2-times that of compressing it to over 10,000 psi. When added to the energy to create the H2 in the first place, this means the total energy required to create LH2 is about 10% higher than that to create compressed H2. This higher energy input typically results in a corresponding 10% higher cost per kg of LH2.
Despite this energy penalty – and resulting cost increase – of producing LH2, it is still the fuel of choice for many applications. As illustrated above, hydrogen stored as a liquid in one tank would be about half the volume as that stored as a gas at 10,000 psi in another tank – including the volume of the tanks themselves. Weight is another issue. A tank of 10,000 psi compressed hydrogen weighs nearly 3-times more than a tank of the same amount of hydrogen in liquid form.
But perhaps the most important distinction between compressed gas and liquid hydrogen storage is the ability to scale. It is more and more difficult to make larger compressed hydrogen tanks. The stresses from the high pressure require thicker and thicker walls. Eventually it becomes prohibitive. The largest commercially-available compressed hydrogen tanks hold less than 20 kg. This works fine for applications which don’t use a lot of hydrogen, such as forklifts and cars, but anything more than this requires multiple tanks piped together in an array. While an array of many tanks can function as well as a single tank, there is a significant increase in the overall volume of the array because of unused space between tanks. In one example of a commercially-available array of eight hydrogen tanks at 5,000 psi (a common storage pressure for heavier-duty applications), the array’s volume is nearly twice as big than if the gas could have been stored in a single tank.
LH2 tanks have the reverse trend. As an LH2 tanks gets larger, the insulating layer around the tank takes up a smaller and smaller portion of the overall volume. While inefficient at storing small amounts of hydrogen, this allows them to store massive quantities in a single tank, such as the 100 ton (100,000 kg) tank at Praxair’s LH2 production facility in Ontario, CA, or the 380 ton tank planned for NASA’s Kennedy Space Center. Coming back down to earth, LH2 storage tanks for industrial facilities are commonly in the 500 to 2,000 kg range.
The quantity that can be transported by truck is an important result of this scaling difference. While LH2 tanker trucks are commonly sized between 3,000 to 4,000 kg each, the largest truck trailer of compressed hydrogen (with multiple tanks in arrays) carries 880 kg, and most carry just 250 kg. That means that, at best, it takes more than three truckloads of compressed hydrogen to equal a single truckload of LH2, and at worst the ratio can be over 10:1. Every truck trip adds a significant amount of energy use to the overall energy requirement of the fuel. It has been shown that for a usage facility more than just 50 miles away from a production facility, the energy savings of trucking liquid hydrogen more than makes up for the energy penalty required to make it.
All in all, the choice between compressed hydrogen and liquid hydrogen should be made with careful consideration of the usage. For mobile applications this is, at the simplest level, a consideration both of the available volume and weight on-board, and of the consumption rate. At the ends of the spectrum this is a simple analysis. A forklift requires 2 kg to last an 8-hour shift, and at this size an LH2 tank would be too large because of the required insulation layers. Case closed, has to be compressed gas. At the other end, a cargo ship needs to store 60 tons of hydrogen to last the 12-day journey across the Atlantic ocean. The corresponding compressed gas array is much too large for this, so the choice must be liquid. Done. But in many cases this becomes a tradeoff analysis.
For example, let’s look at a 600-passenger tourist boat that uses about 200 kg per day. The boat has sufficient space for about 260 kg of compressed gas at 5,000 psi, or in the same space it can fit about 1,050 kg of LH2. Compressed gas will work, and we know that compressed gas is likely going to be about 10% cheaper than LH2, so do we go with that? Looking a little deeper, going with this option means that it must be refueled every day, but with 1,050 of LH2 on-board the refueling could be spaced out to every four or five days. Today’s delivery logistics are structured such that there are two components to the cost: (1) the cost of the hydrogen and (2) the cost of the truck. In this case, the four- or five-times higher delivery cost will certainly dwarf any cost savings of the hydrogen itself, resulting in a higher overall cost to the operator.
There are other, more subtle considerations as well. Where in the world does this need to be refueled? While hydrogen is made just about everywhere in the world, liquefaction facilities are relatively uncommon. Currently there is a robust, 300 ton/day LH2 production and distribution network in North America (built up primarily to support the US space program), but this is not the case around the world. The EU has a small amount (26 ton/day) as well as Japan (35 ton/day) but in the rest of the world the availability of LH2 is nearly non-existent.
Another consideration is safety. While both forms of the fuel have decades of experience developing and using safe handling practices, in some applications the high pressure of compressed gas is a concerning hazard, in others the cold temperatures of cryogenic liquids is a concern. Long term storage is another factor. Even with super-insulation, LH2 tanks absorb a small amount of heat that boils the hydrogen. Some of this can accumulate within the tank, but if more time passes and the tank is not used, it must be slowly released into the atmosphere. After a long time of non-use, all of the LH2 in the tank will boil away. For applications that are sitting unused for long periods of time, compressed gas may be the only choice.
The options for storing hydrogen are not limited to liquid or compressed gas, but these are by far the most common today. Other ways to store hydrogen include reversible (rechargeable) materials such as chemical hydrides, sorption materials, and metal hydrides. There are also substances that are made from hydrogen, such as ammonia and synthetic methane, where hydrogen is stored as a compound that is irreversibly broken apart later for use. I’ll address these in a subsequent column.
When it comes to selecting the method of hydrogen storage today between LH2 and compressed gas, a rule of thumb we’ve developed through experience over the years is that applications requiring less than 200 kg on-board are probably better suited for compressed gas, while those over 500 kg are more likely to work best with LH2, notwithstanding the other considerations discussed above. Between 200 kg to 500 kg the choice becomes more complicated but can become clear with a deeper understanding of the tradeoffs.
The fundamental chemistry of hydrogen helped us to understand why hydrogen is such a “volumetrically-challenged” fuel. Compression and liquefaction are the two primary ways to reduce hydrogen’s volume to manageable proportions. Each method has its pros and cons, and there is not one solution for everything. An understanding of the tradeoffs allows us to make the best decision and enables us to use this remarkable fuel across a wide variety of applications, from small forklifts up to the largest ships.
]]>No carbon means no carbon dioxide. No fossil fuels. No pollution, and no global warming. This is fantastic: we can create a fuel – pure hydrogen – that is 100% renewable and sustainable!
]]>No carbon means no carbon dioxide. No fossil fuels. No pollution, and no global warming. This is fantastic: we can create a fuel – pure hydrogen – that is 100% renewable and sustainable!
We also see that hydrogen from electrolysis is simply a way to convert electricity to another form. Electricity by its nature is fluid, it’s dynamic, always moving. The only way we can directly save it for later is with batteries. But batteries, even the most advanced kinds today, can reach immense sizes and costs to store the amounts of energy needed for industrial or power generation applications. Hydrogen is a way to store electricity in a much lighter, more compact, and – key point – more transportable form. This is why hydrogen is sometimes called an “electrofuel.” The image of hydrogen as stored electricity is a powerful and useful one when trying to understand its importance and potential.
We have to be careful, though, because the electricity to make hydrogen via electrolysis has to come from somewhere, and if we use electricity created from fossil fuel power plants we haven’t really gained much; it kind of defeats the purpose. What we want to do is create electricity from a 100% renewable and sustainable source, and that source is the Sun. The photons in sunlight can make electricity directly though solar photovoltaic (PV) panels. The heat of the sun causes temperature differences on the earth’s surface leading to wind, which in turn also leads to waves; it evaporates water and causes precipitation which enables hydroelectric power; and it can be focused to boil water and make electricity through generators powered by steam.
Sunlight and wind occur everywhere on earth in varying degrees, waves happen everywhere there are bodies of water, and hydroelectric power is available wherever there is precipitation and differences in elevation. This is another important distinction from fossil fuels, which are concentrated in various underground deposits, because it means we can make renewable electricity – and thus renewable hydrogen – anywhere on the globe! And compared to the machinery and complexity needed to extract oil, gas, or coal from the ground and process it to usable fuel, solar energy is so easy and simple to capture that a two-year old can create electricity – and thus renewable hydrogen – just by holding a small solar panel out their window.
Creating hydrogen everywhere in the world is not just possible, but desirable. Hydrogen production facilities that use fossil fuels, as we saw above, are based on chemical reactions at high temperatures. These kinds of plants are most efficient – both from an energy standpoint and a cost one – when they are very big. Combine that with the fact that over 90% of hydrogen produced today is used by just two industries, crude oil refining and ammonia production, which also needs to be done in very large plants, and it starts making sense why today’s hydrogen production is limited to fossil fuel-based methods in a few large facilities.
But as we transition to the widespread use of hydrogen for industry, for homes, and for transportation we now have the option to create hydrogen anywhere, by anyone. Imagine every house or apartment complex capturing solar energy and using small electrolyzers to convert that to hydrogen, which you then use to fill your car. The scenario can be repeated at businesses, manufacturing plants, train depots, farms; the list goes on and on. If you create more hydrogen than you need, you can sell it to your neighbors for some extra income.
It’s not just individuals who can benefit from this. In our work over the past few years we have had discussions with municipal and national governments around the world about strategies to combine their solar energy resources with hydrogen production to not only eliminate the need for fossil fuel imports, but to also turn an energy importer into a clean energy exporter. There are immense beneficial implications of this scenario for governments.
Because electrolyzers do not rely on high temperature chemical conversions, they are not affected by economies of scale and thus enable these visions to occur. It becomes much more efficient from a cost and energy perspective to create the hydrogen where it will be used, and this also allows us to capture more of the solar energy given to us (for free) every day by our Sun.
Uh-oh, I can hear the entrepreneur in me laughing. “It seems like the engineer has just concluded that hydrogen not only can, but should be found under every rock in the world,” he smiles. “Can we keep marketing hydrogen as, ‘the most abundant element in the universe’ then?”
I’m not sure I’m ready for that quite yet. Let’s try: “Hydrogen enables the world to completely remove fossil fuels from its power mix and rely exclusively on the sustainable, renewable power of the sun to meet all of our energy needs.”
The marketer groans…
]]>As an entrepreneur, this brilliant bit of marketing makes me smile. It’s a true statement – about 90% of atoms in the universe are hydrogen, according to scientists who know that kind of thing. And it makes people think that it's as easy as turning over the nearest rock and, “Oh! Look at the hydrogen! Quick, put it in your tank and let’s be off with this amazing fuel!”
As an engineer, the statement makes me groan – loudly, if you believe Mr. Motlow and Mr. Kemper. Because the hydrogen in the universe is either inaccessible (nobody has figured out how to mine the sun yet), or is already tied up in compounds such as water (H2O, 67% hydrogen atoms) and methane (80%), and makes up part of everything from tigers (60%) to Levi’s jeans (50%). When it comes to using hydrogen as a fuel, that’s a problem. We can’t just put water or jeans in our gas tanks and expect the car to go. We need to pull the hydrogen out of where its hiding, separate it, and use it by itself. That’s not easy, but fortunately people have figured out a few ways to do this.
99% of all hydrogen made today comes from fossil fuels, specifically natural gas (76%) and coal (23%). Fossil fuels are essentially different combinations of carbon and hydrogen, so it is just a matter of separating the hydrogen from the carbon.
To produce hydrogen from methane (CH4), which is what natural gas is mostly made of, and water (H2O), you mix them together and heat them up to around 900 °F in a special tank called a reformer. At this temperature, and with the help of a special material called a catalyst, both the methane and water break apart, then recombine to make hydrogen (H2) and carbon monoxide (CO). Although a decent fuel by itself, carbon monoxide is quite poisonous, so this and some more water is passed through another reactor called a shift reactor which makes more hydrogen and turns the carbon monoxide into carbon dioxide (CO2). If all this is making your head spin, just think of it as some weird chemical square dance where everyone ends up with a different partner in the end.
Although as we saw this is a two-step process, most people just talk about the overall result and call that “Steam Methane Reforming” or “SMR” for short. The heat required for the SMR process comes from burning some extra natural gas, which releases air pollutants and CO2 (a greenhouse gas and a primary cause of climate change).
The mixture of CO2 and H2 coming out of the SMR is passed through separation equipment to get a pure stream of H2 and a stream of CO2. Today at most H2 production plants, this CO2 is also released into the air, although some newer plants are capturing the CO2.
Coal is converted to hydrogen in a similar way, but since it is a solid and a more complex molecule than methane, a simple reformer won’t work. Instead, coal is ground into fine particles and blown through a furnace with oxygen and water. What comes out is H2 and CO. And you know what happens next: this is fed into a shift reactor to make hydrogen and carbon dioxide. Except this time, because coal has much more carbon in it than methane does, you get about two times more carbon dioxide per ton of hydrogen produced than you do from methane, and you get more pollution and CO2 from the coal burned to provide heat for the process.
It’s understandable if all this talk of methane, coal, fossil fuels, and greenhouse gases is making you a little sick to your stomach. “Wait,” you say, “I thought hydrogen is a clean fuel. What is this, some big scam?” There are two points to remember here. The first is that is how hydrogen is made today, and the second is there is another way to make it that I think you’ll like better.
Read Hydrogen Production 102 for an overview of Electrolysis
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