Hydrogen Hype — A story of energy loss
Recently, hydrogen has been promoted as a new clean fuel. Hydrogen is predicted to be a decarbonization solution for various sectors. This potential has led multiple institutions to encourage a “hydrogen economy”, where, in the future, hydrogen is produced and transported in large quantities while utilized in a broad range of consumer segments.
How true is this?
Based on my engineering sense, I am sceptical. Likewise, many scientists, analysts and engineers who understand the nature of hydrogen view hydrogen as a very inefficient fuel. Because it is inefficient, it won’t be used unless there is no other option besides using hydrogen. Therefore, the actual use of hydrogen will be limited to a very specific sector and small volume, which is very different from the picture of a hydrogen economy.
This article represents an unpopular view. But this fact needs to be understood by the wider community, especially policymakers, so that they can prioritize the limited capital we have for fighting climate change more efficiently.
The main message of this article is:
Hydrogen is a very inefficient form of energy. You won’t use it unless absolutely needed.
Visualizing the energy flow
Energy is a flow. It flows from the source of energy to another form. Humans extract energy from nature by converting the primary form of energy (like the sun, wind, chemicals in coal, etc.) into a useful energy form (heat, electricity, motion, etc.). Whenever energy is converted from one form to another, there are always losses. The best way to visualize the energy flow and the loss is by using a Sankey diagram.
This is an example of energy flow in our current electricity system. Assuming the original energy contained in coal is 100 units, the electricity delivered to houses is only 38 units since the remaining is loss due to conversion and transmission processes. Say you are using the electricity for lighting, depending the type of lamp you have, the light you enjoy for reading is just 2–29 units of energy.
Note that coal comes from the photosynthesis of plants millions of years ago, which has an efficiency of less than 1%, from the sun to biomass matters. The sun-to-electricity conversion via coal is actually very, very low. Thank god we are lucky enough to live in this era to skip the million years of coal forming by directly mining it.
System efficiency by renewable energy
The new invention of power plants powered by renewable energy improves our way of extracting energy much more efficiently. Solar PV can directly convert the sun’s energy into electricity, a form of energy that we like the most.
It may need to account for storage, like a battery, to stabilize the output. The battery is also efficient storage; on average, it has 80% round trip efficiency.
Why does efficiency matter?
In this article, I will talk about efficiency a lot. If you’re not an engineer, you may wonder why putting a lot of attention on efficiency. Isn’t it ultimately cost? Yes, you are right, cost is the ultimate comparison, let’s discuss cost in the next article. However, remember that efficiency is a significant factor that brings down costs; this principle applies to all business processes.
It is more prevalent if you look at the energy industry. Throughput efficiency is one of the most crucial parameters that scientists and engineers have been working to press down near the theoretical minimum level. Try to look at any powerplant or energy-consuming equipment. What has been improving since the Industrial Revolution is efficiency.
Hydrogen production
Now, what about hydrogen?
I will discuss it step by step. Let’s start with the production.
There are various ways of producing hydrogen (you know, the many colours of hydrogen). In this article, I will only talk about hydrogen from electrolysis. This process is 50–70% efficient, meaning that from 100 kWh going into the electrolyzer, only around 60 kWh worth of hydrogen is produced while the other 40 is lost as heat to the environment. In the common term, it is 50 kWh/kg hydrogen (1 kg of hydrogen has an internal energy of 33 kWh or 120 MJ — LHV) (read further IRENA, 2020).
Starting from now, the Sankey diagram will begin with electricity made from renewable or other clean energy sources.
Hydrogen pipeline
The most common mistake people make is to stop at this point, at hydrogen production. This is wrong because the process doesn’t stop here. Unless you’re making hydrogen at your factory, the transportation process from where it is made to the point of consumption is definitely needed.
Hydrogen transportation is the tricky part. The method/logistic scheme will differ depending on the route (short distance, overseas, small or large volume).
The most efficient way of transporting it is via pipeline. A hydrogen pipeline will be economically viable if it satisfies the following conditions: 1) the hydrogen volume/flow rate is huge, 2) the distance is less than 1000 km. An example of this is transporting bulk amount of hydrogen from a country with abundant RE (e.g., Spain) to neighbouring/nearby countries with high demand (e.g., Germany).
For the gas to flow along the pipe, hydrogen gas from the electrolyzer plant needs to be compressed. Compressor stations are usually installed at intervals of 100 km or more. I couldn’t find a reference for the hydrogen compressor’s performance, but learning from the natural gas industry, gas compressors along pipelines consume approximately 3 to 5% of the transported gas (read further: Elshiekh, 2015).
Hydrogen shipping
What about importing hydrogen from overseas? Shipping is the answer. But this is a very energy-inefficient process.
Due to hydrogen having very low density (taking a lot of space but containing a small amount of energy), it needs to be compacted to make logistic viable.
There are various ways of compacting hydrogen gas:
· Compress it into 700 bar,
· Liquify it to -253 degC, or
· React it with another compound that holds hydrogen molecules into a more compact size.
Apparently, for hydrogen shipping, the last method is the most viable one. Hydrogen needs to be converted into ammonia (NH3 — one nitrogen atom holds 3 hydrogen atoms), which is much easier to handle than compressed or liquid hydrogen. Ammonia liquefy at only -33 degC and is currently a globally traded product for making fertilizer. This task is much preferred than liquifying hydrogen close to the universe’s coldest temperature (-253degC is just 20 degree above the absolute temperature). Doing so will eliminate 30–40% of the stored hydrogen energy (read further: DOE, 2009).
Converting hydrogen into ammonia via the Haber-Bosch process takes energy. Additionally, nitrogen, obtained from separation from the air, is needed, adding to the energy loss. After the reaction, liquifying ammonia is also taking energy. Ammonia made by electrolysis and the Haber-Bosch process takes 9–10.5 MWh of electricity to produce 1 ton of ammonia, equivalent to 56–64% conversion efficiency.
Still about hydrogen shipping
But that’s not the end! Shipping needs fuel to sail. Ideally, it utilizes the green ammonia in the cargo rather than bunker fuel, which is highly polluting.
Moreover, any cryogenic storage experiences an effect called “boil-off”. Because of the heat leakage at the storage tank wall, liquid ammonia constantly evaporates. Boil-off rate of liquid ammonia is around 0.04% per day. If the sailing trip takes 30 days, more or less 1% of the cargo is lost due to boil-off. The reason why ammonia is preferred to liquid hydrogen is exactly because of this boil-off issue. Liquid hydrogen boil-off at a rate of 1–5%. Imagine how much it left after one month across the ocean (read further: Cryoworld BV, 2019).
The boil-off gas must be released from the tank to avoid overpressure. It is either wasted, fed to the ship engine, or re-liquified (the latter consumes energy, obviously).
Upon arrival at the destination port, ammonia cannot be directly utilized unless by a fertilizer factory. Ammonia must be converted back to hydrogen via a cracking process to separate the nitrogen from the ammonia molecule. As you guessed it, it takes another bulk of energy. There is limited reference since the technology is evolving; the only reference I found states 76% efficiency of ammonia to hydrogen (read further: Brown, 2017).
You may already realize that hydrogen shipping will tremendously waste energy along the way.
Trucking to smaller consumers
What about a smaller volume? It will be trucked, as it already does for the existing hydrogen refuelling station for fuel cell vehicles.
Hydrogen will be filled into tubes/tanks. Because hydrogen gas in ambient pressure has a very low density, it should be compressed into 350 or 700 bar. Some stations generate hydrogen onsite, but it still requires compressing to that level to store the hydrogen. Also, hydrogen is stored in this pressurized form in every fuel cell vehicle.
Compression to this level of pressure takes a significant amount of energy. Theoretically, it takes only 1.4 kWh to compress 1 kg of hydrogen to 700 bar. However, real consumption is much larger, 3.2 kWh in the actual refuelling station. This is due to the requirement of overpressure to 880 bar and cooling the gas afterwards. In relative value, 3.2 kWh equates to the 10% of the hydrogen energy content (read further: DOE, 2009).
Final consumption, there are still energy losses
Are we done? Yes, if you’re considering only up to hydrogen received by consumer.
But! Hydrogen is not something you can consume directly (except for specific purposes like making fertilizer or flying a Zeppelin). Hydrogen is basically a chemical compound containing chemical energy (similar to coal, gas, or gasoline). Electricity, heat, or motion are the desired energy forms useful for humans. As you guess it, another conversion is necessary and there you go, another energy loss.
1. Hydrogen for heating
Converting hydrogen into heat is more straightforward: burn them like natural gas. The current players in gas distribution and boilers are betting and spending a lot to promote hydrogen piping and boilers. Burning anything is theoretically 100% efficient since the definition of energy content of any chemical compound is the “heating value”.
Let’s make a distinction, low (under 200 degC) vs high temperature heat. Large chunck of heat demand is residential/building thermal comfort. Anyone proposing hydrogen for residential heat never studied the first course in the energy world: thermodynamics.
There is a commercially available device called heat pump (usually one package with air conditioning for cooling). This device is 300% efficient, which makes burning hydrogen for low-temperature heat is mindless idea.
2. Hydrogen for power generation
Converting hydrogen into electricity requires a fuel cell (electrolyzer runs in opposite direction). This device is 50–60% efficient (read further DOE, 2015).
Alternatively, novel way of generating electricity from hydrogen is by using a gas turbine. By the way, this technology is the last hope of big turbine manufacturers, like GE, Siemens, and MHI, as the turbines’ sales are declining since fewer are building coal or gas power plants. The hydrogen turbine test from Kawasaki shows 40% efficiency. At best, it will reach the highest efficiency for combined cycle gas turbines, around 55% (read further: Kawasaki, 2023).
Japan is a particularly interesting case. Japan plans to import hydrogen and then use it to replace LNG for power generation (h2-view, hydrogeninsight, ammoniaenergy). As an engineer, I find this plan painful to hear; it is just against thermodynamics law.
Why would you burn hydrogen? Making it is a highly energy-intestive product. Burning guarantees another energy loss.
3. Hydrogen for transportation
Hydrogen is proposed to decarbonize transportation sector. The best converter for generating motion is an electric motor, which is today highly efficient at 90% if run at optimal speed. So, hydrogen is first converted to electricity using fuel cell in any hydrogen-fueled vehiches.
Combined with fuel cells, the literature suggests tank-to-wheel efficiency of FCEV is 30–50%. This is worse than BEV, having an efficiency of up to 85%, since storing electricity in the battery is 80–90% efficient depending on its age (read further: McKinsey, 2021).
Expectation of innovation
Innovation will solve it, right? Yes, but to a limited degree.
When discussing heavy equipment, please do not put your mind in semiconductors or digital technologies. They are totally different. Progress takes time and little by little. Retake a look at the efficiency history of solar PV and gas turbine figure above: how many decades it took to raise a 10% efficiency?
Second, there is a theoretical minimum energy use; energy loss is inevitable. Energy conversion cannot be 100% efficient by the law of physics. What is terrible about hydrogen is that it is not a new technology. We have been making hydrogen since the beginning of the industrial revolution. Scientists have been perfecting the efficiency of hydrogen making. Similar to the fuel cells, it was first utilised during the space era for powering satellites.
Following figure shows the best illustration for this. Hydrogen/ammonia production is already very close to the theretical minimum and efficiency; efficiency figures has been flat in the last decades (read further: Smith, 2020).
Final thought
Here you go, the overall energy loss of the hydrogen economy considering an entire value chain from upstream production and transportation to usage by consumers.
Now compare it with direct electrification without the hurdle of converting to hydrogen as an energy carrier.
I hope it is clear for you that electrification is always superior to hydrogen, when electrification is possible.
This doesn’t mean that hydrogen won’t be used. Instead, it will be used in very specific sectors where direct electrification is not practical. Fertilizer, refinery, steel, and other high-temperature processes are good candidates. In those kinds of areas, hydrogen might be the only viable alternative.
The implication is simple: a hydrogen-based economy (for sectors that can be directly electrified) needs to build 3–5x more RE powerplants to deliver the same amount of energy to the consumer. Not to mention the infrastructure of hydrogen piping, shipping, fuelling stations, etc. With this, you can expect that the hydrogen economy will bring more expensive energy prices to consumers.
Reference
For those interested in delving into the numbers and assumptions I use, feel free to check my Excel file calculation, where you can review the references.
