The Truth about Hydrogen

This episode of Real Engineering is brought
to you by Skillshare, home to over twenty thousand classes that could teach you a new
life skill. As the world grapples to eliminate fossil
fuels from our energy diet, electric cars have seen an incredible boom over the past
few years. Last year, over one million electric cars
were sold around the world. The number of Nissan Leafs, Teslas, and other
electric vehicles in circulation worldwide is now more than three million. And while there are many brands of electric
car to choose from, there are only two choices when it comes to powering electric vehicles:
fuel cells or batteries. Both produce electricity to drive electric
motors, eliminating the pollution and inefficiencies of the fossil fuel powered internal combustion
engine. Both hydrogen and electricity for batteries
can be produced from low­ or zero ­carbon sources, including renewable energy like solar
and wind, and therefore both are being pursued by car manufacturers and researchers as the
possible future of electric vehicles. However, a great debate is being waged by
supporters of each technology. Elon Musk has called hydrogen fuel cell technology
“incredibly dumb,” claiming they’re more of a marketing ploy for automakers than
a long-term solution. In contrast, Japan has announced its intention
to become the world’s first hydrogen society, with the Japanese government and the auto
industry working together to introduce 160 hydrogen stations and 40,000 fuel-cell vehicles
by March 2021. So which is actually better? At first glance, hydrogen seems like an extremely
clever way to power a car. Compressed hydrogen has a specific energy
(aka energy per unit mass) of neary 40,000 watt hours per kilogram. Lithium ion batteries at best have a specific
energy of just 278 wh/kg, but most fall around 167 wh / kg. That’s 236 times as much energy per kg for
hydrogen. And because of its energy density and lightweight
nature, compressed hydrogen and fuel cells can power cars for extended ranges without
adding much weight, which as we saw in our last video is a gigantic road block for incorporating
the technology into the aviation industry. The designers of electric vehicles are caught
in a catch 22 with energy density and range. Each extra kilogram of battery weight to increase
range requires extra structural weight, heavier brakes, a higher torque motor, and in turn
more batteries to carry around this extra mass, This weight compounding limits how far
a battery powered vehicle can travel, until new technology can help reduce the weight
of the batteries. For hydrogen fuel cell vehicles, this weight
compounding is not an issue. Additionally, a hydrogen fuel cell vehicle
can be refueled in under 5 minutes, where a battery powered electric vehicle, like the
Tesla model S, takes over 3 hours to fully recharge. When looking at the range and refuel times
hydrogen can offer, you can see why some car manufacturers are investing in this technology. On the face of it. Hydrogen is a clear winner, but it falls behind
when we start considering the end-to-end production process. While both batteries and hydrogen fuel cells
are both forms of electricity storage, the cost differ drastically. Fully charging a Tesla Model 3 with a 75 kiloWatt
hour battery, costs between 10-12 dollars depending where you live. With a rated range of 500 kilometers, that’s
between 2 and 2.4 cent per kilometer. A great price. In a previous video, I visited a petrol station
that introduced a hydrogen pump, fed by its own on-site production facility. which used off-peak electricity to produce
hydrogen. The hydrogen from this station cost $85 dollars
to fill the 5 kg tank of the Toyota Mirais on site, which had a range of 480 kms. That’s 17.7 cent per kilometer, 8 times
the price. And here lies the problem, Hydrogen simply
requires more energy to produce. To understand the economic viability of hydrogen
let’s dig deeper into the production process. Before any hydrogen vehicle can hit the road,
you first need to produce the hydrogen, but hydrogen is not a readily available energy
source. Even though hydrogen is the most abundant
element in the universe, it is usually stored in water, hydrocarbons, such as methane, and
other organic matter. One of the challenges of using hydrogen as
an energy storage mechanism comes from being able to efficiently extract it from these
compounds. In the US, the majority of hydrogen is produced
through a process called steam reforming. Steam reforming is the process of combining
high-temperature steam with natural gas to extract hydrogen. While steam reforming is the most common method
has less energy than the natural gas that the steam reforming began with. And while hydrogen fuel cells themselves don’t
produce pollution, this process does. So if we want to assume a future scenario
with as little carbon emission as possible, this method won’t cut it. Another method to produce hydrogen is electrolysis
– separating the hydrogen out of water using an electric current. While the electricity needed for this process
can be provided from renewable sources, it requires even more energy input than steam
reforming. You end up losing 30% of the energy from the
original energy put in from the renewables when you carry out electrolysis. So we are sitting at 70% energy efficiency
from hydrogen fuel cells if traditional electrolysis is used, before the car even starts its engine. A slightly more efficient method of producing
hydrogen is polymer exchange membrane electrolysis. Using this method, energy efficiencies can
reach up to 80%, with the added benefit of being produced on site, which we will get
to in a moment. But this is still a 20% loss of energy from
the original electricity from the renewables. Some experts say the efficiency of PEM electrolysis
is expected to reach 82-86% before 2030, which is a great improvement, but still well short
of batteries charging efficiency at 99%. [1] A 19% difference in production costs doesn’t
explain the difference in costs yet, so where else are we losing energy. The next hurdle in getting hydrogen fuel cell
vehicles on the road is the transport and storage of the pure hydrogen. If we assume the hydrogen is produced on site,
like it was for this petrol station, then we eliminate one energy sink, but the cost
of storage is just as problematic. Hydrogen is extremely low density as a gas
and liquid, and so in order to achieve adequate energy density, we have to increase its actual
density. We can do this in two ways. We can compress the hydrogen to 790 times
atmospheric pressure, but that takes energy, about 13% of the total energy content of the
hydrogen itself. Alternatively we can turn hydrogen into liquid,
cryogenically. The advantage of hydrogen liquefaction is
that a cryogenic hydrogen tank is much lighter than a tank that can hold pressurized hydrogen. But again, hydrogen’s physical properties
means hydrogen is harder to liquefy than any other gas except helium. Hydrogen is liquified by reducing its temperature
to -253°C, with an efficiency loss of 40%, once you factor in the added weight of the
refrigerators and the refrigeration itself. So pressurisation is a better option at a
13% energy loss. Once the hydrogen is produced and compressed
to a liquid or gas, a viable hydrogen infrastructure requires that hydrogen be able to be delivered
from where it’s produced to the point of end-use, such as a vehicle refueling station. Where the hydrogen is produced can have a
big impact on the cost and best method of delivery. For example, a large, centrally located hydrogen
production facility can produce hydrogen at a lower cost because it is producing more,
but it costs more to deliver the hydrogen because the point of use is farther away. In comparison, distributed production facilities
produce hydrogen on site so delivery costs are relatively low, but the cost to produce
the hydrogen is likely to be higher because production volumes are less. While there are some small-scale, on-site
hydrogen production facilities being installed at refuelling pumps, such as the station mentioned
in the last hydrogen video. until this infrastructure is widespread, we
have to assume that the majority of hydrogen is being transported by truck or pipeline,
where we know that energy losses can range from 10% up to 40%. In comparison, assuming that the electricity
that we use for charging the batteries comes completely from renewable resources (like
solar or wind), we just have to consider the transmission losses in the grid. Using the United States grid as a reference
for typical grid losses, the average loss is only 5%. So in the best case scenario for hydrogen,
using the most efficient means of production and transport, we lose 20% of energy during
PEM electrolysis, and around 13% for compression and storage, amounting to a 33% loss. In other systems, this could be as much as
56%. For battery power, up to this point, we have
lost just 6% to the grid and recharging. Bringing our best case efficiency difference
to 27% and our worst case to 50%. The next stage of powering electric vehicles
is what is called the tank to wheel conversion efficiency. For hydrogen fuel cell vehicles, once the
hydrogen is in the tank, it must be re-converted into electric power. This is done via a fuel cell, which essentially
works like a PEM electrolyser, but in reverse. In a PEM fuel cell, hydrogen gas flows through
channels to the anode, where a catalyst causes the hydrogen molecules to separate into protons
and electrons. Once again the membrane only allows protons
to pass through it, while electrons flow through an external circuit to the cathode.This flow
of electrons is the electricity that is used to power the vehicles electric motors. If the fuel cell is powered with pure hydrogen,
it has the potential to be up to around 60% efficient, with most of the wasted energy
lost to heat. Like hydrogen fuel cells, batteries also come
with inefficiencies and energy losses. The grid provides AC current while the batteries
store the charge in DC. So to convert AC to DC, we need a charger. Using the Tesla Model S as an example, its
peak charger efficiency is around 92%. The Tesla model S runs on AC motors; therefore,
to convert the DC current supplied by the batteries into AC current, an inverter has
to be used with an efficiency of roughly 90%. Additionally, lithium ion batteries can lose
energy due to leakage. A good estimate for the charging efficiency
of a lithium ion battery is 90%. All of these factors combined lead to a total
efficiency of around 75%. However, hydrogen fuel cell vehicles also
have some of these same inefficiencies. Any kind of electrolysis requires DC current,
and therefore, a rectifier will be required to convert the AC current from the grid to
DC. The conversion efficiency here is 92%. We also need to convert the DC current produced
by the fuel cell to AC to power the motor through an inverter with an efficiency of
90%. Finally, the efficiency of the motor must
be considered for both fuel cell and battery powered vehicles. Currently, this is around 90-95% for both
of them, which is amazing when you consider that internal combustion engines running on
petrol have an efficiency of only around 20-30%. If we add up all these inefficiencies and
compare current generation batteries, to the best and worst case scenario of current gen
hydrogen. We can see how they measure up. Even with the BEST case scenario. Not taking into account any transport due
to onsite production, and assuming very high electrolysis efficiency of 80%, and assuming
a HIGH fuel cell efficiency of 80%, hydrogen still comes out at less than half the efficiency. The worst case scenario is even worse off. So while you may be able to go further on
one fill-up of hydrogen in your fuel cell vehicle over a battery powered electric vehicle,
the cost that is needed to deliver that one fill up would be astronomically higher compared
to charging batteries due to these energy losses and efficiencies. Based on our worst case scenario, we would
expect the cost per kilometre to be about 3.5 times greater for hydrogen, but as we
saw earlier it’s actual 8 times the price. So additional costs of production unrelated
to efficiencies are obviously at play. The cost of construction of the facility is
one and the profit the station will take from sale is another. For now, these inefficiencies and costs are
driving the market, where most investment and research is going into battery powered
electric vehicles. So which wins? Both are equally more green than internal
combustion engines, assuming equal renewable resources are used to power them. Fuel cells allow for fast fill up times and
long ranges; a big advantage. But battery powered vehicles might catch up
in range by the time there are enough hydrogen stations to ever make fuel cell vehicles viable. While fuel cells are efficient relative to
combustion engines, they are not as efficient as batteries. They may make more sense for operation disconnected
from the grid or as we saw in our last video using hydrogen for planes actually could make
a lot of sense, but once again that’s a topic for another video. For now, battery powered electric vehicles
seem to be the sensible choice going forward in the quest for pollution free consumer transport. As battery-powered cars become more common,
we’re also starting to see self-driving cars become the norm. If the job of driver is slowly automated away
and consumers have a bunch of free time to read or watch online video, it may be wise
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skill to gain. As usual thanks for watching and thank you
to all my Patreon supporters. If you would like to see more from me, the
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