Few thoughts on Energy

New ways to harness energy (collect, transform, store, distribute, consume) have transformed many industries. Look at what has happened with electricity storage through lithium-ion batteries that have enabled the smartphone industry, not to mention the car industry undeniably shifting towards EV vehicles. Hydrogen is more and more referred to as the future of clean energy while the "green" virtue of diesel over gasoline seems to have faded after a few regulatory/compliance scandals.

This article isn't meant to replace the voice of many experts in this field (I am always inspired by the analysis of Jean-Marc Jancovici for example), but to highlight a few interesting data points and metrics I don't often see discussed and that are quite fundamental.

Energy metrics and density

Not speaking of cost or general availability, the graphic below shows the energy density per litre or kilogram for different energy sources/materials in Mega Joule (MJ).

Before I comment on this graphic, let me give you a sense of what Mega Joule mean: to simplify, 1 Joule is equal to the force required to move 1 kg over 1 (linear) meter in 1 second. The Joule metric is particularly interesting because it can be used in several contexts and it gives you a sense of magnitude for different scenarios:

• kinetic force: 1 Joule = 1 Newton per meter or Nm (or more precisely, the force which gives a mass of 1kg an acceleration of 1 metre per second squared). It's the product of mass (kg) x acceleration (m/s^2). For example, lifting an apple (~150 grams) by one meter takes 1 Joule. Another way to say this is that to "fight" the effect of gravity, you need ~10 Joules/second to sustain a mass of 1 kg above the ground (earth gravity acceleration is 9.8 m/s^2).
• electricity: 1 Joule = 1 Watt per second (Watt is the result of voltage multiplied by the amount of current that goes through an electrical circuit or Volt x I(ampers)). 100 Joules will light up a ~100W bulb (or a 110V bulb using 1Amper) for one second. Your house's electrical bill will often reflect the amount of kilo (1000) Watts per hour you use (kWh). Confused? Ok, let's take an example: 10 hypothetical "aways-on" 100W bulbs for 1 month represent 10x100x31x24x60x60/1000^2=2678 mega (1000^2) Joules (MJ) or 2678x1000/(60x60)=743 kWh. So there is a x3.6 factor between kWh and MJ. In California you'll pay ~20 cents per kWh so these 10 "always-on" hypothetical bulbs will cost you 148$ per month. For comparison, a Tesla will hold a ~100kWh lithium-ion battery or 3.6x10^8 Joules. At ~4.2 miles per kWh, you'll get a bit more than ~300 effective miles. A full Tesla charge will cost 100kWh x .20$=20$ in California - less than 10 "always-on" bulbs for a month and less than a gasoline car for the same distance (~5$/gal x 300miles / 23 mpg = $65). So 2 take-away: (1) the cost of energy for an EV vehicle is ~1/3 cheaper than its gasoline equivalent to travel the same distance (2) charging a modern EV ~7 times in a month will allow you to travel ~2000 miles and cost as much as paying for 10 "always-on" 100Watts bulbs.
• heat: 1 joule is the energy needed to raise the temperature of a mass by 1 degree Celsius and it's a function of the type of material. For water, it's 4.18J/gC (or 4.18 Joules per gram per degree Celsius). For example, a 50-litre water heater (for water 1liter=1kg) will need 4.6MJ to raise water temperature from 15C to 37C (4.18*1000*50*(37-15)/1000^2=4.6MJ). Also, food is often rated based on its calorie "effect" on human bodies and guess what: 1 calorie = ~4.2 Joules (same as the amount of energy needed to raise 1L of water by 1 degree).

Ok, enough Physics (or almost) and back to the graphics:

• First, you'll notice that hydrogen is the most dense source of energy (no wonder why it's used for rockets to combat gravity), particularly in its liquid form (which happens when the gas is brought down to -253 Celsius!). Hydrogen isn't cheap to produce (i.e., as opposed to extracting crude oil) but its density is unmatched. Most hydrogen vehicles today use standard 700-bar tanks - or 700kg of force per square meter which is as much pressure as diving 70 meters down (the Toyota Mirai is one of the few successful consumer hydrogen car ever produced):

So the material stress is intense and that is why hydrogen tanks are often reinforced with carbon fiber layers and they can expand with temperature yet stay resistant.

Now, what you need to realize with hydrogen energy is that (1) you'll need to mix gas or liquid hydrogen with oxygen to produce emission-free energy (apart from water) and use a "fuel cell" to convert the chemical reaction into electricity (in the case of rockets like Ariane, the mixture is "simply ignited" and heat coming from the explosion used to sustain the reaction). Because hydrogen cars are NOT H-bombs, they use "fuel cells" to gently produce electricity and hence need electric motors. So hydrogen cars are essentially electric vehicles but do not use standard battery storage technology (2) a 700-bar hydrogen gas tank is 3-4 times the volume of an equivalent gasoline tank - so you'll need space (3) on the pro side of things, the mixture of hydrogen and oxygen only produces a bit of water (a reaction that is actually used by space ships). Saying it's "carbon-free" is inexact because a lot of carbon is needed to not only produce hydrogen but also to build the storage tanks (that have several carbon layers)...

• Second, the graphic tells us that many forms of natural gas remain one of interesting energy sources (no wonder it's the subject to geographical tension like the Ukrainian war). It is a great compromise between energy density, cost and transportability (via trans-country pipes)
• Third: then comes traditional gasoline. Diesel is almost as good as gasoline and methanol is a bit less dense. The graph doesn't really talk about all the conversion losses which are key. For example, refining crude oil into jet-quality (kerosene) fuel induces costs (20% more than your 95 unleaded gas price). You might not know that some large boat tankers/freight ships still use crude oil to power engines - not exactly the most carbon-free way to burn energy but certainly quite cost-effective. As I was writing this article, I asked myself where energy goes for a barrel of crude oil and I found this interesting graph:

The first graph shows that less than half the volume of an oil barrel is actually used for gasoline production and that a barrel can be used for jet fuel production or even converted to gas...

• Fourth: Lithium-ion battery is actually at the bottom of the scale for its MJ/L or MJ/kg capability!!! (1 gram of lithium-ion holds 720 Joules while a gram of gasoline holds 47200 Joules) Yes, you heard me: while your battery cell phone may seem to be the best thing ever, it sucks from an efficiency perspective. Smartphone batteries are rated around ~10Wh on average with a core electronic system (processor, display, wireless radio, GPS) at around 0.2-0.5mWh so no wonder your phone will only last a day or two depending on usage. If your phone was powered by a fuel cell and a small hydrogen tank, you would be good for months. Off course, I realize that it may not be practical but it gives you a sense of how much volumetric plays a role in energy storage and consumption. No wonder why several automotive leaders are warning the industry that EV vehicles may not be the best option (at the same time, they fail to mention that electricity is cheaper than gas and that hydrogen is perhaps great for the environment but where are the charging sites?). It's all a matter of tradeoffs (* see bottom note).

Conclusion

I hope you enjoyed this short article. I wish that the energy topic would be more publicly "educated" as opposed to being the victim of an ever-increasing energy bill. Yes, Electric cars cost more but look at the gasoline saving (can quickly add up to $400 a year). And while your smartphone may not use the most dense source of energy, lithium-ion storage can be made small, compact and above all, easily rechargeable via standard electrical outlets.

I find physics to always be a great source of truth.

More to come on the energy topic.

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(*) Important note: regarding EV vs gasoline car efficiency, I need to clarify one thing. My Tesla M3 (long-range version) is equipped with a ~480kg lithium-ion battery pack that stores ~300MJ/82kWh for a maximum range of 300 miles when fully charged (or ~1MJ per mile / or 82 kWh). This would correspond to 8.5 litres of equivalent gasoline (300MJ/(47200(J/g) x 1000(to get to kg)) x 0.74^-1 (1 litre of gasoline is 0.74kg)=8.5liters of gasoline or 2.2 gallons. With an average ~23mpg gasoline car, this would mean that the corresponding energy stored in my Tesla battery pack would only correspond to 23mpg*2.2g or ~50 miles. So where is the catch with the 300-mile range of my Tesla if lithium-ion is that NOT efficient? Well, it comes from the fact that EV motors can recapture energy when you break and recharge the battery pack - something that a gasoline or hydrogen engine CANNOT do. So yes, harnessing regenerative forces is what makes EV vehicle competitive from a range standpoint compared to their "ICE"/gasoline or hydrogen equivalents. This is one of the reasons why Hydrogen engines are always paired with a lithium-ion battery anyway so that the breaking kinetic energy can be recaptured.

#energy #metrics #joules #hydrogen #lithoum-ion #tradeoffs #emission #polution

As always, feel free to contact me @ [email protected] if you have comments or questions about this article (I am open to providing consulting services).

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