Category Archives: Engineering

Transparent, super wood

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As mentioned in a previous post, wood is more among the strongest materials per unit weight, making it ideal for table tops and telephone polls. On a per pound basis, most species of wood are more than twice as strong as aluminum or mild steel. Wood’s structure is is the reason; it’s a natural composite of air-filled, aligned tubes of crystalline cellulose, held together by natural glue, lignin.

In terms of raw strength though, pounds/in2, wood is not particularly strong, only about 7000 psi (45MPa) both in tension and compression, about half the strength of aluminum. It is thus not well suited to supporting heavy structures, like skyscrapers. (I calculate the maximum height of a skyscraper here), but wood can be modified to make it stronger by removing most of the air, and replacing it with plastic. The result is a stronger, denser, flexible composite, that is typically transparent. The flower below is seen behind a sheet of transparent wood.

A picture of a flower taken through a piece of transparent super-wood.

To make a fairly strong, transparent wood, you take ordinary low-density wood (beech or balsa are good) and soak it in alkali (NaOH). This bleaches the wood, softens the cellulose, and dissolves most of the lignin. You next wash off the alkali and soak the wood in a low viscosity epoxy or acrylic. Now, put it in a vacuum chamber to remove the air — you’ll need a brick to hold the wood down in the liquid. You’ll see bubbles in the epoxy as the air leaves. Then, when the vacuum is released, the wood soaks up the epoxy or acrylic. On curing, you get a composite strong and transparent, but not super strong.

To make the wood really strong, super-strong, you need to compress the uncured, epoxy soaked wood. One method is to put it in a vice. This drives off more of the air and further aligns the cellulose fibers. You now cure it as before (you need a really slow cure epoxy or a UV-cure polymer). The resultant product have been found to have tensile strengths as high as 270 MPa in the direction of alignment, over 40,000 psi. This is three times stronger than regular aluminum, 90 MPa, (13,500 psi). It’s about the strength of the strongest normal aluminum alloy, 6061. It’s sort of expensive to make, but it’s flexible and transparent, making it suitable for space windows and solar cells. It’s the lightest flexible transparent material known. It’s biodegradable, and that’s very cool, IMHO. See here for a comparison with other, high strength, transparent composites.

Robert Buxbaum, November 10, 2022. I think further developments along this line would make an excellent high school science fair project, college thesis, or PhD research project. Compare different woods, or epoxies, different alkalis, and temperatures, or other processing ideas. How strong and transparent can you make this material, or look at other uses. Can you use it for roof solar cells, like Musk’s but lighter, or mold it for auto panels, it’s already lighter and stronger, or use it as bullet-proof glass or airplane windows.

A new, higher efficiency propeller

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Elytron biplane, perhaps an inspiration.

Sharrow Marine introduced a new ship propeller design two years ago, at the Miami International Boat show. Unlike traditional propellers, there are no ends on the blades. Instead, each blade is a connecting ribbon with the outer edge behaving like a connecting winglet. The blade pairs provide low-speed lift-efficiency gains, as seen on a biplane, while the winglets provide high speed gains. The efficiency gain is 9-30% over a wide range of speeds, as shown below, a tremendous improvement. I suspect that this design will become standard over the next 10-20 years, as winglets have become standard on airplanes today.

A Sharrow propeller, MX-1

The high speed efficiency advantage of the closed ends of the blades, and of the curved up winglets on modern airplanes is based on avoiding losses from air (or water) going around the end from the high pressure bottom to the low-pressure top. Between the biplane advantage and the wingtip advantage, Sharrow propellers provide improved miles per gallon at every speed except the highest, 32+ mph, plus a drastic decrease in vibration and noise, see photo.

The propeller design was developed with paid research at the University of Michigan. It was clearly innovative and granted design patent protection in most of the developed world. To the extent that the patents are respected and protected by law, Sharrow should be able to recoup the cost of their research and development. They should make a profit too. As an inventor myself, I believe they deserve to recoup their costs and make a profit. Not all inventions lead to a great product. Besides, I don’t think they charge too much. The current price is $2000-$5000 per propeller for standard sizes, a price that seems reasonable, based on the price of a boat and the advantage of more speed, more range, plus less fuel use and less vibration. This year Sharrow formed an agreement with Yamaha to manufacture the propellers under license, so supply should not be an issue.

Vastly less turbulence follows the Sharrow propeller.

China tends to copy our best products, and often steals the technology to make them, employing engineers and academics as spys. Obama/Biden have typically allowed China to benefit for the sales of copies and the theft of intellectual property, allowing the import of fakes to the US with little or no interference. Would you like a fake Rolex or Fendi, you can buy on-line from China. Would you like fake Disney, ditto. So far, I have not seen Chinese copies of the Sharrow in the US, but I expect to see them soon. Perhaps Biden’s Justice Department will do something this time, but I doubt it. By our justice department turning a blind eye to copies, they rob our innovators, and rob American workers. His protectionism is one thing I liked about Donald Trump.

The Sharrow Propeller gives improved mpg values at every speed except the very highest.

Robert Buxbaum, September 30, 2022

A clever range extender for EVs

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Electric vehicles work well for short trips between places where you can charge with cheap electricity. Typically that’s trips from home to a nearby place of work, and to local shopping malls and theaters with low-cost charge spots. If you drive this way, you’ll pay about 3.2¢/mile for home electricity, instead of about 17¢/mile for gasoline transport (e.g. 24 mpg with $4/gallon gas). Using an EV also saves on oil changes, transmission, air filters, belts, etc., and a lot of general complexity. Battery prices are still high, but much lower than they were even a few years ago.

The 10 kW Aquarius Engine is remarkably small and light, about 10kg (22 lb).

EVs are less attractive for long trips, especially in the cold. Your battery must provide the heat, as there is no waste heat from the engine. Expect to have to recharge every 200 -250 miles, or perhaps twice in the middle of a long trip. Each charge will take a half-hour or more, and fast charging on the road isn’t low cost. Expect to pay about 15¢/mile, nearly as much as for gasoline. See my full comparison of the economics here.

One obvious solution is to have two cars: a short commuter and an EV. Another solution is a hybrid. The Toyota’s Prius and the Chevy Volt were cutting edge in their day, but people don’t seem to want them. These older hybrids provided quick fill-ups, essentially infinite range, and about double the gas milage of a standard automobile, 30-45 mpg. The problem is you have even more complexity and maintenance than with even a gas automobile.

Aquarius liner engine as a range extender

I recently saw a small, simple, super-efficient (they say) gas engine called Aquarius. It provides 9.5 kW electric output and weighs only 22 lbs (10 kg), see picture above. A Tesla S uses about 16 kW during highway driving, implying that this engine will more than double the highway range of a Tesla S at minimal extra weight and complexity. It also removes the fear of being stranded on the highway, far from the nearest charge-station.

The energy efficiency is 34%, far higher than that for normal automobile engines, but fairly typical of floating piston linear engines. The high efficiency of these engines is partly due to the lack of tapper valves, risers, crank-shaft, and partially due to the fact that the engine always runs at its maximum power. This is very close to the maximum efficiency point. Most car engines are over sized (200 hp or so) and thus must run at a small fraction of their maximum power. This hurts the efficiency, as I discuss here. The Aquarius Engine makes electricity by the back-forth motion of its aligner rods moving past magnetic stator coils. Slots in the piston rod and in the side of the cylinder operate as sliding valves, like in a steam engine. First versions of the Aquarius Engine ran on hydrogen, but the inventors claim it can also run on gasoline, and presumably hythane, my favorite fuel, a mix of hydrogen and natural gas.

At the moment shown, slit valves in the piston rod are open to both cylinder chambers. The explosion at left will vent to the exhaust at left and out the manifold at top. The sliding valve is currently sending fresh air into the cylinder at right, but will soon send it into both cylinders to help scavenge exhaust and provide for the next cycle; engine speed and impression are determined by the mass of the piston.

A video is available to show the basic operation (see it here). The drawing at right is from that video, modified by me. Air is drawn into the engine through a sliding valve at the middle of the cylinder. The valve opens and closes depending on where the piston is. At the instant shown in the picture, the valve is open to the right. Air enters that chambered is likely exiting through slits in the hollow piston rod. It leaves through the manifold t the top, pushing exhaust along with it. When the piston will have moved enough, both the slits and the intake will close. The continued piston motion (inertially driven) will compress the air for firing. After firing, the piston will move left, generating electricity, and eventually opening the slit-valve in the piston to allow the exhaust to leave. When it moves a little further the intake will open.

The use of side-opening exhaust valves is a novelty of the “Skinner UniFlow” double-acting, piston steam engines, seen on the Badger steamship on Lake Michigan. It’s one of my favorite steam engine designs. Normally you want a piston that is much thicker than the one in the drawing. This option is mentioned in the patent, but not shown in the drawing.

Aquarius is not the only company with a free-piston range extender. Toyota built a free-piston extender of similar power and weight; it was more complex but got higher efficiency. It has variable compression though, and looks like a polluter. (the same problems might affect the Aquarius) They dropped the project in 2014. Deutsch Aerospace has a two headed version that’s more powerful, but long and heavier: 56kg and 35kW. Lotus has a crank-piston engine, also 56kg, 35kW; it’s more complex and may have service life issues, but it’s compact and relatively light, and it probably won’t pollute. Finally, Mazda is thinking of bringing back its Wankel rotary engine as a range extender. Any of these might win in the marketplace, but I like the Aquarius engine for its combination of light weight, compact size, and simplicity.

This is not to say that Aquarius motors is a good investment. Aquarius automotive went public on the Toronto exchange in December, 2021, AQUA.TA. The company has no profits to date, and the only chance of them making a profit resides in them getting a good licensing deal from an established company. The major car companies have shown no interest so far, though they clearly need something like this. Their plug in hybrids currently use standard-size, 4 stroke engines: 110-150 kW, 100-150 kg, complex, and low efficiency. Consumers have not been impressed. Tesla autos could benefit from this engine, but Musk shows no interest either.

Robert Buxbaum May 5, 2022. I have no stock in Aquarius motors, nor have I received any benefits from them, or any auto company.

A more accurate permeation tester

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There are two ASTM-approved methods for measuring the gas permeability of a material. The equipment is very similar, and REB Research makes equipment for either. In one of these methods (described in detail here) you measure the rate of pressure rise in a small volume.This method is ideal for high permeation rate materials. It’s fast, reliable, and as a bonus, allows you to infer diffusivity and solubility as well, based on the permeation and breakthrough time.

Exploded view of the permeation cell.

For slower permeation materials, I’ve found you are better off with the other method: using a flow of sampling gas (helium typically, though argon can be used as well) and a gas-sampling gas chromatograph. We sell the cells for this, though not the gas chromatograph. For my own work, I use helium as the carrier gas and sampling gas, along with a GC with a 1 cc sampling loop (a coil of stainless steel tube), and an automatic, gas-operated valve, called a sampling valve. I use a VECO ionization detector since it provides the greatest sensitivity differentiating hydrogen from helium.

When doing an experiment, the permeate gas is put into the upper chamber. That’s typically hydrogen for my experiments. The sampling gas (helium in my setup) is made to flow past the lower chamber at a fixed, flow rate, 20 sccm or less. The sampling gas then flows to the sampling loop of the GC, and from there up the hood. Every 20 minutes or so, the sampling valve switches, sending the sampling gas directly out the hood. When the valve switches, the carrier gas (helium) now passes through the sampling loop on its way to the column. This sends the 1 cc of sample directly to the GC column as a single “injection”. The GC column separates the various gases in the sample and determines the components and the concentration of each. From the helium flow rate, and the argon concentration in it, I determine the permeation rate and, from that, the permeability of the material.

As an example, let’s assume that the sample gas flow is 20 sccm, as in the diagram above, and that the GC determines the H2 concentration to be 1 ppm. The permeation rate is thus 20 x 10-6 std cc/minute, or 3.33 x 10-7 std cc/s. The permeability is now calculated from the permeation area (12.56 cm2 for the cells I make), from the material thickness, and from the upstream pressure. Typically, one measures the thickness in cm, and the pressure in cm of Hg so that 1 atm is 76cm Hg. The result is that permeability is determined in a unit called barrer. Continuing the example above, if the upstream hydrogen is 15 psig, that’s 2 atmospheres absolute or or 152 cm Hg. Lets say that the material is a polymer of thickness is 0.3 cm; we thus conclude that the permeability is 0.524 x 10-10 scc/cm/s/cm2/cmHg = 0.524 barrer.

This method is capable of measuring permeabilities lower than the previous method, easily lower than 1 barrer, because the results are not fogged by small air leaks or degassing from the membrane material. Leaks of oxygen, and nitrogen show up on the GC output as peaks that are distinct from the permeate peak, hydrogen or whatever you’re studying as a permeate gas. Another plus of this method is that you can measure the permeability of multiple gas species simultaneously, a useful feature when evaluating gas separation polymers. If this type of approach seems attractive, you can build a cell like this yourself, or buy one from us. Send us an email to reb@rebresearch.com, or give us a call at 248-545-0155.

Robert Buxbaum, April 27, 2022.

A Nuclear-blast resistant paint: Starlite and co.

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About 20 years ago, an itinerate inventor named Maurice Ward demonstrated a super insulating paint that he claimed would protect most anything from intense heat. He called it Starlite, and at first no one believed the claims. Then he demonstrated it on TV, see below, by painting a paper-thin layer on a raw egg. He then blasting the egg with a blow torch for a minute till the outside glowed yellow-red. He then lifted the egg with his hand; it was barely warm! And then, on TV, he broke the shell to show that the insides were totally raw, not only uncooked but completely unchanged, a completely raw egg. The documentary below shows the demonstration and describes what happened next (as of 10 years ago) including an even more impressive series of tests.

Intrigued, but skeptical, researchers at the US White Sands National Laboratory, our nuclear bomb test lab, asked for samples. Ward provided pieces of wood painted as before with a “paper thin” layer of Starlite. They subjected these to burning with an oxyacetylene torch, and to a simulated nuclear bomb blast. The nuclear fireball radiation was simulated by an intense laser at the site. Amazing as it sounds, the paint and the wood beneath emerging barely scorched. The painted wood was not damaged by the laser, nor by an oxyacetylene torch that could burn through 8 inches of steel in seconds.

The famous egg, blow torch experiment.

The inventor wouldn’t say what the paint was made of, or what mechanism allowed it to do this, but clearly it had military and civilian uses. It seems it would have prevented the twin towers from collapsing, or would have greatly extended the time they stayed standing. Similarly, it would protect almost anything from a flame-thrower.

As for the ingredients, Ward said it was non-toxic, and that it contained mostly organic materials, plus borax and some silica or ceramic. According to his daughter, it was “edible”; they’d fed it to dogs and horses without adverse effects.

Starlite coasted wood. The simulated nuclear blast made the char mark at left.

The White sands engineers speculate that the paint worked by combination of ablation and intumescence, controlled swelling. The surface, they surmised, formed a foam of char, pure carbon, that swelled to make tiny chambers. If these chambers are small enough, ≤10 nm or so, the mean free path of gas molecules will be severely reduced, reducing the potential for heat transfer. Even more insulting would be if the foam chambers were about 1 nm. Such chambers will be, essentially air free, and thus very insulating. For a more technical view of how molecule motion affects heat transfer rates, see my essay, here.

Sorry to say we don’t know how big the char chambers are, or if this is how the material works. Ward retained the samples and the formula, and didn’t allow close examination. Clearly, if it works by a char, the char layer is very thin, a few microns at most.

Because Maurice Ward never sold the formula or any of the paint in his lifetime, he made no money on the product. He kept closed muted about it, as he knew that, as soon as he patented, or sold, or let anyone know what was in the paint, there would be copycats, and patent violations, and leaks of any secret formula. Even in the US, many people and companies ignore patent rights, daring you to challenge them in court. And it’s worse in foreign countries where the government actively encourages violation. There are also legal ways around a patent: A copycat inventor looks for ways to get the same behavior from materials that are not covered in the patent. Ward could not get around these issues, so he never patented the formula or sold the rights. He revealed the formula only to some close family members, but that was it till May, 2020, when a US company, Thermashield, LLC, bought Ward’s lab equipment and notes. They now claim to make the original Starlite. Maybe they do. The product doesn’t seem quite as good. I’ve yet to see an item scorched as little as the sample above.

Many companies today are now selling versions of Starlite. The formulas are widely different, but all the paints are intumescent, and all the formulas are based on materials Ward would have had on hand, and on the recollections of the TV people and those at White Sands. I’ve bought one of these copycat products, not Thermashield, and tested it. It’s not half bad: thicker in consistency than the original, or as resistive.

There are home-made products too, with formulas on the internet and on YouTube. They are applied more like a spackle or a clay. Still, these products insulate remarkably well: a lot better than any normal insulator I’d seen.

If you’d like to try this as a science fair project, among the formulas you can try; a mix of glue, baking soda, borax, and sugar, with some water. Some versions use sodium silicate too. The Thermoshield folks say that this isn’t the formula, that there is no PVA glue or baking soda in their product. Still it works.

Robert Buxbaum, March 13, 2022. Despite my complaints about the US patent system, it’s far better than in any other country I’ve explored. In most countries, patents are granted only as an income stream for the government, and inventors are considered villains: folks who withhold the fruits of their brains for unearned money. Horrible.

Wood, the strongest material for some things, like table-tops

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Natural wood has a lower critical strength than most modern materials, and a lower elastic constant, yet it is the strongest material for some applications because it is remarkably light and remarkably cheap on a per-volume or weight. In some important applications, high strength per volume is the important measure, and in virtually every case high strength per dollar is relevant. Consider the table top: it should support a person standing on it, as one might do to change a lightbulb, and it should not weigh too much, or cost too much.

A 250 lb man on a table. The table should not weight too much, nor cost too much, yet it should support the man.

I’ve drawn a 9 foot by 4 foot table at left, with a 250 lb person in the center. Assuming that the thickness of the table is t, the deflection in the center, ∂, is found by the formula ∂ =FL3/4Ewt3. Here, F is the downward force, 250 lbs (a bit higher if we include the weight of the table), L is the length between the supports, 6 feet = 72 inches, E is the elastic constant of the table top, 2,300,000 psi assuming ash wood, w is the width of the table, 48″, and t is the thickness, let’s say 1″.

Using the formula above, we fid that the deflection of this tabletop is 0.211″ for a force of 250 lbs. That’s not bad. The weight of the 9′ table top is 125 lbs, which is not too bad either, and the cost is likely going to be acceptable: ash is a fairly cheap, nice-looking wood.

By comparison, consider using a 1/4″ thick sheet of structural aluminum, alloy 6061. The cost will be much higher and the weight will be the same as for the 1′ thick piece of ash. That’s because the density of aluminum is 2.7 g/cc, more than three times that of ash. Aluminum 6061is four times stiffer than ash, with an elastic constant of 10,000,000 psi, but the resistance to bending is proportional to thickness cubed; and 1/4 cubed is 1/64. We thus find that the 125 lb tabletop of Al alloy will deflect 3.11 inches, about 16 times more than ash, far too much to be acceptable. We could switch to thicker aluminum, 3/8″ for example, but the weight would be 50% higher now, the cost would be yet 50% higher, and the deflection would still be too high, 0.92 inches. Things get even worse with steel since steel is yet-denser, a 1/4″ sheet of steel would deflect about as much as the 3/8″ aluminum, but would weigh about twice as muc. For this application, and many others like it, wood is likely the best choice; its light weight per strength and low cost can’t be beat.

Robert E. Buxbaum, January 11, 2022

Low temperature hydrogen removal

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Platinum catalysts can be very effective at removing hydrogen from air. Platinum promotes the irreversible reaction of hydrogen with oxygen to make water: H2 + 1/2 O2 –> H2O, a reaction that can take off, at great rates, even at temperatures well below freezing. In the 1800s, when platinum was cheap, platinum powder was used to light town-gas, gas street lamps. In those days, street lamps were not fueled by methane, ‘natural gas’, but by ‘town gas’, a mix of hydrogen and carbon monoxide and many impurities like H2S. It was made by reacting coal and steam in a gas plant, and it is a testament to the catalytic power of Pt that it could light this town gas. These impurities are catalytic poisons. When exposed to any catalyst, including platinum, the catalyst looses it’s power to. This is especially true at low temperatures where product water condenses, and this too poisons the catalytic surface.

Nowadays, platinum is expensive and platinum catalysts are no longer made of Pt powder, but rather by coating a thin layer of Pt metal on a high surface area substrate like alumina, ceria, or activated carbon. At higher temperatures, this distribution of Pt improves the reaction rate per gram Pt. Unfortunately, at low temperatures, the substrate seems to be part of the poisoning problem. I think I’ve found a partial way around it though.

My company, REB Research, sells Pt catalysts for hydrogen removal use down to about 0°C, 32°F. For those needing lower temperature hydrogen removal, we offer a palladium-hydrocarbon getter that continues to work down to -30°C and works both in air and in the absence of air. It’s pretty good, but poisons more readily than Pt does when exposed to H2S. For years, I had wanted to develop a version of the platinum catalyst that works well down to -30°C or so, and ideally that worked both in air and without air. I got to do some of this development work during the COVID downtime year.

My current approach is to add a small amount of teflon and other hydrophobic materials. My theory is that normal Pt catalysts form water so readily that the water coats the catalytic surface and substrate pores, choking the catalyst from contact with oxygen or hydrogen. My thought of why our Pd-organic works better than Pt is that it’s part because Pd is a slower water former, and in part because the organic compounds prevent water condensation. If so, teflon + Pt should be more active than uncoated Pt catalyst. And it is so.

Think of this in terms of the  Van der Waals equation of state:{\displaystyle \left(p+{\frac {a}{V_{m}^{2}}}\right)\left(V_{m}-b\right)=RT}

where V_{m} is molar volume. The substance-specific constants a and b can be understood as an attraction force between molecules and a molecular volume respectively. Alternately, they can be calculated from the critical temperature and pressure as

{\displaystyle a={\frac {27(RT_{c})^{2}}{64p_{c}}}}{\displaystyle b={\frac {RT_{c}}{8p_{c}}}.}

Now, I’m going to assume that the effect of a hydrophobic surface near the Pt is to reduce the effective value of a. This is to say that water molecules still attract as before, but there are fewer water molecules around. I’ll assume that b remains the same. Thus the ratio of Tc and Pc remains the same but the values drop by a factor of related to the decrease in water density. If we imagine the use of enough teflon to decrease he number of water molecules by 60%, that would be enough to reduce the critical temperature by 60%. That is, from 647 K (374 °C) to 359 K, or -14°C. This might be enough to allow Pt catalysts to be used for H2 removal from the gas within a nuclear wast casket. I’m into nuclear, both because of its clean power density and its space density. As for nuclear waste, you need these caskets.

I’ve begun to test of my theory by making hydrogen removal catalyst that use both platinum and palladium along with unsaturated hydrocarbons. I find it works far better than the palladium-hydrocarbon getter, at least at room temperature. I find it works well even when the catalyst is completely soaked in water, but the real experiments are yet to come — how does this work in the cold. Originally I planned to use a freezer for these tests, but I now have a better method: wait for winter and use God’s giant freezer.

Robert E. Buxbaum October 20, 2021. I did a fuller treatment of the thermo above, a few weeks back.

Exercise helps fight depression, lithium helps too.

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With the sun setting earlier, and the threat of new COVID lockdowns, there is a real threat of a depression, seasonal and isolation. A partial remedy is exercise; it helps fight depression whether you take other measures not. An article published last month in the Journal of Affective Disorders reviewed 22 studies of the efficacy of exercise, particularly as an add-on to drugs and therapy. Almost every study showed that exercise helped, and in some studies it helped a lot. See table below. All of the authors are from the University of British Columbia. You can read the article here.

From “Efficacy of exercise combined with standard treatment for depression compared to standard treatment alone: A systematic review and meta-analysis of randomized controlled trials.” by JacquelineLee1 et al.In virtually every study, exercise helps fight depression.

For those who are willing to exercise, there are benefits aside from mental health. Even a daily walk around the block helps with bone strength, weight control, heart disease, plus the above mentioned improvement in mood. More exercise does more. If you bicycle without a helmet, you’re likely to live longer than if you drive.

For those who can’t stand exercise, or if exercise isn’t quite enough to send away the blues, you can try therapy, medication, and/or diet. There is some evidence that food that are high in lithium help fight depression. These food include nuts, beans, tomatoes, some mineral waters, e.g. from Lithia springs, GA. The does is about 1/100 the dose given as a bipolar treatment, but there is evidence that even such small doses help. Lithium was one of the seven ingredients in seven up — it was the one that was supposed to cheer you up. See some research here.

Robert Buxbaum, October 7, 2021.

Lithium Battery prices fell 98%, solar prices fell more.

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Most people have heard of Moor’s law, the law that computing power keeps doubling every two years, with the price remaining the same, but the same law is observed with other tech products, notably lithium ion batteries and solar cells.

By my calculation the price of lithium ion batteries has fallen 98% so far, at a rate of 12.5% per year. That’s a remarkable drop given that the chemistry has hardly changed. The size has dropped too; it’s nowhere near as much as the price but enough to make batteries a reasonable choice for powering automobiles, scooters, and power tools. Batteries still lack the range and fast charging for some applications, but even there the low cost means that hybrids become attractive, combining for cars and truck, the long range of gas with a reduced cost per mile. The rate of decrease suggests that prices will be below $100 per kWh by 2025. That’s an $8000 cost for a battery powered car with 300 miles of range.

As for where the electricity comes from, the price of electricity is going up and becoming less reliable. In part that’s because of regulations on coal and nuclear power and the inherent problems with large-scale wind and solar. But decentralized solar may turn out to be a winner. Solar prices have fallen 99.6% since 1976. Even though the rate of decrease is slower, about an 8% drop in price per year, there is a sense that solar power has entered the mainstream. Combined with cheap, home batteries, it may soon make sense to power your home and car by solar cells on the house; there isn’t enough area on a car to quite power it.

Robert Buxbaum, September 27, 2021

Automobile power 2021: Batteries vs gasoline and hydrogen

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It’s been a while since I did an assessment of hydrogen and batteries for automobile propulsion, and while some basics have not changed, the price and durability of batteries has improved, the price of gasoline has doubled, and the first commercial fuel cell cars have appeared in the USA. The net result (see details below) is that I find the cost of ownership for a gasoline and a battery car is now about the same, depending on usage and location, and that hydrogen, while still more pricey, is close to being a practical option.

EV Chargers. They look so much cooler than gasoline hoses, and the price per mile is about the same.

Lithium battery costs are now about $150/kwh. That’s $10,000 for a 70 kWh battery. That’s about 1/5 the price of a Tesla Model 3. The reliability that Tesla claims is 200,000 miles or more, but that’s with slow charging. For mostly fast charging, Car and Driver’s expectation is 120,000 miles. That’s just about the average life-span of a car these days.

The cost of the battery and possible replacement adds to the cost of the vehicle, but electricity is far cheaper than gasoline, per mile. The price of gasoline has doubled to, currently, $3.50 per gallon. A typical car will get about 24 mpg, and that means a current operation cost of 14.6¢/mile. That’s about $1,460/year for someone who drives 10,000 miles per year. I’ll add about $150 for oil and filter changes, and figure that operating a gas-powered car engine costs about $1,610 per year.

If you charge at home, your electricity costs, on average, 14¢/kWh. This is a bargain compared to gasoline since electricity is made from coal and nuclear, mostly, and is subsidized while gasoline is taxed. At level 2 charging stations, where most people charge, electricity costs about 50¢/kWh. This is three times the cost of home electricity, but it still translates to only about $32 for a fill-up that take 3 hours. According to “Inside EVs”, in moderate temperatures, a Tesla Model 3 uses 14.59 kWh/100 km with range-efficient driving. This translates to 11.7¢ per mile, or $1170/year, assuming 10,000 miles of moderate temperature driving. If you live in moderate climates: Californian, Texas or Florida, an electric car is cheaper to operate than a gasoline car. In cold weather gasoline power still makes sense since a battery-electric car uses battery power for heat, while a gasoline powered car uses waste heat from the engine.

Battery cars are still somewhat of more expensive than the equivalent gasoline car, but not that much. In a sense you can add $400/year for the extra cost of the Tesla above, but that just raises the effective operating cost to about $1,570/year, about the same as for the gasoline car. On the other hand, many folks drive less than 50 miles per day and can charge at home each night. This saves most of the electric cost. In sum, I find that EVs have hit a tipping point, and Tesla lead the way.

Now to consider hydrogen. When most people think hydrogen, they think H2 fuel, and a PEM fuel cell car. The problem here is that hydrogen is expensive, and PEM FCs aren’t particularly efficient. Hydrogen costs about $10/kg at a typical fueling station and, with PEM, that 1 kg of hydrogen takes you only about 25 miles. The net result is that the combination hydrogen + PEM results in a driving cost of about 40¢/mile, or about three times the price of gasoline. But Toyota has proposed two better options. The fist is a PEM hybrid, the hydrogen Prius. It’s for the commuter who drives less than about 40 miles per day. It has a 10kWh battery, far cheaper than the Tesla above, but enough for the daily commute. He or she would use charge at home at night, and use hydrogen fuel only when going on longer trips. If there are few long trips, you come out way ahead.

Toyota 2021 Mirai, hydrogen powered vehicle

Toyota also claims to have a hydrogen powered Corolla or debut in 2023. This car will have a standard engine, and I would expect (hope) will drive also — preferably — on hythane, a mix of hydrogen and methane. Hythane is much cheaper per volume, and more energy dense, see my analysis. While Toyota has not said that their Corolla would run on hythane, it is supposed to have an internal combustion engine, and that suggests that hythane will work in it.

A more advanced option for Toyota or any other car/truck manufacturer would be to design to use solid oxide fuel cells, SOFCs, either with hydrogen or hythane. SOFCs are significantly more efficient than PEM, and they are capable of burning hythane, and to some extent natural gas too. Hythane is not particularly available, but it could be. Any station that currently sells natural gas could sell hythane. As for delivery to the station, natural gas lines already exist underground, and the station would just blend in hydrogen, produced at the station by electrolysis, or delivered. Hythane can also be made locally from sewer gas methane, and wind-power hydrogen. Yet another SOFC option is to start with natural gas and convert some of the natural gas to hydrogen on-board using left-over heat from the SOFC. I’ve a patent for this process.

Speaking of supply network, I should mention the brown outs we’ve been having in Detroit. Electric cars are part of the stress to the electric grid, but I believe that, with intelligent charging (and discharging) the concern is more than manageable. The driver who goes 10,000 miles per year only adds about 2,350 kWh/year of extra electric demand. This is a small fraction of the demand of a typical home, 12,154 kWh/year.It’s manageable. Then again, hythane adds no demand to the electric grid and the charge time is quicker — virtually instantaneous.

Robert Buxbaum, September 3, 2021

A useful chart, added September 20, 2021. Battery prices are likely to keep falling.