this post was submitted on 01 Mar 2024
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[–] MystikIncarnate@lemmy.ca 56 points 8 months ago (23 children)

So, I understand what Toyota is saying. I'm not sure I agree, but I get it.

Simply put, until we figure out a good solution to the battery problem, EVs are kind of at a dead end. They are about as good as they could be with current technology. There's a big push right now towards better energy storage tech, aka battery tech, for EVs and beyond (everything from cellular/mobile/device applications, to EVs, to "grid scale" storage).

The problem is basically twofold: first, limited energy storage. This is compounded by fairly slow charging... Second, current lithium tech used in EVs tends to be rather.... Flammable. Specifically, the most common chemistries are pyrophoric; aka, they burst into flames on contact with air. .... I'll emphasize that pyrophoric battery chemistries are commonly used in just about all consumer goods. This includes every Tesla, and every cellphone.

The only reason that your phone doesn't spontaneously combust in your hand is because the batteries are sealed so no air can get at the chemistry. The issue with Tesla's EVs is when one cell's seal fails, and it combusts, then the chances that adjacent cells will have their air seal compromised, dramatically increases. This can quickly lead to a chain reaction of failures.

Current research is ongoing into batteries. The golden battery for EVs will have, fast charging, high discharge capability (also known as the "C rate"), similar or better energy density to current cells, and longer charge/discharge cycle life. Since we're already comfortable giving pyrophoric batteries to the general public to carry around in their pockets, I don't think anyone is focused on eliminating that, but, if they can, while achieving the other goals, so much the better.

Other battery chemistries exist that are not pyrophoric, but they lack the energy density of their pyrophoric counterparts. One notable chemistry is LiFePO4, which, by sacrificing some energy density, you get much longer cycle life, and no pyrophoric materials.

Solid state batteries are being researched which should extend cycle life significantly if it can be achieved as a "commercially viable product" (which is corporate talk for something that can be mass produced). Thus far, while sold state batteries exist, they're either done in very small batches, and are very hard to produce, or, they simply don't have the same, or similar, energy density to the lithium/cobalt cells that currently dominate the market.

One alternative is hydrogen. Hydrogen fuel cell technology isn't perfect, with a loss of about 20-30% IIRC, from the energy in vs the energy out. The benefit to hydrogen is that it can be stored, highly compressed (a large volume of gas in a relatively small container), and it doesn't degrade or go bad, so it can be stored indefinitely, aka no significant loss over time. But hydrogen is a far more dangerous material than lithium/cobalt, and a tank rupture from a full tank of hydrogen in an EV, could create an explosion of significant size. It's far more dangerous than the pyrophoric batteries. For more information, see: Hindenburg.

Other alternatives exist, but generally are not being used in EVs for various reasons. Among these are RITEGs. An RITEG outputs a consistent and stable power flow indefinitely, even a relatively small unit could be used to power a vehicle, with a small buffer battery, for upwards of 40 years without needing to "refuel" so to speak. Possibly longer depending on the fuel used. The reason they're not considered is right in the name. The full name for an RITEG is "radio isotope thermal electric generator". Aka, nuclear. The unique thing about an RITEG is that the power output is dependent on the differential between the heating provided by the fuel, versus the temperature of the surrounding material (usually some sort of passive heatsink). They're very safe unless the seal is broken, in which case, you need Hazmat to clean up the mess. Their energy conversion is very very low. The power is stable, but only a small amount of wattage can be generated. It's constant, but it's a small amount. So the presence of a "buffer" battery for acceleration (and most driving) would be required, and often you can get more power from a small solar array, dependent on the weather. I like the idea of RITEGs, but more as a home generator type option, where you could bury one into the ground and dissipate the heat geothermally. No options exist for this and research into thermal electric tech has been stalled for many years. Nevertheless, I think it's awesome. The idea of having a mostly solid-state, base load generator in your back yard, seems like a really good idea, but nobody has done it, since IMO, the regulations would be a nightmare.

Anyways, the battery problem outlined here is what we're all waiting for... A commercially viable product that is on par with the current battery front runner, lithium/cobalt, for energy density, while having a much higher cycle life and a high "C rate".

[–] dual_sport_dork@lemmy.world 5 points 8 months ago* (last edited 8 months ago) (1 children)

RITEGs ... Their energy conversion is very very low.

Yeah, no kidding. These will never be viable for personal vehicular applications because they are A) by necessity incredibly heavy, large, and expensive with the casings, shielding, heat exchangers, etc. required, and B) can't produce enough energy to meaningfully propel something the size of a car any useful distance in any realistic time frame. A 1500 kilogram unit the size of a refrigerator only generates ~35 watts. That's not enough to do anything with, from a transportation perspective. There is no "new technology" that's going to get around this, either. Isotope half lives are what they are. The decay heat is what it is. The temperature differentials that you can safely maintain in a consumer environment can only be so large. That's physics.

You'd literally be better off with a $200 worth of solar panels from Harbor Freight to recharge your EV. And yes, that includes taking into account that solar panels don't work at night.

That, and you'd never get any random member of the public to willingly park anything that is known to contain radioactive isotopes in their own back yard. Radiophobia would ensure that such a proposal would be completely dead on arrival. People are already deathly frightened enough of radioisotopes existing in tightly regulated, very competently run nuclear power plants.

[–] MystikIncarnate@lemmy.ca 1 points 8 months ago

I'd happily have a RITEG buried in my back yard to sustain my base load from my house. Using geothermal cooling for the unit seems like a good idea, and it would be underground where nobody can fuck with it.

RITEG research and use hasn't stopped, but most of the terrestrial units have been long decommissioned. The most recent example of note was the MMRTG unit used in curiosity (now on Mars), which is 45 KG and can produce 110W of output. The most notable terrestrial examples were the IEU units used by the Soviets for light houses, weighing upwards of 2-3 tones and producing less than 120W at their peak, mostly fueled by strontium 90 (the MMRTG uses plutonium 238). The only modern RTG for terrestrial use is the Sentinel units used for monitoring stations in the arctic by America, which top out under 60W and weigh more than a ton, closer to 2 ton. There are others but information is limited.

A lot of weight is due to the fuel (which is classified as a "heavy metal") and the casing, which on earth is more robust than you would need in space, since it's feasible that people would be nearby the unit for extended periods of time and any breach could be fatal.

Even with the weight, if we're effectively burying it in a yard, deep enough to take advantage of geothermal cooling, then weight isn't really a problem. Even size isn't a problem since it can be the size of a large consumer vehicle and most homeowners have more than enough land to accommodate that... With little more than an access hatch for inspections and maintenance, it would be a viable option to contribute to offsetting the base load of your home. Even a 100W unit would trim about 2.4kWh from a household electricity bill per day for something like 100 years. That's in the ballpark of 8.5 GWh over the lifetime of the unit before the fuel needs to be replaced (based on the half life of the material. Strontium 90 would need to be refueled every 40-50 years or so).

I'm not saying it's a fix to the problem by any stretch, but it could trim about 1/4 of electricity costs per home, based on an average consumption of around 10 kWh per day.

This is why I like RTGs, they're stable and long lasting, relatively safe (unless the housing/shielding fails) and solid state with basically no maintenance.

I'm a fan of the idea, but I'm not going to say it's a one stop fix, nor do I think the regulatory people will green light any implementation of such a system for home use, ever. Nor do I think that even if such a solution were to be given approval, that the general public would ever accept it being installed "in [their] back yard" either literally or figuratively.

You're right that a pair of 200W panels and a small battery system would have a similar effect (at least until the batteries needed replacing... or simply grid tie it), and as long as you can average ~2 kWh/day of generation, you'd be fine... You might need 4-5 panels to get the same daily output, but a system like that is probably still less than $1000, and will probably last ~20 years. So to make it economically viable such a system would need to cost the consumer less than ~$5000 or so before it becomes a better option.

I'm still a fan of the technology, and I find it immensely interesting, but I try to keep my expectations realistic. Due to the excessive weight of a terrestrial RTG, it's not viable for a vehicle, but wouldn't it be cool to have a car that charges itself all the time no matter where you park it or whether it's in the sun or not?

I think that would be cool.

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