I remember when people thought that solar Stirling generation might become a thing. Then the price of PVs never stopped plummeting.

Yes, and that machinery is analogous in use to the fast chargers that currently exist.

I do not swap out the empty fuel tank for a full one. Go ahead, describe the process.

Describe to me how you think this might work. Swappable batteries that do not need to be loaded by heavy machinery, and also don't need to be lifted by anyone. I'm dying to know your design.

You want to use one of those every time your battery is empty? It may not be hard but you have to account for the stupidest person in the room, someone will manage to crush themselves.

Ok, hands up who wants to hand load 25 heavy batteries. There's no audience but I'm imagining a stadium with no hands up.

There are engineering problems and then there are physics problems, making a battery with enough energy to be useful for a car and light enough to be lifted by an average person is the latter.

Not going to happen.

Batteries for these bikes weigh maybe 20kg (~45 lbs), whereas an electric car battery is closer to 500kg (~1200 lbs).

One of these can be swapped by hand, the other needs heavy machinery.

Power per square metre is far more important. There's maybe two EVs which aren't even on the market yet with solar panels on them and one of them is absolutely optimised for efficiency (aptera). They're typically not worth it, you're better off just having panels on a roof facing the right direction and charging a battery.

I can't think of a single example of someone saying "solar sure is nice, if only it weren't so heavy!"

Possibly useful for space applications, but then you need to take the weight of the structure you apply it to into account.

It's kind of different though, molten salt "batteries" before this were really thermal storage, while this is regular old chemical storage. That means no moving parts, just sit it in place and use it like any other chemical battery.

The downside compared to most other batteries though is that the operating temperature is hundreds of degrees. The batteries need to be "thawed" before use, and if they ever freeze (which they will if they aren't used, they are insulated but still need to use the waste heat from charging/discharging cycles) they need to be thawed again. You can do this just by running power through them, but it takes a lot of energy.

These could be legitimately groundbreaking for 24 hour cycling if coupled with solar in regions with very few cloudy days, but they can't be used for anything the way lithium can.