Defining a straight solar EV

[bananu7]

Size and gyroscopic effects are going to be a huge problem, in addition to safety ( you are riding next to an extremely powerful grenade, therefore you need a way to shield it, which would be very heavy ).

A 10lbs fly wheel can rip through a car's engine. 10lbs might not be enough for a considerable amount of energy on an ebike.

There are a lot of engineering problems to solve with that route..

All you said is true, but so is the fact that those problems have been solved in practice and the technology successfully used. It's not a hypothetical; it can be done, given enough time and resources, we can just talk about whether it would work for this particular vehicle.

A 4.5kg disc at 1m diameter, spun up to 20k rpm can store about 300Wh of energy. That's more than enough for the OP's case, which was to drive directly off of solar, and not really charge any batteries to speak of. The goal wasn't to choose a perfect battery chemistry, it was to make the vehicle go ~indefinitely.

 

[neptronix]

Don't you need at least another 4.5kg of material to survive the blast if it grenades itself?

They have started putting these flywheel storages underground lately because they have exploded and destroyed so much property and also killed some people inside storage facilities. And this is happening as we just barely start to adopt them.

Inside automobiles where there's many inches of steel between the driver and the freewheel, exploded freewheel fragments become bullets and have killed auto mechanics. And car flywheels aren't all that big, nor spin that fast.

This wouldn't meet my risk to reward ratio personally, since the required amount of metal to prevent being killed by a flywheel is probably 5x the flywheel's weight.

Most people survive a lithium battery fire. Lithium battery fires at least have warning signs. Fly wheel explosions don't.

 

[JackFlorey]

Don't you need at least another 4.5kg of material to survive the blast if it grenades itself?

Depends on the flywheel. Cast metal flywheels? Definitely. Fiberglass or carbon fiber flywheels? They tend to shred and turn into dust and confetti, not large fragments. Still a very exciting event thermally (all that energy gets dissipated at once) but not grenade like.

 

[neptronix]

do fiberglass and carbon fiber flywheels have much lower energy density, therefore you need a frickin' huge one, which wouldn't be suitable to put on a bike?

I'm thinking that the energy unit of storage is mass x RPM. The less dense the mass, the more the flywheel solution looks bedroom-sized.

 

[offGridDownUnder]

A 4.5kg disc at 1m diameter, spun up to 20k rpm can store about 300Wh of energy. That's more than enough for the OP's case,

As I posed the problem of generally enabling a solar vehicle with regen capability, I certainly don't want to dissuade any discussion. Someone will benefit from it, and as noted, there are human-scale vehicles that use this capability now.

But as an aside, I'm thinking this would offer me orbital launch capability from my trike.

 

[amberwolf]

But as an aside, I'm thinking this would offer me orbital launch capability from my trike.

Like this?

SpinLaunch - Wikipedia

en.wikipedia.org

 

[bananu7]

do fiberglass and carbon fiber flywheels have much lower energy density, therefore you need a frickin' huge one, which wouldn't be suitable to put on a bike?

I'm thinking that the energy unit of storage is mass x RPM. The less dense the mass, the more the flywheel solution looks bedroom-sized.

It's something closer to mass x diameter x rpm^2. The larger you make it the more use you can make of every unit of weight, and spinning faster offers massive gains.

The same amount of mass will work better as a rim rather than a solid disk, so using a strong core and heavy weights on the perimeter isn't that bad of an idea. And if your material is very strong, you can spin it up more, which can add more storage than making it heavier, but then the aforementioned gyro effects start being important too.

 

[fechter]

Lithium Titanate batteries are probably the most practical for this kind of application. A bank of supercapacitors could work but would be much more complex due to the wide voltage range they would need to use. If the total storage capacity of a small battery isn't enough to capture all the regen going down a hill, it wouldn't be too hard to add a resistive dissipator to dump the excess energy once the storage is full. Lead-acid batteries wouldn't last very long and need frequent replacement. Nimh batteries like from a Toyota Prius might be OK but LTO would most likely live a lot longer.