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SoylentRox t1_iwhhk1l wrote

Reply to comment by purple_hamster66 in A typical thought process by Kaarssteun

Agree totally on the solar. The only thing the fusion does for you is it saves you having to develop a long term method of energy storage. There are lots of ways to do this but there are tradeoffs.

Flow batteries being the most promising because they are efficient - you get 80 percent plus of the stored energy back - so you just need some electrolyte chemistry that is not too toxic and cheap and can be stored in gigantic cheap unpressurized tanks.

You can also make hydrogen, maybe store it in metal or as ammonia or just pressurized gas, and burn it in fuel cells. This loses a lot of energy and is also expensive equipment.

There are also various pressurized air and heat storage concepts - they all have cheap storage material but poor efficiency.

Note that hydroelectric and lithium battery storage is not long term, it's short term storage. It's for the next couple days. You need something to store energy to make up for seasonal shortfalls and for black swan periods of little renewable production for a while

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purple_hamster66 t1_iwzjdiz wrote

I think the coolest hybrid energy storage solution is melting salt stored in tracker trailers and trucking it to the destination substation where it generates electricity as it cools. This can allow us to truck energy to places that didn’t get enough renewable energy (black swan event), or to emergency sites (earthquake takes out a power plant; floods; tsunami), or as long-term energy storage. The trucks can use the energy they are transporting to power the transport, too, so fossil fuels are not needed either.

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SoylentRox t1_iwznvv0 wrote

Maybe? Why salt. Why not just heat up a bunch of ceramic bricks to almost their melting point. Salt especially hot salt can corrode and melt things. With the bricks, if the truck crashes, you just end up with glowing pottery on the ground. Don't touch it but it won't flow to you.

You also have poor efficiency converting from the heat back to work, you need a steam engine.

Frankly probably better to just transport diesel.

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purple_hamster66 t1_ix0847c wrote

Salt is used in thermal energy storage systems because of it’s enormous capacity to hold heat. I don’t know how ceramic compares, but the latent heat involved in the state change (from solid to liquid) is important because it extends the heat that can be trapped. As I understand it, it’s not pure salt, but may also have thermal oil and high-pressure water & pumps. Depends on the usage.

I don’t think they’ve thought about crashes because none of these systems are currently mobile. Even though I would imagine that molten salt flows quite slowly, the amount of energy in it would melt/damage most things. But when it finally cools, though, it’s just salt, so cleanup is easy.

Some systems use a Rankine Cycle steam turbine, like you said. Others have been designed to use thermocouples, devices that convert nearly 100% of heat differences (over a threshold) to electricity and vice versa. It’s a form of heat pump, like those used in houses, but this thermocouple is designed for much higher heat differences. Since it’s trivially reversible, the same device is used for both directions.

One other cool hybrid is heating the salt using mirrors in a vast field, then generating the electricity from the steam engine. This means you can store the energy until later if you have more mirrors than your current grid needs.

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