Metal Hydride Heat Engine | Hacker News Reader

Metal Hydride Heat Engine

ergenics.com

34 pointsblacksqr17 comments

What is the efficiency of such an engine?

Google found a source[0] that says around 57%. The link here is describing a solar panel as the heat source, but the technical report I found implies it usually uses waste heat from other industrial processes.

[0]: https://www.sciencedirect.com/science/article/pii/S036031991...

Neat. I wonder whether you have to refill the hydrogen eventually because of leaks.

Certainly. But you can make it locally. Matching the leakage rate probably doesn't consume much power.

Meh. A heat engine. So it is subject to the Carnot engine efficiency limit. No thanks. Direct solar cells ought to be much better.

I suspect the best option would be an integrated hybrid system of PV and heat systems. A friend of mine measured the efficiencyo of his solar panel roof. They got much less efficient when they're hot, and they heat up quickly in the sun. So we speculated that of we were to apply some kind of water cooling system behind the solar panels that would store the excess heat somewhere in the ground for winter, we might get even higher energy savings than just the sum of its parts

Yes -- photovoltaics waste heat, thermals waste light. Collect both, and you get maybe double the areal efficiency. Most of us can't put up a bigger roof, but we can make better use of it.

And the fun part would be to make the cooling system self-powered yet magically more efficient! I'm surprised I haven't seen any hard-core tech geek nerd out on trying to optimize their home installation like this.

The various experiments by the Low Tech Magazine people come closest, I think.

Water cooling electronics is pretty tough. I agree in principle with you. My instincts say it’s not been done because it requires lots of custom manufacturing.

Having said that, I wish EV charging stations also hooked up to a battery coolant system. Circulate the coolant with a bigger apparatus to really cool the unit during charge. I had a “fever dream” one time about using such stations to evaporate sea water. Ie have the network of gas/charging stations serve as a way to pull in sea water inland.

> My instincts say it’s not been done because it requires lots of custom manufacturing.

Yes, but OTOH: when has that kind of technical challenge stopped a bunch of nerds before? If anything I'd expect it to provoke them to try!

If you like Low Tech Magazine, check out Build It Solar: https://builditsolar.com/

I have a quasi-passive solar home (from the early 80s) that I’m looking to optimize, and so have been researching a bunch of solutions. The most clever build I’ve found is from Resystech (ie some guy in Canada), who built a heat collector off his solar panels and then built a duct switch to either pump hot air directly into this house or, if not quite hot enough, to duct it through his heat pump.

His build video is here: https://m.youtube.com/watch?v=dmckigvz7Hg

Surely this would be an energy storage option, rather than a generation option.

You heat up water during the day, to generate electricity at night.

I wonder how this compared to Stirling engines.

The big question is probably whether it works with a smaller temperature difference than your typical Stirling cycle.

Either that, or better efficiency, or better reliability, or lower construction cost.

You probably want to compare it to a molten salt system. Since heat engines are limited by temperature differences and molten salts get really hot.

https://en.wikipedia.org/wiki/Solar_thermal_energy#Molten_sa...

>A heat engine. So it is subject to the Carnot engine efficiency limit. No thanks. Direct solar cells ought to be much better.

Perhaps surprisingly, photovoltaic cells are also subject to Carnot's efficiency limit! The hot reservoir temperature is the optical temperature of the Sun, and the cold reservoir temperature is the panel temperature. Plugging in numbers we can see that Carnot's theorem limits solar cell efficiency to ~95%.

I do agree with your conclusion though: PV is much better. It's a simpler, cheaper system.

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