From the math I looked at, that doesn’t seem to be the case. What we’re actually doing is fighting radiative and convective heat loss, basically requiring more energy per second to compensate for increasing heat losses per second. An adequately insulted sand battery would negate a lot of that.
The easiest method is using sand as an electrical resistor allowing the resistance to heat the sand up. I’ve also wondered about other methods too, such as solar ovens or baking the sand in some way and dumping the hot sand into the battery.
Thanks for the input! I’ve had several more thoughts:
You’re absolutely right about the cost, but it could be contained with refractory cement and would not have to rely solely on metal casings. It seems like buying either in bulk has comparable pricing.
interest problem. I tried to find some info, but there’s a lot of engineeting math (I’m an English teacher who also loves the sciences) I don’t have the time to sort out right now. I think that using rock wool and refractory cement (see number 1) could help offset this energy loss.
I knew that water could be kept liquid under pressure, but for the purposes of citizen science and making tech more democratic, high pressure systems are a lot of risk and can be devastating when mistakes are made.
Absolutely. And that’s the goal of my thoughts. Finding a cheap material that can hold high temperatures and remain solid. The transfer to electricity could be done by using the heated mass to heat a hot pumped liquid or using transfer rods made of a solid material with a high heat transfer coefficient.
Good question, not being an expert I don’t have a great answer. But maybe doing a composite sand that combined something like copper, iron, it aluminum dust with the sand to increase the ability of the battery to more easily move heat around. Or using the chosen metal in a bar or pipe as heat transfer out of the center. The only issue with that is it lowers the operating temp and would require more active cooling, this negating some of the self-insulating benefits of sand. This could be solved by treating them like control rods, and make them movable so they could be drawn out when extracting energy is not necessary.
Please share! My wife and I are starting a homestead and are always looking for ways to make it more solarpunk. We’d love the inspiration you could provide!
You’re right about rapid transfer out. I guess I wasn’t clear about the imagined scenario where the battery may sit untapped for hours or more, and that could definitely cause issues with the metal melting at the upper end of operator temps. Interesting idea for solarpunk story conflict: for whatever reason heat isn’t being extracted fast enough so the batteries are overheating and ‘slagging’ themselves.