I think they're planning to heat up big chunks of graphite to thousands of degrees C with electric heaters powered by the grid and then attach these thermocouples when the renewable sources start to flag (windless nights) to cover the gap.
Heat radiation losses (scaling with the fourth power of the temperatures) would obliterate such a storage solution. I could only imagine it as very short-term, at which point heating using electricity and converting back shortly after quickly becomes pointless.
I don't know how they mitigate the radiation losses (huge amounts of insulation?), but it appears that graphite has some interesting properties when heated, like it gets stronger 1000-2500C and doesn't expand much when heated [1]. Perhaps those properties help it to store heat effectively at those extreme temps.
> I don't know how they mitigate the radiation losses (huge amounts of insulation?)
My guess is a vacuum flask made of tungsten. Tungsten sheet metal is a thing and it has the second highest melting point of currently known elements, which is 3,422C.
Then for the 'battery' you will want to find a material that has a phase change around the temperature required for this heat engine to operate. The energy required for water to go from 100c water to 100c steam is considerably more significant than the energy required to go from 0c water to 100c water.
Graphite will likely come into play because you need to have electrodes to heat the material up to storage temperature. Graphite is a good for this sort of thing. Although gradual erosion will likely limit the life of the battery.
If that's the case, would the tungsten flask heat up to 2000C and give off the photons that are absorbed by the TPV? I still don't understand how they will control transmission of the heat at those temperatures.
Maybe insulate with reinforced carbon-carbon? I'm not an expert on this, but it doesn't seem outright impossible on the surface, but the details are always what get you.
The insulation I sort of understand. It's how they temporarily breach the insulation to let out the photons to strike the TPV that I don't understand. With normal heat->electricity conversion, you transfer heat to a turbine via a fluid (i.e. water) that is allowed to contact the exterior of a heated vessel, but in this case you need to somehow open a slot to let the photons radiate out.
Install a hinge on the side of the insulation box, swing it open then swing closed a different section that includes the thermocouples?
Or just slide the insulation down in front of the thermocouples when they aren't needed. I have to assume these things mostly work on radiant heat at those temperatures.
You need vacuum super insulation.
Basically take a thermos, and fill the vacuum with (mostly) non-touching reflective foil. It's the golden stuff satellites are wrapped in.
