Back here - https://news.ycombinator.com/item?id=39929842 - the US Govt. was calculating that their (funded) pilot project for heated sand energy storage could get 50% real-world efficiency. Or 55% if they used a more-complex turbine cycle.
If true - then this new U-M thermophotovoltaic system will either need a whole lot of improvement, or its use will be confined to corner cases.
Energy efficiency is nice, but capital efficiency is more important.
There are a lot of grids that have excess generation from solar or wind that drive prices very low on a routine basis. As long as the difference between the low and high price is enough, the question is more about capacity than efficiency, IMHO.
That other system seems mechanically complex, you've got to move sand through silos. This system seems a lot simpler, make a big box of sand/whatever, run heating elements through it, put modified solar cells on the outside, apply heat when power is cheap, draw power when power isn't cheap.
I was hoping Battery in every home would have solved this issue. We would basically have a distributed battery storage system in every home to balance capacity.
But it seems we are still far from it happening. Tesla PowerWall 3 isn't that much of an improvement.
If true - then this new U-M thermophotovoltaic system will either need a whole lot of improvement, or its use will be confined to corner cases.