I was thinking more about the efficiency of the mechanism that transfers the heat from battery to the TPV engine. The article said that the device has to be exp

I was thinking more about the efficiency of the mechanism that transfers the heat from battery to the TPV engine. The article said that the device has to be exposed to photons coming off a white-hot source. I suppose that if the TPV devices are closely coupled with the white-hot source this should be minimal but it's not clear from the article whether there is an intermediary step, or how they plan to control the TPV's exposure to the heat source to discharge the battery. Given that this works via radiation (vs convection like a traditional heat engine), the path between the heat source and the TPV would have to be fairly direct, and not lose much heat to any adjacent non-TPV material. Maybe they have some kind of massively insulated opening/closing heat shield that they can use in a manner similar to the gates used to control water in hydroelectric plants.