If you point concentrated solar at a vantablack object, heatsinked to this 40% efficient TPV, do you get an easy 39.94% efficiency, easily outpacing mass produced photovoltaic or am I missing a loss?
This is just a multi-junction photovoltaic cell optimized for temperatures of the radiant body between 1900 and 2400 Celsius degreees.
Such multi-junction photovoltaic cells, but optimized for the higher temperature of the Sun, have existed for many years and efficiencies over 45% are well known.
So there is no point in heating anything, the concentrated solar light must be directed to an appropriate multi-junction photovoltaic cell, for the best efficiency.
Despite their very high efficiency, the multi-junction photovoltaic cells are seldom used for solar energy, because they are expensive, so they can only be used together with light-concentrating mirrors, to achieve a reasonable cost.
Even with mirrors, the price is still much higher than for normal solar panels, so they might be chosen only when space constraints would prohibit the use of a larger area with solar panels.
The exact price is unknown, because you will not find them at retail.
They have been used for solar panels in satellites or space probes, where maximum efficiency is more important than the price, and in experimental solar plants with movable mirrors that concentrate the solar light from a very large area onto a small photovoltaic cell.
In both applications, the complete systems are very expensive and the cost of the photovoltaic cells is a very small part of the total.
Well any area is enough area for solar power, you just don't get much out of it. I think for a car I remember some calculation at some point was that if you covered the whole thing in panels and let it soak in the sun for a day you'd get a few miles of driving out of it.
Having more efficient cells would give you a few more miles I presume. Not too useful for the everyday user, but if you're doing an off grid trip it would be very useful if you camp somewhere and let your car charge for a few days. I guess might as well roll out some proper panels in that case though.
Planes do have a reasonably large wing surface area that could be panelled up if they're not too heavy (you can make quite large RC planes fly perpetually in the sun even with regular monocrystalline panels) so there would definitely be some fuel savings from it if you had like a hydrogen powered jet that already uses electric propulsion.
What you suggested is more similar to what Solar Thermal systems do (https://en.wikipedia.org/wiki/Solar_thermal_energy). They are known to be more efficient than solar photovoltaics. They have their own downsides of course.
They are more efficient because converting anything to heat is trivial. Heat is just losses basically. A process consisting of 100% losses is great for heat generation.
However, extracting exergy (electricity is pure exergy) from a flow of energy is the tricky part and will always be associated with efficiencies way below unity, based on fundamental principles.
Yes, but labs have also produced 40% efficient multijunction solar cells that work directly from sunlight without the intermediate heat absorber. Off-the-shelf multijunction PV for space applications is I think 36% efficient.
Also, you don't need Vantablack, a regular cavity absorber would be fine.)
The article says, if I'm not mistaken, that the heat source must be between 1900 and 2400 degrees (Celcius), and I would bet that Vantablack loses its blackness at such temperatures?
Wikipedia indicates the melting point of vantablack being 3000C. I would think a black coloring is pretty heat resistant. It looks like it needs to be 500-750C to create it as well
It sounded like it wasn't the heat that got converted to electricity, but rather the photons emitted by the hot object glowing, and since your vantablack object is not glowing you would expect to get nothing.
But maybe not, the glowing comes from black body radiation, so the vantablack material would presumably glow as well (ironically). As long as the heatsink coupling did not block the visible "white" light produced, or glowed itself, then at least the photons from the back would get used. I expect that getting a heatsink paste rated for 2200 C is ... challenging, but, conveniently, you'd do better if you just skipped the paste.
The vantablack material would indeed "glow", as everything in the universe glows. It just does so outside the visible spectrum. The difference between this thermo-voltaic cell and a photo-voltaic cell is that photo is visible spectrum and thermo is IR. It's all just photons!
> I expect that getting a heatsink paste rated for 2200 C is ... challenging, but, conveniently, you'd do better if you just skipped the paste
Liquid metal is some of the best performing thermal paste around. In computer applications that's normally an alloy made from Gallium, Indium and Tin, but at 2200C the majority of metals should work. Maybe Gold to reduce oxidation.
Apart from the vantablack heating issues sibling comments have already mentioned, you'd also need to take into account the energy used by the cooling system for the cold end of the TPV. In practice you'd need to pump either water or air past some form of heatsink and the energy consumption of the pumps would reduce the efficiency below that of the 40% of just the TPV.
This would be a heck of a lot of waste heat to deal with. You could probably boil water with the leftover energy to turn a steam turbine to power the cooling apparatus. A dual stage solar plant.
The reason for the high level of waste heat is that the system has to operate at thousands of degrees C. There is still a huge potential above room temperature. Most systems work closer to room temperature so there is space to squeeze them in after this system has extracted all of the energy it can.
Yes, but the pumping power is about 0.2% of the total power, so this is not a significant consideration in practice. If it was, people would use solar chimneys instead of mechanical fans and pumps.
One minor issue is diffusion due to clouds, similar to all concentrated solar power systems it needs direct sunlight. Normal solar panels can produce some power even under a thin cloud layer.
I’m guessing the vantablack would be destroyed by the concentrated heat or UV. Or is there an industrial formulation that could withstand the high temperatures?
