Eh, concentrated PV solar used to seem like a good idea, back when panels were expensive, but now all that stuff is more expensive than the actual solar panels. You physically can’t increase incident light per surface area using a thin coating without tracking, so that solar metamaterial thing seems questionable from a basic physics perspective. But maybe you can explain how it works, exactly?
People have tried to do IGCC, but for power generation, gasification just isn’t competitive with boilers. For stuff with higher water content than coal, it’s even worse. Some people are working on wood gasification but that’s just to make “renewable” plastics.
For sure, panels and land are cheap, and there’s no good reason to increase $/W just to gain efficiency. Except sometimes on rooftops where you want a specific building to gain maximum power from limited space, but you obviously wouldn’t use CPV with all the extra equipment in that kind of application.
The metamaterial thing (or to a lesser degree even just other advanced optics, like GRIN lenses) is that you can make thin films that behave, electrically, like non-flat optical elements. Metamaterials can give you properties like anomalously high or low absorption coefficients and refractive indexes, negative refractive indexes, and highly tunable wavelength specificity. In some designs (see: Kymeta, Echodyne and their sibling companies) you can make electrically reconfigurable flat, unmoving antennas that act like a steerable parabolic dish. The “how” involves sub-wavelength-scale patterning of the surface, and a lot more detail than I can fit in a comment.
And I don’t mean IGCC, I agree about that. I have spoken with several dozen companies in the waste gasification space, their technologies vary quite a bit in design and peformance, but at the frontier these companies can extract ~50% of the chemical energy of mixed organic wastes (with up to 20% water content) in the form of syngas (~30% if you have to convert back to electricity and can’t use the extra heat), 2-4x what you get from a traditional incinerator+boiler (which are about 10-12% energy recovery).
I understand physics and material science as well as a grad student, you don’t need to explain basic diffraction. What I’m asking is how these metamaterials increase solar power output. Are they increasing the light that hits the solar panel? Where would that light have otherwise gone, if not for the metamaterial thing?
I’m also confused by why waste gasification would be more energy-efficient than boilers. Are they comparing the chemical energy content of syngas to electrical power generation at 30% efficiency, or something? Gasification uses more energy input than burning stuff. It’s better to convert methane to syngas and burn coal than vice-versa. And biomass is further in that direction, it’s better to gasify coal and burn biomass than vice-versa. This is a basic fact and any startup who won’t admit it is either delusional or lying.
Sorry, got it. Sometimes it’s hard to guess the right level of detail.
First point: The comparison to make is “An area covered with solar panels” vs “an area covered with a metamaterial film that optically acts like the usual CPV lenses and trackers to focus the same light on a smaller area.” The efficiency benefit is for the same reasons CPV is more efficient than PV, but without the extra equipment and moving parts. It will only ever make sense if the films can be made cheaply, and right now they can’t. The usual additional argument for CPV is that it also makes it viable to use more expensive multi-junction cells, since the area of them that’s needed is much smaller, but we may be moving towards tandem cells within the next decade regardless. In principle metamaterials can also offer a different option beyond conventional CPV, though this is my own speculation and I don’t think anyone is doing it yet even in the lab: separating light by frequency and guiding each range of frequencies to a cell tuned to that range. This would enable much higher conversion efficiencies within each cell, reducing the need for cooling. It would also remove the need for transparency to make multi-junction cells.
Second point: I’ve talked to the people operating these gasification systems, not just the startups. The numbers are all consistent. Yes, gasification costs energy, and gasifying coal would not make sense (unless you’re WW2 Germany). But the process can work with any organic material (including plastics and solvents), not just fossil fuels or dry biomass and the like, as long as the water concentration isn’t excessive (I’ve been told up to ~20%), and consumes a bit less than half the energy content of the fuel. The rest is what you can get from the syngas, most of which is in the hydrogen, and fuel cells are about 60% efficient if you want to use it to make electricity. That’s where the 30% number comes from. There are plants doing this using agricultural waste, MSW, ASR, construction waste, medical waste, hazardous waste, food waste, and other feedstocks that otherwise either have little value or are expensive to dispose of.
You can certainly make Fresnel lenses that focus light, but without some sort of active control, it’s not physically possible to focus light from an unknown direction onto the same spot. That would be a thermodynamic law violation by focusing blackbody radiation. So what’s the advantage of this metamaterial stuff over Fresnel lenses? (Those work well enough, but of course aren’t quite economically practical.)
Also, that metamaterial company you mentioned, their website shows regular solar panels with this metamaterial coating on them, not a system that focuses light onto smaller PV panels.
I’m of course aware of the split-spectrum solar proposals using diffraction gratings, but that’s another thing that died off with the fall in PV prices.
Coal gasification typically has exergy efficiency <50%. You can get ~60% exergy efficiency, but biomass would certainly be worse than coal. Some plastics might be similar, I guess, but for wood you’d be looking at maybe 1.6x the losses, so something like 36% exergy efficiency from biomass to syngas. Then with 60% conversion to electricity you have ~22% efficiency, worse than boilers & steam turbines and with higher capital costs.
Yes, some simulations of wood gasification have given better numbers, but I don’t trust them. Coal gasification is much better understood, it’s used on a large scale in China, we know how it performs in practice, and we know biomass gasification is worse.
Combined cycle gas turbines can do 60% efficiency, and fuel cells are more expensive than those, so you probably wouldn’t use fuel cells.
Eh, concentrated PV solar used to seem like a good idea, back when panels were expensive, but now all that stuff is more expensive than the actual solar panels. You physically can’t increase incident light per surface area using a thin coating without tracking, so that solar metamaterial thing seems questionable from a basic physics perspective. But maybe you can explain how it works, exactly?
People have tried to do IGCC, but for power generation, gasification just isn’t competitive with boilers. For stuff with higher water content than coal, it’s even worse. Some people are working on wood gasification but that’s just to make “renewable” plastics.
For sure, panels and land are cheap, and there’s no good reason to increase $/W just to gain efficiency. Except sometimes on rooftops where you want a specific building to gain maximum power from limited space, but you obviously wouldn’t use CPV with all the extra equipment in that kind of application.
The metamaterial thing (or to a lesser degree even just other advanced optics, like GRIN lenses) is that you can make thin films that behave, electrically, like non-flat optical elements. Metamaterials can give you properties like anomalously high or low absorption coefficients and refractive indexes, negative refractive indexes, and highly tunable wavelength specificity. In some designs (see: Kymeta, Echodyne and their sibling companies) you can make electrically reconfigurable flat, unmoving antennas that act like a steerable parabolic dish. The “how” involves sub-wavelength-scale patterning of the surface, and a lot more detail than I can fit in a comment.
And I don’t mean IGCC, I agree about that. I have spoken with several dozen companies in the waste gasification space, their technologies vary quite a bit in design and peformance, but at the frontier these companies can extract ~50% of the chemical energy of mixed organic wastes (with up to 20% water content) in the form of syngas (~30% if you have to convert back to electricity and can’t use the extra heat), 2-4x what you get from a traditional incinerator+boiler (which are about 10-12% energy recovery).
I understand physics and material science as well as a grad student, you don’t need to explain basic diffraction. What I’m asking is how these metamaterials increase solar power output. Are they increasing the light that hits the solar panel? Where would that light have otherwise gone, if not for the metamaterial thing?
I’m also confused by why waste gasification would be more energy-efficient than boilers. Are they comparing the chemical energy content of syngas to electrical power generation at 30% efficiency, or something? Gasification uses more energy input than burning stuff. It’s better to convert methane to syngas and burn coal than vice-versa. And biomass is further in that direction, it’s better to gasify coal and burn biomass than vice-versa. This is a basic fact and any startup who won’t admit it is either delusional or lying.
Sorry, got it. Sometimes it’s hard to guess the right level of detail.
First point: The comparison to make is “An area covered with solar panels” vs “an area covered with a metamaterial film that optically acts like the usual CPV lenses and trackers to focus the same light on a smaller area.” The efficiency benefit is for the same reasons CPV is more efficient than PV, but without the extra equipment and moving parts. It will only ever make sense if the films can be made cheaply, and right now they can’t. The usual additional argument for CPV is that it also makes it viable to use more expensive multi-junction cells, since the area of them that’s needed is much smaller, but we may be moving towards tandem cells within the next decade regardless. In principle metamaterials can also offer a different option beyond conventional CPV, though this is my own speculation and I don’t think anyone is doing it yet even in the lab: separating light by frequency and guiding each range of frequencies to a cell tuned to that range. This would enable much higher conversion efficiencies within each cell, reducing the need for cooling. It would also remove the need for transparency to make multi-junction cells.
Second point: I’ve talked to the people operating these gasification systems, not just the startups. The numbers are all consistent. Yes, gasification costs energy, and gasifying coal would not make sense (unless you’re WW2 Germany). But the process can work with any organic material (including plastics and solvents), not just fossil fuels or dry biomass and the like, as long as the water concentration isn’t excessive (I’ve been told up to ~20%), and consumes a bit less than half the energy content of the fuel. The rest is what you can get from the syngas, most of which is in the hydrogen, and fuel cells are about 60% efficient if you want to use it to make electricity. That’s where the 30% number comes from. There are plants doing this using agricultural waste, MSW, ASR, construction waste, medical waste, hazardous waste, food waste, and other feedstocks that otherwise either have little value or are expensive to dispose of.
You can certainly make Fresnel lenses that focus light, but without some sort of active control, it’s not physically possible to focus light from an unknown direction onto the same spot. That would be a thermodynamic law violation by focusing blackbody radiation. So what’s the advantage of this metamaterial stuff over Fresnel lenses? (Those work well enough, but of course aren’t quite economically practical.)
Also, that metamaterial company you mentioned, their website shows regular solar panels with this metamaterial coating on them, not a system that focuses light onto smaller PV panels.
I’m of course aware of the split-spectrum solar proposals using diffraction gratings, but that’s another thing that died off with the fall in PV prices.
Coal gasification typically has exergy efficiency <50%. You can get ~60% exergy efficiency, but biomass would certainly be worse than coal. Some plastics might be similar, I guess, but for wood you’d be looking at maybe 1.6x the losses, so something like 36% exergy efficiency from biomass to syngas. Then with 60% conversion to electricity you have ~22% efficiency, worse than boilers & steam turbines and with higher capital costs.
Yes, some simulations of wood gasification have given better numbers, but I don’t trust them. Coal gasification is much better understood, it’s used on a large scale in China, we know how it performs in practice, and we know biomass gasification is worse.
Combined cycle gas turbines can do 60% efficiency, and fuel cells are more expensive than those, so you probably wouldn’t use fuel cells.