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.
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.