3 ms·

If your implication is that one can simply stack more junctions, that is fine to try from a research standpoint and for mass-constrained applications like space

by _6kzb 5y ago

If your implication is that one can simply stack more junctions, that is fine to try from a research standpoint and for mass-constrained applications like space exploration, but the economics get substantially worse for normal applications. It's also the case that multi-junction cells (at the infinite limit) have a max theoretical efficiency that is about double the theoretical max of the best single-junction systems. That also ignores recombination effects at the interfaces between systems, which are also almost pretty gnarly.

whatshisface 5y ago
That's my point, it's an economic limitation masquerading as a physical limitation.
- _6kzb 5y ago
  Given the definition of economics, I'd say whether it is technically one or the other is kind of meaningless. If you throw enough resources at something, you can achieve all manner of things that don't make any practical sense. Whether such a situation can be more properly understood in terms of "just needing a lot of money," or "having physical limitations making it impractical" is a pants vs. trousers type question. ETA: I didn't follow up my point very strongly earlier, but "double" is important here. Spending many multiples of resources to get cells that at most have double the efficiency of standard single junction cells is not what we usually think of when we think scientific breakthrough. It's certainly not scaling on the level of Moore's law, the expectation that the economy grow something like 3% a year, or various other exponential growth patterns we have come to take as normal. A fun chart to look at for efficiency is provided by NREL [1]. Half the talks on photovoltaics seem to add it somehow. An important point is technologies can get stuck in a particular parameter space for large amounts of time despite tons of money being poured in. Efficiency improvements are not guaranteed, they cost a lot, and they are often tiny when they occur. My macro point, if I have one, is society is best off trying to grab low hanging fruit from multiple disciplines that feed into photovoltaics, and media should try to emphasize that effort rather than pushing cell efficiency improvements, which are not going to do a whole lot by themselves. [1] https://www.nrel.gov/pv/cell-efficiency.html https://www.nrel.gov/pv/cell-efficiency.html

by _6kzb 5y ago

whatshisface 5y ago

That's my point, it's an economic limitation masquerading as a physical limitation.

_6kzb 5y ago
Given the definition of economics, I'd say whether it is technically one or the other is kind of meaningless. If you throw enough resources at something, you can achieve all manner of things that don't make any practical sense. Whether such a situation can be more properly understood in terms of "just needing a lot of money," or "having physical limitations making it impractical" is a pants vs. trousers type question. ETA: I didn't follow up my point very strongly earlier, but "double" is important here. Spending many multiples of resources to get cells that at most have double the efficiency of standard single junction cells is not what we usually think of when we think scientific breakthrough. It's certainly not scaling on the level of Moore's law, the expectation that the economy grow something like 3% a year, or various other exponential growth patterns we have come to take as normal. A fun chart to look at for efficiency is provided by NREL [1]. Half the talks on photovoltaics seem to add it somehow. An important point is technologies can get stuck in a particular parameter space for large amounts of time despite tons of money being poured in. Efficiency improvements are not guaranteed, they cost a lot, and they are often tiny when they occur. My macro point, if I have one, is society is best off trying to grab low hanging fruit from multiple disciplines that feed into photovoltaics, and media should try to emphasize that effort rather than pushing cell efficiency improvements, which are not going to do a whole lot by themselves. [1] https://www.nrel.gov/pv/cell-efficiency.html https://www.nrel.gov/pv/cell-efficiency.html