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> PS: Photovoltaic panels with 20% efficiency are already close to the theoretical limit (see this chapter’s endnotes Current, world record for concentrated sol

> PS: Photovoltaic panels with 20% efficiency are already close to the theoretical limit (see this chapter’s endnotes Current, world record for concentrated solar is 46%. They are likely referring to the theoretical limit for crystalline silicon based cells (~30% IIRC). This is due to silicon's particular band gap. The record is held by multi-junction cells, which don't suffer from this limitation (which is part of their problem, as they use materials far more expensive than silicon).

Retric 11y ago
I don't think you need to be overly generous when they suggest the UK needs to be both 100% energy independent and 100% free from fossil fuels, and grow 100% of it's food locally, when the UK imports ~35% of it's electricity in 2013 and ~40% of it's food (1). Let alone fossil fuels. And if we can't meet those goals we need to do X. 1: In 2010, the UK produced 73% of ‘indigenous-type foods’, and is about 60% self-sufficient when exports and local consumption are set against production http://www.foodsecurity.ac.uk/food/uk-facts.html http://www.foodsecurity.ac.uk/food/uk-facts.html
- johncolanduoni 11y ago
  I wasn't arguing for all his calculations, it's just that his evaluation of the theoretical limit of crystalline silicon cells is accurate. He is correct that it is unlikely that they will get much closer to the theoretical limit than 20% in real life situations. Some GenIV nuclear reactor technologies have a somewhat clearer path to viability than multi-junction solar cells, which have not been able to beat traditional cells in a price-to-performance ratio. We don't even know if there exist materials and processes that can replicate the performance without the costs; see high temperature superconductivity for a technology that's been stuck at that stage for a while, even in the face of the helium shortage.
  - selimthegrim 11y ago
    There are multiple well-attested routes around the Shockley-Quiesser limit most of which do not involve just silicon. One, which MacKay touches upon, is multi-junction systems. Another, which he does not (not being an expert in the field) is via so-called multiple-exciton generation systems. Contrary to most engineers' understanding, this phenomenon is pretty well explained from the point of a low-energy continuum QFT for the materials that most care about for implementation. The real game changer would be to mate these systems with topologically nontrivial materials with surface charge transport protection. Unfortunately with current fabrication capabilities, 70% of the conductivity is in the bulk, which does not possess the topological prohibition to one-particle (or one e-h pair) backscattering. (It would also be interesting to see if the known allowability of 2 particle backscattering applies to excitons in these systems)

Retric 11y ago

I don't think you need to be overly generous when they suggest the UK needs to be both 100% energy independent and 100% free from fossil fuels, and grow 100% of it's food locally, when the UK imports ~35% of it's electricity in 2013 and ~40% of it's food (1). Let alone fossil fuels. And if we can't meet those goals we need to do X. 1: In 2010, the UK produced 73% of ‘indigenous-type foods’, and is about 60% self-sufficient when exports and local consumption are set against production http://www.foodsecurity.ac.uk/food/uk-facts.html http://www.foodsecurity.ac.uk/food/uk-facts.html

johncolanduoni 11y ago
I wasn't arguing for all his calculations, it's just that his evaluation of the theoretical limit of crystalline silicon cells is accurate. He is correct that it is unlikely that they will get much closer to the theoretical limit than 20% in real life situations. Some GenIV nuclear reactor technologies have a somewhat clearer path to viability than multi-junction solar cells, which have not been able to beat traditional cells in a price-to-performance ratio. We don't even know if there exist materials and processes that can replicate the performance without the costs; see high temperature superconductivity for a technology that's been stuck at that stage for a while, even in the face of the helium shortage.
- selimthegrim 11y ago
  There are multiple well-attested routes around the Shockley-Quiesser limit most of which do not involve just silicon. One, which MacKay touches upon, is multi-junction systems. Another, which he does not (not being an expert in the field) is via so-called multiple-exciton generation systems. Contrary to most engineers' understanding, this phenomenon is pretty well explained from the point of a low-energy continuum QFT for the materials that most care about for implementation. The real game changer would be to mate these systems with topologically nontrivial materials with surface charge transport protection. Unfortunately with current fabrication capabilities, 70% of the conductivity is in the bulk, which does not possess the topological prohibition to one-particle (or one e-h pair) backscattering. (It would also be interesting to see if the known allowability of 2 particle backscattering applies to excitons in these systems)