[idibidiart]

Solar is not free above sunk cost? We've ran a whole house in AZ exclusively on solar the last 7 years, with a ~$40K investment. Would this consume so much electricity that the initial cost will not be recouped before the solar system degrades beyond use? What's the math you're inferring from?

[Retric]

Solar is ~20% efficient LED's are less than ~40% efficient so you would need more land area for solar farms than you save by growing indoors. On top of that you need to pay for all your capital costs.

There are other issues, but if this was close to cost effective you would be seeing this in Iceland which gets little sunlight in the winter and has cheap energy costs. Instead they use suplimental lighting inside green houses to boost production.

[idibidiart]

I thought the vertical stacking makes more efficient use of the light than the single layer you find in a farm or green house. I thought that means even though the light is produced inefficiently the vertical stacking cancels out that inefficiency. Moreover, the optimization of the plant's exposure to light through automated means adds to increased efficiency in the plant's use of the light.

[Retric]

Numbers matter.

45% of the light is in the photosynthetic active wavelength range in a normal farm vs ~20% solar panels w/ transmission conversion losses etc + 40% LED = ~8% of the incoming light is now useful for photosynthesis.

So, you need a huge increase in efficiency ~400+% just to break even.

PS: Not that their using solar power, but it's still worth considering.

[idibidiart]

What does the 45% of light that is in the photosynthetic range have to do with the with the efficiency of solar cells and LEDs? It would be more direct to compare % of natural light that is in photosynthetic range with % of LED light that is in that range. If you have a formula on which you're basing your assumptions then write it down so I can understand and examine your logic without any misunderstanding. Else, you're making hand wavy assumptions, with statements like "numbers matters" without clearly stated relationship between said numbers.

[Retric]

Ideally 100% of LED light is in the photosynthetic rage. It looks like there using white LED's which are less efficient AND not optimal for plants. Sill, assuming the 'best case' using current mass market tech.

  Sunlight > photosynthisis (45%)   = 45%.
  Sunlight > solar cell (22%) > conversion, storage, transmission (90%) 
  > LED (40%) > photosynthisis(100%) = 8%

reality is LED efficecy drops over time and LED light is not quite 100% ect but this is the optomistic best case numbers.

[idibidiart]

but what stops a structural technique for maximizing light usage by plants (like stacking or some more optimal structural pattern, such as the natural tree pattern [1] optimized by nature) from achieving 4X or more increase in efficiency of light usage?

1. http://online.wsj.com/news/articles/SB1000142405297020355030...

[Xixi]

You are forgetting a "small" difference between Japan and Iceland: Japan is overpopulated and doesn't have enough land to grow its own food, thus relying on importations to feed itself. On the other hand Iceland is mostly empty.

As you can imagine the price of land is quite different...

[Retric]

68.4% of Japan is forests. (Just look at some aerial maps). The issue is japan is not flat not that it's overcrowded. Even still they have enough room for 1.2 million cows which is horribly inefficient use of farm land.

PS: They have had rice subsidies over 700% and it's still not cost effective to convert more forests to farmland. Growing food in doors works due to subsides but it's hardly necessary.