
LEDs Are Set to Revolutionize Greenhouse Farming (2014) - legodt
https://www.technologyreview.com/s/528356/how-leds-are-set-to-revolutionize-hi-tech-greenhouse-farming/
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Lerc
One question I have had on my mind is about solar powered LED lighting.

Solar cells capture a wider spectrum than plants (plants are green ergo not
green eaters).

At what levels of efficiency do solar cells and LEDs have to be before you
receive a net gain by having the solar cells in the sun instead of the plants.
How far away from that are we now?

Underground farming in arid regions seems like the best scope for something
like this.

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mdorazio
I don't have a definitive answer for you, but you can kind of back into a
rough approximation (someone please correct my math if I went astray).

High-efficiency solar cells are about 20% efficient across the daylight
spectrum.

For some reason, no one gives hard stats on how much energy LEDs waste as
heat, but the claims are that incandescents waste about 90% of energy input as
heat, and LEDs are about 80% more efficient than that. So let's say LEDs
convert about 80% of input power into light at their operating wavelengths as
a guess.

So if we put these together, we'll get about 16% of the input daylight back
out as light at the wavelengths we want.

According to wikipedia [1], about 47% of light that falls on chlorophyll is
wasted because it falls outside the ideal range for plants (400-700nm).
Another 3% or so is lost due to wavelength conversion. The rest we can't
really do anything about because it has to do with biological limitations. Put
another way, our total system has to be about 50% efficient to be better than
just putting the plants in the sun. As you can see, we're not even close. In
fact, it's not even possible since the theoretical maximum efficiency of solar
panels is only about 34% [2].

[1]
[https://en.wikipedia.org/wiki/Photosynthetic_efficiency](https://en.wikipedia.org/wiki/Photosynthetic_efficiency)
[2]
[https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...](https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit)

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TTPrograms
The Shockley-Queisser limit only applies to single-layer cells under
unconcentrated light. Different cell designs have surpassed it by significant
amounts in practice already.

~~~
mdorazio
Do you have a link where I can read more? I'm aware of light concentrators
being more efficient, but that defeats the whole point since the surface area
required is far more than size of the panel itself.

~~~
jsight
[https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...](https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit#Tandem_cells)

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tomeast
The Economist had some related content in this week's Technology Quarterly
([http://www.economist.com/technology-
quarterly/2016-06-09/fac...](http://www.economist.com/technology-
quarterly/2016-06-09/factory-fresh#section-2)) - I made note of the 2 LED
producers they mentioned: [http://www.valoya.com/](http://www.valoya.com/) and
[https://www.heliospectra.com/](https://www.heliospectra.com/)

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technotony
The next step is optimizing the plants to grow better in these greenhouse
conditions - currently the plants waste lots of energy. For example my
company, TAXA Biotechnologies[1], has identified a gene that doubles the rate
of growth of lettuce per unit light energy. It wouldn't work in the wild as
the cost is reduced pest-resistance but growing indoors there are other ways
to control that. [1]www.taxa.com

~~~
lisivka
Optimize for taste, not for fast growth, please. I don't want to pay for
lettuce with taste of straw.

~~~
thatswrong0
Last time I checked (it's been a while since I had a salad), lettuce already
doesn't have too much of a taste. I'd be surprised if they managed to mess
that up.

~~~
maxerickson
It really depends on the lettuce.

Iceburg seems to be intentionally useless. Romaine starts to have a little
flavor. Leaf lettuces have a wide range of flavors.

~~~
slyn
Iceberg is a texture, not a taste per se. Used in combination with other
greens and veggies it has a place.

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hooloovoo_zoo
Link to the paper
[http://arxiv.org/abs/1406.3016](http://arxiv.org/abs/1406.3016).

They do not seem to have accounted for the fact that the "waste" heat from
current solutions reduces the overall heating bill. Of course, electrical
heating is not usually as cost effective as other methods.

~~~
jacquesm
Greenhouses in NL use natural gas to heat and they are getting a serious
discount compared to homes and offices, compared to what they are paying for
gas heat any conversion from electricity to heat is a loss to them.

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groktor
Greenhouse farming really could be a good way to help tackle the waste/runoff
problem. I think Greenhouse farms could easily be closed systems with no need
to push polluted water back into the world. The dead zone in the gulf of
Mexico (all ocean dead zones actually) HAS to be dealt with pretty damn soon
as I understand it...

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1QAm1
Ceramic Metal Halide bulbs, at much lower wattage than HPS, but with more
power than LED seems to be the immediate compromise. A 315w Phillips Ceramic
MH will deliver a huge spectrum to the plants with less than half of the heat
of a comparable 600w HPS/MH. The cost is getting very close to traditional HPS
lights. LEDs do work, but they still use plenty of power, and are largely
unproven. Try to find a greenhouse/grow store that stocks ANY led fixures.
They have been cheap China crap for so long, that the better ones cost quite a
bit of $.

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known
It's already revolutionizing in India
[http://www.ujala.gov.in/](http://www.ujala.gov.in/)

