growing crops under artificial lighting

I'm getting tired of the widely-repeated claim that it is impractical to
grow crops under artificial light (particularly if your power source is
solar). It just doesn't make sense, for two reasons. First, if your
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth. Second, though there are losses in converting the sunlight to
electricity and back to light, you can make the light you convert it to
be 100% pure clorophyll-absorbed prime wavelength, whereas the light
that falls on Earth is mostly wavelengths that plants can't use anyway.

Put those factors together, and I suspect that a km^2 of solar cells (or
similar solar power collector area) could grow MORE than one km^2 of
crops.

But suspicions aren't worth much; I really need some numbers. And here
my ignorance is getting in the way, and I'd like to correct that.
Can anyone point me to sources of data on absorption spectra for
important crop species, etc.?

I've started googling but have turned up surprisingly little so far.
(E.g., I know the difference between chlorophyll A and B, but I have no
info on what the relative balance between them is for any relevant
plant.)

Thanks,
- Joe

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| Joseph J. Strout Check out the Mac Web Directory: |
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Joe Strout wrote:
I'm getting tired of the widely-repeated claim that it is impractical to
grow crops under artificial light (particularly if your power source is
solar). It just doesn't make sense, for two reasons. First, if your
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth. Second, though there are losses in converting the sunlight to
electricity and back to light, you can make the light you convert it to
be 100% pure clorophyll-absorbed prime wavelength, whereas the light
that falls on Earth is mostly wavelengths that plants can't use anyway.

There are a couple of caveats.
Current crop plants need more than one wavelength to thrive.
If you just feed them one then the plants do not perform as well as they
might as they use the spectrum of light to deduce the crowding of the plant,
as obviously the solar spectrum can't change...


Put those factors together, and I suspect that a km^2 of solar cells (or
similar solar power collector area) could grow MORE than one km^2 of
crops.

Unless you really have to use solar cells, you probably don't want to.

Unless you need to beam the energy over long distances, the best way
seems to simply be to use mirrors.
The solar collector points at the sun, and bounces the light through
a small window in your rotating greenhouse.
Distribute the light internally.

This beats current solar cells/lights by a factor of several per unit
area.

"Ian Stirling" wrote in message
...
Joe Strout wrote:
I'm getting tired of the widely-repeated claim that it is impractical to
grow crops under artificial light (particularly if your power source is
solar). It just doesn't make sense, for two reasons. First, if your
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth. Second, though there are losses in converting the sunlight to
electricity and back to light, you can make the light you convert it to
be 100% pure clorophyll-absorbed prime wavelength, whereas the light
that falls on Earth is mostly wavelengths that plants can't use anyway.

There are a couple of caveats.
Current crop plants need more than one wavelength to thrive.
If you just feed them one then the plants do not perform as well as they
might as they use the spectrum of light to deduce the crowding of the
plant,
as obviously the solar spectrum can't change...


Put those factors together, and I suspect that a km^2 of solar cells (or
similar solar power collector area) could grow MORE than one km^2 of
crops.

Unless you really have to use solar cells, you probably don't want to.

Unless you need to beam the energy over long distances, the best way
seems to simply be to use mirrors.
The solar collector points at the sun, and bounces the light through
a small window in your rotating greenhouse.
Distribute the light internally.

This beats current solar cells/lights by a factor of several per unit
area.

If you have a multi-layered facility, it might be difficult to bounce light
to all floors.

Joe Strout wrote in message ...
I'm getting tired of the widely-repeated claim that it is impractical to
grow crops under artificial light (particularly if your power source is
solar). It just doesn't make sense, for two reasons. First, if your
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth.

Most pundits assume that if you're in orbit, you're going to use
reflected light, simply because its cheaper and more efficient.
However, if your solar power units are cheap enough, then there's no
reason why you can't use electrical power. But why would you bother?

Second, though there are losses in converting the sunlight to
electricity and back to light, you can make the light you convert it to
be 100% pure clorophyll-absorbed prime wavelength, whereas the light
that falls on Earth is mostly wavelengths that plants can't use anyway.

Put those factors together, and I suspect that a km^2 of solar cells (or
similar solar power collector area) could grow MORE than one km^2 of
crops.

The problem arises for growing food on the moon, and here it's not a
question of energy production, but of storage during the night. A
couple of solutions a

- use plants that can grow for 7 / 14 days. This appears to be
practicel for many plants if chilled at night to just above 0.
- Use a lunar orbiting power plant. The issue here is that there is no
Lunar Stationary orbit near to the moon, so it could be a long way to
beam the power.
- Use a lunar grid to transport electricity from one side to the
other. This could work, but is capital intensive.


But suspicions aren't worth much; I really need some numbers. And here
my ignorance is getting in the way, and I'd like to correct that.
Can anyone point me to sources of data on absorption spectra for
important crop species, etc.?

I've started googling but have turned up surprisingly little so far.
(E.g., I know the difference between chlorophyll A and B, but I have no
info on what the relative balance between them is for any relevant
plant.)

Can't help here, but bear in mind you want to optimise output, so it
won't be worth saving electricity if it reduces your yield.

For that matter, there seems to be no conclusions as to what yield you
could get with the optimum lighting, CO2 concentration, timings,
temperature, water etc, with good GM crops. I would suspect you could
get 100 tons per hectare per year for carbo hydrate crops.

Lets say with the right wavelengths, you need 500W/m2, mx = 300W / m2
average, = 3MW per Hectare. At 100W / m2 solar cell output, and 75%
efficient lighting, That needs 4 Hectares of solar panels weighting 40
tons. A 1 hectare "green house" will weigh a lot more than 40 tons, so
it would appear that using electricity is reasonable.

100 tons would feed 200 people. If they want more than rice and
potatoes, make it 100 people, and if they want chicken, you're
probably down to 50 people.

Thanks,
- Joe

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'

In article ,
Ian Stirling wrote:

There are a couple of caveats.
Current crop plants need more than one wavelength to thrive.
If you just feed them one then the plants do not perform as well as they
might as they use the spectrum of light to deduce the crowding of the plant,
as obviously the solar spectrum can't change...

True, I was oversimplifying. Still, my basic point is that with
gas-discharge and solid-state lighting, we have great control over the
spectrum of the light we generate. We can generate light which is more
or less perfectly tuned to what our crops need. Compare this with
sunlight, which is about half unusable (most of it is infrared, which
plants simply don't use).

Unless you really have to use solar cells, you probably don't want to.

Unless you need to beam the energy over long distances, the best way
seems to simply be to use mirrors.
The solar collector points at the sun, and bounces the light through
a small window in your rotating greenhouse.
Distribute the light internally.

This beats current solar cells/lights by a factor of several per unit
area.

Yes, I know, I'm not saying that artificial lighting is better than
natural lighting when natural lighting is available. My point is that,
when natural lighting is not available or practical for whatever reason,
you don't give up on the whole idea and conclude that crops can only be
grown on Mars or some such. Instead, you put in artificial lights, and
this is a perfectly reasonable thing to do.

Basically I'm trying to debunk claims I hear bandied about, from Zubrin
and others, that growing crops under artificial light is thoroughly
impractical due to energy requirements. I believe that's a
politically-motivated load of crap, and I'd like to demonstrate that.

Cheers,
- Joe

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'

Joe Strout wrote:
In article ,
Ian Stirling wrote:

There are a couple of caveats.
Current crop plants need more than one wavelength to thrive.
If you just feed them one then the plants do not perform as well as they
might as they use the spectrum of light to deduce the crowding of the plant,
as obviously the solar spectrum can't change...

True, I was oversimplifying. Still, my basic point is that with
gas-discharge and solid-state lighting, we have great control over the
spectrum of the light we generate. We can generate light which is more
or less perfectly tuned to what our crops need. Compare this with
sunlight, which is about half unusable (most of it is infrared, which
plants simply don't use).
snip
This beats current solar cells/lights by a factor of several per unit
area.

Yes, I know, I'm not saying that artificial lighting is better than
natural lighting when natural lighting is available. My point is that,
when natural lighting is not available or practical for whatever reason,
you don't give up on the whole idea and conclude that crops can only be
grown on Mars or some such. Instead, you put in artificial lights, and
this is a perfectly reasonable thing to do.

Perhaps.

How much does your garden weigh.
With silver pumps,
And Cabbage Heads,
......

Basically I'm trying to debunk claims I hear bandied about, from Zubrin
and others, that growing crops under artificial light is thoroughly
impractical due to energy requirements. I believe that's a

Maybe also mass requirements too.
Solar cells can be quite heavy, as can lights, thermal radiators, hydroponic
systems, growing plants, pressure vessels, even atmospheres.

Considering only dried food, you can get down to under around 1Kg/day.

(recycling most water into water and O2, using metabolic water to makeup
losses)

A garden at the very least means that you need (over stuff yuu wouldn't
need) lights (meaning either extra solar panels, or mirrors) extra volume
so a larger pressure vessel, segmented enviromental system (plants and
humans don't want quite the same things), thermal radiators, ...

I don't think it's a clear win until you'r into 5 year missions.

Joe Strout wrote:
I'm getting tired of the widely-repeated claim that it is impractical to
grow crops under artificial light (particularly if your power source is
solar). It just doesn't make sense, for two reasons. First, if your
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth. Second, though there are losses in converting the sunlight to
electricity and back to light, you can make the light you convert it to
be 100% pure clorophyll-absorbed prime wavelength, whereas the light
that falls on Earth is mostly wavelengths that plants can't use anyway.

Put those factors together, and I suspect that a km^2 of solar cells (or
similar solar power collector area) could grow MORE than one km^2 of
crops.

But suspicions aren't worth much; I really need some numbers. And here
my ignorance is getting in the way, and I'd like to correct that.
Can anyone point me to sources of data on absorption spectra for
important crop species, etc.?

I've started googling but have turned up surprisingly little so far.
(E.g., I know the difference between chlorophyll A and B, but I have no
info on what the relative balance between them is for any relevant
plant.)

Umm... If google for it in this group you'll find fairly detailed
calcualtions I posted on this.


Thanks,
- Joe

,------------------------------------------------------------------.
| Joseph J. Strout Check out the Mac Web Directory: |
| http://www.macwebdir.com |
`------------------------------------------------------------------'

--
Sander

+++ Out of cheese error +++

"Mike Rhino" wrote in message ...
"Ian Stirling" wrote in message
...
Joe Strout wrote:
solar power plant is in orbit where it receives sunlight 24/7, you've
already got about seven times as much sunlight to start with as a field
on Earth.

I don't think this is true unless you are in an extremely high orbit.
In LEO orbits, like the space station's, satellites go through a
sunrise and sunset about every 90 min. That seriously cuts the amount
of actual light you're getting. Of course as you go higher up, you're
getting less and less earth shaded night--but from about 250-1500 nm
you're in the thick of the Van Allen belts. Any plant growing station
is going to need significant rad protection in htis area.
Anyway the best place to do this would be GEO or lunar L-1, as you're
well above most Van Allen radiation and rarely blocked by the earth.

There are a couple of caveats.
Current crop plants need more than one wavelength to thrive.

Chloraphyll is not the only bit of cell machinery that requires
sunlight to work. Many other proteins are formed with help from the
sun, and not all at even visible wavelengths. This is true of nearly
all species on earth, even humans, as UV helps regulate folic acid and
Vitamin D, and is a cause of the existence of different skin colors.
Of course, the result of a frequency deprivation won't always be
death--but less overall crop health is likely.

Unless you need to beam the energy over long distances, the best way
seems to simply be to use mirrors.
The solar collector points at the sun, and bounces the light through
a small window in your rotating greenhouse.
Distribute the light internally.
This beats current solar cells/lights by a factor of several per unit
area.

If you have a multi-layered facility, it might be difficult to bounce light
to all floors.

Not really. Fibre optics, light pipes, and solar diffusers can be used
quite effectively (and still many times more efficiently than solar
cells/lights). The Artemis Project and the Lunar Reclamation society
have done quite a bit of study and research in these areas, although
their focus is on lunar day/night cycles that require a mix of both
natural and artificial light.

Tom Merkle

Joe Strout wrote in message ...

Yes, I know, I'm not saying that artificial lighting is better than
natural lighting when natural lighting is available. My point is that,
when natural lighting is not available or practical for whatever reason,
you don't give up on the whole idea and conclude that crops can only be
grown on Mars or some such. Instead, you put in artificial lights, and
this is a perfectly reasonable thing to do.

Basically I'm trying to debunk claims I hear bandied about, from Zubrin
and others, that growing crops under artificial light is thoroughly
impractical due to energy requirements. I believe that's a
politically-motivated load of crap, and I'd like to demonstrate that.

-Joe

That depends on what you mean by thoroughly impractical. From NASA's
closed cycle experiments, we've determined that it takes about 5 acres
of crops to fully support a single human being (for both staple food
and CO2 scrubbing). However, if you're willing to scrub your CO2
elsewhere and just look to plants for food, it still takes about 1.5
acres of well chosen plants to support that human. That means if
you've got a colony of 20 people, you already require 30 acres of
producing crops to fully support them. If you have to provide that
light artifically, you really are talking about a damn lot of energy.

Of course, in all likelihood in the beginning of space colonization
only 10% of food would actually be fresh produce grown in situ. This
is more than enough for most people to feel healthy, and for a colony
of 20 people would only require a modest 3 acres--more reasonable,
really.

The fault in Zubrin's logic lies not in the analysis of how much light
is required to fully support a human, but in the assumption that fully
supporting a human with in situ crops would be reasonable at an early
stage of exploration/conolization. Clearly it would not be.

No matter that day/night cycles on Mars are similar to earth's--the
first group of 10 colonists/explorers are not going to be able to
erect 15 acres of sun lit habitable volume/soil for their life
support. The primary driver will not be sunlight anyway but habitable
volume. Zubrin's own analysis of Martian conditions concluded that
solar power was not sufficient for a two year stay--some sort of
nuclear power would be required for life support. If you already have
to have a 500KW nuclear reactor, it makes little difference in weight
or volume if you quadruple the power to 2 MW and allow most of that
for growing crops.

Zubrin conveniently forgets the scaleability of nuclear power when he
argues for 'natural' crop growing on Mars, not considering that it
would be an extreme burden to erect a greenhouse with even one acre of
soil, especially one with a transparent top. Far more likely for early
colonists are volume saving stacks of hydroponic crops, with solar
collectors and light diffusers providing the majority of light and
some help from articial light for light-intensive crops.

Tom Merkle

In article ,
Joann Evans wrote:
But will most plants grow normally under 24/7 sunlight? Would you not
have to 'create' a nighttime period for some of them?

As I understand it, most of them have no problems at high latitudes on
Earth, where there is no real night in mid-summer. (They may have
problems with the short growing season, but not with the light.)
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