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Crops under solar panels can be a win-win

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"Solar panels might seem like they’re in direct competition with plants. One is catching sunlight to do photosynthesis, the other wants to take it to push electrons. Surely Highlander rules apply, and there can be only one on a plot of land, right?

In reality, it’s not a zero-sum game. Some plants will burn in direct sun, after all, and so there are plenty of food crops that would be happy to share their space with panels. And as a new study led by the University of Arizona’s Greg Barron-Gafford shows, the combination isn’t even necessarily a compromise—there are some synergies that can bring significant benefits to a solar-agriculture."

https://arstechnica.com/science/2019/09/crops-under-solar-panels-can-be-a-win-win/

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It strikes me that even sun-loving plants could be accomodated, with taller panels and perhaps a slightly less dense panel coverage. The more we learn about it the better the yeild for both. 

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Too bad we can't just create something like a Triffid and put it on a treadmill. But as some plants and vines are capable of movement, or at least of exerting mechanical force, perhaps the idea is not as crazy as it sounds.

As far as panels go, well, plants don't seem to like green light too much and end up chucking most of it back at us. Otherwise, we would see them as black. Am I right? So how about panels designed and positioned to take advantage of that?

Also, as I understand it, the efficiency of most panels, on the market today, is only about 20%. Meanwhile, the efficiency of plants, like sugar canes, is about 8% (chemical) and with advances in technology, those ratios could well change. Something to think about.

Edited by Star Walls

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6 hours ago, Star Walls said:

Too bad we can't just create something like a Triffid and put it on a treadmill. But as some plants and vines are capable of movement, or at least of exerting mechanical force, perhaps the idea is not as crazy as it sounds.

As far as panels go, well, plants don't seem to like green light too much and end up chucking most of it back at us. Otherwise, we would see them as black. Am I right? So how about panels designed and positioned to take advantage of that?

A solar cell that only absorbs green light? Is that really going to improve things? The solar cell gets less efficient, and the plant gets the same sunlight as before, just without the green. Things cool off a bit for the plant, which improves growing, perhaps. But you cut out maybe half the light for the cell, since the solar spectrum peak is in the yellow/green part of the spectrum. I'm not seeing that as a win-win, since you compromise the solar production.

There are applications where the solar cells are transparent, and only grab a fraction of the light, such as being used on top of windows in office buildings. (in development; I don't know if they are commercially available). Maybe you could apply the idea to greenhouses, where the emphasis is on plant growth rather than electrical generation (so the electricity would be the bonus), but for solar utility installations I don't see how it improves things

 

6 hours ago, Star Walls said:

Also, as I understand it, the efficiency of most panels, on the market today, is only about 20%. Meanwhile, the efficiency of plants, like sugar canes, is about 8% (chemical) and with advances in technology, those ratios could well change. Something to think about.

You think there's a lot to be had in the efficiency of photosynthesis?

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I have read of improved pasture growth on some solar farms (which shared with sheep). This was in Australia - but whilst I can't recall the source or details it was a result of both partial shade and rain runoff from panels. In low rainfall situations they will concentrate the rainwater in rows along (in S. Hemisphere) the Northern edge of panel rows, where wetter soil will support plant growth both in front as well as under that edge. I think between rows got advantage from the partial shading, with more shading in Winter as well as mornings and afternoons,  less in Summer and middle of the day; rather than see this as less than ideal I suspect it just changes the plant species selection. 

I don't recall the spacings between panels were changed; these were set up for maximum solar output from the land area. But they were mounted in "conventional" angled rows and there are different mounting setups that are growing in popularity. I've noticed the growing use of nearly flat, tightly packed arrays for solar farms that are relatively low to the ground and that won't suit crops or pasture and grazing. I believe that, whilst they lose some efficiency by not being ideally tilted, these are using construction methods that significantly reduce setup costs and that makes up for it.

I suspect most solar farms won't be giving much consideration to combining agriculture with solar farms.

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11 minutes ago, Ken Fabian said:

I suspect most solar farms won't be giving much consideration to combining agriculture with solar farms.

I suspect that that will depend on location, here in the UK farmers are constantly looking to maximise their profits, and grass pretty much grows everywhere and livestock often bennefits from shade.

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Quote

I suspect most solar farms won't be giving much consideration to combining agriculture with solar farms.

The best place to put solar panels are: roofs and roads. Roofs don't require any special treatment. As showed by Musk, solar-tile can be indistinguishable from regular tile. Roads would require rethinking entire solar panel design. The most optimal IMHO would be invention of special photon-absorbing paints. Agricultural farms should be in agricultural skyscrapers with hydroponics. It has many advantages over traditional farming. Much smaller water usage. Minimal or none usage of pesticides. Entire year fresh vegetables and fruits near house.

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5 minutes ago, Sensei said:

Much smaller water usage.

But much more energy to distribute it, the most efficient balance is, almost, always in a comprimise. 

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9 hours ago, swansont said:

A solar cell that only absorbs green light? Is that really going to improve things? The solar cell gets less efficient, and the plant gets the same sunlight as before, just without the green. Things cool off a bit for the plant, which improves growing, perhaps. But you cut out maybe half the light for the cell, since the solar spectrum peak is in the yellow/green part of the spectrum. I'm not seeing that as a win-win, since you compromise the solar production.

There are applications where the solar cells are transparent, and only grab a fraction of the light, such as being used on top of windows in office buildings. (in development; I don't know if they are commercially available). Maybe you could apply the idea to greenhouses, where the emphasis is on plant growth rather than electrical generation (so the electricity would be the bonus), but for solar utility installations I don't see how it improves things

I was just thinking it's a waste of time chucking green light at plants. It gets reflected into space or wherever.  So, yes, something like a greenhouse that skims off the part of the spectrum the plant does not need. Meanwhile, our plant can happy produce oxygen and food. And, as you point out, the temperature drop could aid plant growth. And, yes, the emphasis would be on plant/crop growth and perhaps making more efficient use of land.

 

Quote

You think there's a lot to be had in the efficiency of photosynthesis?

I believe in principle you can get up to 26% efficiency with photosynthesis; not easy in practice.  But It would certainly be progress if we could ever match, say, the efficiency of panels. You could have oxygen giving plants in place of those costly things.

 

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7 minutes ago, Star Walls said:

I was just thinking it's a waste of time chucking green light at plants. It gets reflected into space or wherever.  So, yes, something like a greenhouse that skims off the part of the spectrum the plant does not need. Meanwhile, our plant can happy produce oxygen and food. And, as you point out, the temperature drop could aid plant growth. And, yes, the emphasis would be on plant/crop growth and perhaps making more efficient use of land.

In that context, the green light is wasted, and you would be recovering that wasted energy. In that scenario, doing so makes theoretical sense. Whether it ends up being practical requires more thought and study.

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7 hours ago, dimreepr said:

I suspect that that will depend on location, here in the UK farmers are constantly looking to maximise their profits, and grass pretty much grows everywhere and livestock often bennefits from shade.

Australia does have an abundance of available land with low agricultural value - so yes, co-existence might look better where that is not the case.

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7 hours ago, Sensei said:

The best place to put solar panels are: roofs and roads. Roofs don't require any special treatment. As showed by Musk, solar-tile can be indistinguishable from regular tile. Roads would require rethinking entire solar panel design. The most optimal IMHO would be invention of special photon-absorbing paints. Agricultural farms should be in agricultural skyscrapers with hydroponics. It has many advantages over traditional farming. Much smaller water usage. Minimal or none usage of pesticides. Entire year fresh vegetables and fruits near house.

I think the endgame for solar is ubiquitous incorporation into built structures, including roads as well as roofs.

I do expect to see ever more incorporation of solar into roof (and wall) materials. I think it needs to be either very durable - able to last as long as the roof - or easily replaceable. Photon absorbing paints that can be re-done at low cost might be an alternative to durability - but I have a particular liking for durability. If roofing sheets and tiles can be done at low cost I don't doubt it will be a popular inclusion that could become ubiquitous. 

Roads? This seems like something that demands either durability or systems that allow easy replacement. I've long liked the idea but I think it will be much harder; solar awnings over roads or just alongside may continue to be more cost effective. I don't buy the arguments that PV is too fragile; solar powered blinking road studs appear to be durable and they are made to cope with tyres hitting them at speed, deliberately, so impacts can be felt and heard to alert drivers. Highest wear areas on roads as well as those that are excessively shaded can be avoided entirely and still leave large areas available. 

I wonder if induction charging capability could be built into roads where vehicles stop - approaches to intersections as well as parking. The synergy of sun exposed surfaces that connect to towns and cities and major centres of energy demand as well as more directly for transport does make it appealing. I think incorporating PV into road is being shown to work, but it is a long way from cost effective. Yet.

Edited by Ken Fabian

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Sorry for reviving this fallen thread...

I was viewing solar energy price as bottom-limited by land lending prices. The described co-usage of land might drive solar-energy prices further down, at least in theory.

But knowing about low efficiency of plants (and being a chemistry idiot), I want to ask if an alternative solution is more likely - could it be, again in theory, more efficient to produce edible sugars from PV-produced electric energy than by plant photosynthesis?

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On 9/6/2019 at 8:55 AM, dimreepr said:

It strikes me that even sun-loving plants could be accomodated, with taller panels and perhaps a slightly less dense panel coverage. 

I do have to question the benefits of decreasing the density of solar panels, and how much more that increases the cost for each watt hour capacity you add.

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On 9/28/2019 at 10:50 AM, Danijel Gorupec said:

Sorry for reviving this fallen thread...

I was viewing solar energy price as bottom-limited by land lending prices. The described co-usage of land might drive solar-energy prices further down, at least in theory.

But knowing about low efficiency of plants (and being a chemistry idiot), I want to ask if an alternative solution is more likely - could it be, again in theory, more efficient to produce edible sugars from PV-produced electric energy than by plant photosynthesis?

So the problem is less the efficiency of translating photons into energy, but the issue is more regarding the carbon fixation process (i.e. the Calvin cycle). Such pathways are generally incredibly difficult and costly to set up in a cell-free system. So even if we could generate more net energy using PV system we still need to have something that actually integrates CO2 into hydrocarbons. There are efforts in creating that in an artificial system but I am only aware of ways to potentially increase efficiency of the cycle (which especially in so-called C3 plants is especially inefficient). But I doubt that there are actual artificial systems that come close to even that.

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