Quantum solar cells could explain why plants are green

[CurtisOliver]

I just wanted to share an article I found to be quite interesting.
Enjoy!

https://www.newscientist.com/article/2115224-quantum-solar-cells-could-explain-why-plants-are-green/

 

[Benm]

I agree with Cogwells critisism here.

Plants don't have much of a problem with light fluctiation at all, they even survive things like night.

Plants are not like electrical systems where demand must match supply exactly at all times either. The normal operation of a plant is to use sunlight to convert CO2 and water to sugars and eventually strach, cellulose, lignine etc. This is not a direct process however: There is an intermediate step where ADP is converted into ATP, which can provide a considerable buffer for a plant.

Also, plants do not typically go for maximum efficieny of the whole process at all. Light is not always a limiting factor in growth, and plants are very inefficient as it comes to their use of water: In a typical plant only 1 in about 1000 molecules of water is used for growth, the remainder just evaporates off.

The latter is quite a thing. If you have a sizeable house plant that needs 1 liter of water a week during summer (not that uncommon for something a meter tall), it would grow absolutely enormous if it fixed all that water. In fact it would grow a few kilograms of dry matter a weak, and since plants are 90% or so water, tens of kilograms a week in total weight. After one summer that 1 meter plant would fill your house with brances poking out on all sides.

Photovoltaic cells are more efficient than plants in capturing energy, by a large margin by now. The efficiencly of a plant is (usually far) under 1%, while a PV system can be well over 10%.

If this was not the case we'd be better off just planting trees and shoving them in the fireplace or power plant instead of installing any PV.

 

[AngelG]

I have read about another solar cells being proposed by a teenager - William Yuan has invented the nanotube solar cell in 2008 https://www.google.bg/url?q=http://...ggmMAk&usg=AFQjCNEjd89-TtE_0mQj_Zb4mIOuFZJd7g
but there is still no prototype. Afaik the most effective solar cell which exists is the 3-band cell invented by Australian researchers. It has 35% efficiency at the cost of 3 junctions of different semiconductors utilized. It won't be available for the households.

 

[Benm]

35% efficiency can be achieved under lab conditions with such exotic cell designs indeed. For the consumer market this is not economically viable though.

There is no way to get efficiency beyond 100%, which would be 5 to 10 times better than is currently installed rooftop. More recent rooftop systems are getting closer to 20% though.

None of this matters however. What counts in application on the ground, roofs etc is the price per watt generated. Space usually is -not- the limiting factor in a PV system, cost is. Lets say you had $5000 to invest in a PV system for your home. You could buy 20 m2 of 10% efficient solar panels for this, or 8 m2 of 20% efficient, state of the art, ones.

Provided your roof is 20 m2 or larger the less efficient system would be the more cost effective one (considering installation work cost is included in the price).

Very high efficiency solar panels are good for remote locations, such as space, but not for general purpose use.

In the other extreme case we could have some fairly rubbish panels that only produce 1% effiency, but if they are the same price as shingles to cover a roof they would still be a very sensible choice when replacing or building a new roof: 'free' power, albeit not that much of it per m2.

 

[AngelG]

Talking about costs, the governments could play better role in encouraging the green energy usage.
For example, they could remove the VAT tax on the solar cells when the citizens buy them to install them on their own roofs. They could also free/reduce "The green fee" tax on the consumed electricity for these households.
Now we have this tax, designed as response to an EU policy (they told us so) to sponsor the businessmen who decided to make money from the green energy powerhouses. The EU loves the regulations despite that this is against the capitalism and the free market idea...

The inefficient solar cells can be cheaper: The a-Si cells (no crystal) have about 6-9% eff. and have environmentally friendly technology.

 

[Seoul_lasers]

I was just going to add that this green phenomenon had been solved quite some time ago.
They're just publishing the findings to put all doubts to rest... Plants take in Red and Blue light... Green light is reflected due to the colour of Chlorophyll (a - f) C55H72O5N4Mg


On the subject of solar cells.
Si-photo cells are only sensitive on the blue side of the spectrum and cannot take in red light at all. They are quite poor at transforming light to electricity.




Breaking down 2 alternatives to Si photocells.

CdZeTe --
1. High absorption coefficient.
2. Ideal single junction bandgap (~ 1.5 eV).
3. Bandgap tunable from 1.5 to 2.24 eV (Cd1-xZnxTe).

GaAs --
1. Bandgap ~1.424eV
2. High absorption rate esp. IR
3. Held record for highest efficiency @28.8% back in 2014 for a single photocell. (now 39-42%)

GaAs is highly toxic... this is a big negative of this particular technology.


Have a look at the below link to see the other solar cell types and forms...
https://en.wikipedia.org/wiki/Cadmi...edia/File:Best_Research-Cell_Efficiencies.png

 

[Benm]

There are some interesting technologies out there for sure.

But as I said, what matters most is cost per installed kW, with available space usually not being the limiting factor in that.

Back in the 80s it was common to remark that waiting for more efficient solar cells would be worth it, as well as better leds in the 90s and such.

Nowadays both technologies are good enough to be economically viable. We commonly see LED lighting used by consumers since it just is a good deal overall - bulb cost has come down and power-cost savings over incandescent are huge. People will buy these things even without any legislation to ban incandescent lamps just because they save them money in the first year of operation.

Solar panels are currently in a similar situation: if you can supply back power to the grid at the same price per kWh you pay for taking power from the grid, this is a no brainer and putting PV up will earn itself back rapidly.

As i live in a highrise and don't own the roof of that i cannot do this, but if i had a house with a roof i'd certainly put PV up there under current dutch rules. Those rules are that you can deliver back power at the same price you pay for it, so you can abuse the grid as a bigass battery.

This system is prone to failure if many people do it tough, and in germany there are already large problems with grid stability on very sunny days. On a clear summer day so much PV power is produced that it overwhelms demand, so the excess is delivered for free to the european grid or even sold at a negative price. Something like that cannot be sustained.

This is where plants are smarter than human technology: Plants actually have different mechanisms to cope with the variability of sunlight both during the day cycle and the annual one.

For many plants the amount of light normally is not the limiting factor on growth rate, and they would rather conserve some water even if it meant wasting sunlight. There are plants that are limited by light availability and these have developed more efficient mechanisms to capture light. Plants should be considered a wide variety including things like algea that are often have abundant amounts of water but limit light especially at depth.

 

[AngelG]

Yes, cost per kW is that really matters on the Earth. In the Space, probably the efficiency and the radiation-resistance (endurance).
Do you have such rules who subsidize the businessmen who run solar powerplants ? Do you pay "green energy tax" as part of your monthly electricity bills ?
Here, in BG, they get subsidized, the green energy's bought at 10x the regular price and we're forced to pay for this. This was presented as demand coming from EU (that's said from Germany). It is then no wonder that many solar power plants are owned by members of the parliament.... How to love the "green" energy then ? Everywhere sbd. (the EU) imposes artificial business segments he(it) creates possibilities for great corruption.
It was forbidden to put solar cells on fertile land (arable land) but they put'em on such land because they managed to get documents that state that the land is not fertile....

The population needs food. E.t. our bodies want what the inefficient green batteries (the plants) produce. If we cover the arable land with solar cells, then there simply won't be enough food...
During the day there is light, it's warmer than the night, so the household's need of energy is reduced. But there's demand in the factories so it compensates the natural conditions.

@Seoul_lasers: Germanium has even lower 0.66 eV bandgap so in theory, it could absorb IR.
The Tellurium and Cadmium are also poisonous. And yes, we should not put fried GaAs semiconductors in our mouths . Sony even put this in some datasheets LOL.
The Tellurium is rare element so if exploited, it will come to an end soon....

 

[Seoul_lasers]

Yes, cost per kW is that really matters on the Earth. In the Space, probably the efficiency and the radiation-resistance (endurance).
Do you have such rules who subsidize the businessmen who run solar powerplants ? Do you pay "green energy tax" as part of your monthly electricity bills ?
Here, in BG, they get subsidized, the green energy's bought at 10x the regular price and we're forced to pay for this. This was presented as demand coming from EU (that's said from Germany). It is then no wonder that many solar power plants are owned by members of the parliament.... How to love the "green" energy then ? Everywhere sbd. (the EU) imposes artificial business segments he(it) creates possibilities for great corruption.
It was forbidden to put solar cells on fertile land (arable land) but they put'em on such land because they managed to get documents that state that the land is not fertile....

The population needs food. E.t. our bodies want what the inefficient green batteries (the plants) produce. If we cover the arable land with solar cells, then there simply won't be enough food...
During the day there is light, it's warmer than the night, so the household's need of energy is reduced. But there's demand in the factories so it compensates the natural conditions.

@Seoul_lasers: Germanium has even lower 0.66 eV bandgap so in theory, it could absorb IR.
The Tellurium and Cadmium are also poisonous. And yes, we should not put fried GaAs semiconductors in our mouths . Sony even put this in some datasheets LOL.
The Tellurium is rare element so if exploited, it will come to an end soon....

Germanium is exclusively IR sensitive as far as I have been told, with an exception at super high purities at extremely low temperature where it can be sensitive to Gamma photons.
It was tried as a semi-conductor material for experimental solar cells and proved to be a poor choice.
GaAs is another technology still being sought after. However, the key is to be able to seal it in such away that moisture cannot interact with the material. Upon exposure to H2O,
GaAs releases As2O3 (Arsenic trioxide) which is highly toxic / being able to be directly absorbed through the skin as well as being an inhalation hazard.

@Benm
Very interesting what you are saying regarding solar energy in Germany and the stability of the grid. I knew that Germany was the leading for adoption of alternative power, but that is a funny outcome.
I guess a more balanced approach is needed as well as more local industries to use the power or sold at price to neighbouring countries?
We could definitely use Germany's system in Canada as energy prices here are getting flat out ridiculous esp. in Ontario.

 

[Benm]

In the netherlands there are several taxes on electricity. There is a base tax that goes to government, another tax for renewable energy development, and since a few years another one for -storing- renewable energy. Afaik we don't have any storage facility for it, but the tax is there already, perhaps for future developments.

As for subsidies and such: The most profit can actually be made by private home owners. They get paid back the full amount they pay when taking a kWh from the grid, which is vastly more than a powerplant or such would get. And by vastly i mean 22 cents per kWh (which is what we pay including taxes and transport cost). The price excluding taxes and transport cost is about 4 cents, so you get a 5 times bonus effectively.

A limitation on this is that you can only get this amount back when you don't deliver more than you consume during a year. So you can have an oversized solar system that delivers power to the grid in summer, which you can re-use in winter.

Alternative energy subsidies mostly go to wind turbines (netherlands is not a very sunny country). There sometimes are some muncipal subsidies that help private people purchase panels, but afaik no otherwise usable land is used for solar farms - all panels are on rooftops etc.

 

[AngelG]

IMO you suffer similar taxes in NL. But if your country doesn't use usable land for Solar cells, you do it better. Here, almost all land is usable except the rocks in the mountains. But nobody tries to put solar cells in the mountains (because it's difficult) and thanks God, because the last thing I want to see is the beautiful mountains defaced with solar cells and wind turbines. It's .. ugly it'd hurt me. But there are rivers that were *very* beautiful but no more - water turbines and related buildings defaced the sight.... It's lost. Before (2 yr ago), the place looked as in a scene from "The Lord of the Rings"... You could have seen it if you have traveled from Sofia to Veliko Tarnovo (the previous, ancient capital of the country) w train.
...
For solar cells - my brother built his own dream house, but he didn't put 'em, because he roughly calculated, that with the prices in 2010, he would need 18 years to get ROI and the cells would get then almost worn out. Probably, He calculated with monocrystal Si panels in mind.
...
About the storage facility for green energy - it is very interesting how your country is going to build it - what technology.
It might sound unbelievable, but we had them back in the socialism era. And yes, as technology, they were green as 532 nm can be . But their color was blue . I don't know if we still use them.

 

[Benm]

Considering the netherlands is entirly flat, building something like a lake and hydropower system would not be very feasible - we can do the pump to pump water up when there is too much power, we can do the turbine to take the energy back out, but we have no place to put such a lake unless we construct a mountain to put in on. This is not impossible (dutch companies built those artificial islands near dubai and all) but quite expensive.

As for green energy destoying landscapes: I've recently seen a lot of that going on in albania. Being mountainous with lots of rivers there are plenty of options there and more being constructed all the time.

This totally changes ecosystems, though they don't have to become barren places at all. In fact, nature around them can still be quite beautiful and varied, but it will differ from the prior situation. The lakes behind those hydropower dams make decent habitats for numerous species, but probably not for the ones originally present. This could be a problem, or just an acceptable change, depending on how unique the situation was to begin with.

We don't have much land space either. With 17 million people on an area roughly 200 by 350 km in size it's pretty packed, one of the most densely populate countries on earth, the most densely populated one if you don't count city-states like singapore.

 

[AngelG]

You guessed it right - they are systems of 2 lakes at different height with water pumps and turbines. Giant underground supercapacitors could work as energy storage to compensate for the day/night differences in the load instead. Don't know how feasible is such solution though.
.....
For the dense population - it again causes me to think that the population of EU is dense enough and it would be healthy if it could be left to get auto regulated to a lower number (by the politicians) in the name of the sustainable development and peace.
...
I didn't think for the ecosystems. They are important of course. I thought that the number of the natural places without industrial signs is going down and the green energy facilities rapidly increase the rate at which we change the nature. Sometimes I need to be at place wo industrial marks on the nature.

 

[Benm]

Hydropower is just one of those things that has an immediate effect on the ecosystem around the installation. If you build a dam, water levels and flow rates change both up and downstream instantly, destroying habitats for some species but creating ones of different species.

This change is visible within a year, and even more prominent after a few. It does not mean there will not be beautiful nature afterwards though, it will just be different from what it used to be.

As for population density: the figure for the netherlands is over 4 times that of the average in the EU. The only EU state more denselity populated is the island of malta, which is very small. If you were to put amsterdam city on malta (which would easily fit) and leave the rest empty the density would be over double the current figure for malta.

You have it pretty good in bulgaria in terms of space: about 7 times more than we have in the netherlands. Then again most people live in cities that are pretty crowded, i think sofia is comparable to amsterdam in that regard. Overall though, we have well over twice the population of bulgaria in a country that would fit bulgaria 3 times when placed in side by side, so you get an idea of how crowdy things get (also in terms of traffic congestion etc).

 

[AngelG]

@Benm:
Would you feel happier if the population of Bulgaria had become as dense as it's in NL ?
I live in Sofia and it already needs space and fresh air...
Our politicians since the socialism have taken measures to ensure population growth: The government gives money to the mothers per child. IMO, the effect is not good, but they don't change this.
What's the effect: The families who work, educate their children and pay taxes (for the politicians to spend them) begun to have even *less* children (often 1 instead of 2), because the government money are a small fraction of the household income. But the opposite happened to the tribes of *** (to speak about them w/o being accused of discrimination, I'll use "***" ).
I'll describe 'em: The *** do not take much care for their children; They believe that they came from India. They rarely send their children to school even though it's free of charge, they live in tribes or form ghettos, they live on social welfare, stolen goods, prostitution and mix of the above. To me, they often are ugly and look wild, probably because of close relations (incest). They receive also help for alone mothers, because many of them do not get married by the official laws or the Church but in their internal customs. Sometimes the mother takes financial aid for having a daughter, because the kid's under 18 and the daughter also has become a mother (at 13-14)... Most of them don't care about laws, ethics, moral, culture, nature and other common values.
So if our population increases, they won't be Bulgarians, but from the *** who also are called Bulgarians in the criminal news, but rarely can write or speak Bulgarian without their specific accent. They have learned that they can exploit the social systems of "rich" countries, so many of them went abroad. The other tribes Merquel invited in the EU, lets call them "&&&" are more aggressive and determined to conquer this land. They have a term in their language standing for "conquer by breeding". I have seen only men of their tribes so far.
More people of these 2 kinds are coming, they are easy to be produced, but ... why this is considered a good thing by the EU politicians ? I wonder whether they are trying to betray and destroy the countries and communities they rule upon in the name of a greater ... goal ?

 

[Benm]

I'm sure i feel the same way that you do about this issue really.

I don't really care on avoiding naming groups though.

If you mean the problematic group are essentially gypsies, i would agree on your observations. And it IS important to point out this difference when it comes to migration in europe.

In the netherlands we have numerous migrant workers from countries like poland, romania, bulgaria, hungaria and several other countries. The actual migrant workers are not a problem at all, they do what they are paid for and cause little trouble besides a bit of drunken disorderly conduct in public just as our own student population does.

On the other hand we also get a big influx of pickpockets and such 'from eastern europe'. Sometimes people mistake all eastern european migrants for such folks, which i think is incorrect. What we see is 'trash people' on the streets begging, robbing and stealing.

This is very unfair to legal migrant workers though. I've worked in fulfillment opertions and found that migrants from eastern europe make excellent workers. The ones i dealt with where overall fast and efficient at their jobs, and should earn a bit more than what they were paid.

I've actually tried this with a another IT collegue to see how hard the job actually was as to check we did not demand unrealistic work performance. We outperformed every group of workers as we were motivated to prove a point, except from equally motivated polish workers in that tast that were about as fast as we were with maximum effort. And we did recommend to keep the middle eastern workers over those from other areas because of that.