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This is a cross-cutting question but I think its core is about biology. Our society's need for energy is dramatically growing and we are messing up with our environment to answer them. Maybe another way to proceed would be to use the primary energy source that is the sun in the same way as it has been used throughout the ages: photosynthesis.

I know the energy effiency is not as good as a solar panel's but it could clearly be compensated by volume. I found surprisingly little information about harvesting energy from photosynthesis which is why I began to wonder where we are at today.

Thanks!

Edit I meant transforming the chemical energy generated by photosynthesis into electrical energy. For instance, the first algae powered building was unveiled at the International Building Exhibition hosted in Hamburg. This is a whole different approach. The most basic example of what I would like to talk about seems to be the algae powered lamp that has (apparently) been developped. In other words, it seems that some sort of plant solar panels are under development and I don't understand how it's done.

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    $\begingroup$ Yes, planting trees and burning them afterwards is a way to harvest energy from plants that's with us since millenia. $\endgroup$ – Christian Nov 10 '14 at 15:59
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    $\begingroup$ We can't currently use that energy directly, and if your question is "how can we indirectly extract the energy captured by plants" the answer is "see almost all of human history" (e.g. agriculture, burning wood, even fossil fuels)! $\endgroup$ – jonrsharpe Nov 10 '14 at 16:40
  • $\begingroup$ Do you have a link to this house? $\endgroup$ – Chris Nov 10 '14 at 17:22
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    $\begingroup$ If you want to use plants as glorified solar panels it's not a good idea, the best photosynthesizers are around 10% efficient at converting solar energy to chemical energy, modern solar panels can reach about 20% efficiency pretty easily. If you consider the energy lost when converting plant matter to electricity your efficiency gets even worse. $\endgroup$ – user137 Nov 10 '14 at 17:36
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    $\begingroup$ @Thibault Solar panels are mostly silicon, which is abundant. Furthermore, old solar panels can be mostly recycled. And anytime you use plants for energy you get into the food vs fuel debate. We only have so much farmable land, and population is expected to peak around 2050 with over 9 billion people. How do you feed all those people AND their stuff? You need to get your electricity from other sources, such as solar, wind, or nuclear, not plants. Keep in mind climate change could reduce farmable land and crop yields by that time too. $\endgroup$ – user137 Nov 10 '14 at 17:51
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The most basic example of what I would like to talk about seems to be the algae powered lamp that has (apparently) been developped.

I think you misunderstood the idea. That lamp uses bioluminescence and not electric power. Normally living cells don't like to give you energy. The trick we use is anaerob fermentation. Without the presence of oxygen (good electron acceptor) they cannot extract more energy from compounds like ethanol, etc... so they get rid of them. After that we can "burn" these compounds with oxygen and get a lot of energy. So currently there is no solution which uses sunlight and microbes to produce electricity directly, however it might be possible.

There are many ways to use photosynthesis in order to produce energy.

  • The simplest way to burn the plant itself when it has grown enough. You can burn wood, energy plants (e.g. energy grass), etc... and use a generator.
  • A more sophisticated approach to ferment biomass and produce methane, ethanol, etc... which you can burn. This works very well by starch (e.g. corn bioethanol), and there is active research about cellulose conversion.
  • There is active research about artificial photosynthesis as well.

    • You can feed microbes with electric power coming from a photovoltaic system (solar panel), so they can produce ethanol, methane, etc... This might be better than storing energy in batteries.
    • You can use electric power coming from solar panels to split water. After that microbes can use the hydrogen as electron donor to fix $CO_2$, so they can create ethanol, etc...
    • You can use light to split $CO_2$ into $CO$ and $1/2O_2$. You can use $CO$ in biological systems to create ethanol, etc... You can use $CO$ in shift reaction to create $H_2$. It is a new technology to use copper nanoparticles to convert $CO$ into ethanol in a completely artificial system.

You can use a photovoltaic system instead of photosynthesis if you need electric power instead of chemical compounds.

Related articles:

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It is not possible to do this directly. Indirectly, it is possible, this is actually done by harvesting fruits - they contain the energy of the sunlight conserved in chemical compounds like sugars or starch and their cellular structures. The basic process for this is photosynthesis.

The products from the fields are used technically to produce gas by fermentation, which then can be burned to produce electricity. Read reference 1 for more details. What is also done is the use of sugar cane (done widely in Brazil) or corn to produce ethanol which is then used in the fuel of cars. See references 2-4.

Besides these technical processes, there is of course still the possibility to simply burn whole plants or the wood of trees, which is also the result of the fixation of sun energy.

References:

  1. Biogas Production from Maize Grains and Maize Silage
  2. Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower
  3. Ethanol fuel in Brazil
  4. Corn ethanol
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  • $\begingroup$ Then I don't quite understand what has been done here blog.ted.com/2013/10/02/a-streetlamp-powered-by-algae I might be daydreaming but if this technology was enhanced, and scaled, it would be marvellous $\endgroup$ – 7hibault Nov 10 '14 at 17:46
  • $\begingroup$ @Thibault I'll have a look at it. $\endgroup$ – Chris Nov 10 '14 at 20:24
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I found surprisingly little information about harvesting energy from photosynthesis

Photosynthesis does not produce energy as such, it produces sugars/carbohydrates/chemical energy, which the plant then converts into energy via respiration.

enter image description here


You can burn the sugar to produce heat. But this is basically what your doing when you burn a plant. So no, photosynthesis cannot be used (directly) to produce electrical energy.


In a Standford university research they did successfully harvest electrictity from photosynthesis:

The Stanford research team developed a unique, ultra-sharp nanoelectrode made of gold, specially designed for probing inside cells. They gently pushed it through the algal cell membranes, which sealed around it, and the cell stayed alive. From the photosynthesizing cells, the electrode collected electrons that had been energized by light and the researchers generated a tiny electrical current.

But it goes on to say:

Ryu said they were able to draw from each cell just one picoampere, an amount of electricity so tiny that they would need a trillion cells photosynthesizing for one hour just to equal the amount of energy stored in a AA battery. In addition, the cells die after an hour.

So this is be no means practical at the moment

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Another alternative is using plants to generate biomasse using photosynthesis and letting bacteria convert that into electricity.

There is research being done about this method and you can read more about it on the following websites:

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    $\begingroup$ I'm totally not an expert on this but read a news report on this only yesterday. I wouldn't mind and even appreciate if someone would integrate this into a bigger and more complete answer. $\endgroup$ – Zombaya Nov 11 '14 at 1:26
  • $\begingroup$ That sounds more like what I expected. As @Zombaya said, could elaborate on this and integrate it in a more complete answer? $\endgroup$ – 7hibault Nov 13 '14 at 20:42
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I can highly recommend Prof David MacKay's online book http://www.withouthotair.com/ where puts things into perspective. You can find him on YouTube and TED too.

e.g. http://www.withouthotair.com/c18/page_103.shtml "Can we live on renewables"

POWER PER UNIT LAND OR WATER AREA
Wind            2 W/m2
Offshore wind   3 W/m2
Tidal pools     3 W/m2
Tidal stream    6 W/m2
Solar PV panels 5-20 W/m2
Plants          0.5 W/m2
Rain-water
  (highlands)   0.24 W/m2
Hydroelectric
  facility      11 W/m2
Geothermal      0.017 W/m2

Table 18.10. Renewable facilities have to be country-sized because all renewables are so diffuse.

So it doesn't look good for plants as direct energy source (except for food) (in UK at least)...(or most renewable things for that matter).

Essential reading for anyone interested in energy.

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  • $\begingroup$ this is more of a comment than an answer. $\endgroup$ – rg255 Nov 19 '14 at 9:49
  • $\begingroup$ i didn't have enough points to comment. Then I got 100 more so maybe i do. Nor can i format comments $\endgroup$ – xcxc Nov 19 '14 at 9:50
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    $\begingroup$ Ok - It's kind of annoying that it needs more than 1 point to comment... $\endgroup$ – rg255 Nov 19 '14 at 9:51
  • $\begingroup$ I'll definitely read that, thanks. It does put things in perspective. $\endgroup$ – 7hibault Feb 23 '15 at 13:34
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Everyone's looking at photosynthesis for direct energy conversion, but it's not the only approach. Another function of most plants is to pump water up to altitude, to serve its own needs.

Tap into that - picking plants where the sap is watery, not inconveniently sticky like maple syrup, resinous, or likely to congeal into rubber, and you have at least hypothetically, the potential for micro hydro power...

I'm making no claims for energy density or efficiency.

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