Plant Generated electricity
Reporter: Sebastian Ordoñez
UN-Bogotá Team
International Physicists' Tournament-Colombia
Online version
2021
statement
Some internet post suggest that it is possible to generate electricity from photosynthesis by charging a battery connected to a metallic network that winds through the roots of a plant. In response, a skeptic may claim that the setup is just a voltaic pile, and therefore, photosynthesis is irrelevant.
statement
Some internet post suggest that it is possible to generate electricity from photosynthesis by charging a battery connected to a metallic network that winds through the roots of a plant. In response, a skeptic may claim that the setup is just a voltaic pile, and therefore, photosynthesis is irrelevant.
- Explain the phenomenon .
- Determine whether photosynthesis is indeed involved.
- Determine the main factors affecting the phenomenon
PhotoSynthesis
The oxigenic photosynthesis in plants is described by the overall equation
\boxed{6\text{H}_{2}\text{O}+6\text{CO}_{2}+\gamma\Longrightarrow \text{C}_{6}\text{H}_{12}\text{O}_{6}+6\text{O}_{2}}
- This process takes place in organelles called choloroplasts.
G.S Singhal. et al. Concepts in photobiology. Photosyntesis and Photomorphogenesis. Springer, 1999.
Solar energy is used to fix carbon dioxide in the form of carbohydrates.
- Where is the chemical energy going?
- How is related photosynthesis with the surrounding soil environment?
Rhizodepositon
Rhizodeposition drives the interactions between plant, soil, and microbial populations.
- "Depending on plant species, age, and environmental conditions up to 60% of the net fixed carbon can be transferred from its leaves to the roots" (Strik, 2008)
- Rhizodeposits contain carbon that can be employed by microorganisms.
K. Hassan et. al. The interactions of Rhizodeposits with Plant Growth-Promoting Rhizobacteria in the Rhizosphere, Int. J. Energy Res. 2019.
Release of carbon compounds from plant roots into the surrounding soil environment.
Soil & microorganisms
Mixture of organic matter, minerals, liquids and organisms that together support life.
- Organic Matter and living micoorganisms
- pH, moisture, temperature
"It has been estimated that bacterial populations in the rhizosphere are 10-100 times higher than in bulk soil" (Strik, 2018)
In bacteria we have, as result of respiration, the temporary release of electrons which are handy for generating electricity.
\boxed{\text{C}_{6}\text{H}_{12}\text{O}_{6}+6\text{O}_{2} \Longrightarrow 6\text{CO}_{2} + 24\text{H}^{+}+24\text{e}^{-}}
There is a symbiosis between plants and bacteria in the rhizospehere.
Voltaic Pile
In order to have a simple voltaic pile we need two metals with different electronegativity, and a medium to increase the electrolyte conductivity.
The strength of the pile is expressed in terms of its electromotive force given in volts.
Mechanism
B. Strik. Green electricity production with living plants and bacteria in a fuel cell, Int. J. Energy Res. 2008.
- The plant produces organic matter from sunlight and CO2 via photosynthesis.
- Up to 60% of this organic mather ends up in soil as rhizodeposits.
- This organic matter is oxidized by bacteria, releasing CO2, protons and electrons.
- These electrons flow due to a potential difference, from the anode through an electrical circuit.
In summary we have:
Photosynthesis is indirectly involved in the generation of electricity on the roots
Experimental setup: Prototype
- Cupper and zinc electrodes connected in serie in each row.
- Cell tray with the metallic network. On the right, flower pot version.
- Final prototype version including plant
Experimental setup: Prototype
- Cell trays with soil added.
Measuring instruments
Soil tester
- Moisture
- Temperature
- pH
Multimeter
- Voltage: uncertainty \(\pm 0.01 V\)
The plant
- "Perennial plants, however, can transfer 70-80% of the net fixed carbon to the roots, of which 8-65% is released as rhizodeposition" .(Helder, 2012)
M. Helder. Design criteria for the Plant-Microbial Fuel Cell. Electricity generation with living plants – from lab to application. PhD thesis. 2012
THE PLANT
A special slide for the plant and its properties....
Groups under consideration
- Plants light: prototypes with plants and exposure to light throughout the experiment.
- Plants no light: prototypes with plants and no exposure to light throughout the experiment.
We consider four different gruops and for each of them we use five replicas
- Dead soil: high temperature sanitization process, negligible content of microorganisms.
- Living soil: coming directly from the healthy rizosphere of plants, high content of bacteria.
DARk ROOM
Temperature inside is the same than for other groups
DEAD Soil
We are able to see a first clear effect of humidity on voltage.
From the simplest group to the most complex
Living soil and DEAD Soil
Now, we are able to see the effect of having microorganisms.
Living soil and plants No light
Living soil and plants light
Plants with and without light
Plants with and without light
Multiple comparison test
By using a two-way ANOVA we are able to make a multiple comparison test between our gruops in different time points, with a 95% confidence interval.
MD: mean difference
CI: confidence interval of difference
BT: below treshold
Sum: summary
P value: adjusted p-value
A very small p-value means that an extreme observed outcome would be very unlikely under the null hypothesis
Multiple comparison test
Multiple comparison test
Multiple comparison test
Multiple comparison test
By using a two-way ANOVA we are able to make a multiple comparison test between our gruops in different time points, with a 95% confidence interval.
| Compared groups | MD | 95 % CI | BT | Sum | P value |
|---|---|---|---|---|---|
| Living Soil vs. Plants Ligth | 0,4915 | -0.2826 to 1.266 | No | ns | 0,3108 |
| Living Soil vs. Plants No Light | 0,4789 | -0.3028 to 1.261 | No | ns | 0,3431 |
| Plants Ligth vs. Plants No Light | -0,0126 | -0.1556 to 0.1304 | No | ns | 0,995 |
Multiple comparison test
By using a two-way ANOVA we are able to make a multiple comparison test between our gruops in different time points, with a 95% confidence interval.
| Compared groups | MD | 95 % CI | BT | Sum | P value |
|---|---|---|---|---|---|
| Dead Soil vs. Living Soil | -1.012 | -1.804 to -0.2203 | Yes | ** | 0.0091 |
| Dead Soil vs. Plants Light | -0.5206 | -0.7285 to -0.312 | Yes | **** | <0.0001 |
| Dead Soil vs. Plants No Light | -0.5332 | -0.7732 to -0.293 | Yes | **** | <0.0001 |
Conclusions
- We conclude that photosynthesis in those setups plays the role of keeping the plant and the environment healthy, but is not a determinant factor beyond that for electricity .
- We find that the main parameter affecting electricity generation is the amount of electrolytes, in this case humidity coming from watering
- We observe that the presence of microorganisms in the environment is an important factor in electricity production.
- We obtain electricity without the presence of plants, then, in principle effects of photosinthesys is secondary.
[IPT-Colombia] Plant Generated Electricity (Reporter)
By Sebastian Ordoñez
