Electricity from the marshes

An unexpected source of new, clean energy has been found: the Plant-Microbial Fuel Cell that can generate electricity from the natural interaction between living plant roots and soil bacteria. The technique already works on a small scale and will soon be applied in larger marshland areas throughout the world.

On 23 November, researcher Marjolein Helder will defend her PhD research on via plants at Wageningen University. She has also founded a spin-off company called Plant-e with her colleague David Strik.

The Plant- draws electricity from the soil while the plants continue to grow. Plants produce via photosynthesis. The roots excrete up to 70 % of this material (unused) into the soil. Bacteria around the roots break down the organic residue, thereby forming a new source of electricity. The causes electrons to be released. Marjolein Helder and her colleagues placed an electrode close to the bacteria to absorb these electrons and generate electricity via the potential difference thus created.

The Plant-Microbial Fuel Cell can currently generate 0.4 Watt per square metre of plant growth. This is more than is generated by fermenting biomass. In future, bio-electricity from plants could produce as much as 3.2 Watt per square metre of plant growth. This would mean that a roof measuring 100 m2 would generate enough electricity to supply a household (with an average consumption of 2,800 kWh/year). Plants of various species could be used, including grasses such as common cordgrass and, in warmer countries, rice.


Plant-Microbial Fuel Cells can be used on various scales. Initially on flat roofs or in remote areas in developing countries and later, when larger effective surface areas become feasible, central grids can be realised in areas of marshland. The researcher thinks that -producing roofs will become a reality within a few years and production on a larger scale will follow suit soon after 2015. Although the technology is promising, it is not yet fully developed. Techniques for making the system renewable and sustainable still need improvement, and ways must be found to limit the amount of material used by the electrodes. Placing the electrodes in the optimum position around the plant causes production to rise and material use to drop by two-thirds. In remote areas, the current capacity of Plant-Microbial Fuel Cell is already making them an economic rival for solar panels.

Marjolein Helder's PhD research did not only focus on the technical aspects of the Plant-Microbial Fuel Cell, but also on how the technology could be integrated into society. It appears that this new renewable source is economically viable, will curb the pressure on the environment and is likely to be socially acceptable. It does not pollute the horizon (like wind turbines or ugly solar panels), does not interfere with nature (like dams) and the system does not compete with agricultural land in the debate on food and biofuels.

The Plant-Microbial principle was discovered and patented in 2007 by the Environmental Technology Group at Wageningen University. Bert Hamelers conceived the concept, and David Strik carried out the first tests. Larger projects followed, such as the EU PlantPower project.

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Nov 23, 2012
the organic material is unspecified but ok it's a feedstock for bacteria however where does the other electrode go to complete the circuit? What's the physical separation distance? Potential gradient between the electrode close to the plants and earth? What's the voltage potential of a cell? How many electrodes per square metre to get 3.4W? What about when the plants die? There is a lot missing from this writeup.

Nov 23, 2012
This would mean that a roof measuring 100 m2 would generate enough electricity to supply a household (with an average consumption of 2,800 kWh/year).

That is only attainable if the household uses something else than electricity for heat and hot water. For example, the average household in the UK uses about 3,300 kWh of electricity and 16,000 kWh of natural gas a year.

Replacing the natural gas is actually the trickier proposition, and the more acute problem.

Besides, a solar panel with a modest efficiency of 10% can produce three times as much energy throughout the year.

Nov 23, 2012
If you look at typical electric appliances, running a stove on electricity adds another 750 kWh per year, and a water heater adds a whopping 4000 kWh.

That is the big elephant in the room that people refuse to aknowledge when discussing about renewable energy. To actually get rid of fossil fuels, you need to stop heating your houses and water and food with gas and oil, and start using electricity instead.

But that means you actually need 6-7 times more of it, and the windmills you've built so far are but a scratch on the surface.

Or we could get back to polluting the place with soot and smog by burning wood in every home. I don't think we have enough forests for it though.

Nov 24, 2012
I really didn't see this one coming. At 3.2 Watts/ M2, if they can succeed in obtaining that, a healthy 1500 square foot roof could generate 11 kwh/ day, with variations due to weather and temperature that affect the microbes.

That's 2 to 4 times what the average house uses. And buildings, etc, could be made more stingey...

Since a living roof reduces the heating and cooling costs of a building,increases biodiversity, and purifies rainwater and slows run-off, the mere ~potential~ of turning the roof into an electric generator is an added incentive to install these in future, and some existing, buildings.

I am wondering if one might also be able to use available lawn space for this as well, but that remains to be seen. That may not be technically possible/feasible.

I really hope this one works out.

Nov 24, 2012
Gung ho! Within the natural limits of the technology, of course. It has not been my understanding that there will be a magic bullet that will immediately solve all of our energy and pollution problems at once. At this stage the world is just beginning to search for less harmful technologies. The earth, to me, is a network of systems which work together for the health of the planet, and my suspicion is that our lives are moving toward a more fragile, but more sustainable system of networks to try to save our planet and ourselves. My hope is that the right wingers can be stopped this time and that our children will inherit something other than a smoking pile of polluted rubble, god willing.

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