How to generate electricity from living plants

Plant-e is one of the World Economic Forum’s 2015 class of Technology Pioneers. The company is developing technology that generates electricity from living plants without damaging them. Especially suitable for wet areas such as rice paddy fields, it could provide clean power to remote communities. Nanda Schrama, chief marketing officer, discusses its potential.

How can you generate electricity from living plants?

In simple terms, electrons are a waste product of bacteria living around plant roots – plants excrete organic matter into the soil, which is broken down by bacteria. In the breakdown process electrons are released. It is possible to harvest them using inert electrodes and turn them into electricity, without affecting the plant’s growth in any way.

While the principle may sound straightforward, the challenge of course is generating useful amounts of electricity cost-effectively. My colleagues Marjolein Helder and David Strik worked on developing this technology at Wageningen University in the Netherlands, based on the ideas of assistant professor Bert Hamelers. Plant-e is a result of this research.

What are the technology’s current capabilities?

Our first commercial product is a modular system, consisting of 100 square-metre installations, each comprising 400 individual modules equipped with our technology and plants. Since November last year the first two of these systems have been in operation in the Netherlands, both powering outdoor lighting. They can also be used for other small-to-medium scale applications such as WiFi or charging mobiles, or incorporated into a green roof to generate electricity for a building as well as insulating it.

There are limits to how far you could realistically scale up this kind of modular system, so we’re also developing a tubular system – the ambition is that we will be able to generate large amounts of electricity from wet areas such as peat land, mangroves, rice paddies and deltas. We hope to start large-scale tests imminently and to have a market-ready product in two or three years.

How deep will the tubular system need to be installed? Would it require digging up the ground?

There’s no need to dig the surface or disturb the plants that are already growing, as we can use existing technology to make the tunnels for the tubular system non-invasively. As for the depth, the electrodes need to be within plants’ root system to harvest the electrons, which means somewhere between around five and 30 centimetres.

The optimum depth is something we expect to become clearer with large-scale testing, as the level of oxygen in soil changes with depth and affects how well the system works. Oxygen levels are also why the system will function better in wetlands, though testing will tell us more about whether it will work only in wetlands or if it will also be feasible to look at applications in dryer areas.

How cost-effective is the system now? Can you hope to compete with other renewables on price?

We’re not yet able to compete on price with the likes of wind and solar power, although of course that is the intention as we work on increasing the efficiency of the technology itself. And a lot of scope for savings will come through achieving greater scale.

In the lab we’re currently generating about one watt per square metre, and we believe it’s possible to get that up to about three watts. To put that in perspective, at three watts per square metre, in principle you’d need approximately 125 square metres of suitable land to power an average family home in the Netherlands.

Is the cost mostly upfront, or will the system need much maintenance?

The bulk of the cost is indeed in the installation. Once the tubes are installed under the ground, we see no reason why they shouldn’t be capable of generating electricity for hundreds of years – any parts that might need replacing will be above ground.

How have you funded the work you’ve done so far?

We’ve got this far on subsidies and awards. We have been talking to investors but haven’t yet found the right fit, as we are very committed to focusing the development of the technology on where we believe it could do most good in the world – and, at least in our case, that’s not necessarily the fastest route to profit.

Deciding on the right avenue for financing can be challenging for a company that’s trying to develop radically new technology with a social focus. The recognition of being named as a Technology Pioneer is a welcome validation for what we’re trying to achieve.

Thinking forward 10 or 20 years, what is the dream for this technology?

The dream is that we are generating clean electricity around the world in any suitable wetland or wet area – including rice paddy fields, mangroves and salt marshes, which takes us to some of the most remote and impoverished parts of the world. It is in these off-grid communities that we believe the technology can make a real difference to people’s lives.

Full details on all of the Technology Pioneers 2015 can be found here. 

Author: Nanda Schrama is Chief Marketing Officer of Plant-e, a World Economic Forum Technology Pioneer

Image: The Alto Madre de Dios river, part of the Manu Biosphere Reserve, is seen from Peru’s southern Amazon region of Madre de Dios July 15, 2014. REUTERS/Enrique Castro-Mendivil