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These Green Roofs Are More Than Just A Garden, They’re Also A Power Plant

Green roofs produce food, cool buildings, and add a dash of color to the skyline. In the future, could they also generate electricity?

That’s the vision of Marjolein Helder and her Dutch startup Plant-e. Helder has developed a modular system that generates power from submerged plant roots. Eventually, it could power whole households, she says.

Normally, plants produce organic matter when they convert sunlight to energy during photosynthesis. But some of this matter isn’t used for growth, but instead is excreted into the soil, where it’s broken down by bacteria. This process produces electrons that Plant-e captures with a carbon electrode. That’s coupled with a “power harvester” and a counter-electrode, creating an organic battery.

The startup recently set up two 100-square-meter systems on roofs near its office in central Holland to prove its technology works. The next step is to build a “power plant” in a less controlled environment, such as a wetland area. Helder says the system works well with any species that lives in water, including grasses, rice, and mangrove trees. Her plan is to start field tests by spring 2015, with the hope that it would hit the market in 2017. The modular system is already available via the Plant-e web site.

The current pilot generates only enough power to charge a mobile phone. But Helder says that will improve to as much as 28 kilowatt hours of energy per square meter per year. If so, 120 square meters of roof-space should be enough to power an average Dutch home, she says.

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