Science - October 8, 2009

Reaping electricity from green roof

Wageningen's Agrotechnion boasts the world's first electricity-generating green roof. Ten pots of cord grass, some wires and a few computer screens sheltered from weather and wind: this experimental set-up belongs to Plant-e, the newest company in Wageningen UR. Plant-e (pronounced as in 'plenty') is developing a plant-microbial fuel cell.

Plants discharge sugars and simple organic acids through their roots; these are then broken down by bacteria under low oxygen conditions. The electrons released in the process together produce a small amount of electricity. In fact, the bacteria are the ones which produce the electricity with fuel provided by the plants.
Plant-e is formed to convert this patented process into usable technology. The roof-top construction is its first move. 'We want to find out what happens when the system is placed outdoors', explains PhD student Marjolein Helder. She and colleague David Strik are both in charge of Plant-e. The initial results are surprising. The plants do as good a job in producing electricity outdoors as they do under controlled conditions in the lab. Whether it is day or night, warm or cold, there seems to be no difference in electricity production. 'Our first goal is to be able to charge a mobile phone with electricity from a few plants by next summer', says Helder. In theory, a green roof can produce a maximum of three watts per square metre.