(A column highlighting scientific, technological, engineering and design innovation in Africa)
Nigerian-born Justus A. Nwaoga discovered a way to manufacture solar energy using the organic medicinal African weed, mimosa pudica. Called “kpakorukwu” or “kpakochuku” in Igbo, the plant is referred to in the English-speaking tropics as “Touch-me-not,” “Sensitive plant,” “Shameful plant,” and “Humble plant,” because of its reaction to touch.
Fascinated, Nwaoga, a researcher in the Department of Pharmaceutical and Medicinal Chemistry, University of Nigeria Nsukka, Pharm., wanted to find out why the leaves of the plant close when touched during daylight, only to open minutes later. He decided to investigate what happens to the mimosa leaves during the night and discovered that the leaves remain folded even when exposed to bright artificial light. They open up only to natural solar energy.
From these observations, Nwaoga concluded that the Mimosa Pudica had solar properties capable of producing solar cell electricity. He also concluded that the movement of the leaves when touched was related to some form of electrical transmission. “I look at the plant as a natural solar plant because it opens in the mornings and closes in the evenings,” he explained.
Nwaogo managed to isolate the active substance in the plant that responds to sunlight and made several attempts to show its electric power, using copper and other metals as electrodes, but these attempts failed. Copper/zinc electrodes did not work because the mimosa extract was so powerful that it corroded the zinc plate.
Once he understood the chemical makeup of the extract, Nwaoga and his team were able to generate a steady direct current to light a 4.5-volt lamp. The breakthrough allowed for the construction of a mimosa solar panel with the plant extract, designed in such a way that the electrical potential of the cells can be restored on exposure to direct sunlight after they have been discharged.
Nwaoga has presented the mimosa solar panel prototype at numerous exhibitions, including the 26th European Union Photovoltaic Solar Energy Conference in Hamburg, Germany. He was also a finalist for the 2013 Innovation Prize for Africa and took second place at the NUC Research and Development show in Niger State.
The mimosa solar innovation has been incorporated in various domestic and industry electrical appliances.
