Nigerian develops solar cells from weed (Mimosa pudica)





Mimosa pudica commonly called ‘Touch-me-not’, Sensitive plant’, ‘Humble plant’ or ‘Shameful plant’ because of its reaction to touch, is a weed found throughout the tropics. Apart from its many traditional medicinal uses, a researcher at the Department of Pharmaceutical and Medicinal Chemistry, University of Nigeria Nsukka, Pharm. Justus Nwaoga, has discovered that the weed has solar properties suitable for the production of solar cell/electricity. Nwaoga spoke with Vanguard Learning in Ibadan recently. Excerpts:


Fascinated by the behaviour of mimosa pudica popularly called kpakorukwu or kpakochuku in Igbo, Pharm. Nwaoga decided to explore the relationship between sunlight and mimosa leaves. “I have always been eager to appreciate the behaviour of Mimosa pudica. The question has been; ‘why do the leaves collapse when touched, only to open again within minutes in daylight?

“I look at the plant as a natural solar plant because it opens up in the mornings and closes in the evenings, therefore, must have solar materials in it. The search for knowledge took me to Mimosa locations to find out what happens at nighttime. I observed that the leaves remain folded when bright artificial light is shone on them. It became clear that the plant responds to solar energy, artificial light has no effect on it.

“I believe that the movement of the leaves when touched, is connected with some form of electrical transmission. It can be likened to the behaviour of other living creatures. For example, when a person is touched unexpectedly, electrical impulses are transmitted to the brain, and the person moves with a jerk,” he said.

Isolating the active material:
Nwaoga subsequently, went to work to isolate the particular solar substance in the plant that responds to sunlight alone. “Nature has shown us that there is something there which is in fact, even more sensitive than the regular solar cell.

“The generation of electrical energy with a solar-sensitive isolate from Mimosa pudica was achieved after series of designs to safeguard the electrical properties of the material. To convert the mechanical energy observed as spontaneous movement of the leaves to electrical energy, was an uphill task.

A strong oxidation-reduction reaction was noticed in the extract, which quickly dissipated any trapped energy. After several attempts, however, it was possible to retain some quantum of electrical energy within the cells due to subsequent isolation of the principal compound,” noted Nwaoga.

How it works:
“The innovation is based on constructing bio-accumulators using the electrolytes derived from the mimosa plant. Solar cells constructed with the weed extracts and exposed to sunlight were found to accumulate solar energy which was converted to electrical energy,” said Nwaoga who is one of the 10 finalists for the forthcoming Innovation Prize for Africa.


Refusing to give up:
“The only meaningful way of demonstrating the electrical potential of the plant isolate was to use the cells to power an electrical circuit after combining the appropriate compound as electrodes. Experiments were performed initially using copper and other metals in turns as electrodes, but these failed.

The conventional copper/zinc electrodes also did not work as the mimosa extract  powerfully corroded the zinc plate. At that stage, the entire aspiration appeared to have turned illusive. Later, however, with more effort, the chemistry of the material was better understood, which guided the generation of steady DC current that lit a 4.5 V lamp.

“With this breakthrough, it was possible to construct a functional mimosa solar panel with the plant extract. The solar panel is designed in such a way that the electrical potential of the cells can be restored on exposure to direct sun rays, after they have been discharged.”


Prototype:
“I have come up with the prototype which I have presented at so many exhibitions including the 26th European Union Photovoltaic Solar Energy Conference and Exhibition in Hamburg Germany, and the NUC Research and Development show in Niger State where I came second. Mimosa pudica is now accepted as a new material for solar energy development,” he stated.

On whether solar electricity will be cheaper if generated from this plant than from traditional silicon solar panels, he said; “It will be cheaper. About 0.5ml of one per cent concentration of mimosa extract can give you 0.25 volts or more when properly set. Again, some of the imported solar panels even crash or separate due to the intensity of the sun here.”

Explaining further, Nwaoga said that there are scientific explanations to show that Mimosa pudica has electrical potential, which is energized by the sun’s radiation. “In conventional electricity, when ‘positive’ and ‘negative’ wires touch, there is a spark, and a situation known as short circuit occurs. This interrupts electric current and there may be power outage.

“A similar process is believed to occur in mimosa pudica. When touched, the flow of electricity is interrupted and the leaves collapse. It may well be that a touch on this plant interferes with the flow of electric charges through the conducting parts and root hairs to or from the leaves. It is believed that the solar radiation incident on the leaf surface releases electrons that result in electric current,” he said.



Vanguard