Now, leaves that sweat to generate electricity!

A team of scientists has built synthetic glass leafs that would sweat to generate electricity.

According to a report in New Scientist, the new synthetic leaves were developed by Michel Maharbiz at the University of California, Berkeley, working with colleagues at the University of Michigan and MIT.

They built their leaves from glass wafers shot through with a branching network of tiny water-filled channels arranged like the veins of a leaf.

The smaller channels extend to the edge of the plate and have open ends that allow water to evaporate, drawing fluid along the leaf's central stem at a rate of 1.5 centimeters per second.

The researchers added metal plates to the walls of the central stem and connected them to a circuit.

The charged plates and the water within the stem create a sandwich of two conducting layers separated by an insulating layer - in effect, a capacitor.

The leaf is transformed into a source of power by periodically interrupting the water flowing into the leaf with air bubbles.

Thanks to the different electrical properties of air and water, every time a bubble passes between the plates the capacitance of the device changes and a small electric current is generated, which passes to an external circuit where it's used to pump up the voltage on a storage capacitor.

"We use the mechanical energy in the liquid flow to change the capacitance and add energy to the capacitor," said Maharbiz.

Each bubble results in an increase in output voltage of some 2 to 5 microvolts, and the device has a power density of some 2 microwatts per cubic centimetre.

"I think we could easily reach hundreds of microwatts per cubic centimetre (with modifications)," he said.

That is still a fraction of the power density of power systems such as fuel cells or batteries, but it's a respectable figure for an energy scavenging system, according to Maharbiz.

The device could be scaled up to produce artificial trees that generate power entirely through evaporation wherever there's a cyclical change in humidity.

Although the modest power output is not enough to rival solar technology, Maharbiz thinks it could act as a complementary technology.

The sunlight that generates solar power could also drive transpiration to boost the electricity generated.