Harnessing energy from falling rain has the potential to generate huge amounts of electricity.
If rain falls into a tube connected to a circuit, the individual plunks of raindrops will produce more charge than continuously falling water.
This method could eventually be a cheaper and more efficient alternative to hydroelectric power.
Have you ever absentmindedly run your hand over the fabric of your shirt, then touched a light switch and gotten zapped back into consciousness? That same effect could soon generate massive amounts of electric power with rain.
Hydroelectric power may produce clean energy, but in order for it to work, the movement of water needs to activate some sort of mechanical system (like a turbine). This complex equipment cannot be used everywhere, and may even harm the environment in certain situations. Rain, on the other hand, bypasses the need for any equipment other than a tube for it to run through. It also generates energy magnitudes greater than continuously flowing water, because the charge created by drop after drop of rain takes much longer to decay.
This is what engineer Siowling Soh—from the National University of Singapore—and his research team realized when they tried to generate electricity by catching rainwater in tubes.
“The setup is simple; no equipment is needed,” they said in a study recently published in ACS Central Science. “Hence, it is inexpensive and environmentally friendly to install, operate, and maintain […] scaling up can be achieved readily in three dimensions for large-scale harvesting of energy from nature. It can be used anywhere, including in urbanized areas.”
Previous experiments had tried to use water flowing through nanoscale tubes to capture electric charge. However, not only does the charge from flowing water decay more rapidly, but when tubes that small are used, that charge becomes just about negligible. It is also unnatural for water to flow through nano-tubes, which is why Soh stresses that macroscale tubes on the scale of at least millimeters wide should be used to harvest electricity from natural sources of water.
The way droplets of rain flow through a tube (with pockets of air between them) is known as plug flow. Positively charged hydrogen ions and negatively charged oxygen ions separate spontaneously at the interface of liquid and solid, but the charge is much greater for individual sparks that result from the ‘plunk’ of raindrops than from water which continuously flows through the tube. This charge separation is also the reason for the sudden electric jolt you experience turning on a lamp.
Soh and his team set up a tube and a stainless steel cup partially filled with uncharged water, and connected to a series of resistors (which regulate the flow of electricity) to the cup and tube with wires for electrical contact. The charge accumulated in the tube and cup powered circuits, and an electric current was created, achieving an energy output about 100,000 times higher than the output generated by a continuous flow.
Another advantage of plug flow is that the power it generates is consistent in the long term. So, what does that amount of energy mean when translated into utilities that add up on your electric bill, such as the lightbulb in the lamp that shocked you? Say that it uses an LED lightbulb. For the duration of a rainfall, 20 seconds of rain plinking and plunking into four of tubes connected to an external circuit would power 12 of those bulbs. Soh thinks it can be easily scaled up for longer stretches of time and higher voltages.
“Importantly,” he said in the same study, “the combination of high efficiency and use of macroscale tubes enables plug flow to harvest renewable and clean energy from nature freely, including directly from rain.”
In the future, maybe that electric bill will trigger less of a shock.
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