TECH: Rain Power? Really?

We’ve heard about energy harvested from the footfalls of pedestrians. We’ve heard about backpacks that store the energy expended by its carrier. We’ve even seen, back in 1984, the expansions and contractions of a dog’s rib cage harvested as vibrational energy. So what’s the next frontier in obscure sources of energy? It turns out its raindrops.

Scientists from Europe’s Atomic Energy Commission (CEA), in Grenoble, France, have found a way to recover the vibrational energy from a falling raindrop using a piezoelectric material, which can translate a mechanical force into electric energy. The French scientists examined raindrops that range in diameter from 1 millimeter (drizzle) to 5 millimeters (downpour), and the group’s simulations suggest that it’s possible to collect up to 12 milliwatts of instantaneous power from one large drop. The hope is that strips of the material, in the right settings, could provide the energy needed to power numerous kinds of sensors.

Traditionally, the quantities of energy collected through a piezoelectric material are far too small to be of use to an electronic device, which is why researchers studying environmental sensors are also looking into ways to store the energy in a battery or capacitor until enough energy has accumulated to power a device.

The other problem with using rain as an energy source is, naturally, the intermittent behavior of Mother Nature. Presumably, a sensor’s utility is limited if it only works in a downpour. That’s why it makes more sense for a rain-based energy-harvesting technique to supplement something else—say, a small solar panel. 

We’re going to continue to hear about micro-generation schemes, so here are some questions to consider when you read those stories:

-          How much energy and money went into making the material and installing it in the ground?

-          How durable is it when exposed to the wear and tear of bad weather? (The materials are very thin and may wear out quickly.)

-          What other techniques will the piezoelectric structure be combined with to form a more reliable source of energy?

Here’s the rain power paper, which was published in Smart Materials and Structures and is free for 30 days.

For more on older piezoelectric concepts, here’s 'sidewalk crowd-farming' from MIT, and some more crowd power, this time from climbing stairs…

…And from railway ticket gates… 

…Not to mention a backpack...

…And a critique suggesting that siphoning watts off of footsteps might actually make us expend more energy, therefore making us hungrier and causing us to convert more land into farms. (Wait, wouldn’t this also count as more exercise for the sedentary masses?) This paper provides a nice overview of the history and challenges of using piezoelectric materials to harvest energy.


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