It’s time to get rid of that dehumidifier — you are just throwing away free energy by sucking all the moisture out of the air, according to some new research published by a team from MIT. Postdoc researchers Nenad Miljkovic and engineering professor Evelyn Wang figured out last year that water droplets jumping off a hydrophobic surface could gain an electric charge, but now they’re worked out how to capture that energy, essentially pulling power out of thin air.

The team happened upon this mechanism quite by accident. The goal when the leaping water was discovered was to design a more efficient heat transfer material for power plants. That’s not nearly as sexy as conjuring power from humidity, but Miljkovic and Wang noticed something odd when working with a super-hydrophobic surface (pictured above). The condensing water droplets sometimes spontaneously jumped away from the hydrophobic surface, which was the goal as it cools much more efficiently. They didn’t expect the water droplets to produce an electric charge in the process, and that may have significant ramifications.

It’s the natural tendency of water to flow away from a hydrophobic surface, but in turning the leaping water into a viable method of power generation, the researchers had to give it somewhere to go. To encourage the water droplets to take a leap, a hydrophilic surface was placed just above the hydrophobic one. So the water really wants to make the trip from hydrophobic to hydrophilic, and it brings a few electrons along for the ride. The charge difference between the two plates can then be used to provide power.

The stunning thing here is how simple the generator is — it’s composed of two interleaved metal plates with coatings that either attract or repel water, with no moving parts. The prototype used copper because it’s highly conductive (the same reason it’s used in telecommunications), but a cheaper metal like aluminum could work too. The main property that makes the leaping water generator good for producing power is surface area — just like a radiator’s fins dissipate heat. The more fins you can pack in, the more water droplets are going to be going on a trip to the hydrophilic side.

You’re probably wondering how much power this process produces. Well, let’s just say you won’t be breaking free of the power grid just yet. In their experiments, Miljkovic and Wang were able to harvest about 15 picowatts per square centimeter of metal, but they believe at least 1 microwatt is possible with some tweaking. At that efficiency level, a cube-shaped generator 50 centimeters on a side (like a small camping cooler) could charge a cell phone in 12 hours. It also needs to be in a humid environment to capture the condensing water from the air. So your damp basement, sure. The living room? Probably not. Many tropical regions are also sufficiently humid for the system to work. [Read: Ambient backscatter: Free energy harvesting from TV signals, to power a ubiquitous internet of things.]

This isn’t going to power nations or anything, but the water condensing generator is about as close to free energy as you can get right now. There are no moving parts to replace, no hazardous waste from manufacturing, and it works passively all the time so no one needs to know how to operate it. A larger unit could juice up cell phones in remote areas, or even give your electric car a few extra milliampere-hours when there’s not a plug available.