The world is awash in our waste heat. Our computers, our motors, our electrical generating plants—all of them shed heat into the environment. That’s in part because there’s no easy way to capture its energy and put it to use. All the existing methods we have for harvesting waste heat are either inefficient or uneconomical.

Now, some researchers have come up with a new method of grabbing some of that waste heat and potentially putting it to work. Their system relies on nothing more complex than water and a polymer membrane and, even in its first test form, it’s already capturing roughly half of the possible Carnot efficiency available to the system.

We already generate lots of electricity via heat differences. It’s just that those differences are large—large enough to create the pressure differences needed to drive turbines. Waste heat often becomes waste simply because the temperature differences are small, on the order of dozens of degrees Celsius, rather than hundreds.