AirplaneIn 2016, Solar Impulse 2 was the first solar-powered electrified aircraft to make a trip around the world. But that aircraft wasn’t the first to partake in electric flight, nor will it be the last.

Since the development of the battery-powered Militky MB-E1 in the early 1970s, there has been excitement surrounding the promise of an electric aircraft. However, many of the concepts being floated around by aerospace companies assume huge improvements in current battery technology.

The problem? According to a recently published article in Wired, current battery technology does not offer the power-to-weight ratio needed to make battery-powered planes feasible.

But battery technology has taken leaps over the past few years. Energy storage devices are become more efficient and lighter simultaneously. But how long will it take to be able to pack enough energy into a device while remaining light enough to glide through the sky?

“There’s already been a lot of progress,” Venkat Srinivasan, battery expert with Argonne National Lab, told Wired. “It’s not the same ballpark as Moore’s law progress because it’s chemistry, not electronics, but it’s still very good.”