Electric Airplane Powered By Solid-State Batteries Completes Test Flight

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If you have been following battery energy storage developments for a while, you know the prospect of solid-state batteries is both real and seems to perpetually not arrive. Many of us might like to speculate what will happen when solid-state batteries are readily available to be used in electric vehicles and stationary energy storage because they have greater energy density and weigh less — two distinct advantages over current battery chemistries.

Helios Horizon recently completed a test flight of an electric airplane using solid-state batteries while carrying a human pilot. That is, it wasn’t an unmanned electric airplane or “drone,” but one with a normal human pilot.

Miguel Iturmendi, founder and chief test pilot for Helios Horizon, answered some questions about the test flight for CleanTechnica.

What is the plane size and how many passengers were there?

As this was a test flight, the only occupant was the chief test pilot. (Note: The aircraft is an experimental concept demonstrator operated by a nonprofit, so it’s not intended to carry passengers or to be certified for commercial operation.) The plane is 25 feet long with a 61-foot wingspan and a 1,300 lb max takeoff weight.

How far did the plane fly, how high and at what speed?

Friday’s flights were abbreviated pattern flights below 500 feet, with the only goal being to assess changes to center of gravity and handling with the new batteries installed.  (Helios Horizon had already completed tethered ground runs of the aircraft running at full power until battery depletion, as well as many other tests of the electrical system under load.) The short test flights Friday pave the way for the resumption of stratospheric envelope expansion, which is scheduled for the fall. The speed was approximately 60 miles per hour.

What company made the battery and what is the cost to make it?

The battery packs were assembled by Helios Horizon using commercially available solid-state battery cells sourced from several different resellers. It’s worth noting that Helios Horizon is not a battery manufacturer or supplier; they are simply a consumer and end-user like anyone else. The total battery pack price was $30,000, which was about 3-4 times what it costs to build a battery pack with conventional LiPo cells. Miguel expects prices to come down substantially in coming years as the technology becomes more widely available and adopted.

How much does the battery weigh, what is the energy capacity and what is the chemistry?

Each battery weighs about 80 pounds. The aircraft can fly with either two batteries or four, so a total of either 160 or 320 lbs. of battery weight.

The energy density of the solid-state cells in the batteries is 410 watt-hours per kilogram, compared to 260 Wh/kg in the previous (non-solid-state) cells Helios Horizon used. Each battery carries 14.8 kilowatts.

Regarding the chemistry, it’s similar to contemporary LiPo batteries, but we couldn’t speak to the specifics since Helios Horizon did not manufacture the cells and is just an end-user.

What are the battery’s dimensions?

The batteries are 6.5 inches x 11 inches x 20 inches. Each solid-state cell inside the batteries is 9.2mm x 152mm wide x 242mm.

How long before a solid-state battery is commercially available to use in an electric plane?

We can only speculate, but we hope to see commercial certification of solid-state batteries within the next 2-3 years. Ultimately, that will depend on the battery manufacturers and regulators.

What are the benefits of using a solid-state battery in an electric plane?

There are three main benefits of the solid-state batteries: energy density, charging time, and safety. Compared to the lithium-ion cells previously used in Helios Horizon (and which power almost all electric vehicles today), the solid-state batteries available today offer 60%-80% greater energy density, and within the next two years we expect to see that increase by another 40%. They can also be charged from almost empty to 80% charge in less than 15 minutes. And unlike the traditional cells used in everything from electric cars to cell phones, solid-state batteries are much more stable when subjected to high temperatures or even punctures, drastically reducing the risk of combustion.