On August 9, 1977, the United States Patent Office approved an application from three researchers at NASA’s Lewis Research Center in Cleveland. The patent was for a “solar cell shingle,” and it’s one of the earliest — if not the earliest — designs for putting solar cells on people’s roofs to bring power to their homes. Exactly 40 years later, companies like Tesla and others are on the verge of making solar-powered roofs a reality.

It’s been a long road to that point, and NASA’s proto-shingle was one of the earliest signposts of what could be achieved in the years to come. While a New York Times article published in August 1977 mentions NASA had received several inquiries about licensing the patent for commercial development, the idea of a solar shingle was probably too far ahead of its time four decades ago.

“Well, it was far out,” Americo Forestieri — “Moe” to his friends — who is one of the three researchers listed on the patent, tells Inverse. “As a matter of fact, it probably didn’t fall into the realm of what NASA was doing at the time because we were a space organization, of course.”

But it had been NASA that first found a practical application for solar cells. Until the launch of the solar-powered satellite Vanguard 1 in 1958, the cells were so primitive and inefficient that they has been little more than a toy for researchers at places like Bell Labs. Even if solar power wasn’t yet practical on Earth, it was the ideal way to power satellites, making NASA a natural hub for solar research.

This little guy, Vanguard 1, was a solar pioneer.

Not that this necessarily meant the space agency was on the brink of discovering practical, inexpensive solar power, as that wasn’t the task before it. “If you’re putting up a billion-dollar satellite, the cost of the power system, while it may be millions of dollars, it’s not the most important thing,” Sheila Bailey, a solar energy researcher at what has since been renamed the Glenn Research Center, tells Inverse. “You want reliable, and you want something that’s durable, and you want something that’s efficient because the real estate on a satellite is limited. You want the most efficient cell you can possibly produce.”

But there were times when NASA’s space-focused research could dovetail with potential uses back on the Earth. “We knew about solar cells, we knew that they worked, we knew that they had some terrestrial applications,” says Forestieri. This was of growing interest in the 1970s, as a pair of oil embargoes sent gas prices skyrocketing in the United States and had researchers beginning to think seriously about alternative energy.

Forestieri credits colleague Anthony Ratajczak, one of the other researchers on the patent, with the original idea for the shingle. It stood out as an unusually Earth-centric idea. “We had the equipment to do that and we put one together and it worked,” he says. “We understood it was low-efficiency, we didn’t think it that it would have come to what it is today. But it certainly is all around the world right now.”

Figure 2 from Forestieri, Ratajczak, and Sidorak's design for a solar shingle U.S. Patent Office

The design of their solar shingle is simple enough: The patent calls for an array of solar cells to be placed atop a material like fiberglass cloth and covered with a weatherproof, transparent material. They take advantage of the fact regular roof shingles are already designed to overlap one another, with connectors placed at the edges of the shingles to share and transmit the collected power between them.

“You have to make an electrical connection from one shingle to the next to build up the power level,” Leroy Sidorak, the third researcher on the patent, tells Inverse. Just as you do inside any solar module, each cell is attached to the other cell by some method. Then you add those up because each solar cell at that time only develops a little less than one half volt of power. You have to have a way of adding those up to get to a certain power level that you want.”

The patent stresses their solar shingle is meant to not only serve as an energy collector but also as an ordinary shingle in its own right. In that regard, this 40-year-old design is closer to what Tesla is doing now with its solar roofs than just putting a bunch of solar arrays on top of a roof.

The Raven Run solar house in Kentucky from the 1970s Green Building Advisor

“I think at that time solar collectors, which was just putting panels up on your roof… that was the extent of it,” Sidorak says. He was the materials scientist of the trio, meaning it was his job to translate Forestieri and Ratajczak’s design into reality.

This wasn’t the easiest task. Before he started working on the shingle, Sidorak had been able to put solar cells on a hard surface like aluminum to help protect them. The fiberglass material, however, was initially soft so that it could work as a shingle.

Figure 3 from Forestieri, Ratajczak, and Sidorak's design for a solar shingle U.S. Patent Office

Finding the right material to protect the shingle was also a challenge. After all, roofs are expected to last as long as 30 years, all while standing up to rain, snow, heatwaves, and anything else the weather can throw at them. The Vanguard 1 satellite, by contrast, had the relatively easy time of being in the vacuum of space, and it only operated for six years before losing contact with Earth.

The original solar shingle never got put on anybody’s roof, but the researchers did try it out in the field outside Lewis Research Center alongside the commercial solar arrays NASA tested. The experiment was necessarily limited — they didn’t have 30 years to prove the solar shingle could work atop someone’s house — but Forestieri says they came away satisfied.

Americo "Moe" Forestieri working at the Lewis Research Center in 1965, a decade before his work on the solar shingle. NASA

“I think the thing that was guiding us was that we were wondering if something like that would work,” he says. “When we put it together, we did see that the way we put it together, it would last probably a long time depending upon the film that we used to put it on and to cover it. They were pretty much impervious to the weather. So we thought, yeah, that would be a pretty good idea.”

Their shingle was a long way from commercial viability. The initial cost of a Tesla solar roof is about $50,000, minus various tax incentives. That’s expensive but within the realm of affordability for affluent homeowners, especially when you factor in three decades of potential energy savings. Forestieri estimates it would have cost anywhere between $250,000 and $400,000 in 2017 dollars to install enough of their solar shingles to power a home.

“If you were not concerned about the cost, I’m sure that we felt it would work on a house,” he says. “But it was going to be pretty expensive for a house. It was five percent efficiency at the time I believe. You would have had to make plenty of those to get on a roof of a house.”

A Tesla solar roof, the spiritual descendant of NASA's solar shingle. Tesla

Questions of cost and practicality may have meant 1977 wasn’t ready for their solar shingle, but 2017 and onward could prove a very different story for the technology’s spiritual descendants. “I think it’s just a matter of time,” says Sidorak, pointing out that solar cells become a better and better idea as power consumption generally becomes more efficient. Forestieri is similarly optimistic.

“It’s tremendous actually,” says Forestieri. “I’m really awestruck at how fast it has moved. It doesn’t cause any pollution at all, it’s a great idea. I’m just surprised it came as fast as it did.”

Figures 4 and 5 from Forestieri, Ratajczak, and Sidorak's design for a solar shingle U.S. Patent Office

There’s also a chance the story of NASA’s solar shingle could come full circle. What began as these researchers’ attempts to apply their knowledge of space-based solar technology to Earthbound roofs could one day head back out beyond our planet, says Sheila Bailey.

“That solar shingle would also be just fine on a habitat in Mars or on the moon,” she says. “It’s not a technology that you would want to ignore. It’s something that you might put to use on a planetary or lunar surface.”

Given Tesla founder Elon Musk’s own hopes to establish a Martian settlement with SpaceX, that thought puts a potential whole new complexion on his interest in solar roofs. And with NASA’s own return to space exploration beyond Earth orbit, perhaps the solar shingle is headed home, more than four decades since three NASA scientists in Cleveland first came up with the idea.