Solar Impulse 2 Shows the Possibilities, and Limitations, of Movable Solar



Author: Mike Montgomery

I write about the many issues technology entrepreneurs confront.

Anyone who thinks even a little about energy is thinking about renewables. According to REN21, new investments in renewable power and fuel climbed from $45 billion in 2004 to $270 billion a decade later.

That makes it an incredibly appealing market for entrepreneurs. The vast majority of that money has been focused on renewable energy that can go into the grid and power our homes and offices. But the Solar Impulse 2, a long, thin plane that is powered completely through the use of solar panels, has shown another side of renewable energy: solar-powered transportation.

Is the Solar Impulse 2 a breakthrough or a novelty? It may be a little of both.

Bertrand Piccard, one of two Swiss pilots who have been flying the plane in tandem, sees promise in the new technology. “Today we do not have the technology for a [commercial] solar airplane,” he says. “Nevertheless, it will happen.”

But not anytime soon. “It’s not years away, it’s decades,” adds Tom Werner, the CEO and president of SunPower, the company that manufactured the solar cells for the Solar Impulse 2.

Werner explains that when developing solar-powered transportation, you need to consider cost, weight and efficiency. Although the Solar Impulse 2 shows that it’s possible to power a vehicle solely from mounted solar cells, today the challenges for a typical passenger car or commercial airplane far outstrip any benefits. For example, in order to drive 200 miles a day only on solar power, a typical passenger car would need 10 times as many solar cells than would fit onto that car’s roof.

The Solar Impulse 2 was built out of carbon-fiber materials to carry one person, so it’s fairly light. Its wings, which span 236 feet, are covered with 17,248 thin solar cells, which power the propellers and the plane’s lithium polymer batteries. Thanks to these batteries, the plane can even fly at night. It can travel between 28 and 56 mph, depending on the altitude, but it is very sensitive to rain and wind. It has the right balance of weight and efficiency, but it is not a practical form of transportation.

Solar cells will need to become lighter and hardier before they can really be used on vehicles and planes. “One of the biggest challenges with cars is that solar cells are delicate,” says Kelsey Josund, team lead on the Stanford Solar Car Project, which builds a solar racing car every two years for the Bridgestone World Solar Challenge. “Dust and rocks can damage them quite a bit and decrease performance.”

And then there’s the cost. The Solar Impulse 2 will end up costing approximately $170 million, funded mostly by private corporate sponsors and individuals.

In the short term, a more realistic use for solar in transportation is using renewable grid power to charge vehicles. Roof-based solar panels or solar farms can help charge electric vehicles. In Chile, SunPower recently announced it will help supply electricity to the Santiago subway system. “The transportation system runs on solar energy, but the solar system is off-site, then transmitted to run the metro train,” says Werner. “That’s what we can do today.”

Although we aren’t quite there yet with transportable solar panels, the Solar Impulse 2 has given us a glimpse of just how powerful — and trustworthy — solar can be.

“We need explorers to open the door and show that impossible things can happen,” Piccard says. “In one way, this is a feat of exploration and adventure and pioneers. But it’s also very practical and realistic and will help the world to be cleaner. At the same time, it will create jobs and make profits and start new markets because the world needs to be cleaner — this is a trend. The replacement of the old technologies is inevitable.”