Is the Solar Plane the Future of Commercial Airlines?

Joel Anderson |

On Wednesday, the EPA announced that it would be setting new emissions standards for airplanes. On the one hand, the environmentalist deep within me was jumping with joy. A part of me loves it when the EPA does ANYTHING. Especially something addressing global warming.

However, my second reaction was “is that really necessary?”

Here’s the thing, I’m all for government regulations where the needs/wants of the people aren’t aligned with the economic incentives provided by the market. People don’t like rat parts in their meat. The market favors producers who get meat to market as cheaply as possible – regardless of rat issues at their facilities. Ipso facto, we need regulations about rat parts in meat that’s sold to consumers (thank you Upton Sinclair).

But is this most recent set of regulations something we NEED? Is this a place where the market won’t push airlines to cut emissions on their own? Seems like a no to me. Airlines spend vast, VAST sums of money on jet fuel. In fact, one Wall Street Journal article found that nearly a third of the cost of each airline ticket goes to fuel costs.

Simply put, airlines have every reason to use less jet fuel with or without the EPA.

However, the timing of this announcement, coming in the midst of the excitement over the Solar Impulse and its (temporarily grounded) attempt to circumnavigate the globe in an aircraft powered by the sun, does raise some interesting questions about the future of aviation. If the electric car is now a reality, is the electric airplane also forthcoming? Are we nearing a future where we zip from city to city in the 600-seat Boeing (BA) Prius Spruce Goose?

Let’s look a little closer…

Airplanes Aren’t Causing Much Carbon Pollution…For Now

The current portion of carbon emissions that can be attributed to airplanes is about 2%. So, yeah, hardly our most pressing air pollution issue. Why is the EPA even digging into this when there are so many other, more worthy culprits to focus on?

In a word? Growth.

Current estimates have emissions growing by some 70% by 2020, driven largely by the rapidly expanding middle class in China and India. China saw an annual growth rate of 15.5% in domestic air travel from 2000 to 2006, so airline carbon emissions could feasibly become a serious problem in the near future, and getting out in front of the issue could be a pretty smart move. If you can set things on the right path now, it will pay dividends that will grow exponentially with the industry.

Physics Comes to Rain on Our Parade

“But if we can convert all of our airliners into solar craft like the Solar Impulse, we’ll effectively eliminate all of those emissions, right?”

Slow your roll. Yes, we are all excited about the solar airplane. But then, we seem to get pretty excited about all things solar – even when they’re really dumb ideas that won’t work.

So while the technological achievements represented in the Solar Impulse are pretty swank, the application of that technology to the sort of airplanes used to ferry people from city to city is limited by a few simple factors – one of which is unfortunately Newtonian physics. Now, I have little to no background in engineering, but Wired’s Aatish Bhatia certainly does, and he outlines some pretty clear issues facing anyone working on building a solar/electric airplane for use by the airlines in his excellent article on the subject.

Firstly, weight is pretty much the biggest issue facing any aeronautic engineer. It takes tremendous amounts of energy to get something in the air and keep it there. Every 5.5 pounds of weight on a commercial airliner, for instance, is roughly equivalent to a full ton of carbon emissions over the course of the year. So, any gains you might make in energy efficiency are probably going to be completely offset if the technology creating them adds weight to the airplane.

Can you replace the metal skin of an airplane with solar panels and the necessary electronics without adding weight? I have no idea. However, you’re combining the energy expended to accelerate solar panels to the speed necessary for take-off and then carrying them for the duration of the flight to the energy collected by those panels during the flight. Again, I’m no engineer, but my guess would be that that’s probably going to offer a pretty marginal return at best.

So How is the Solar Impulse Doing It?

Simply put, the solar plane is primarily succeeding by sacrificing all of the other elements of functionality in favor of being a solar plane. The comparison of dimensions in the Bhatia article illustrate this pretty clearly. The Solar Impulse has approximately the same wingspan as a 747, about 80 meters. However, the total weight for the Solar Impulse is about 2 tons. A 747? That would be 560 tons. Yowza.

Speed is also different by orders of magnitude. The Solar Impulse is apparently moving at 43 mph, a pretty slow pace that I suspect is likely geared toward optimizing its energy efficiency. A 747? Try 570 mph.

Airliners have two really clear and important purposes: get as many people as possible somewhere as fast as possible. Any innovation that sacrifices either of those elements is likely not one that will get a ton of penetration in this market. Would you purchase a ticket on a solar plan over a traditional gasoline model if it meant it would take more than 10 times longer to reach your destination? I’m guessing not.

Physics and Safety Go Great Together

It’s also worth noting that even marginal reductions in safety, no matter how dramatically they can improve fuel efficiency – can pretty much be immediately discounted. You’re not going to get a lot of takers on the “we’re just trading the OCCASIONAL crash for much better fuel efficiency” argument.

Further still, no commercial airliner is going to adopt a technology where you might lose thrust because of unexpected changes in the weather. For an airplane, where even relatively slight failures can have catastrophic consequences, you need a steady, reliable source of energy. Even beyond safety, the amount of lost revenue for having to cancel flights on cloudy days (not to mention angry customers) makes this unrealistic.

Hybrid Technology and Lighter Batteries Do Create Possibilities

Okay, so solar-powered 747s are probably never going to happen. But that doesn’t mean that using electricity to generate thrust can’t have some promising applications. In fact, there are already airplanes built using hybrid technology, and there are also plans for commercial-scale airplanes that would make use of this. Granted, the massive, airline-scale versions aren’t expected prior to 2050, but it does speak to the potential of the concept.

Essentially, building a gas-electric hybrid like a Toyota Prius was always less feasible for airplanes based on the weight of the batteries involved. However, with advancements in battery technology, things are changing. That’s actually a big part of why the Solar Impulse was possible. So, with lighter batteries, and a combination of electric and fuel driven motors working together, these planes could operate with dramatically improved fuel efficiency.

Take-Off vs. Cruising Speed

I have previously written about how our electric grid can’t operate at peak efficiency because of a peak need paradox. Namely, your utility needs to be able to generate enough electricity to meet demand at peak hours, even if those peak hours are relatively brief. Airplanes have a similar issue. The amount of energy required to take off vastly exceeds what you need to cruise once you reach altitude. You may very well end up carrying a lot more engine than you need for most of the flight just to be sure you can get off the ground in the first place. And, as noted earlier, with weight being such an important consideration, your overall fuel efficiency can be seriously hurt.

That gap is where the potential of hybrid technology appears to have a chance to get a real toe hold. The engines used in commercial airlines are currently using very little jet propulsion most of the time. Instead, the engines are using the fans in the front of the engines like propellers to create most of the power. Those fans could just as easily be powered by electric sources. A battery bank could store the energy needed for those extra oomph moments at take-off and while climbing. Those batteries, in turn, would be charged by a small jet engine or even through regenerative braking as the plane slows down during landings.

Push comes to shove, solar or completely electric aircraft are already on the market, but their limitations mean they will probably never be a part of commercial airlines. The technology they use, though, could definitely be part of a tandem solution that still does a great deal to improve efficiency and reduce emissions.

Biofuels Fuel Other Options, and Traditional Tech May Be Adequate On its Own

Of course, all of this is assuming that there aren’t plenty of options available for improving fuel efficiency without revolutionizing the engines. However, there are actually plenty of options for reducing weight and drag that are well within the near-term capacity of aeronautical technology.

Biofuels are already getting a long, hard look by airlines. Of course, not as long or hard since last fall’s crash in oil prices, but, if (when) those rebound, you can expect this solution to be in vogue again. Currently, Alaska Airlines (ALK) , the leading airline in fuel efficiency, is already deep into plans to use fuels developed from cooking oils and alcohol.

There are also some common sense fixes to reduce drag, like a shorter tail or plane skins that don’t accumulate squished bug parts. And the fight against excess weight is always an area that pays great dividends. Finding ways to build lighter jet engines and parts, often involving 3-D printing, also offers immediate benefits.

All of this points to the EPA potentially making the right call by jumping into the fray. If there are current technologies that aren’t getting adopted because their cost-benefit isn’t quite there yet or, perish the thought, the airline industry being horribly inefficient in implementing changes even when they’re beneficial.

Aircraft Fuel Efficiency Likely to Have Its Day In the Sun

Certainly, the future of airline travel is likely going to change a lot to accommodate its rapid growth. That’s partially due to the need to reduce carbon emissions in the future. It’s also due to the fact that airlines are scraping out profits and cutting their fuel consumption is necessary to their survival as companies.

So, at the end of the day, is the EPA over-reaching by stepping into aircraft emissions? Maybe. There’s certainly plenty of market incentives driving airlines in that direction anyway. But then, perhaps relying on the market-savvy of the airline industry is not the best way to go.

It’s hard to say for sure.

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