High-altitude wind energy from kites! - Saul Griffith

If you're at all like me, this is what you do with the sunny summer weekends in San Francisco: you build experimental kite-powered hydrofoils capable of more than 30 knots. You realize there is incredible power in the wind and it can do amazing things. One day, a vessel not unlike this will probably break the world's speed record. But kites aren't just toys; like this kite, I'm going to give you a brief history and tell you about the magnificent future of every child's favorite plaything.

So, kites are more than a thousand years old. The Chinese used them for military applications and even for lifting men, so they knew at that stage they could carry large weights. I'm not sure why there is a hole in this particular man. In 1827, a fellow called George Pook actually pioneered the use of kites for towing buggies in races against horse carriages across the English countryside. Then, of course, at the dawn of aviation, all of the great inventors of the time, like Hargrave, like Langley, even Alexander Graham Bell, inventor of the telephone, was flying this kite, doing so in the pursuit of aviation.

Then these two fellows came along, and they were flying kites to develop the control systems that would ultimately enable powered human flight. So this is, of course, Orville and Wilbur Wright and the Wright Flyer. Their experiments with kites led to this momentous occasion where we powered up and took off for the first-ever 12C human flight. That was fantastic for the future of commercial aviation, but unfortunately, it relegated kites once again to be considered children's toys. That was until the 1970s, where we had the last energy crisis, and a fabulous man called Miles Lloyd on the outskirts of San Francisco wrote this seminal paper that was completely ignored in the Journal of Energy about how to use basically an airplane on a piece of string to generate enormous amounts of electricity.

The real key observation he made is that a free-flying wing can sweep through more sky and generate more power in a unit of time than a fixed-wing turbine. Turbines grew, and they can now span up to 300 ft at the hub height, but they can't really go a lot higher, and more height is where more wind is and more power—almost twice as much. So cut to now: we still have an energy crisis, and now we have a climate crisis as well. You know, humans generate about 12 trillion watts, or 12 terawatts, from fossil fuels. Al Gore spoke to why we need to hit one of these targets, and in reality, what that means is in the next 30 to 40 years, we have to make 10 trillion watts or more of new clean energy somehow.

Wind is the second-largest renewable resource after solar: 3,600 terawatts—more than enough to supply humanity 200 times over. The majority of it is in the higher altitudes above 300 ft, where we don't have a technology as yet to get there. So this is the dawn of the new age of kites. This is our test site on Maui, flying across the sky. I'm now going to show you the first autonomous generation of power using every child's favorite plaything.

As you can tell, you need to be a robot to fly this thing for thousands of hours; it makes you a little nauseous. Here, we're actually generating about 10 kW, so enough to power probably five United States households with a kite not much larger than this piano. The real significant thing here is we're developing the control systems, as did the Wright brothers, that would enable sustained long-duration flight. It doesn't hurt to do it in a location like this either.

So this is the equivalent for a kite flyer of peeing in the snow—that's tracing your name in the sky. And this is where we're actually going. So we're beyond the 12C steps, and we're working towards megawatt-scale machines that fly at 2,000 ft and generate tons of clean electricity. So you ask, how big are those machines? Well, this paper plane would be maybe enough to power your cell phone. Your Cessna would be 230 kW. If you'd loan me your Gulfstream, I'll rip its wings off and generate you a megawatt. If you give me a 747, I'll make 6 megawatts, which is more than the largest wind turbines today. And the Spruce Goose would be a 15 megawatt wing.

So, that is audacious. You say, "I agree," but audacious is what has happened many times before in history. This is a refrigerator factory churning out airplanes for World War II. Prior to World War II, they were making 1,000 planes a year; by 1945, they were making 100,000 with this factory. And 100,000 planes a year? We could make all of America's electricity in about 10 years.

So really, this is a story about the audacious plans of young people with these dreams. There are many of us, and I am lucky enough to work with 30 of them. I think we need to support all of the dreams of the kids out there doing these crazy things. Thank you.