Monday, February 25, 2013

Renewables in the Sky

Renewable energy generation at the utility scale in the US was derived from multiple sources in 2011. Hydropower was the largest source (63% of renewable energy) followed by wind (23%). Solar power contributed less than one percent of renewable energy that year. Renewables as a whole represented 13% of the overall electricity generation mix, according to figures from the US Energy Information Administration. Renewable energy sources are well-known in the transportation industry (e.g., electric vehicles, hybrid gas-electric vehicles, natural gas vehicles, fuel cells, etc.). Efforts are underway to develop biofuels for the aviation industry.

Not to be forgotten are proponents of solar energy that hope to develop and demonstrate solar-powered airplanes.

The Invention

US Patent 8,002,216, “Solar powered wing vehicle using flywheels for energy storage,” was issued to inventor Darwin Kent Decker in August 2011. His patent is for “[a] solar powered air vehicle that can stay aloft for indefinite periods of time. The vehicle employs photovoltaic solar cells for primary power and high speed counter-rotating flywheels for energy storage and steering of the vehicle. The flywheels are placed in the wing to reduce airfoil drag. A control law provides three-axis stabilized control of the vehicle by controlling propeller pitch to vary the speeds of the flywheels.” His purpose for the solar flying wing clearly falls within the clean tech realm:

”With the threat of global warming and increasing gasoline prices, the interest in solar powered aircraft using photovoltaic solar cells has increased.”

Advantages of a solar-powered plane include:

”… it can stay aloft for indefinite periods that may extend into years of time similar to the operation of a satellite. Further, the solar powered aircraft can perform many of the present functions of a satellite without the cost of an expensive launch vehicle and without eventually creating orbital waste. The solar powered aircraft can return to earth for maintenance and be re-configured for a variety of missions. Typical applications include surveillance and tracking, homeland security, communications, oceanography, and meteorology. Many of these applications require operation at high altitudes greater than 60,000 feet where air breathing engine are less efficient.”

He notes that:

”A more appropriate energy storage device [i.e, than batteries or fuel cells] for use with long life solar powered airplanes is a high speed flywheel with a composite rotor and magnetic bearings. High speed flywheels provide superior energy per unit weight than batteries in applications where long cycle life is required. Composite rotors have demonstrated over 112,000 cycles in laboratory tests. Furthermore, flywheels provide a more efficient energy to thrust ratio for this application than batteries since batteries store energy chemically. Converting electrical energy to chemical energy, then back to electrical energy and then to rotational energy is inherently less efficient than converting the electrical energy directly to rotational energy in the flywheels and then using torque conversion to apply the energy directly to rotating propellers. Furthermore, flywheels produce moments and gyroscopic couples that can be used to steer the aircraft and eliminate or reduce the need for additional steering devices such as flaps, fuselage and a tail section that create additional drag on the vehicle. To date, flywheel energy storage has not been used in solar powered air vehicles.”

Note the similarity of the body structure of the ‘216 patent to that of the Northrup XB–35 flying wing from the 1940s.

Other Renewable Energy in Aircraft?

Decker proposes to use solar power. Various companies, including Amyris Biotechnologies (see our 1/12/12 post linked above), are developing aviation biofuels. What about wind power?

Interestingly, the earliest patent cited by Decker in the ‘216 patent is US 1,245,902, issued in November 1917 to Frank Gretsky of Coal Center, PA. His invention “Aeroplane motor” had the object of providing,

“a simple, practical and efficient attachment of strong, durable and comparatively inexpensive construction comprising a wind wheel adapted to be mounted on the propeller shaft and connected with the same by a train of gears so that the wind from the propeller, or resulting therefrom by the passage of the aeroplane through the air, will act on the wind wheel and assist in rotating the same and thereby effect a saving of fuel.

A further object of this invention is to provide a motor of this character adapted, in event of the internal combustion engine of the aeroplane becoming inoperative while the aeroplane is in the air, to serve as a wind motor for actuating the propeller and thereby rendering the aeroplane more easily handled and comparatively safe under such conditions.”

Gretsky was awarded a patent for mounting a windmill on an airplane to aid in, or wholly provide, its propulsion, and his intent in 1917 was to save fuel using wind power. Once again, we see that clean tech is not new, and our forebears were no less interested in energy savings, renewable energy and conservation than we are.

A Third-Generation Explorer Counts on The Sun

Bertrand Piccard is now a decade in to his Solar Impulse project that seeks to develop solar-powered planes. The Solar Impulse plane will be conducting test flights at NASA’s Moffett Field in May, and then is planned for a demo cross-country flight to Washington DC and New York. Piccard ultimately hopes to fly the plane around the world. The plane, a single-seater, has a 208-feet wingspan (equivalent to an Airbus A340), weighs a little more than 3,500 pounds, and is powered by four 10-horsepower electric motors. It will store electricity in lithium polymer batteries during the day for use during night flight. The plane’s upper wing surface and horizontal stabilizer house 11,628 solar cells.

These cells are manufactured by SunPower, one of the solar companies receiving patents under the USPTO Green Technology Pilot Program. Although this is a high-profile opportunity for SunPower, it has not been without its troubles in a turbulent solar market.

Piccard is the third generation of a family of noted explorers. His grandfather Auguste Piccard was a balloonist that established world records for high altitude balloon flight (a predecessor of Felix Baumgartner’s amazing flight last October on the anniversary of Chuck Yeager’s breaking the speed of sound). Piccard’s father, Jacques Piccard, was the first submariner (along with his dive companion Don Walsh) to reach the Challenger Deep in the Pacific Ocean’s Mariana Trench. They used the submersible Trieste to descend to 35,797 feet below the ocean’s surface on January 23, 1960. The Trieste was designed by Jacques’ father Auguste. The Challenger Deep was not re-visited by humans until March 2012 when the film-maker James Cameron reached the deepest point on earth in the Deepsea Challenger. Bertrand Piccard fulfilled Jules Vernes’ dream expressed in “Around the World in Eighty Days” when he co-piloted the first non-stop circumglobal balloon flight. Fascinating articles on all three men may be found in back issues of National Geographic magazine. A good article on Solar Impulse was recently published by Gigaom.

Clean technologies and renewable energy are being applied to aviation - but they have been for a long time.

End Note:
Gretsky’s windmill-on-a-plane, 1917. We’ve written it before, but the old patent drawings are art, unlike the sterile CAD depictions in today’s patents. It is not progress when aesthetics and beauty are abandoned.