Alternative Energies

How green is my airplane.



Clean, green, pristine. These are the hoped-for descriptions of future energy sources. We’ve been here before. More than 100 years ago, the British periodical The Automobile predicted the horseless carriage would bring a new era of clean streets, unencumbered by the tons of horse manure left by London’s equines each day.

Green power makes up a thin slice of where electricity comes from, and each type of green technology only a small part of that slice.

We hope that batteries, fuel cells and biofuels will clean the air of the residue left by today’s vehicles, including our beloved private aircraft. When I took folks for rides in a Piper J-3 or Cessna 172, they often suffered sticker shock as I filled the rental planes with high-priced avgas. When they learned that the Cub used 4 to 5 gallons of fuel each hour to carry two of us about 70 miles, they realized that even “cheap” flying is not terribly economical. A Cessna burning through 8 to 9 gph for possibly four passengers is not any better, though it can carry those four lucky souls about 100 to 120 miles in that hour.

That works out to about 44.5 passenger miles per gallon for the Cessna (100 miles/9 gallons = 11.11 mpg x 4 passengers = 44.44 pmpg). The Cub is even worse, getting only 17.5 mpg at 4 gallons an hour x 2 = 35 pmpg. Light Sport Aircraft don’t fare much better. A full-up Rotax-powered LSA cruising at 120 mph and sipping 5 gph will give about 48 pmpg. A Beech Bonanza with four on board cruising at 169 knots (195 mph) and consuming 16 gph also manages about 48 pmpg. Speed and weight cost fuel. Low and slow doesn’t necessarily save it.

Green Flight Challenge electric aircraft were clearly superior in this regard. The winning Pipistrel G4 cruised with four passengers (two represented by concrete and sandbags) at 403.5 pmpg, roughly double what a Prius could do (but not at 100 mph average). The second-place e-Genius, with two aboard, managed 378.3 pmpg.

No V-12 engine here. The battery pack and motor lurk in the 850-hp Lola-Drayson Le Mans prototype.

The Le Mans prototype will run on a planned racetrack that uses Halo Inductive Power Transfer much like a big slot-car run.

However, critics ask, what about the unseen use of coal and other fossil fuels to generate the electricity that charges these electric aircraft? That’s an environmental price for which we need to account. We will face new challenges as electric vehicles, including airplanes, become more of a factor in our transportation network.

Alan Soule, a CAFE Foundation board member who drove me in his Tesla Roadster during the GFC, uses the chart shown here in talks on electric vehicles. Note that solar, wind, hydro and even natural gas generation of electricity knock some carbon off the tailpipe, and that West Coast emissions are lower than elsewhere. The latter come from the hydroelectric dams in Oregon and Washington, vast Northern California geothermal fields, and solar farms and nuclear plants in the South. Photovoltaic systems and wind generation almost eliminate carbon, at least at the generating site. The residual carbon emissions are related to the manufacture and transport of the generating elements.

Soule points out that about half of the electricity generated in the U.S. is from coal. “California has only a few coal-fired plants and a relatively large proportion of renewable energy sources,” he explained. “Thus, in California, when you consider that the electric motors are around 90% efficient and the batteries store about 85% of the power that is input to the charger, the carbon ‘footprint’ of an electric vehicle is considerably less than an IC vehicle.”

Last fall, Soule also discovered that the electric airplanes in the GFC were about 50% more efficient than his electric vehicle, “with the electric airplanes about the cleanest way to get around.”

Charging Ahead

The I-5 freeway connects Canada with Mexico and will soon be the “Electric Highway.” Washington and California are completing their installations, and soon one will be able to drive a Nissan LEAF or Fisker Karma the 1388 miles from Surrey, British Columbia, to Tijuana, Mexico, without suffering range anxiety. AeroVironment supplies quick-charging stations that “fill up” an average electric car in less than half an hour. Nine are distributed every 40 to 60 miles along the freeway in Washington, eight are spotted every 20 to 25 miles from the California border to Cottage Grove in Oregon, and several slower Level 2 chargers await users between Eugene and Portland. California is most ambitious, with more than 200 public quick-charging stations and an additional 1000 plug-in stations planned that will feature 10,000 individual

charging units. Private enterprise will supplement these government efforts, with many chain restaurants, motels and others offering this service.

Only one aircraft recharging station exists anywhere near this line now (or anywhere else in the country): a six-aircraft installation at Charles M. Schulz Sonoma County Airport in Santa Rosa, California.

Alan Soule uses this chart to show that electric cars are cleaner overall, regardless of their energy source.

What If This Gets Really Big?

Imagine that we do have two million EVs on the road by 2030. How will we provide enough electricity for them?

Many are investigating the possibilities of cleaning up power at the generated level. Despite incentives and investments, only a small wedge of electric power comes from renewables.

Nuclear alternatives are almost too controversial to consider, though proponents claim thorium reactors avoid the long-term consequences of current nuclear plants. It’s been almost three decades since the last nuclear reactor was commissioned in the U.S., and environmental concerns, insurance issues and governmental policies often block planned development.

Wind and solar power have their own problems, critics say. Both are variable, relying on not-always-reliable sources of natural power to make electricity. The grid needs to store energy to balance the difference between demand and available electricity. Batteries currently store only a small part of the needed power, with pumped hydro the biggest source of stored electricity.

Self-Powered Private Enterprise

Private enterprise can lead in generating power for its own use and in alleviating the load on the grid. On its web site, Pipistrel displays the daily solar output at its Slovenian factory, awarded a prize as the cleanest plant in the European Union. (One of my favorite beers comes from a totally wind-powered brewery.) As more factories become wind or solar powered, the emissions used to bring us goods and even make solar cells and panels will dwindle. Such facilities may even offer their employees charging stations.

Geothermal Generation Heating Up

Power for the GFC came from Calpine generators at The Geysers geothermal site north of Santa Rosa, near where the event took place. Geothermal relies on volcanic activity 6000 to 7000 feet below the earth’s surface and requires drilling to access it. Heat seekers look for an ideal situation, an overhanging thick layer of insulating rock, a middle layer of fragmented stone that allows the flow of heated steam through its fissures and an underlying heat source: the magma coming from the earth’s core. Instead of bringing up oil, the layered pipes installed in the drill hole bring up superheated steam, which drives a turbine to generate electricity. Geothermal power requires tons of water, and Santa Rosa and Windsor municipalities have come up with a clever way to supply that need. The two cities pump their treated excess waste water (that would otherwise be stored in expensive holding ponds) to The Geysers for use in generating power.

Oregon and Utah are currently investigating enhanced geothermal production, the use of “fracking” or fracturing underground rock layers to enhance steam production. Oregon’s project uses water, but Utah’s will rely at least partly on unidentified fracking fluids to split the rocks. Either approach has drawbacks. Oregon’s uses scarce water in a high-plains desert, and Utah’s lacks transparency about what goes into the ground.

Pumped Hydro

Living in the Pacific Northwest, I’d thought that big dams were the only way to generate electricity with a good head of water. Such dams stop the Columbia at several points along its run from Canada to the Pacific with giant walls of concrete, into which are set strategically placed generators. They warm the water and slice migrating salmon in their turbines, both detrimental to future fish harvests. Even a green approach can have downsides.

The greatest source of water-produced electricity is pumped hydro, which uses power from sun, wind and the dams themselves to pump water uphill into holding dams, releasing the water through turbines as needed—especially during high-demand periods—allowing load balancing on the electric grid. More than 110,000 megawatts of electricity are stored this way worldwide.

Different Pumped Hydro

Dams take up vast plats of land, alter the landscape and are subject to the vagaries of weather, snowmelt and flooding. Three Gorges Dam in China is big enough to have changed the social ties of a country. Even a pumped-hydro storage project consumes valuable real estate, takes up to 15 years to build and costs as much as $1 billion.

A huge weight in Gravity Power’s closed tube system drives a turbine and generates electricity.

Gravity Power, an offshoot of LaunchPoint Technologies (that makes what they claim to be the highest power-to-weight-ratio electric motor), uses another approach: digging a big, cylindrical hole, filling it with water and dropping a weight in. The company explains that pumped-hydro storage is the most widely used, large-scale electricity storage technology today. Gravity Power goes into the earth to reduce its non-carbon footprint and projects that in-town installations are possible with such systems, because the subterranean installation can support buildings above them.

The prototype is small, about 5 feet in diameter and 192 feet deep, but plans for ancillary and “peaking” plants (to take overloads during peak demand) involve 32-foot-diameter storage tubes running 3000 to 6000 feet deep, but which, in no more than 2.5 acres, could generate up to 2400 megawatts. Gravity Power claims a payback time of five to 10 years with a 30-year expected lifetime.

This overhead view shows how Gravity Power could concentrate gigawatts of electricity production in a city block’s area.

A New Kind of Turbine

Wind turbines are large, sometimes topping more than 300 feet, with huge blades that critics say threaten birds and bats and create a low-frequency noise that causes something called wind-turbine syndrome, a collection of nervous and physical ailments. This is not proven and may be apocryphal. Growing residential neighborhoods in Mojave and Tehachapi, California, would probably be a hard sell, with 5000 large turbines covering the hills between them.

Sheerwind, a 2011 CleanTech award winner, promises a different kind of turbine: smaller, requiring less acreage, quieter. An INVELOX (increasing the velocity) wind turbine is 50% shorter, requires 90% less space and has blades 84% shorter than those on typical wind farms, according to Sheerwind. The company also claims that for 100 megawatts, INVELOX reduces generation costs 16% to 38% and maintenance costs 40% to 45%.

The venturi-like horns in Sheerwind’s INVELOX design would speed up wind, triggering at 2 mph, and drive a compact turbine system.

Power Given and Taken Away

Several companies are developing highways (or, conceivably, taxiways) that provide power and even retrieve it from cars passing over their surfaces. Israeli firm Innowattech has laid its first section of piezoelectric highway, which transforms the motion of cars passing over it into electricity that might power streetlights and be stored for use as needed. Idaho startup Solar Roadways promotes a glass-topped (!), solar-collecting highway that would light up to warn drivers of hazards and display information in bold LED lighting. They think such highways alone could more than meet America’s energy needs. The inventor, Scott Brusaw, claims the solar-collecting highway could be built for less than the cost of asphalt currently being used and would pay back the investment in power generated. The company recently announced that it won a $750,000 Small Business Innovation Research grant.

Place an inductive power strip down a road’s centerline. Drive a car with a collector plate attached to its chassis over that and collect the power to give your EV unlimited mileage. Too wild? Lola-Drayson’s racing team’s 850-horsepower Le Mans prototype will do just that on a planned racetrack using Halo Inductive Power Transfer (IPT). Future Formula 1 racing could look like a giant slot-car run. Halo has long-term plans to do the same for electric highways.

Airbus and several partners have tested powered landing gear that taxis the airplane out to the runway on its own batteries or fuel cells. Some promise that the gear could have an inductor plate that would take power from the runway and allow the airplane to carry less fuel or more payload. For airliners and electric aircraft, perhaps even the initial takeoff acceleration and roll could be ground powered, allowing smaller battery packs or enhanced performance.

More Ahead

Energy options exist in a growing range of technologies that will help meet our future energy needs. Start looking for the startling realities headed our way.

Dean Sigler has been a technical writer for 30 years, with a liberal arts background and a Master’s degree in education. He writes the CAFE Foundation blog and has spoken at the last two Electric Aircraft Symposia and at two Experimental Soaring Association workshops. Part of the Perlan Project, he is a private pilot, and hopes to get a sailplane rating soon.

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Dean Sigler
Dean Sigler was a technical writer professionally for 34 years, with a liberal arts background and a Master's degree in education. He writes the Sustainable Aviation and CAFE Foundation blogs. He has presented at several symposia and at several Experimental Soaring Association workshops. Part of the Perlan Project, he is a private pilot with a great love for low and slow aircraft.


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