“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Sunday, June 03, 2018

Requiem for LightSail Energy

Image Credit: LightSail Energy
I've published multiple posts concerning LightSail Energy and its Chief Science Officer, Danielle Fong. I was enthusiastic about the the Lightsail Energy compressed air energy storage technology concept, wherein a water mist was to have been used during compression in order to produce a quasi isothermal compression process and consequently reducing thermal losses. And I wasn't alone in my enthusiasm, such notables as Vinod Khosla, Bill Gates, Peter Thiel, Total, and others invested somewhere in the vicinity of $80MM in LightSail.

But, despite the confidence of these very bright investors and the large amount of capital invested, LightSail Energy is, according to co-founder Stephen Crane, in a state of "hibernation." I follow Ms Fong on Twitter and, off and on, have corresponded with her. I haven't read anything from her with respect to the fate and apparent demise of LightSail, but the tenor of her Tweets is that she's moved on.

This saddens me because, the potential of near-term success of hydrogen fusion as an energy source notwithstanding, I am firmly convinced of the urgency of weaning ourselves from near-total reliance on fossil fuels for energy and saving those resources for applications for which substitution is extremely difficult such as transportation fuels (airlines, transoceanic shipping for example). Electricity is the low-hanging fruit here, albeit a pretty high low-hanging fruit! We have wind, solar, hydro, geothermal, and other ways to harvest energy that don't directly involve the burning of fossil fuels and all of them result in the generation of electricity.

But the most bountiful categories are solar and wind (hydro, while certainly a large contributor, has mostly been "built out," i.e., the best sources have already been exploited) and those are intermittent sources. In order for them to provide so-called "base load" power, a method of eliminating this intermittency must be employed. This can be accomplished in part by wide geographic dispersion, but the holy grail would be the ability to store energy when the wind blows and the sun shines.

Currently, nearly all new storage installations involve large lithium ion battery installations. But Li ion batteries, while good and continuing to improve, have downsides. They degrade over time, they require assiduous management both to preserve lifespan and to prevent issues of thermal runaway. And, in comparison to large scale pumped hydro storage (PHS) and compressed air energy storage (CAES), the energy capacity of Li ion battery installations is not as large (see chart below, note the log-log scale).

Image credit: unknown

Image credit: LightSail Energy
In the chart, you'll find the "Large CAES" installations in the upper right hand corner. However, the two installations plotted use underground caverns as their containment vessel and need natural gas heating in order to function. LightSail was developing modular units of much smaller size using above-ground storage in tanks. And, in what now seems to have been a last-ditch effort to continue, LightSail began an attempt to market the tanks they'd developed and, apparently, delivered at least one.

Unfortunately, the LightSail web site is gone and with it, I'm afraid, is the investors' money and the hopes and dreams of Danielle Fong.

Saturday, April 28, 2018

My airline fuel use

Undoubtedly to the disdain of those who seek to minimize energy use and, in particular, energy use that involves travel via the burning of fossil fuels, I do a significant amount of airline travel. And, beginning in August of 2017, I added fuel burn (by asking the flight crew, who is invariably happy to entertain my questions), distance traveled, and number of passengers on each flight to my log. I calculate such things as passenger miles per gallon, joules of fossil fuel energy used per passenger, and a variety of other pieces of data.

For the “big numbers,” I’ve flown 27,068 miles on 25 “legs.” Over these miles, I’ve been responsible for 383 gallons of jet A being burned, for a mileage of 70.7 m.p.g. As my patient readers likely would infer, despite my having exchanged my Lexus CT 200h in which I achieved over 50 m.p.g. for a Jeep Grand Cherokee SRT that achieves about 16.5 m.p.g., I still obsessively log my driving fuel burn. In the time that I’ve traveled the 27,000 miles in airliners, I’ve driven 12,573 miles and burned 758 gallons of gasoline for a mileage of 16.46 m.p.g. I very rarely have a passenger in my car. I'd estimate that, of the 12,573 miles, I've had a single passenger for something like 750 miles which results in a passenger mileage of 17.6 m.p.g. Miles driven with more than one passenger were negligible. Had I traveled those same miles in the CT 200h, I'd have burned about 241 gallons of fuel.

What can I make of this? 68.3% of my miles traveled have been in airliners (ignoring when I've been in the road vehicles of friends and associates) but only 33.6% of the volume of fossil fuels burned have been in those airliners. Again, had I still been driving the Lexus CT 200h, the figures would be 68.3% (of course) and 61.4%.

The fact of the matter is that modern airliners are amazingly efficient. If I drove my Jeep with three passengers, I'd still not exceed the fuel economy of the airliner, though the same four people in the Lexus would far exceed that fuel economy. But I'm not aware of anyone who carries a full car load of people any for any significant fraction of their driving.

The most common engines on my flights are the CFM56-7B series (the dash 7B24 variant was the culprit on Southwest flight 1380 that suffered a fan blade rupture resulting in the death of a passenger). The dash 7B24 variant produces a maximum thrust of 24,200 lbf (pounds force) and the dash 7B26 produces 26,300 lbf, though these thrust levels are only used during takeoff and early climb. A typical number in cruise is more like 5,800 lbf. Giving that a little thought, it's pretty startling that a force of 11,600 pounds is all that's needed to push a vehicle with a weight on the order of 150,000 pounds through the air at 530 m.p.h.

There's no doubt that my travels, both now in the Jeep and multiple times per year in the "big silver bird" are contributing more than my fair share of carbon emissions. If I use very rough figures, the 39,641 miles that I've traveled since August of 2017 annualize to the emission of something like 15 tons (Imperial short tons that is) per year of carbon dioxide attributable to my travel with about 36% of those emissions due to airline travel.