LightSail’s Danielle Fong on the Most Exciting Science

As 2013 was winding down, I asked Danielle Fong what she considered the biggest scientific breakthroughs in the last year.

Fong is the co-founder and chief scientist at LightSail Energy, a Khosla-backed company trying to reinvent the energy grid by storing excess energy in the form of compressed air. (Fascinating profile of Fong, who started college as a teen, and LightSail here.)

Fong’s answer arrived a little late for the obligatory wave of looking-back-at-the-year-that-was stories. But … the response was so compelling we decided to run it in full (edited lightly for clarity, length and to make Paul Graham look sexist — kidding!).

Stick through to the end for hints of some potentially exciting things coming up for LightSail, a company I’m planning to watch closely in 2014.

Photo Credit: Robert Schlatter Danielle Fong, chief scientist at LightSail

My top two picks are, really, themes, and they represent a deepening of our understanding, and an increasing perfection of technology.

It’s hard to pin down exactly one “breakthrough.” The paradigmatic examples are in fact not what they seem.

For example, Alexander Fleming isn’t even the first one to have discovered or written about antibiotic properties of penicillin (as early as the 1870s the mould was written about). He was in a position to look for antibiotics, given his work on antibacterials during the war. And he made the initial discovery in 1928, abandoned clinical work on it in 1931, restarted in 1934, and continued to try to get a chemist to purify it until the 1940s. The development of antibiotics was not just one thing.

For that matter, the lightbulb was a filament, plus a vacuum, plus a high resistance, plus a whole electrical system — generator, mains, feeders, the works. Bulbs existed before Edison, but he brought a system forth to provide lighting.

And the Wright Brothers weren’t the first ones to have achieved flight, but heavier than air (Zeppelins were first) *controlled* flight. They needed to invent new flying paradigms, wing warping, new engines, new propellors, control systems, developed elevators and wings. They tested in wind tunnels, an invention of their own. It wasn’t just one thing — though there certainly was a moment of truth in the air!

Hence, themes. My two picks for the most exciting things in science last year:

1) Exoplanets! – so many worlds teeming with life, all in the sky, perhaps within reach.

So much happened this year. We are in a galaxy with perhaps 100 billion worlds, 17 billion “earth like.” The galaxy may be a fertile garden of life.

What’s driving all of this is an incredible refinement of the transit technique for the detection of exoplanets, culminating in the Kepler spacecraft.

Researchers are really finding their stride in data analysis and techniques, and a plethora of discoveries have resulted.

These discoveries have helped make it possible to imagine humanity spread throughout the stars, and innumerable worlds, and lifeforms abound, waiting to be discovered.

2) How Genes Really Work

Specifically, steadily increasing control and understanding. Take a look at how many of these advances listed here involve epigenetics or gene therapy or the discovery of an important gene or the sequencing of a new species or the use of genetic modification to understand a new organism.

We’re still only scratching the surface here. But genetics isn’t like computer code; it’s chemistry and systems science and ecology. Genes are regulated by the environment, and other genes, and genes regulate the environment in turn. We’re understanding more and more how to introduce genes into new lifeforms, how they’re expressed, regulated, how they mutate, change, how they fold (we caught a ribosome in mid fold!).

We can now even make machines — it is a stretch to call them robots — but machines, nanomachines, out of DNA. (See video below.)

I’m both excited and disappointed with my two picks. They give us amazing new capabilities — dreamt of for a long time, now made real. But they are not the broad new continents of possibility that some hope for in breakthroughs.

Personally, I think that at least one of three things I’ve been working on in 2013 should be on there, eventually. In the future, perhaps, on whatever Wikipedia page you’d read, you’d read that I came up with the idea in 2013. But since none of it is public, and none of it has been proven yet, you’ll only hear about it in a few years, and if LightSail is any indication, it will be another three years before anyone writes about it as a breakthrough, and another three until it is actually real.

ORIGINAL: ReCode

By James Temple

January 6, 2014

A Brief Note on Thermodynamics

ORIGINAL: Danielle Fong
by Danielle Fon. 
a wick for ideas

One of these days, I’ll try to write up the rules of thermodynamics so that people stop getting mislead. This is not a particularly well edited essay, but it should go up somewhere. Apparently there was a considerable armchair debate about what we are trying to do at LightSail on SciAm.com. Rebuttal below:

Ok, I’ll bite.

First of all if you’re actually looking for rebuttals, it’s usually easier if you post it to my email or some website I own (e.g. daniellefong.com) and have notifications for. We get an awful lot of media coverage and I don’t monitor everything.

Second, the efficiency we’re targeting is 70%. Not 91%. I don’t know where people got that from. We include all of the practical losses that people have mentioned —

• motor inefficiency (at our scale, typically 5% loss, not 10%, as some people seem to believe — it depends upon scale), 
• friction, 
• heat loss through our insulated tanks, etc. 

We are not actually there yet. If our first product is between 60% – 70% efficient we’ll be pleased, but we’re determined to push that as high as we can.

Third, it appears you are under some confusion about thermodynamics.

It is a slippery field, and I don’t blame you: both Bill Gates and his advisors made similar mistakes the first time through.

a) We’re not doing isentropic compression or expansion. The whole point of the water spray technique is to approximate an isothermal compression and expansion cycle — the water absorbs heat from the air rapidly. The correct first order approximation is that the heat capacity of the *mixture* is effectively added to the heat capacity of the air. Try deriving this from the 1st law, starting from T_water = T_air, and following the derivation of adiabatic compression without heat exchange to the outside that you see in any thermodynamics text.

Actual results have our output ∆T < 20 C and maximum hotspot ∆T = 60 C. Water spray actually cools. It is surprising how controversial this has been in the 21st century…

b) You’re using Carnot efficiency in an erroneous way. Compression and expansion are only part of the cycle. While it’s true using the generated heat alone in a heat cycle would grant you the efficiencies you describe, this is irrelevant, because we’re not doing that. There’s a whole other thermodynamic resource: *the compressed air* that this is wasting. So we’re not doing that.

Here’s an illustrative exercise.

A Carnot Cycle is perfectly reversible: run the cycle backwards, and 100% of the heat turns back into mechanical energy. How is this possible, one might ask, while at the same time being compatible with Carnot efficiency?

Several reasons: as a heat pump, the Carnot cycle turn W units of work into 1/(1 – Tc/Th) units of Th heat! There’s more heat, in joules, pumped than work put in.

This might seem to violate intuitions, but you can purchase heat pumps at any hardware store. You will notice that there are heat pumps and refrigerators with a coefficient of performance much greater than 1 widely available. This really works.

Now, draw a T-S diagram of a Carnot cycle for an ideal gas. It’s a rectangle in T-S space, the isothermal compression and expansion processes are horizontal lines, and the adiabatic processes are vertical.

Shrink the adiabatic processes to nothing, so that isothermal compression and isothermal expansion are at the same temperature. No heat is moved, and there is no net work. It is still a reversible Carnot cycle. But it doesn’t seem to do anything.

Why would you do a thermodynamic cycle if you get no net work energy out?

Answer: if you get energy out at a *better time*!

If you get 100% of the energy out that you put in, but at a different time, then this is an *IDEAL* energy storage cycle. You can’t get more efficient than that!

However, by your mathematics, you’ll have a 0% efficient heat engine.

The thermodynamic equations for a full heat cycle are *different* than for an energy storage cycle. You cannot just use them blindly. You have to go back to the first principles: the first and second law. (which, by the way, are never violated here — there is never entropy destruction in this or any other ideal reversible cycle).

—

All this said, this is an idealization. In fact there are losses in the process.

• Friction, for example. 
• Resistance in our motor coils. 
• Air turbulence running through valves. 

All this goes to heat.
What we do with this heat is that we collect it so that we expand air at as high a temperature as we can.

We don’t get as much energy out as if the energy never went to heat, but it is a small boost if we can get it. About 10% relative energy storage efficiency (E_out/E_in) for a 30 C heat increase if we’ve got it, nothing to sneeze at.

But even if we lose 100% of the extra heat, and have to expand at ambient temperature, our efficiency only goes down by that same 10% relative efficiency. It is not bad.

Also, it’s not so hard to insulate a large tank.

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In general, while I applaud the efforts of people to work out things for themselves, you have to be extra careful that you’re not deluding yourself. It is worse to take a well known equation, misapply it, and declare impossibility, than it is to say that you heard about something but haven’t worked to complete understanding from the fundamentals yet.

It’s not actually working something from first principles if you get them wrong…

Cheers,

Danielle Fong
LightSail Energy