

Q&A: Danielle Fong, Chief Scientist, LightSail Energy - foobarqux
http://fortune.com/2014/12/31/danielle-fong-lightsail-energy/

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partition
The part at the end where she is against top-down thinking, and instead
promotes bottom-up inductive thinking where you first figure out how to make
airplane parts well before tackling the whole aircraft, is a lesson I've
learned the hard way an almost unhealthy number of times. She also seems to
understand the difference between leadership and management.

Other than that, the 90% figure seems pretty believable to me. If you are
playing with containers of gas, you can do stuff that is quite close to the
physics textbooks' chapters on thermodynamics. The water is probably so they
can get to 750 kwh per tank.

Are there any other processes where the engineered efficiency is that close to
ideal? Pumped-storage hydroelectric is close.

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pjc50
It says 90% _thermal_ efficiency, which makes me wonder what the electrical
efficiency is. Also, "500 hours reliable operation" doesn't look great.

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fpp
Combined heat and power (CHP) might be indicative for that - nevertheless 90%
roundtrip what they say on their website is very impressive.

Compressed Air storage has been around for some time and one of the limits is
of course the low energy density. They mention 750 kWh modules containerize -
how many containers will that be at what pressure - 20 ? 50 ? 100 ? (so that
they can still match safety standards while being closer than e.g. 1km to
residential areas)

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DaniFong
Hi there,

This is Danielle Fong -- I'm also a longtime HN'er.

1 container is 750 kWh at 200 bar.

We adhere to the ASME codes which have an impressive set of tests you need to
pass -- for example you need to cycle 60000 times in an oven, cycle to 1.5x
design pressure with two deep gashes in the outwear walls (40% of the depth of
the wall), and survive without bursting a 50 caliber armor piercing round shot
from an anti-tank rifle.

You are right that 90% thermal efficiency doesn't account for electrical or
mechanical losses.

Unfortunately it is a little confusing and we need to fix that. The gold
standard is electrical to electrical efficiency, but we had not optimized or
demonstrated that at the time. (We are very close!)

What we _had_ done (2011 - 2012) is demonstrated the thermodynamic, scientific
viability of the process. The 90% one-way thermal efficiency compared to what
a typical adiabatic process would have of about 65%. The one way efficiency of
a typical compressor is further reduced by friction, etc. to about 59%, and
still further by electrical losses to about 55%.

At the moment we can achieve a bit above 71% one way in our best runs
(including electrical) and are trying to drive to 80% this year -- that's a
50%+ or 64% electric to electric efficiency. We want to be near to 60% across
a whole operating cycle.

Note that with 55% one way efficiency from the best previous compressors,
that's only about 30% efficiency. So the promise of our tech is that we double
efficiency overall for energy storage -- and that's enough to make it viable.

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fpp
Many thanks for the explanations Danielle - this sound like some quite
substantial improvements over numbers I know from large scale CHP solutions
e.g. Turboden (turboden.eu) that are providing about 19% as gross electric
efficiency. They have been building large scale CHP solutions for more than 15
years in Europe but of course they are using turbines and their applications
(heat recovery, biomass energy production, Rankine Cycle / ORC) are seemingly
quite different from what you're currently working on.

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davedx
The LightSail website has a nice comprehensive overview of how the technology
works. Well worth a read:
[http://www.lightsail.com/](http://www.lightsail.com/)

Particularly impressive: 90% thermal efficiency.

I want to invest...

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loceng
What I'd like to see a matrix comparing all of the different systems using
compression or stored energy via non-battery means.

They mention low cow air storage tanks - comparable to what though?

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mikeyouse
The DOE has some great resources, I can't the one I'm thinking of, but this
document:

[http://energy.gov/sites/prod/files/2013/12/f5/Grid%20Energy%...](http://energy.gov/sites/prod/files/2013/12/f5/Grid%20Energy%20Storage%20December%202013.pdf)

On page 30 has a matrix of the different attributes of different energy
storage systems (but unfortunately not cost or capacity).

