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Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

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Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#101

Post by DaniFong »

robomartin wrote: post #83
DaniFong wrote: post #70

Earlier quoted context omitted.

You have to store both. Also, you can't vaporize much air at low temperatures, which we aim for. You have to hold onto water for its sensible (no evaporation) heat capacity.

Do you have a number for the amount of air and water you need to store per kW-h of energy delivered to the load? What's the real energy efficiency of the system? What's the estimated energy loss per unit time of the storage system?

1^m3 of 300 bar air = approx. 30 kwhr. Approximately 1/4th of that in water storage will hold the heat.

We're aiming at a daily loss of 1%, but it caps out at 10% relative (~7% absolute) because the Energy Out/Energy In is proportional to T_exp/T_comp (in an absolute scale) -- if the temperature drops to ambient, T_exp is only slightly lower in an absolute scale.

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#102

Post by DaniFong »

D_Alex wrote: post #92
Gravityloss wrote: post #90

Earlier quoted context omitted.

Air heats as it compresses. If you cool it, you lose pressure and thus energy. So you would have to keep it hot. It's problematic because it's less dense then and because you'd have to insulate it. Water stores much much more heat per volume and you don't have to handle the pressure if you keep the heat modest. This way your air pressure vessel can be smaller and probably uninsulated.

As I read it, in the proposed system the heat generated during compression is stored, and then recovered, hence the advantage over the plain old air compression. But I'm going to be that guy who says it will not work, and cannot work, based on fundamental thermodynamic theory. Here goes: 1. The best efficiency of a thermodynamic cycle is 1-TL/TH, where TL is the temperature of heat rejection from the cycle, and TH is…

Consider a big Carnot cycle. It's 100% reversible -- as efficient as you can get. No losses. And it's 100% reversible no matter what temperature it operates at.

The Carnot cycle is:

1. Isothermal compression (T_c) 2. Adiabatic compression (T_c -> T_h) 3. Isothermal expansion (T_h) 4. Adiabatic expansion. (T_h -> T_c)

The adiabatic compression and expansion processes are just to get between the two temperatures, T_hot and T_cold.

Suppose T_hot = T_cold.

Then there's no adiabatic section, and it's just

1. Isothermal compression (T) 2. Isothermal expansion (T)

The amount of energy out/energy in is T_h/T_c = 1.

This is a 100% efficient energy storage system. It is also our idealized cycle -- a gigantic, single Carnot cycle, storing energy in heat and in low entropy, highly compressed air.

Now, the Carnot efficiency, or the efficiency of a heat engine, is a completely different kind of efficiency. It's the TOTAL energy out divided by the heat in. This is

(W_out-W_in)/Q_in

In our case, the Carnot efficiency is zero, even though the cycle is reversible, and the energy storage process is completely reversible.

Interesting, no?

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#103

Post by DaniFong »

rdl wrote: post #25
DaniFong wrote: post #14

Earlier quoted context omitted.

A knee-jerk reaction by poorly informed and motivated reviewers, which included a fear of: - Hydrolock (solved by default) - Corrosion (solved) - Inability to separate water and air (easy to solve and quickly solved) - a lack of understanding that water could provide heat to air on expansion (proven...) We actually disproved all of their claims within 2 weeks of their decision. The problem, however, is that you don't…

I am curious how you solve corrosion in a high pressure thermal cycling environment for what are presumably very tiny water fog nozzles. But maybe that is trade secret or whatever. Naively I'd just switch out the air for N2, since it's mechanically the same and cheap. But then, once you're using special gas, I'd look at using low and high molecular weight (say, He and maybe some long chain which isn't going to detona…

You have to choose the right materials of course. That's part of it. Then you should avoid too many minerals in your water -- recycle the water in a closed process.

Air is nice because you don't have to hold onto it at low pressure :-)

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#104

Post by DaniFong »

jacoblyles wrote: post #91
jacquesm wrote: post #67

Earlier quoted context omitted.

Here's one: http://daniellefong.com/2010/02/11/how-law-shapes-the-busine...

I'm surprised at the difficulty I have in convincing people that eliminating the FDA is a good idea. The FDA makes the build-compile-run cycle in medicine 10x longer and more expensive. That's a mighty brake on technological progress.

Government is an accretive process. Like evolution. What you want is a separate program, with some fast track process. :-)

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#105

Post by DaniFong »

Gravityloss wrote: post #86
DaniFong wrote: post #73

Earlier quoted context omitted.

Hopefully our website might be more enlightening... lightsail.com I give a 3 minute TR35 award talk on the concept at the emTech conference this year. Starts at 5:27 http://www.livestream.com/emtech2012/video?clipId=pla_cdd4c6...

Very concisely laid out. I want to believe. Stupid question: why can't you store all the energy in warm water, eliminating the problematic (big, dangerous) pressure vessel altogether? I envision a compressor, a heat exchanger (mist or otherwise) and an expander. The expander and compressor are connected mechanically (they can be the same device like in a piston engine or can be rotating machinery connected via shaft…

The trouble with your arrangement is that if there ∆T is low, there must be very many cycles between mechanical and heat energy into order to store an equivalent unit of energy. This gives very many opportunities to lose efficiency.

There's a company out there, Isentropic Systems, that's trying this. A steep mountain to climb.

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#106

Post by zem »

jacquesm wrote: post #67
cpeterso wrote: post #62

Earlier quoted context omitted.

> some of your more off the beaten path ideas Any references? I'd love to read more.

Here's one: http://daniellefong.com/2010/02/11/how-law-shapes-the-busine...

depressing to see it all spelt out like that.

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#107

Post by akiselev »

jpdoctor wrote: post #32
akiselev wrote: post #28

Earlier quoted context omitted.

Yes because only in magic software wonderland can you have millions of users before you have any money. Once you exit the software bubble, almost everything, especially new technology, becomes a lot "harder" and takes a lot longer.

> Once you exit the software bubble, almost everything, especially new technology, becomes a lot "harder" and takes a lot longer. I've done hardware in spades, so I'm well aware of the differences. In hardware, Series D was either a Mezzanine round or a something-has-gone-wrong = inside/major-dilution round Maybe the world has changed, but having no product at D is not a sign that things are going well on the biz sid…

If you are a consumer hardware company, yes. If you're on the edges of what we as humans know to be possible, it can take far beyond Series D to get there. If you look at the early telecoms, they were essentially series Z with the government before becoming accessible.

If you're talking about anything that has impact on utility scale power or anything else on a massive scale, series D is just the beginning. LightSail needs to build a product that not only works but is so damn good that someone will be willing to put it into a system that has to last 10-30 years for an ROI.

Re: Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal

#110

Post by jswanson »

ck2 wrote: post #109

Why not use excess energy to lift millions of tons of worthless rock off the ground and then when power source fails, use the winding down via gravity to turn generators? Gravity is never going away and never going to run out.

This is already being done, by pumping water uphill: http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

I'm sure there are a bunch of interesting tradeoffs between using water or a bunch of rocks though.

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