Peter Thiel, Bill Gates, Khosla fund LightSail Energy in $37M Deal
blogs.wsj.com
blogs.wsj.com
If there is one person that I wish would find a connection like this it is you, I'm sure you'll amaze us all with what you're going to achieve now that your toolbox is filled.
This is really great news!
Any references? I'd love to read more.
I just don't see how we can circumvent RCTs as the burden of proof for efficacy and safety. Probably, yes, we could slash a lot of fat from the FDA, and trim a lot of processes... But do away with it entirely?
I would be interested to hear what your alternatives are
1) Opt-out. Allow anyone to opt-out of the FDA. That is, allow terminal patients/early adopters/test pilots to voluntarily buy products from companies before the FDA certifies them as safe and effective. For example, people might decide that they will use drugs that have cleared Phase I trials and proven safe, and use their own judgment for whether the drug is effective. Essentially this is a rollback of cases like Cowan vs. United States, a 1998 case in which the FDA sued to prevent a terminal AIDS patient from using a drug that they had not yet approved:
2) Multiple regulators. The purpose of sites like Metacritic or Rotten Tomatoes is that any one reviewer is flawed, but an aggregate will usually be better. But for most drugs and devices, only a very small number of people within the FDA plus perhaps a 15 person expert panel are involved. FDA does not have the internal expertise to evaluate all fields of medicine, so frequently gets outside experts from Harvard Medical School, the Mayo Clinic, and the like to serve on its panels. Here is an example where the chair is from Mayo:
The multiple regulators concept would allow any of these institutions to certify drugs and devices, just as we allow multiple medical schools to certify MDs. As another analogy, a company rejected by one regulator can get a second opinion from another, just as academics can submit to multiple journals if the first one rejects a paper. Indeed, much FDA review is already subcontracted out to expert panels from these institutions anyway. In return for doing approvals, Harvard Med or Mayo would get the user fees authorized under PDUFA/MDUFA that would otherwise go to FDA. People could wait for a drug to be approved by the FDA, or they could take a drug which had Harvard Medical School's stamp of approval.
These two proposals - opt-out and multiple regulators - are relatively simple to implement yet will cause huge changes in the system.
Right now we have a crude version of both in that a wealthy patient can opt-out of the FDA by flying to Europe, and a company can to some extent have multiple regulators by going for the EU's CE Mark first rather than the FDA. Indeed, within the medical devices space they now say "Europe first" just like internet startups today say "mobile first".
But it would be better if a patient could opt-out without flying to another country, and a company could get a second opinion from a different regulator without launching outside the US.
I don't disagree with pt 1, but feel that multiple regulators or regulatory aggregates can complicate the process and allow a lot of trash in... At the moment (and I must say I come from Australia so I don't fully understand the intricacies of the FDA, but we have a similar body here; and I am involved in Medicine so that is where this next bit of perspective comes from) having a single body in charge of approved treatments also serves a role of keeping the trash out. By this, I mean alt-med and all the rest of it.
For example, what would stop a total charlatan from coming to market, using all the tricks of personality and promotion that alt-med treatments do today, but in the absence of a single body meant to represent society's best interests to say 'this is fraud', winning the favour of, for example, cancer patients, taking their hard earned, getting good reviews, and then the patients dying?
It's hard enough to stop this kind of thing from happening even now, but in the absence of a single regulator/presence of multiple agencies the scammers can slip through the cracks, their clients die so there aren't any bad reviews, and they build nice houses and piles of money.
I would also hate to be a Doctor in this environment; it is hard enough being a GP in this day and age with Dr Google suggesting treatments and diagnoses to patients and more and more patients presenting with reams of paper fresh from the internet insistent that they have some deadly tropical disease; Under this system we would have patients presenting with serious conditions insisting that they want this treatment over that one because they read a review online saying this or that.
Food for thought anyway. I agree that something needs to be done and think it is a bit of a minefield trying to work out how to strike the right balance of regulation whilst also reducing red tape
Funding isn't the constraint now, it's time. But believe me there are more off the beaten path ideas where that came from ;-)
I wasn't in the least worried about that ;)
Take care!
Large scale energy storage is an unappreciated problem. Our current grid has to quickly scale up and down with demand, because there is no way store excess capacity when demand is down (and therefore, no way to reuse previous excess capacity when demand is up).
When this problem is actually solved (crossing fingers until LightSail actually ships ...), the grid is going to undergo a serious transformation for the first time - from a just-in-time economy to an inventory management economy.
Hopefully I don't sound like I'm disparaging LightSail or any of the other possible avenues - I think we need continued investment in new methods as we should always be pursuing improvement, and the LightSail approach sounds very promising. I hope Thiel and Gates' involvement in this industry will bring even more visibility to it. However, I do want to make the point that there are people doing this today, in consumer and commercial applications, and having real effects.
I think the difference in fanfare is probably because, unless you change the levelized cost of stored energy to be less than the cost of producing power from fossil fuels in the first place, you can have a significant effect, but you can't really change the way the mainstream grid operates. Existing technologies can't do that.
The companies that have staked their reputation on trying to climb that mountain are those which have attracted the likes of Vinod Khosla, Peter Thiel, Bill Gates -- who are not in it to make a buck or megabuck, but to change the world.
Management and monitoring is an important part of changing the world, but whether or not it happens depends on the cost of the system. The suspense, then, and pressure, is on us. But all players stand to play an important part -- and make a fortune.
We are indeed a battery-based system for now, though we aren't necessarily tied to that technology long term. We've focused on building a strength is in flexibility and ability to distribute storage wherever its needed. It's always exciting to see new methods of storage being developed, as I agree with you about the economics of storage. I'm not quite convinced that batteries are an antiquated option just yet (or aren't feasible financially or environmentally, long term, especially as R&D continues to move there as well), but I'm just a lowly software engineer - I'll leave it for the rest of our team to worry about those problems :)
Congratulations on your successes thus far, and good luck for what the future holds!
You're one of those people where 10 years from now it is going to blow my mind that I got to share an Internet message board with you.
Below is what my understanding: Current energy storage mechanisms (batteries) are inefficient. In theory one way to store energy that would be more efficient (why?) is to use the energy to compress air (with a conventional air compressor?). The air is stored in a container until it is converted to electrical energy through some inverse process (powering rotary screws?). Unfortunately compressed air is very hot and difficult to store. Instead water droplets can be injected into the compressed air container. These droplets will absorb most of the energy of the compressed air. The vapour is separated from the compressed air and stored in other containers (still as vapour?). How is the vapour then converted back to electrical energy? Isn't the vapour just as hot as the compressed air? Is it easier to deal with because it can be stored in a larger volume?
I think maybe the novel thing is to pass the water as a mist through the compressor cylinders where it can transfer energy from air much faster than if, for example there was just a heat transfer closed circuit around the cylinders.
Their website states: "We have achieved these high thermodynamic efficiencies at higher RPMs than many thought possible. This is crucial to achieving low cost: the higher the RPM, the higher the power of the same machine and the lower the cost per kW."
So basically you need fewer compressors and heat transfer systems for the same amount of power. I guess as long as the added complexity and maintenance doesn't add too much cost it could be more economical than using the higher number of compressors.
They do mention in the WSJ article that one challenge is preventing 'hydrolock' which, if I understand correctly, would happen if you accidentally injected too much water in a cylinder. Since water is not compressible, you could bend or break your piston rod, crank shaft or 'cause the cylinder to explode'.
If you compress the air, let it heat up, and THEN cool it by mixing the air with water, the pressure will be high during the compression process, which will take a lot of energy to compress it, and then cool off and reduce in pressure. That's bad.
What you want is to keep the temperature as low as possible during compression, and to keep it as high as possible during expansion. We do this.
And if you do recover the heat by condensing this vapour, it is low grade heat, which CANNOT be efficiently converted back to mechanical power or electricity.
Your web site claims 90% of the "grid" energy goes to heat storage. AFAICT This is NOT POSSIBLE if the heat comes from air compression. Is this an error in presentation? A fundamental error in your concept? Or am I mistaken... please explain.
When you cool the air by mixing it with water spray, a good portion of the energy is now spent producing low temperature water vapour. So... how do you recover that energy? You'd need to condense the water vapour to get at the latent heat.
You're right in direction but not in magnitude. There isn't much vapor produced, because the saturation vapor density is very low. Initially it evaporates, this cools the air before compression, and then it saturates. Any additional vaporization is recovered, because it condenses on expansion.
And if you do recover the heat by condensing this vapour, it is low grade heat, which CANNOT be efficiently converted back to mechanical power or electricity.
Also, interestingly, low grade heat can be converted into energy when you have a source of compressed air. This is not a full thermodynamic cycle because at the end of the expansion, you've also expanded air.
One of the best ways to see this is to imagine an energy storage system that's a giant Carnot cycle. The energy out/energy in is T_exp/T_comp. This is higher than the Carnot efficiency -- because it's not accounting for the energy in! The Carnot efficiency is E_out - E_in/Q_in which is 1 - T_c/T_h, the familiar expression.
Your web site claims 90% of the "grid" energy goes to heat storage. AFAICT This is NOT POSSIBLE if the heat comes from air compression. Is this an error in presentation? A fundamental error in your concept? Or am I mistaken... please explain.
Actually, if the compression is isothermal (and it's an ideal gas), 100% of the energy from the grid is turned into heat, and the energy state of the air is constant. U = 5/2 NRT.
Likewise, upon expansion, 100% of the energy comes from the heat.
The state of the air changes, but not in energy -- in entropy. As the air is compressed, work is added at teh same rate as heat -- and entropy, is removed.
This seems like a really smart feat of thermodynamical engineering, but it does not reference explicitly any technology that would not have been available 30 years ago. I could imagine that being hidden in the subtitles of getting the process efficient enough - e.g. in computer-based component design and CFD simulations.
Not OP but a few comments on what you just said. If you ever tried to manually compress air in a metal pump (say when inflating a bicycle tire), you probably noticed that the outside of the pump gets very hot when you press down. That is because gases have a property of increasing their temperature when pressure increases. So now in order to maximize your ability to store energy efficiently, you are facing two problems: (1) how to prevent gas from escaping, (2) how to prevent heat from dissipating through pipes/pistons. It looks like OP had managed to solve (2) by efficiently capturing the heat using water vapor, though I'm not sure about specifics.
Water vapor sounds like a good (if obvious) solution since water has the third highest specific heat capacity of all liquids, after ammonia and liquid lithium (http://en.wikipedia.org/wiki/Heat_capacity#Table_of_specific...).
We don't rely on water vapor -- the problem is that at low temperatures there's very little vaporization that can even take place. This limits the heat transfer. Though there are alternative approaches that use this effect more fully.
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...
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 like in a turbine).
During storing, or water warming, the expander produces less power than the compressor so you need electrical energy to spin the system.
During energy release, or water cooling, the expander produces more power than the compressor needs and you can use a generator to extract that.
This is pretty much a standard heat pump or refrigerator arrangement.
I assume this is not efficient because of some not at first sight obvious quality of thermodynamics. It'd be cool to get a little bit insight into that.
By the way, your diagram's first picture with the piston is off: either the shaft should be thicker or it should depict sealing between piston edge and cylinder, now the volume of the pressure vessel changes very little when the piston moves.
There's a company out there, Isentropic Systems, that's trying this. A steep mountain to climb.
Many powerplants such as Nuclear or Coal can take hours to startup and shutdown. The power markets and grid management orgs spend a lot of time scheduling power production and balancing supply and demand. Plants tell grid operators, we're running from 2-6pm on Tuesday - and face fines if the power isn't delivered. Some plants get paid to be on "standby" to deal with surges in demand.
The price of power can at times become negative, because for some plants it is cheaper for the operator to get zero or even negative revenue for a short period vs. shutting down. Wind power Tax credits and carbon offsets at times mean windfarms can make money with a negative powerprice.
Wind power can have problems meshing with the grid and scheduling/dispach of power. If you're producing power when you're not scheduled and demand is low the price a plant gets can be very low, even negative, because it isn't needed. Part of this is because of market rules, and part of it is actual operations.
So if the wind is blowing during a period of time that people are not using much power the windfarm operator makes very little or nothing. If you can store energy for even a few hours it can be moved from periods of low demand to high demand which makes a lot of money and ensures you are not fined for failure to deliver power.
Yes, I was an Energy Economist and part of the Enron Power Trading desk years ago.
If that includes Peter Thiel then I'm all for it.
Him being a skeptic of clean tech is a validation of sorts, you can bet that this kind of money isn't thrown around likely and that they had the basic physics checked before the investment. If someone would have been able to raise serious practical doubt about the feasibility then likely there would have been no announcement today. Yes, there is still risk, and there are likely lots of unknown factors. But this is technology development. I'm pretty sure the world will be at their feet if they manage to get the device into production at scale, no matter who the investors were.
And names like Thiel, Gates and Khosla certainly don't hurt.
And for the record, silly rhetoric about boots on the backs of the taxpayer is completely out of place in an article where he should be pimping his investment. It does make it look like he invested for negative sentiment towards the gov't rather than positive sentiment towards the company.
This technology is one missing piece.
Forest fires at scale tend to be pretty much unmanageable, people are more than happy just to put them out without having to think about extracting energy from them.
10 points for out of the box thinking, minus several for a lack of feasibility. But keep at it, maybe one day you'll hit the jackpot!
- 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 get a conversation when talking with grant agencies. So most things are misunderstood and they default to funding based on seniority.
At the time, our competitors were not taking the water based approach...
The advantage of world class investors is that, even if they disagree with you, they think for themselves, so you can actually talk to them.
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 detonate under the working pressure?), and maybe other stuff, to see if it would improve the product.
But maybe corrosion isn't a big problem -- there are some awesome alloys out there. I want to get into firearm sound suppressor design and manufacture (custom, tuned for a given weapon and load) just to justify an HPC/CFD capability and a bunch of awesome Inconel and other alloy samples.
He2 is also very expensive and H2 is very reactive which is not good either..
Fortunately there's very little H2 involved (mainly I think in the later stages), it's mainly CH4.
Air is nice because you don't have to hold onto it at low pressure :-)
Here's my attempt to answer that question:
The first stop is to get a sense of what the realistic energy density of these approaches might be. A quick search lands you here:
http://en.wikipedia.org/wiki/Compressed_air_energy_storage#E...
My take-away: 1 m3 of air = about 300,000 J
How much energy does a typical house in the US use per day?
http://wiki.answers.com/Q/How_much_electricity_does_an_avera...
I'll use 50KWh per day
1kWh = 1,000W x 3,600s = 3,600,000J
This typical house, then, consumes 180,000,000J per day
How much air do we need to compress to provide all of the energy needs of this one house (per day)?
180,000,000J / 300,000J = 600 m3
How many homes in California?
http://quickfacts.census.gov/qfd/states/06/06037.html
Let's say it's about 14,000,000 homes
How much air do we have to compress every day to service these homes:
600 m3 x 14,000,000 homes = 8,400,000,000 m3
OK, there's a number, whatever it means.
Hmmm. How much of the available air are we using?
What's the volume of air of the atmosphere?
Tough question to answer. I think the number we'd want would be that of the Troposphere.
http://en.wikipedia.org/wiki/Atmosphere_of_Earth
I am going to use an over-simplification (you know, "assume a cow is a uniform sphere of milk" type stuff) to try to get a number. Sphere within a sphere to get the volume of the troposphere.
Average Earth diameter: 12,742km
http://www.universetoday.com/15055/diameter-of-earth/
Troposphere thickness: 17km
http://en.wikipedia.org/wiki/Troposphere
Troposphere volume: 4,341,334,943,758,290,000 m3
That means that California would use 0.00000019% of the troposphere per day if every single home was powered using compressed air energy storage.
Put a different way: It would take nearly 1.5 million years to process all of the air in the troposphere.
I'm not sure if the above is complete nonsense or not. The problem is far more complex than these quickie calculations might suggest. On first inspection it sounds like we have plenty of air to go around.
Would there be any environmental and/or air quality issues stemming from this approach? Do we end-up with cleaner air locally because of the process?
Interesting stuff.
.
EDIT: A few more data points.
How big of a container is required to store all of this air?
The original assumption was that 1 m3 of air would compress into a 5L bottle, or 0.005 m3.
Storage cube side length: 348m
Storage sphere diameter: 431m
How much would this much air weigh?
1 m3 of air at 20C = 1.204 kg
8,400,000,000 m3 = 10,113,600,000 kg
The question, for me, begins to be about how realistic it might be to construct enough smaller storage vessels to capture this volume safely.
The article mentions something about 40ft standard shipping containers. Assuming that the storage vessel has the internal dimensions of a standard 40ft container:
http://en.wikipedia.org/wiki/Intermodal_container
Container volume: ~ 67 m3
Containers required to store enough compressed air to supply homes in California: ~627,000 units.
That's a lot of containers, even if the calculations are off by 100%.
This is akin to a battery, so there is a 'charge' and a 'discharge' cycle, you'd be using the charge cycle when there is an excess and the discharge when you need more than is available or when the price of your stored energy is lower than what you'd be buying from the grid. So likely while you're charging (I'm assuming that's the better part of a day) you're not consuming from the device.
So your 50KWh initial value is more likely only half of that or even less, the portion that you'd be consuming that was previously stored. I've lived off a 48KWh lead/acid battery and it would - in a very energy efficient home - power the house for up to 5 days before needing a top-up absent sufficient sun and wind. This still holds when the storage capacity is centralized, only the flow would be slightly different and the houses would be in 'sink' mode all the time.
Another point regarding consumption:
Conservation is the best possible starting point for any renewable installation, large scale or small scale does not matter. It is easier to save a KWh than it is to generate or store one, up to a point, so that low hanging fruit is where you start.
> Conservation is the best possible starting point
Couldn't agree more. I happen to think that this is where we've failed miserably over the years. Homes are just not built to be efficient, despite what the propaganda might indicate.
My guess is that your perception of failure is largely driven by the McMansion trend of the 90's/early 00's. While these large, suburban homes definitely consume more energy than their smaller counterparts, if it wasn't for strict codes and standards and minimum efficiency requirements for appliances, our energy situation would look much worse.
What's the real energy efficiency of the system?
What's the estimated energy loss per unit time of the storage system?
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.
One other way to think of the number of shipping containers needed: actually the average american home uses 30 kwh/day. At our target energy density and efficiency we've been attempting to reach 30 kwh per m^3. 1 m^3 is approximately the internal volume of a refrigerator. So each home gets 1 fridge worth of storage. Not so bad ;-)
Being within an order of magnitude is absolutely fantastic for a quick set of calcs with unverified data pulled out of various 'net sites!
So, about 6,000psi for 1m^3 ?
I was just looking at this:
http://www.nuvair.com/storage-storagetank.shtml
Their NUVT6000 tanks will do it. Specs:
Outside diameter: 9.4in
Height: 52in
Weight (empty): 195lbs.
Air capacity at pressure: 510.5 ft^3
Internal volume: 2640 in^3
To double check, the internal volume of these tanks is given at 2640 in^3. 25 tanks come in at 66,000 in^3, which is just over 1 m^3.
What this highlights for me is just how large a vessel might be required to store such a volume of air at 6,000psi due to how strong it has to be. The external volume of these 25 tanks is approximately 1.5 m^3. Not too bad. We are taking about a 5 x 5 tank layout; about 4 ft x 4 ft and, say, 6 ft high with hoses, fittings and other hardware. They would weigh-in at about 5,000lbs, which might require some accommodations for a typical home garage.
Do these numbers describe what you are trying to accomplish to a reasonable approximation?
How noisy is the process of getting the energy back out of this storage system?
I had to look at a comparison with the energy density of current Lithium-Ion batteries:
http://en.wikipedia.org/wiki/Lithium-ion_battery
Volumetric energy density: 900 to 1,900 J/cm^3
If I assume 1,000 J/cm^3, that would require about 108,000 cm^3 in Lithium-Ion batteries or 0.108 m^3. Yikes! On first inspection, a 1 m^3 bank of Lithium-Ion batteries would allow you to run a house for ten days!
Not sure what that conclusion means, but Lithium-Ion, cost and other issues aside, looks very interesting.
How about gasoline? I know, horrible, but I have to ask.
http://en.wikipedia.org/wiki/Energy_density
Volumetric energy density: 34,000,000,000 J/m^3
I won't do the numbers, but Liquid Propane looks very interesting.
Clearly your long term competition might very well be electrochemical battery or graphene supercapacitor technology.
I realize you are working on a method to be used in storing excess energy for later delivery (or smoothing out the spikes in infrastructure demands). If I was looking for emergency power backup today I think I might have a very serious look at Liquid Propane. I has none of the storage problems of gasoline (namely that it degrades if not attended to) and it is very easy to use for cooking as well as lighting, if required.
Would I want every house in my neighborhood to have LP tanks, gasoline tanks, compressed air tanks or huge banks of Lithium-Ion batteries? Probably not.
All of these options are scary in one way or another. Imagine Hurricane Sandy, Katrina or a good size earthquake here in CA in a scenario where every home has one of these technologies. Could get scary very fast.
Same issues as with electric cars. Very interesting until you have an incident involving several cars. Formula 1 teams had to make special accommodations to use their electrical KERS systems, some of which run at 375V.
Because of this I would think that your technology (or any other high-duration, high energy-density storage solution) might be best deployed at the substation or generation point rather than installed in every home. Most people are not really equipped to intelligently deal with electricity. Sometimes it is a good idea for power to go out.
We aim for it not to be noisy -- any noise from high pressure air rushing out represents wasted energy. Sonic booms from exhaust have this problem in automobile engines, we avoid it.
Lithium ion is indeed much more dense :-)
Consider that every car has a gasoline tank, many houses have fuel oil, and we undergird our streets with natural gas pipes, which burned down San Francisco. I submit that air has its safety issues, but that most of these can be avoided, and in particular, chain reactions, which threaten flammable energy storage, can be made a non-issue.
There's a reason most (recreational) scuba tanks stop around 3000 - 3500 PSI max working pressure: you fairly quickly stop getting linear gains, at the expense of additional tank wall thickness and stronger valves required.
Edit: Nevermind, it appears that 4500 PSI/300 BAR is semi-standard in Compressed Air Powered cars, so I guess there is value in going to that pressure (storage density I guess).
Just guessing that this could be a gating issue once you have something to deploy. People can be irrational, even when faced with facts. I know people that will not go into the water at the beach for fear of being attacked by a shark. Yet, the same people don't think twice about getting into their cars in the morning and driving on Los Angeles freeways.
Here industrial design might be the key. If the unit looks, almost literally, like the typical freezer or refrigerator lots of people have in their garage it might mitigate irrational first impressions.
Good luck! I'll keep an eye on developments.
Gravity is never going away and never going to run out.
I'm sure there are a bunch of interesting tradeoffs between using water or a bunch of rocks though.
More details: http://physics.ucsd.edu/do-the-math/2011/11/pump-up-the-stor...
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.
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 the temperature of heat addition to the cycle. TL and TH are ABSOLUTE scale temperatures.
2. In the proposed system, TH is necessarily low, no higher than the temperature generated during compression. Efficient compressors work at low temperatures, usually no higher than 450 K (certain INEFFICIENT compressors, eg gas turbine compressors go as high as 700 K, the mechanical inefficiency gets converted into heat).
3. If <450 K assumption is correct... and if TL is the local ambient temperature (what else?) of around 300 K the MAXIMUM efficiency of the heat recovery cycle is 1-300/450, or about 33%. At least 67% of the heat energy would be lost, leading to a very low overall cycle efficiency, far less than you would get with say pumped water storage, or batteries.
Dani Fong, please comment on the above. I would be most happy if there was something wrong in my analysis, and the new technology was a success.
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?
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 side.
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.
No I was referring to enterprise, and when it comes down to it, pretty much all VC funded operations. The nuts and bolts of the way VC funds are structured make it necessary to pretty much have the company investment resolved in about 8 years. (Typical funds are LLCs limited to 10 year frames.) Each round should last 1.5-2 yrs. If you are at D with no product, then your A round is up a creek.