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US startup begins producing 40%-efficient thermophotovoltaic cells

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Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#141

Post by badtension »

bluGill wrote: post #134
pjc50 wrote: post #78

Earlier quoted context omitted.

Like computing, having high uptime has a value all its own compared to an unreliable system. Countries which do have regular brownouts you find people buying their own (inefficient, polluting) generators to get round it. Smart demand-response may yet become a thing, but it's not yet a commodity product. You need a system to send out "turn off" notifications, and a system for measuring that in realtime, and a system f…

Many grids do have this for normal residences, but it only covers your air conditioner not everything (and maybe water heater). By running your AC on half duty cycle all day your house still stays cool enough and they are able to reduce substantial peak demand. For most people HVAC and water heating are the two biggest demands, and also ones where simple management can result in a substantial changes in demand withou…

Making thermostats that are aware of dynamic energy pricing or, better yet, are in part controlled by the energy company (I want my house to be 21-24 C, I don't care when the cooling happens) would give us massive flexibility.

All power hungry devices should at least have that capability (maybe other than the kettle, lol). This is literally a cost of $20 hardware in many cases.

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#143

Post by badtension »

adrianN wrote: post #136
badtension wrote: post #64

Earlier quoted context omitted.

I feel like this is one of the biggest missed opportunities. Why do we insist on our energy system to be infinitely flexible and full power available 24/7? Is a habit of doing the laundry at night worth more than additional millions of tons of CO2 in the atmosphere? I understand convenience, laziness and inertia (resisting change) but I also think changing the times when we click "power on" is a simpler solution than…

Demand shaping is part of the plan, but opportunities are currently limited. For most applications demand can only be shifted by a short time.

Water heating, AC, fridges and freezers, maybe even EV charging (in some cases) could be done at any time during the 24 hour period, if setup with proper hysteresis.

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#144

Post by adrian_b »

megaman821 wrote: post #137
adrian_b wrote: post #124

Earlier quoted context omitted.

No, by using both a combustion-gas turbine and three steam turbines to recover the waste heat you get 63% efficiency for electrical energy production. By using the residual heat for hot water and for heating in winter and cooling in summer, the global efficiency typically becomes well above 80%. Even the best Diesel generators may reach around 55% efficiency, while working at much lower maximum temperatures. For a fe…

Different use cases. This is for taking intermittent electricity production and storing it as heat. It will mainly be used for industrial heat; the TPV electricity production adds a little extra utility to the system.

Thermal storage at so high temperatures is even less practical than any other application.

Thermal storage at low temperatures is cheap and easy with molten salts.

Thermal storage at over 2000 Celsius degrees will be extremely difficult, due to the difficulty of preventing heat losses.

The best would be for the hot body to be stored in argon, because in vacuum it would evaporate and heavier inert gases are expensive. The storage vessel would be very expensive in any case, being made from multiple layers with high temperature resistance, an external surface with high reflectance in red and infrared and other layers with low thermal conductivity, so it is hard to imagine that it could have a size large enough to store much energy.

Another obstacle is that the available power is determined by the emitting surface, not by the volume of the hot body, which is another obstacle for scaling to large amounts of stored energy.

Another obstacle to scaling is that when the hot body cools down the conversion efficiency drops extremely quickly (fourth power), which means that it could store energy only e.g. by being heated and cooled between 2400 and 2100 Celsius degrees.

So only a very small fraction of the thermal capacitance of the hot body can be used, many times lower than when the heat stored in that body would be used to power a closed-cycle heat engine.

So no, these devices may have some useful applications, but energy storage is certainly not one of them, because they are much worse than almost any alternative. Even storing compressed air in a pressure vessel is much more practical.

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#145

Post by adrianN »

badtension wrote: post #143
adrianN wrote: post #136

Earlier quoted context omitted.

Demand shaping is part of the plan, but opportunities are currently limited. For most applications demand can only be shifted by a short time.

Water heating, AC, fridges and freezers, maybe even EV charging (in some cases) could be done at any time during the 24 hour period, if setup with proper hysteresis.

Shifting some load by a couple of hours is indeed often possible, shifting it by 12 hours is already difficult.

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#146

Post by badtension »

adrianN wrote: post #145
badtension wrote: post #143

Earlier quoted context omitted.

Water heating, AC, fridges and freezers, maybe even EV charging (in some cases) could be done at any time during the 24 hour period, if setup with proper hysteresis.

Shifting some load by a couple of hours is indeed often possible, shifting it by 12 hours is already difficult.

Interesting, I would have thought in many cases it is maybe not trivial, but easily doable at worst. Do you have some personal experience with that?

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#147

Post by pbmonster »

Tuna-Fish wrote: post #107
pbmonster wrote: post #106

Earlier quoted context omitted.

> combustion in nitrogen-depleted air and chemical looping combustion. Am I misunderstanding this or are both of those concepts basically "just inject pure oxygen"? And I'm no economist, but running a powerplant on rocket fuel doesn't sound that feasible to me. Urea injection into the exhaust gas sounds more sensible to me, and even that is seems economically questionable. Fuel prices would need to be pretty high tha…

No-one sane wants to do combustion in a pure oxygen environment. The solution isn't that, it's to eliminate nitrogen and replace it something else. Typically CO2, because you can get it for free and already preheated by recirculating exhaust.

Ok, so you recirculate exhaust into the combustion chamber and inject new fuel.

Now what? It doesn't burn, since there is no oxidizer. The only way is to inject some. And since you don't want nitrogen, you can't inject air. So you inject pure oxygen, or something like peroxide?

Sounds expensive.

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#148

Post by [deleted] »

londons_explore wrote: post #37

> emitter temperature of 2,400 C GE's combined cycle turbines can get system level efficiency of around 63% from these sorts of temperatures. (For those not familiar with them: They're basically aircraft jet engines followed by steam turbines using the hot exhaust. They are in widespread use to generate electricity from gas, but they can also run off any other liquid fuel, or simply off anything that gets very hot.)

[deleted]

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#149

Post by zackmorris »

londons_explore wrote: post #37

> emitter temperature of 2,400 C GE's combined cycle turbines can get system level efficiency of around 63% from these sorts of temperatures. (For those not familiar with them: They're basically aircraft jet engines followed by steam turbines using the hot exhaust. They are in widespread use to generate electricity from gas, but they can also run off any other liquid fuel, or simply off anything that gets very hot.)

Just so we have it, the efficiency of any heat engine is limited to the Carnot efficiency:

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.htm...

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An internal combustion engine (ICE) uses the Otto cycle:

https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes...

https://www.sciencedirect.com/topics/engineering/otto-cycle

If you click the Read more arrow under 3.4.1 The Efficiency of an Otto Engine, it states that The ideal Otto cycle achieves the Carnot efficiency of an engine working between the maximum, pre-combustion, temperature and the intake temperature. This means that the ideal Otto cycle cannot achieve the Carnot efficiency determined by the highest and lowest temperature during the cycle.

Tlow = T ambient

Thigh = T at highest compression of piston

efficiency ~= 1 - Tlow/Thigh We can find the pre-ignition temperature at maximum compression:

https://www.physicsforums.com/threads/compression-psi-and-te...

T2 = T1 * ((V1/V2)^(y-1)) where y ~= 1.4 for air

So a 14:1 compression ratio at an ambient room temperature of 293 K (20 C or 68 F) gives a pre-combustions temperature of:

T2 = 293 * (14^(1.4-1)) = 842 K (569 C or 1056 F)

So the maximum efficiency (Carnot efficiency) of an Otto cycle 14:1 compression ICE would be less than:

efficiency In practice, an ICE might scavange 50% of that due to losses to entropy, friction and hot exhaust at 600 K (about 300 C or 600 F) and end up at 33% efficiency, not counting drivetrain losses of about 15% to get to maybe 28% at the wheels.

That's why ICE vehicles waste around 75% of the fuel's energy or more. Whereas an electric vehicle will be around 90% percent efficient from batteries to motor and around 75% efficient at the wheels, or at least 3 times better than an ICE vehicle.

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A gas turbine uses the Brayton cycle:

https://web.mit.edu/16.unified/www/SPRING/propulsion/notes/n...

The Brayton cycle thermal efficiency contains the ratio of the compressor exit temperature to atmospheric temperature, so that the ratio is not based on the highest temperature in the cycle, as the Carnot efficiency is. For a given maximum cycle temperature, the Brayton cycle is therefore less efficient than a Carnot cycle.

Tlow = T ambient

Thigh = T at highest compression after compressor

effiency ~= 1 - Tlow/Thigh A jet engine might reach 40:1 compression:

T2 = 293 * (40^(1.4-1)) = 1281 K (1008 C or 1846 F)

So the maximum efficiency (Carnot efficiency) of a Brayton cycle 40:1 compression turbine would be less than:

efficiency In practice, a gas turbine might scavange up to 85% of that and end up at 65% efficiency, not counting generator losses of 5%. But 40-65% overall efficiency is more realistic.

A 45% efficient gas turbine would leave 55% of the energy as waste heat in the exhaust. So a steam turbine scavanging that would only need to be about 35% efficient to reach an overall efficiency of 65%. Depending on exhaust temperature, the article's thermophotovoltaic cells would probably be cheaper and more reliable than additional turbine stages.

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I've never seen a good way to relate Carnot efficiency to quantum efficiency. Thermodynamics measures average emergent behavior like fluid dynamics. So the Carnot efficiency is kind of like the Bernoulli equation or Reynolds number, and may have no analog at microscopic scales. Maybe something like:

https://en.wikipedia.org/wiki/Quantum_heat_engines_and_refri...

Re: US startup begins producing 40%-efficient thermophotovoltaic cells

#150

Post by jjk166 »

hedora wrote: post #100
svantana wrote: post #35

Earlier quoted context omitted.

This looks like it has about 100x higher power density than what solar PV gives at peak. Combine that with 100% uptime and deployment pretty much anywhere, that are some pretty compelling advantages.

How could that possibly be the case? The current best commercially-available solar panels are 20% efficient. Last-gen stuff is 10-15%.

Well if you put those solar panels right up against the sun, they'd be much more power dense. But for the moment building a nuclear reactor on earth is a significantly easier engineering challenge than building a solar plant on the sun.
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