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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

#121

Post by vlovich123 »

nine_k wrote: post #92
vlovich123 wrote: post #29

Earlier quoted context omitted.

Adding more cells won’t help for two reason. Let’s say the extra cells would help absorb, they can only capture 40% which means you’ve got exponentially increasing costs chasing after all the heat you didn’t absorb (+ physical location of where to put the cells). The real reason though is physics, namely the 2nd law of thermodynamics. If you could keep adding cells to capture the heat other cells couldn’t, you’d basi…

Technically, perpetual motion is possible: consider a sphere rotating in vacuum. A source of free energy, a "perpetual engine", is indeed impossible.

A sphere rotating in a vacuum should still experience black body radiation and gravitational drag. Damn kids and their pesky attempts to violate the 2nd law.

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

#122

Post by lazide »

adwn wrote: post #95
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…

> Why do we insist on our energy system to be infinitely flexible and full power available 24/7? I like to heat my home during winter. We have a (modern, highly efficient) heat pump, so we need most electricity during January, just when the least amount of solar insolation is available [1] and when it sometimes stays cloudy and below 0°C continuously for days. But I guess we'll just have to be more flexible and turn…

Regarding [1] - are you being sarcastic?

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

#123

Post by mikeyouse »

hwillis wrote: post #108
gumby wrote: post #103

Earlier quoted context omitted.

> It’s also a peak steady-state number, only achievable under optimal load conditions. For base load generation at least, these run continuously under “optimal conditions”. The big ones are designed to be switched on and run for decades. A turbine is a tuned system (its shape is designed for its operating conditions). For base load generation it’s important to fix those operating conditions thus getting the most outp…

The nationwide average capacity factor for CCGT was 57% in 2020: https://www.eia.gov/todayinenergy/detail.php?id=48036

But that's a naive number that also includes periods when the CCGTs were turned off due to "market conditions" where other energy sources were cheaper, so is mostly unrelated to the technical ability for them to reach much higher capacity factors.

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

#124

Post by adrian_b »

labcomputer wrote: post #79
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.)

You have to do some “energy accounting” sleight of hand to get 63%, though. That number assumes that some of the low-grade waste heat can be used for, e.g., district heating. It’s also a peak steady-state number, only achievable under optimal load conditions.

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 few seconds I thought that this thermophotovoltaic technique is great, until I have seen that the emitter must have a temperature above 2000 Celsius degrees. For such a great temperature it is very easy to make heat engines with much better efficiency and which might even be less expensive, because these multijunction III-V photovoltaic cells are many times more expensive than normal solar panels.

If these were used for solar power, the concentrators would also be very expensive. Already the concentrators that produce temperatures around 1000 Celsius degrees, which is more than enough for easily reaching 40% efficiency with closed-cycle heat engines, are much more expensive than the concentrators that reach only lower temperatures, like 650 Celsius degrees, which would still be good enough for a steam turbine or for a closed-cycle supercritical carbon dioxide engine.

The only real advantage is that these should need less maintenance than turbo-generators, which may be essential outside Earth or in remote locations, but less important than cost and efficiency otherwise.

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

#125

Post by lazide »

AtlasBarfed wrote: post #115
londons_explore wrote: post #84

Earlier quoted context omitted.

I believe that figure is electric efficiency only. For combined heat and power plants, the efficiency routinely goes over 80%, and for heat-only plants, 95+% is common. However, there is still sleight of hand. The efficiency quoted is when the equipment is new and clean. Fouling and wear both take single digit percentages off. Also, they use the lower-heating-value for the gas energy supply. That, in my view, is dish…

And of course carbon removal from burning the natural gas is totally out of the equation.

Since no one is requiring it at scale, and since there is no commonly accepted way of doing it - pretty hard to add it to an equation no?

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

#126

Post by est31 »

AtlasBarfed wrote: post #115
londons_explore wrote: post #84

Earlier quoted context omitted.

I believe that figure is electric efficiency only. For combined heat and power plants, the efficiency routinely goes over 80%, and for heat-only plants, 95+% is common. However, there is still sleight of hand. The efficiency quoted is when the equipment is new and clean. Fouling and wear both take single digit percentages off. Also, they use the lower-heating-value for the gas energy supply. That, in my view, is dish…

And of course carbon removal from burning the natural gas is totally out of the equation.

> And of course carbon removal from burning the natural gas is totally out of the equation.

Sorry for being nitpicky, but burning natural gas does not remove carbon, it adds new CO2 to the atmosphere (if you release the burn products which is usually done).

You probably mean that if you released that natural gas directly into the atmosphere instead, it would have a larger greenhouse effect than the CO2 released by the burning process. This is true, and one should absolutely choose "burn it" when given the choice of releasing only vs burning and then releasing.

But expressing it in the way of carbon removal is misleading. The number of carbon atoms in the atmosphere is the same in both scenarios, they are just bound in a less greenhouse-y form (also, natural gas decays into CO2 plus water eventually, but it's a very slow process). The number of CO2 equivalents goes up in both scenarios as well, just way less if you burn it before. Maybe some people refer to those through "carbon", idk.

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

#127

Post by bluGill »

fnordpiglet wrote: post #116
pjc50 wrote: post #76

Earlier quoted context omitted.

There is an "albedo effect", yes, but it's not cumulative while CO2 in the atmosphere is. Arguably there should be a "white roof" campaign for urban areas, it would be a cheap way of reducing the urban heat island effect.

Many major cities already have such regulations even outside desert areas.

There are also a lot of HOAs that require black roofs. Something else to write your representative about.

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

#128

Post by BobaFloutist »

nine_k wrote: post #92
vlovich123 wrote: post #29

Earlier quoted context omitted.

Adding more cells won’t help for two reason. Let’s say the extra cells would help absorb, they can only capture 40% which means you’ve got exponentially increasing costs chasing after all the heat you didn’t absorb (+ physical location of where to put the cells). The real reason though is physics, namely the 2nd law of thermodynamics. If you could keep adding cells to capture the heat other cells couldn’t, you’d basi…

Technically, perpetual motion is possible: consider a sphere rotating in vacuum. A source of free energy, a "perpetual engine", is indeed impossible.

Solar power is also perpetual motion for our purposes. The sun's going to be around for a loooooong time.

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

#129

Post by bluGill »

londons_explore wrote: post #69
kolinko wrote: post #53

Earlier quoted context omitted.

Carbon or tungsten I don't know, but sand as a thermal energy storage medium can be quite economical. Energy loss scales with the surface area (^2), energy stored with volume (^3). With grid scale, above certain dimensions, you can store energy for months while maintaining economic viability. Even for single days or weeks it makes sense. You need hot water in your home 24/7, but sun doesn't shine every day in most re…

Is the sand flowing or stationary? Flowing sand has issues with blockages and erosion. Stationary sand has pretty low conductivity, so getting all the energy out of your 200 yard cube of hot sand might be a challenge.

You don't really need to get the energy out fast. You typically have 8-12 hours every day where you want energy out, and similar amounts where energy goes in. Just put some pipes through the sand and you can get plenty of transfer.

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

#130

Post by shepherdjerred »

discordance wrote: post #93
svantana wrote: post #16

Could this be used to create a nuclear power generator without moving parts? Some radioactive material in the center, some coating to absorb the radiation, and a shell of these cells to generate electricity.

Yeah, that’s a radioisotope thermoelectric generator: https://en.m.wikipedia.org/wiki/Radioisotope_thermoelectric_... There’s a story about some loggers finding an abandoned RTG in Siberia and sleeping next to it for warmth. They woke up with severe radiation burns.

You'll find a similar story (minus the burns) in The Martian!

https://www.amazon.com/Martian-Andy-Weir/dp/0553418025

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