Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

US startup begins producing 40%-efficient thermophotovoltaic cells

pv-magazine.com

Post reply on HN
Print view View original

81–90 of 174 posts

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

#81

Post by Cymrukicks »

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.

Stationary, this has already been done. It does require a heat exchanger aswell rather than getting a direct current out.

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

#82

Post by Cymrukicks »

svantana wrote: post #54
pbmonster wrote: post #45

I don't get why they go for storage with this. Storing a block of carbon or tungsten at 2000°C for hours or days does not sound like something that will ever be economical. A battery leaking energy this quickly (and it will leak₎ will need to be incredibly cheap to ever make sense. I wonder if you could use this with parabolic mirrors, though. Build a large mirror array, focus sunlight onto a big carbon sphere (maybe…

Couldn't it be just a shell of carbon or tungsten, but the bulk of material inside be molten sand, or something else "dirt cheap"?

Like this? https://polarnightenergy.fi/sand-battery#:~:text=It%20is%20a....

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

#83

Post by hiAndrewQuinn »

pbmonster wrote: post #45

I don't get why they go for storage with this. Storing a block of carbon or tungsten at 2000°C for hours or days does not sound like something that will ever be economical. A battery leaking energy this quickly (and it will leak₎ will need to be incredibly cheap to ever make sense. I wonder if you could use this with parabolic mirrors, though. Build a large mirror array, focus sunlight onto a big carbon sphere (maybe…

Maybe my physics knowledge is off here. Why would storing a block of material at a constant high temperature be infeasible? Can't we surround the heated material with a forced vacuum to nullify any heat loss, or am I underestimating something like the rate of diffusion through a pinprick in such material?

The fact we don't seem to be able to do this yet suggests I'm missing something, probably several things.

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

#84

Post by londons_explore »

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.

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 dishonest - the correct energy measure for gas is the higher-heating-value, which is 10.7% more. The difference comes from how you account for the heat in the steam produced by burning gas. In my view, the energy from that steam should be accounted for when considering efficiency - in GE's view, it shouldn't.

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

#85

Post by londons_explore »

benj111 wrote: post #72
pbmonster wrote: post #48

Earlier quoted context omitted.

They don't ever run those close to this hot, right? There's barely any turbine blade materials able to withstand half those temperatures. At those temperatures, even the best alloys lose a large percentage of their strength. And also, steam this hot is incredibly corrosive.

Afterburner? That wouldn't impact blade temp.

terrible for efficiency.

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

#86

Post by lazide »

pjc50 wrote: post #76
leereeves wrote: post #63

Earlier quoted context omitted.

Wouldn't this process also contribute to climate change by trapping energy on Earth that would have been reflected back into space? Edit: Apparently, yes, current PV solar may also do this: > We found temperatures over a PV plant were regularly 3–4 °C warmer than wildlands at night https://www.nature.com/articles/srep35070 But I suspect/conjecture that turning sunlight directly into heat, then turning some of that he…

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.

Most desert buildings already do white roofs for this reason (new ones anyway), same with commercial buildings. It usually pays for itself in short order. Most available roof coatings now are also white + extra reflective additives.

[https://www.homedepot.com/p/Henry-887-Tropi-Cool-100-Silicon...] [https://maps.app.goo.gl/TwrV57Jt2fGo2obw9?g_st=ic]

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

#87

Post by lazide »

hiAndrewQuinn wrote: post #83
pbmonster wrote: post #45

I don't get why they go for storage with this. Storing a block of carbon or tungsten at 2000°C for hours or days does not sound like something that will ever be economical. A battery leaking energy this quickly (and it will leak₎ will need to be incredibly cheap to ever make sense. I wonder if you could use this with parabolic mirrors, though. Build a large mirror array, focus sunlight onto a big carbon sphere (maybe…

Maybe my physics knowledge is off here. Why would storing a block of material at a constant high temperature be infeasible? Can't we surround the heated material with a forced vacuum to nullify any heat loss, or am I underestimating something like the rate of diffusion through a pinprick in such material? The fact we don't seem to be able to do this yet suggests I'm missing something, probably several things.

Conversion to/from heat and electricity is usually quite lossy. There are numerous approaches to attempt to do this effectively, but often things like pumped storage is cheaper per watt hour and similarly (or more) efficient.

Batteries are faster to charge/discharge and more efficient per wh.

Both usually have less loss over time - it’s very difficult/expensive to avoid significant heat loss over time due to radiative heat loss, if nothing else.

Most batteries or pumped storage have much lower losses over time.

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

#88

Post by nine_k »

pjc50 wrote: post #76
leereeves wrote: post #63

Earlier quoted context omitted.

Wouldn't this process also contribute to climate change by trapping energy on Earth that would have been reflected back into space? Edit: Apparently, yes, current PV solar may also do this: > We found temperatures over a PV plant were regularly 3–4 °C warmer than wildlands at night https://www.nature.com/articles/srep35070 But I suspect/conjecture that turning sunlight directly into heat, then turning some of that he…

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.

Anecdotally, my apartment building's roof was painted silver-white during the latest renovation of it. I live on the top floor, and I did notice the change: it's less hot in the summer.

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

#89

Post by nine_k »

kolinko wrote: post #53
pbmonster wrote: post #45

I don't get why they go for storage with this. Storing a block of carbon or tungsten at 2000°C for hours or days does not sound like something that will ever be economical. A battery leaking energy this quickly (and it will leak₎ will need to be incredibly cheap to ever make sense. I wonder if you could use this with parabolic mirrors, though. Build a large mirror array, focus sunlight onto a big carbon sphere (maybe…

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…

Molten salt heat storage [1] is used relatively widely, with the advantage that the salt is liquid and can directly work as a heat transport fluid (usually to heat water or gas that actually turns an engine).

The same geometry that allows heat to be effectively trapped also prevents its fast extraction as radiation. A fluid that can relatively easily change its volume to surface ratio could have an advantage here, too.

[1]: https://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_...

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

#90

Post by nine_k »

benj111 wrote: post #74

So what are the trade offs between these and peltier devices? They're much more efficient, I assume much more expensive?

Expense is usually a function of scale. Everything new and custom is expensive. Electronic chips with incredibly complex structure of some rare materials inside them are priced in cents.
Post reply on HN