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

131–140 of 174 posts

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

#131

Post by nine_k »

vlovich123 wrote: post #121
nine_k wrote: post #92

Earlier quoted context omitted.

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.

Cooling down would not slow down the sphere, if the radiation is uniform.

Gravitational drag, maybe, but only if there is something to drag nearby, and we postulate a vacuum.

A sphere is symmetric and thus does not emit gravitational waves.

I wonder if an effect akin to black hole evaporation could play a role: if one of the two virtual particles gets accelerated towards the sphere, it may bring some momentum to it. But, assuming that the space is isotropic, statistically such momentums should cancel out.

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

#132

Post by adrian_b »

throwbadubadu wrote: post #8
_hypx_ wrote: post #3

> This cell achieved an efficiency of 41.1% operating at a power density of 2.39 W cm–2 and an emitter temperature of 2,400 C. At those temperatures, this is not very impressive.

> not very impressive vs "a higher performance than conventional solar cells, and produce 100 times more power than similarly sized devices” You have some numbers against that to understand the buzz? Because it sounds pretty impressive? Is it comparing the wrong technology, or are the numbers off for prior performance (in this use case) or how?

The performance is very impressive in comparison with devices of the same type that have been produced in the past.

The performance is not impressive in comparison with the existing alternative for converting heat into electricity, i.e. with electric generators powered by closed-cycle gas turbines or by steam turbines, which can reach a higher efficiency already at much lower temperatures and without using so expensive materials.

Therefore it is not clear whether this direction of research is worth pursuing.

Moreover, triple-junction (very expensive) solar cells with an efficiency of around 45% for the direct conversion of solar light, without passing through heat, have already been demonstrated some time ago. Due to their high cost, they must also be used with solar concentrators, but the concentrators can be much cheaper than those needed to heat something over 2000 Celsius degrees (which requires very precise focusing).

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

#133

Post by bluGill »

ChrisRR wrote: post #77
kgabis wrote: post #50

Earlier quoted context omitted.

We also have this thing called night, as well as weather and seasons.

I don't know why people always comment this on posts about renewables as if it's some kind of gotcha. When there's no sun, then other countries probably have sun. When there's no sun, there's hydro. When there's no hydro there's wind. When there's no wind, there's tidal. When there's no tidal there's geothermal. And when there's none of those, there's stored energy in batteries. And if for some reason all of those co…

While other countries have sun when it is night here, realistically we cannot build the needed wires to get that energy here. We need 20,000km of wire to get power around the earth at the equator.

Wind suffers the same problem as the sun in that sometimes there is no wind anyplace close, and it is even less predictable. While tide power is predictable and consistent, I don't live anywhere close to the ocean so we still need 2000km of wire to get it to me. Geothermo is useful when lava is close to the surface, but I don't live in such an area.

Note that my power is 80% wind, but it was done via several decades of building wind turbines, and I live in Des Moines which nobody would call a big city, if you live in a big city you have even more work to build it (you are both way behind us in building wind, and have a lot more to build)

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

#134

Post by bluGill »

pjc50 wrote: post #78
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…

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 without affecting your comfort.

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

#135

Post by bluGill »

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…

You don't actually need your heat pump 24x7 even on those cold days, if you can run for 15 minutes one, 15 off that would make a big difference to the grid (your neighbor running the same schedule but opposite times) without making your house too cold. Managing the above is tricky though.

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

#136

Post by adrianN »

badtension wrote: post #64
awestroke wrote: post #51

Earlier quoted context omitted.

And we also have this looming thing called climate emergency, which should conceivably motivate us to forge ahead with renewables and adjust our energy usage patterns to match production peaks, lest we doom humanity to extinction

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.

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

#137

Post by megaman821 »

adrian_b wrote: post #124
labcomputer wrote: post #79

Earlier quoted context omitted.

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 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.

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

#138

Post by adrian_b »

londons_explore wrote: post #84
labcomputer wrote: post #79

Earlier quoted context omitted.

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 dish…

I do not think that using the lower heating value is really dishonest, especially in the context of this discussion.

The lower heating value corresponds to the heat actually produced during burning.

The higher value is based on the fact that the exhaust gases contain water as a gas, and if that water were condensed into liquid water, an additional quantity of heat would be produced, the latent heat. Due to the low temperature of condensation, that latent heat cannot be easily recovered, except if it is used for hot water production or for home heating or for home cooling (e.g. with absorption chillers).

If instead of using combustion gases, the same heat engine would use heat from an external source, like also the thermophotovoltaic devices discussed here, the heat engine would function in the same way and with the same efficiency, when receiving the amount of heat corresponding to the lower heating value (assuming no heat losses during heat transfer).

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

#139

Post by crznp »

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.

Do you want it preheated? It might improve ignition, but isn't it a heat engine that gains efficiency from a large temperature gradient?

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

#140

Post by mcpackieh »

rich_sasha wrote: post #97
discordance wrote: post #93

Earlier quoted context omitted.

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.

That's different, isn't it? An RTG only produces heat via radioactive decay. A nuclear reactor is a controlled chain reaction.

Yes, those aren't nuclear reactors. However nuclear reactors with thermoelectric converters for power generation have been built before. There were the Soviet TOPAZ reactors and the US SNAP-10A reactor.
Post reply on HN