Hacker News Reader

Hacker News

Comment by wumms | Hacker News Reader

Parent Full thread

wumms

Yes, the max. energy from sunlight on earth hitting an envelope should be around 20-30 Watts (at 100% efficiency).

Also, the reported 29.1% efficiency have been reached at a temperature of 1,207 °C.

View on HN

Also, the reported 29.1% efficiency have been reached at a temperature of 1,207 °C.

Another 12% and they can compete with a standard steam turbogenerator.

Wouldn't you slap this on top of a steam boiler to get the best of both worlds, though?

Steam turbines have row after row of blades, each successive blade wheel larger and lower pressure than the last. Exit temperatures from modern turbogenerators are around 120° C, where the steam is about to turn into water, and pressure is usually below atmospheric. Almost all the energy which thermodynamics permits to be extracted has been extracted.

I probably should have phrased it better - I was picturing [Furnace] | [Thermophotovoltaics] | [Boiler], so the PV part gets first crack at the light/IR from the furnace and then the boiler cools the PV gear as it boils the water. This is also how it's suggested to be used in a paper linked elsewhere in the discussion above: https://www.sciencedirect.com/science/article/pii/S030626191...

If you make it harder to cool the turbine by putting those neat the radiator, efficiency will go down; if you make it harder to keep the heater hot, by putting those near the fire, efficiency will go down.

As animats already said, turbine efficiency on power plants is very near the theoretical optimum. The only way left to improve it is by increasing the temperature.

The furnace burns at over 900C but the superheated steam (which is your ‘hot’ temperature for your heat engine) is only at ~400C, you might lose some power output but you won’t be losing efficiency.

Perhaps for small scale applications this could be cheaper and more reliable? (if they can also get to 50% and if the materials used are cheap enough)

This isn't about sunlight, but about putting this with a furnace or something else generating heat.

Yes, the original article is about thermophotovoltaics.

Regarding the article posted here (and since a drone with a furnace is not feasible) I went with solar.

The corresponding author to be fair did say unmanned aerial vehicles.

True, though it is combined (in the article) with a maximum power consumption: "those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle"

The original paper says "unmanned vehicles" (no aerial) and has a reference [0] to "unmanned undersea vehicles".

[0] https://www.pnas.org/content/early/2019/07/15/1903001116#ref...

The article says "a wide range of applications, from those that require as little as 100 watts, [such as] a lightweight unmanned aerial vehicle, to 100 megawatts"

I read the 100 watts as referring to lightweight unmanned aerial vehicle.

100 megawatts is followed by "[providing] electricity for 36,000 homes."

The original paper does not mention lightweight aerial vehicles as an application, but a drone is mentioned in the title (and shown in the top image) of the article.

Applications mentioned in the paper are: hybrid cars, unmanned vehicles, deep-space probes, energy storage, enabling efficient cogeneration systems for heat and electricity.

(A less-misleading title might even be: "New thermophotovoltaic engine for deep-space probes")

How about one of the authors talking about a credit-card sized device supplying 100 watts to quad-coptors using liquid fuel and staying airborn for 16+ hours. (https://youtu.be/lDxJsa8miNQ?t=3202)

Is this something you could use a laser for too? To bring heat to the flying drone? Or would that be super inefficient?

Beamed energy always has attenuation problems that make it inefficient.

Reply on news.ycombinator.com