Infrared Photovoltaics: Powering Ham Radios & Cooling Earth?

[J3J33J333]

TL;DR Summary

Can you use infrared solar panels to power a ham radio and turn infrared waves into radio waves to get the energy past the green house gases?

Can you use infrared solar panels to power a ham radio and turn infrared into radio waves to get the energy past the green house gases? Because infrared gets reflected by greenhouse gases and warms the Earth while radio waves don't. Would this help cool the Earth?

 

[berkeman]

Creative idea.

I think the short answer is no. First, you can use regular solar panels to generate the electricity. You only get the IR radiation because the insolation heats stuff up. So use the incoming light directly to generate the power. But solar panels are only (ballpark) 20% efficient, so you still get 80% heat. If the solar panels were 100% efficient, you could probably convert that to an EM band that makes it out of the atmosphere and "radiate away" that insolation.

EDIT/ADD -- A better approach would just be to cover a large portion of the Earth's surface with high-efficiency mirrors. That radiates the insolation back into space as visible light.

 

[DaveE]

The thing about solar panels is that they are basically some form of semiconductor. Semiconductors have a "band gap", which means that incident photons must have enough energy to "be noticed", i.e. to cause a charged particle to jump a voltage barrier (BTW, this is what Einstein won his Nobel Prize for, not the stuff he's famous for). As a really rough rule of thumb, that light needs a wavelength shorter than about 1μm, or "near IR". I know, my explanation is vague and confusing. You would study this in a university EE program. It's a bit complicated. Anyway, IR photons just don't carry enough energy to do this in most materials. An alternative is to use the IR radiation to heat an object and then convert that heat to electricity with another technology, like peltier devices. This wouldn't be a very efficient process.

So, short answer: Is there such a thing as an infrared solar panel? I kind of doubt it for practical applications.

 

[J3J33J333]

The thing about solar panels is that they are basically some form of semiconductor. Semiconductors have a "band gap", which means that incident photons must have enough energy to "be noticed", i.e. to cause a charged particle to jump a voltage barrier (BTW, this is what Einstein won his Nobel Prize for, not the stuff he's famous for). As a really rough rule of thumb, that light needs a wavelength shorter than about 1μm, or "near IR". I know, my explanation is vague and confusing. You would study this in a university EE program. It's a bit complicated. Anyway, IR photons just don't carry enough energy to do this in most materials. An alternative is to use the IR radiation to heat an object and then convert that heat to electricity with another technology, like peltier devices. This wouldn't be a very efficient process.

So, short answer: Is there such a thing as an infrared solar panel? I kind of doubt it for practical applications.

I think there are some thermophotovoltaics in the works that reach 40% efficiency. Also seen some people use materials to combine photons into a new wavelength so maybe that'd be a path to convert the IR to near IR, too.

 

[DaveE]

I think there are some thermophotovoltaics in the works that reach 40% efficiency. Also seen some people use materials to combine photons into a new wavelength so maybe that'd be a path to convert the IR to near IR, too.

I suspect these are heroic numbers, the kind of thing a grad student does but that you can't buy. For example, this from Wikipedia:

"The upper limit for efficiency in TPVs (and all systems that convert heat energy to work) is the Carnot efficiency, that of an ideal heat engine. This efficiency is given by:

where Tcell is the temperature of the PV converter. Practical systems can achieve Tcell= ~300 K and Temit= ~1800 K, giving a maximum possible efficiency of ~83%. This assumes the PV converts the radiation into electrical energy without losses, such as thermalization or Joule heating, though in reality the photovoltaic inefficiency is quite significant. In real devices, as of 2021, the maximum demonstrated efficiency in the laboratory was 35% with an emitter temperature of 1,773 K.[10] This is the efficiency in terms of heat input being converted to electrical power. In complete TPV systems, a necessarily lower total system efficiency may be cited including the source of heat, so for example, fuel-based TPV systems may report efficiencies in terms of fuel-energy to electrical energy, in which case 5% is considered a "world record" level of efficiency.[11] Real-world efficiencies are reduced by such effects as heat transfer losses, electrical conversion efficiency (TPV voltage outputs are often quite low), and losses due to active cooling of the PV cell."

Can you really heat an object to 1800K with your IR radiation?

 

[russ_watters]

The most efficient way to do this would be with mirrors.

 

[bob012345]

Summary: Can you use infrared solar panels to power a ham radio and turn infrared waves into radio waves to get the energy past the green house gases?

Can you use infrared solar panels to power a ham radio and turn infrared into radio waves to get the energy past the green house gases? Because infrared gets reflected by greenhouse gases and warms the Earth while radio waves don't. Would this help cool the Earth?

I think you would do far better using white and cool roofing products as they reflect solar radiation back to space.

https://e360.yale.edu/features/urban-heat-can-white-roofs-help-cool-the-worlds-warming-cities

https://www.energy.gov/energysaver/cool-roofs

 

[sophiecentaur]

So, short answer: Is there such a thing as an infrared solar panel? I kind of doubt it for practical applications.

That answer refers only to PV Solar panels.
Don't forget thermal solar panels, for heating water; very practical and effective and rather under-sold these days.

 

[DaveE]

That answer refers only to PV Solar panels.
Don't forget thermal solar panels, for heating water; very practical and effective and rather under-sold these days.

Yes, or for heating Sodium:

Although in this case you'd just want to send the light straight up, away from earth.

 

[DaveE]

Just because IR radiation is what's reflected by CO₂ et. al., doesn't mean you have to only reflect the IR to cool the planet. A Rube Goldberg type system of thermal solar → electricity → HF radio transmitter may not be the most efficient way.

 

[sophiecentaur]

Can you use infrared solar panels to power a ham radio and turn infrared into radio waves to get the energy past the green house gases?

This proposal involves two forms of energy conversion, neither of which would be very efficient. Thus for every kWh you manage to fire out into space, you will be generating (lets say) a similar amount of IR from hot devices. Then there's the energy needed to make the equipment - more carbon.

My pet thought project is to paint every bit of spare rock, roof, roadside, car etc. a nice shiny white colour, to make up for the snow that has been doing a great job since the last ice age started. This could be encouraged by government subsidised cans of white paint and mountaineering holidays.

 

[willem2]

Summary: Can you use infrared solar panels to power a ham radio and turn infrared waves into radio waves to get the energy past the green house gases?

Can you use infrared solar panels to power a ham radio and turn infrared into radio waves to get the energy past the green house gases? Because infrared gets reflected by greenhouse gases and warms the Earth while radio waves don't. Would this help cool the Earth?

Note that the incoming IR radiation from the sun has higher frequencies than IR radiation produced by the surface of the earth, and this radiation will pass through the atmosphere. Reflecting it will be the best option.
White paint will work for infrared that's close in frequency to visible light. You could try aluminium foil to reflect more.

Solar cells are black and will reflect much less sunligth than the Earth surface without solar cells. To get any cooling from them, It's not enough to just radiate back the energy back to space, but you must use the energy to replace fossil fuels to reduce CO2 output. (or charge the batteries of your drone that spreads sulphate aerosols)

 

[hmmm27]

All-day radiative cooling : The atmosphere has a gap at 8–13 µm, so...

 

[bob012345]

All-day radiative cooling : The atmosphere has a gap at 8–13 µm, so...

What stops the cooling at 10C?

 

[hmmm27]

What stops the cooling at 10C?

The SO complaining that it's too cold.

 

[J3J33J333]

Note that the incoming IR radiation from the sun has higher frequencies than IR radiation produced by the surface of the earth, and this radiation will pass through the atmosphere. Reflecting it will be the best option.
White paint will work for infrared that's close in frequency to visible light. You could try aluminium foil to reflect more.

Solar cells are black and will reflect much less sunligth than the Earth surface without solar cells. To get any cooling from them, It's not enough to just radiate back the energy back to space, but you must use the energy to replace fossil fuels to reduce CO2 output. (or charge the batteries of your drone that spreads sulphate aerosols)

Is there any chance that it could be more efficient because it would be absorbing infrared at night as well?

 

[willem2]

Is there any chance that it could be more efficient because it would be absorbing infrared at night as well?

You can only get any energy from absorbing infrared if there is incoming radiation from a source that is hotter than the absorber.
I believe a recent system that produced some hype radiates away infrared into a cool night sky. If you look at science daily:
https://www.sciencedaily.com/releases/2022/05/220517112246.htm
The sun's enormous energy may soon be harnessed in the dark of night following a significant advance in thermal capture technology.
At least they do provide a linkt to a journal article:
https://pubs.acs.org/doi/full/10.1021/acsphotonics.2c00223
Thermoradiative Power Conversion from HgCdTe Photodiodes and Their Current–Voltage Characteristics
The abstract is rather disappointing:
At a temperature differential of only 12.5 °C, we measure a peak thermoradiative electrical power density of 2.26 mW/m2 for a photodiode emitting near 4.7 μm, with an estimated radiative efficiency of 1.8%.
So they manage to radiate away 0.125 W/m2 with their new diode and get 2.26mW/m2 electrical energy out.

At this temperature difference, a square meter of the Earth's surface would have a net outgoing radiation of about 50 W/m^2, so neither the electric energy produced, nor the radiated infrared energy is significant.