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Gibbons74 t1_ixz4aox wrote

I never realized solar cells were so inefficient. Just imagine the day we reach 95% efficiency.

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seidler2547 t1_ixz4yde wrote

Fact about solar cells you should know:

> The maximum theoretical efficiency calculated is 86.8% for a stack of an infinite number of cells, using the incoming concentrated sunlight radiation. When the incoming radiation comes only from an area of the sky the size of the sun, the efficiency limit drops to 68.7%.

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TimeSpentWasting OP t1_ixzcmaf wrote

Never knew why, now I have the answer without googling. I'm lazy, so thank you

I have high hopes that humanity will reach that maximum value as tech gets smaller. I wonder how much efficiency is reduced under heavy cloud cover?

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skittlesmcgee33 t1_ixzuftk wrote

That maximum is functionally impossible. Functional limit is in the 40-49% range so we’re already most of the way there.

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PM_Your_Wololo t1_iy0pk6k wrote

Can you ELI5 why the difference is so large?

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ThatOtherGuy_CA t1_iy0ubqo wrote

Material costs, eventually the amount of materials you need to add per extra % is more than just building a second panel at the same efficiency. So around 50% in order to get an extra 1% in efficiency, you need a panel with double the cells. So you might as well just build 2 50% efficiency panels rather than 1 51% one.

That’s basically why most panels are stuck around 23% right now, it’s more cost effective to just build 2 panels than to build a panel 1% more efficient.

Basically as technology advances it gets easier to improve the efficiency with less waste, but around 50% is when you can’t really make anything smaller to get those efficiency gains in a similar sized panel.

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LouSanous t1_iy4302w wrote

>So you might as well just build 2 50% efficiency panels rather than 1 51% one

The most recent info I was able to find shows it to be like 300:1. Standard utility scale solar panels in the 20% efficiency range are 1/300 the cost of triple junction GaAs.

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ThatOtherGuy_CA t1_iy47zui wrote

Yup, which is why you pretty much only see them in space applications. Because the weight saved can save enough fuel costs to offset the insane price increases.

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LouSanous t1_iy4fmek wrote

I'm not sure how much it costs spaceX with their reusable rockets (and given that Musk is in charge, I would bet that he never did achieve the multiple orders of magnitude cheaper costs he promised), but prior to the space shuttle cost per kg into space was $18,500. After the space shuttle, $54,500/kg.

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zeuszoso t1_iy10kez wrote

The practical limit given by Shockley and Quiesser for a single-junction solar cell under 1 sun illumination is 33% power conversion efficiency.

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Valmond t1_iy10l2x wrote

So when we close in on the theoretical max, should prices drop more?

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anglesideside1 t1_iy36zrs wrote

Efficiency gains are great, but the bigger gains are to be had in manufacturing, installation, and overhead costs. If we’re just talking residential, companies spend a couple thousand in customer acquisition costs per installation. The utility scale stuff is MUCH cheaper per kW, but can still wring out some more savings in siting, permitting, interconnection, and overheads. Panel efficiency gains tend to help more when space is more of a concern. If you can spread out, then much cheaper, less efficient panels are often the better choice.

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zeed88 t1_iy35ssy wrote

How about using thermoelectric coupler underneath it to absorb the heat and turn it to energy, will that increase the percentage?

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GoldenWizard t1_ixzj1da wrote

Literally impossible lmao

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blastradii t1_ixzx406 wrote

What’s the science behind the inability to reach this type of efficiency?

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Korvanacor t1_iy048w4 wrote

Solar works by using the energy of photons to bump electrons from the valence bands up into the conductive band. These bands are separated by what is called the band gap. If the gap is 2 electron volts (eV) wide and the photon has 3 electron volts, the extra energy is “lost”. Photons with less than 2 eV don’t contribute anything. It’s possible to stack multiple layers with different band gaps to more efficiently capture a wider range of photons but there will still be losses due to interfacial physics that I don’t understand. Each layer adds to the cost of the cell as well

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a11en t1_iy2ijuk wrote

This and many others in this thread are great discussions of solar efficiency and limitations. Thank you for adding to the discussion! One other nasty bit is how the multijunctions are connected. In order to get good efficiency you basically need separate cells one atop the other without direct electrical connection- otherwise you are current limited to the smallest current cell - so they attempt to match the current output- but that’s not always possible (think AM1.5 intensity -v- frequency graph and trying to trap the area under the curve to be equal to the other cell’s conversion). It’s tricky business. It’s much easier just to treat them separately. I need to read the article more. I hope and pray it wasn’t MOCVD growth… that type of growth is so nasty and dangerous and dirty… work in the field. The environmental cost alone of MOCVD would tip the scales against this. Lol. So good for payloads perhaps- but please let’s not attempt to make all our roofs out of this. The environmental disaster alone wouldn’t be worth it. Lol

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LouSanous t1_iy45muh wrote

>solar efficiency and limitations

It's really important to note that this "limitation" isn't much of a limitation.

There is functionally infinite sun. The amount of energy reaching the earth at sea level from the sun every second is well over 100 times the total yearly energy consumption of the entire world.

Modern nuclear uses only 5% of the energy in the fuel. Then, the conversion to electricity is somewhere around 35%. So from the energy contained in the fuel, nuclear is about 1.75% efficient.

Coal plants are around 35% as well.

Combined cycle gas is 55-60%.

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a11en t1_iy4els3 wrote

Combustion is still the most energy efficient.

And Nuclear would be more efficient if they allowed refacing/recycling the rods.

Believe me- the MOCVD toll is huge and does play a factor. We don’t pay attention to cradle to grave, and it’s absurd not to. (Used to be the thing to do- for example for plastics- why ignore it for solar and wind?)

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LouSanous t1_iy4f2dz wrote

Everything not directly a part of profits in capitalism in an externality.

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Sprinkler-of-salt t1_iy05upz wrote

What if we don’t aim for the conductive band of electrons? What if there’s another way to harness the incoming energy?

Or what if there’s a way to “prime” the electrons in the cells such that the valence electrons are already at the conductive band, or somehow less than 2eV away?

If this requires a new atom, why not make one?

What if we forget about atoms altogether, and capture energy at the quarks and gluons?

What if we forget about photons, and harness dark energy instead?

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Haquestions4 t1_iy0cia2 wrote

What if we just forget all this science and get energy through our outlets?

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Sprinkler-of-salt t1_iy0ftr3 wrote

Nah, come on now, that’s unrealistic. The outlets have to get it from somewhere.

Maybe they should be fiber optic instead of electric… then we could send the light directly from the sun into devices!

Sun-powered blender would probably make even healthier smoothies!

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Aspie_Astrologer t1_iy2bhjc wrote

u/Korvanacor explained this in great detail for the reason the limit is much lower in solar cells. But it's interesting that the original comment mentioned 95% because that's actually the maximum possible energy that anything at Earth temperature (300 K) could extract from the sun (6000 K) thermodynamically based on the Carnot efficiency (η=1-Tc/Th=1-300/6000=95%).

The reason that the solar cell limit is lower is because solar cells work based on tradeoffs in terms of current and voltage: if you want high voltage then you need a large band gap so that electrons are extra-excited, but then all the frequencies of light below that bandgap will not get absorbed, meaning less electrons/current. Power output is the product of voltage and current.

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bacondesign t1_iy2kbkt wrote

Just for comparison an internal combustion engine's efficiency is usually between 10-30%

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