Thin Mirrors Boost Solar Efficiency to 29% and Soon 50% For Better Drones and Space Probes

Berkeley researchers raised solar energy efficiency to 29 percent and are now aiming for 50 percent efficiency in the near future.

By adding a highly reflective mirror on the back of a photovoltaic cell, they broke efficiency records at the time and have continued to do so with subsequent research.

They used a simple gold mirror and adding a dielectric layer above the gold will improve our efficiency to 36 percent.

PNAS – Ultraefficient thermophotovoltaic power conversion by band-edge spectral filtering

Thermophotovoltaic conversion utilizes thermal radiation to generate electricity in a photovoltaic cell. On a solar cell, the addition of a highly reflective rear mirror maximizes the extraction of luminescence, which in turn boosts the voltage. This has enabled the creation of record-breaking solar cells. The rear mirror also reflects low-energy photons back into the emitter, recovering the energy. This radically improves thermophotovoltaic efficiency. Therefore, the luminescence extraction rear mirror serves a dual function; boosting the voltage, and reusing the low-energy thermal photons. Owing to the dual functionality of the rear mirror, we achieve a thermophotovoltaic efficiency of 29.1% at 1,207 °C, a temperature compatible with furnaces, and a new world record at temperatures below 2,000 °C.

Thermophotovoltaic power conversion utilizes thermal radiation from a local heat source to generate electricity in a photovoltaic cell. It was shown in recent years that the addition of a highly reflective rear mirror to a solar cell maximizes the extraction of luminescence. This, in turn, boosts the voltage, enabling the creation of record-breaking solar efficiency. Now we report that the rear mirror can be used to create thermophotovoltaic systems with unprecedented high thermophotovoltaic efficiency. This mirror reflects low-energy infrared photons back into the heat source, recovering their energy. Therefore, the rear mirror serves a dual function; boosting the voltage and reusing infrared thermal photons. This allows the possibility of a practical over 50% efficient thermophotovoltaic system. Based on this reflective rear mirror concept, we report a thermophotovoltaic efficiency of 29.1 ± 0.4% at an emitter temperature of 1,207 °C.

23 thoughts on “Thin Mirrors Boost Solar Efficiency to 29% and Soon 50% For Better Drones and Space Probes”

  1. Ridiculous. You don’t need high quality virgin unicorn shavings. All you need to do is run old shed phoenix feathers through a matrix of mermaid hair and dragon slime.

    This is just typical of the way that capitalism denies us freedom from burning fossil fuels.

  2. They waffle on this subject. They are mostly on about thermal generators, but they do wave their hands at improved solar cells too.

  3. You are right. The article DOESN’T mention radioisotope generators. They dance around the subject. They discuss designs that clearly point to the heat source being radioisotopes. They talk about deep space probes which probably have to be radioisotopes. They reference a couple of papers that do use the dreaded word “nuclear” but they act as though they can’t mention the concept themselves.

    Suspicious if you ask me.

    Old thermoelectric stuff was lucky to be a couple of % efficient. So to have say a 2 kW continuous charger for your electric car (which would be enough to just about never need recharging in normal use) you’d need 100 kW thermal output, which would not be something you can carry around in a car and leave in parking garages.

    But at 50% efficiency you only need a 4 kW thermal output, which means it would dump about as much heat as a freshly driven IC engine anyway. Something that is proven to be safe and trouble free.

  4. I think the advantage of the gold over 2 (or more) PV layers is simplicity and price.

    For solar cells that could well make a very thin reflective layer the way to go.
    If you ARE using a high temp radioisotope generator (or at that efficiency you could use a simple chemical heat source) then it’ll be compact and high value enough to use multiple PV layers.

  5. He seems to be saying he’ll reflect the IR photons back into the heat source, thus warming it up (relatively) and encouraging it to radiate more ?
    So, limited to a niche application.

  6. I think it is quite specialized: the tech depends on super thin layers, one … and on IR optimized sensitivity two, and a gold + oxide dielectric backside to help lossy PV layer another chance to convert passthru photons: hot but still mostly IR sources.

    How the heck this is tied to drones is beyond my ken. Even the radioisotopes generator angle feels like a long shot.

    My dumb-as-a-goat instathought is… well, why not just use 2 PV layers? Photons don’t know. Or three?

    Just saying… GoatGuy

  7. It might be better to spend money on improving the manufacturing and installation of solar panel than it improving their conversion efficiency.

  8. That is what I was thinking too. The current thermocouples in “nuclear batteries” RTGs are very inefficient. If these are so efficient and can handle such high temps then you can basically use them to do the main electrical production even with small fission reactors. With no moving parts you would have super reliable power. It would also make super quiet submarines. Interesting.

  9. I am curious if material science could improve PV. It seems that loose electrons or materials with an abundant electron density could make great advances at far cooler temps. Who really wants a 1200 degree panel around them.

  10. Thermophotovoltaic, not PV. These cells extract electricity from heat.

    The big trend in PV is bifacial. Basically, put glass on both sides so cells can get light from reflection off of gravel or sand or whatever happens to be on the ground.

  11. Yes, the article does not mention radioisotope thermoelectric generators but with a well isolated pellet a 1200C spectrum sounds plausible.

  12. When you really need GG or somebody to unpack. Recent developments in thermophotovoltaics have looked good on paper, but only for terribly tiny amounts of actual power.

    I’m just the liberal arts major in the room, though — is this a Solar Chicago Pile? Or just… “yay marginally more efficient small-load thermosolar?”

  13. And in that decade the cost of solar panels in $/W has fallen sharply.
    From about $5-8/W to under a dollar now.

    So how is this not concrete?

  14. This is not about using visible sun light, it is about using a heat source. Different to most solar tech news.

  15. Yeah, nah I say BS. Been hearing about these solar breakthroughs for over a decade and yet to see anything concrete.

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