A new MIT study offers a way out of one of solar power's most vexing problems: the matter of efficiency, and the bare fact that much of the available sunlight in solar power schemes is wasted. The researchers appear to have found the key to perfect solar energy conversion efficiency—or at least something approaching it. It's a new material that can accept light from an very large number of angles and can withstand the very high temperatures needed for a maximally efficient scheme.

Conventional solar cells, the silicon-based sheets used in most consumer-level applications, are far from perfect. Light from the sun arrives here on Earth's surface in a wide variety of forms. These forms—wavelengths, properly—include the visible light that makes up our everyday reality, but also significant chunks of invisible (to us) ultraviolet and infrared light. The current standard for solar cells targets mostly just a set range of visible light.

That makes sense because visible light is the most intense form of light that reaches the Earth's surface. Many other forms, such as microwaves and x-rays, are mostly blocked by the planet's atmosphere, but the full spectrum reaching Earth still extends outward from what's known as the solar cell "band gap." This is the range of frequencies within which a material is able to convert solar energy into electrical energy.

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....here that that new MIT scheme comes in. It's a promising alternative that's known as solar-thermophotovoltaics. Instead of converting solar energy directly to current, these materials convert it all to heat.

Thermophotovoltaics take advantage of the everyday phenomenon of thermal emission. Basically, any material heated above absolute zero will emit some radiation (photons) because anything above absolute zero will feature some motion of charged particles taking place as increased amounts of energy (as heat) increase the kinetic energy of the material's constituent particles. Get electrons really loaded on caffeine (heat) and they start shaking and sweating off photons as radiation.

The neat thing about a thermophotovoltaic element is that it can take in a bunch of different solar wavelengths and convert them to just one, which can then be converted by a standard photovoltaic element to current. This is illustrated above.

The catch with thermophotovoltaics is that in order to be suitably efficient, they need the addition of sunlight concentrators, e.g. those big arrays of mirrors that focus sunlight at one location. That's fine, but concentration means loads of heat and also the need to aim that light at a certain place. Until a material comes out that can withstand loads of heat energy, thermophotovoltaics can't reasonably beat standard photovoltaics.

The MIT team, led by postdoc researcher Jeffrey Chou, suggests a new "two-dimensional metallic dielectric photonic crystal" as the solution. Their crystal is capable of both absorbing light from a wide variety of angles—meaning, a sunlight concentration system doesn't have to have a sun-tracker component—and can withstand temperatures of up to 1,800 degrees Fahrenheit for up to 24 hours at a time.

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The end result, according to the paper, which has just been published in the journal Advanced Materials, is "large-scale, low cost, and efficient solar-thermal energy conversion"—perhaps the first of its kind. Chou estimates that it could be commercially available within five years.



http://motherboard.vice.com/read/mit-thi...fect-solar-cell

Quote: algernonpj wrote in post #2

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ThirstyMan

Thanks for posting.

If this pans out it's really cool.

I remember reading a study done up in central Maine, where they set up a home on solar for heat, electricity, and a small green house. There was back up with conventional energy 'just in case'.

Not only did they not have to use the back up energy but they were able to produce veggies in the green house through a Maine winter.

the only draw back, was the size of the batteries and the cost of the equipment need to capture enough usable solar energy. The end result was that solar was MUCH more expensive than conventional energy.

Well batteries have since gotten much smaller and this sounds like it may turn out to be the solution to the problem of being able to use the energy in what MIT calls the bank gap.

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