Friday, November 22, 2013

Quantum wells

Half or more of the available energy to a solar receptor happens to be infrared radiation.  Capturing that energy and converting it to electricity as well as capturing visible light would mean converting eighty percent of the available energy at whatever the efficiency happens to be.  As the solar fraction can deliver fifteen net percent, it seems possible to harvest a similar amount from the infrared fraction. 

What should be obvious though is that it is impossible to approach even forty percent efficiency without getting a big part of the infrared spectra.  Thus clever stratagems to do just that are welcome.

It should also be obvious that serious absorption of incoming infrared will have a serious cooling effect, at least as good a tree cover.  Some interesting engineering is ahead of us here.

Quantum wells

Researchers analyze a heat engine based on a hot cavity connected via quantum wells to electronic reservoirs. They find that the device delivers a large power of about 0.18 W cm^−2 (1800 watts per square meter) for a temperature difference of 1 K, nearly doubling the power that can be extracted from a similar heat engine based on quantum dots. At the same time, the heat engine also has good efficiency albeit reduced from the quantum dot case. Due to the large level spacings that can be achieved in quantum wells, our proposal opens a route toward room-temperature applications of nanoscale heat engines.

It has 12 % of the Carnot efficiency. The large level spacings of narrow quantum wells pave the way for room-temperature applications. Furthermore, we find our device to be robust with respect to unavoidable well-width fluctuations.

Sunlight in space at the top of Earth's atmosphere at a power of 1366 watts/m2 is composed (by total energy) of about 50% infrared light, 40% visible light, and 10% ultraviolet light. At ground level this decreases to about 1120–1000 watts/m2, and by energy fractions to 44% visible light, 3% ultraviolet (with the Sun at the zenith, but less at other angles), and the remainder infrared. Thus, sunlight's composition at ground level, per square meter, with the sun at the zenith, is about 527 watts of infrared radiation, 445 watts of visible light, and 32 watts of ultraviolet radiation

No comments: