Nanotechnology Solar Cells

How solar energy presently fares

The amount of atmospheric CO2 present has not looked like it is beginning to taper off and instead continues its upward spike past the 400ppm mark since 2013 (NASA). The startling change in CO2 due to fossil fuel consumption has seen a marked increase since relatively stable levels of the past couple hundred thousand years. However, scientists believe that if business-per-usual conditions are maintained atmospheric CO2 could eventually hit 1500ppm, at which point the global average temperature could be anywhere between 18-23 degrees celsius – a big difference from the current 12-14 degrees celsius we experience. This occurrence would return the world to similar conditions where human livability becomes strenuous at best. Therefore, there is a real need to increase our use of non-fossil fuel consuming energy production sources such as solar, wind, hydro, geothermal, and nuclear energy. For this post we will talk of solar energy and the reformation of the solar cell.

In order to stabilize atmospheric CO2 by 2050 we will require 15TW of usable energy from renewable energy sources. Presently, solar energy has the greatest potential of all long-term supply-side sources due to its size and relative acceptability. While other sources such as those mentioned above are renewable, their abilities are limited to regional or local scales rather than global; nuclear energy is the only other source that can meet the world’s massive energy demands. Considering that the power with which the Sun’s rays strike the earth’s surface is 175W/m²  and approximately 10-20% of this incident solar energy could be converted to usable electricity, we would require roughly 2% of the available land in the US alone to provide electricity to the country. That is an area roughly slightly smaller than Washington state and 30 times the US’ available roof space. However, while some may be discouraged by the number of solar panels and area required to curb CO2 emissions, any kind of instalment whether that be roof panels or solar farms will be beneficial in producing electricity.

(source: Kyoto University/Noda Lab)

Nanotechnological efficiency

Researchers from Kyoto University in partnership with those at Osaka Gas may have found a solution to increasing the efficiency of solar panels with a nano-sized semiconductor device. Their semiconductor which consists of rods that are only 500nm in height allows for increased efficiency by narrowing the wavelength bandwidth of light to concentrate the energy.

Currently, the popularly-used Photo Voltaic (PV) solar cells are only able to convert 20% of visible light to electricity and are therefore fairly inefficient in that regard. As higher temperatures emit light at shorter wavelengths solar panels have been built that contain cells to capture light from higher heat temperatures, making them designed to target short wavelengths. The intrinsic silicon semiconductor they were able to design features “etched silicon plates to have a large number of identical and equidistantly-spaced rods, the height, radii, and spacing of which was optimized for the target bandwidth”(Kyoto University). Using this nanoscale semiconductor the conversion rate of solar cells is raised to a minimum 40%.

Implications for solar energy

The value of this technology to solar cells, solar panels, and the overall use of them globally could be overemphasized. Lab head Susumu Noda highlighted the fact that there were two perceivable benefits:

  1. Energy efficiency: Heat can be converted to electricity much more efficiently than before, and;
  2. Design: Smaller and more robust transducers means that the technology can be applied to a range of applications.

If we can apply this technology to present roofs or solar farms it would drastically increase the harnessable energy by several times, thereby decreasing the amount of area required to house these devices and also giving an added incentive to people to construct them. With further research into the manufacturing it is even conceivable that an economic model will allow for widescale use. 

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