Energy sources that do not rely on the consumption of an exhaustible fuel. Tidal, geothermal, and the direct and indirect solar energies (direct: photovoltaics, CSP, solar thermal; indirect: wind, wave, biomass) are renewable energy.

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Why does a window layer is on top of the absorber layer in solar cells and not below it?

In solar cells there is a p-n junction. P-type semiconductor (for example CdTe) is often absorber layer because of its carrier lifetime and mobilities. In case of CdS/CdTe, CdS is n-type window layer ...
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“Single-shot” Heat engine efficiency limits

The sun is 5778K and Earth is ~290K. Using the sun as the hot reservoir and earth as a cold reservoir we get 95% Carnot efficiency. However, the solar power efficiency limit is only 86%, see: ...
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Theoretically speaking what are the limits for super-capacitors in terms of their storage capability?

According to wikipedia, commercially available super-capacitors in 2010 can store 30Wh/kg, with 85Wh/kg achieved in a lab in 2011. Have any theoretical calculations been done to show what can be ...