Parabolic Trough Employing Silicon Solar Cells as a Wavelength-Selective Mirror

Background: Photovoltaic (PV) solar cells directly convert energy from sunlight into electricity whereas concentrated solar power (CSP) systems use focused mirrors to reflect sunlight onto a heat absorbing mechanism that powers an electricity-generating turbine. According to the National renewable energy Laboratory even the best PV cells are less than 45% efficient and the world’s most modern CSP power plant is still under 30% efficient. PV systems are inefficient because sub-bandgap and super-bandgap wavelengths (below and above the absorption range) are not absorbed and the excess energy is lost as heat. CSP systems are inefficient because though they use the whole solar spectrum there are many steps in the energy conversion process that each cause an appreciable efficiency loss. Currently the only PV/CSP hybrid systems couple hot PV cells with a thermal cycle so the PV cell doubles as both an electricity generator and a heat source. The drawback to these systems is that the efficiency of a PV cell decreases rapidly with increasing temperature. Technology Description: Researchers at ASU have developed a parabolic trough that splits the solar spectrum absorbing the wavelengths most efficiently converted to electricity in the PV cells while reflecting all others to a central point to generate heat. A customizable optical coating is applied to the trough that reflects specific wavelengths depending on the type of PV cell used and what is required for the additional absorbing element. The coating allows the PV cells to operate below one-sun illumination levels and thus stay at temperatures well below 100°C. Potentially any type of flexible PV cell can be used – silicon cells multijunction cells CdTe etc. – with any additional absorbing element such as piping filled with thermally enhanced nanoparticle fluid. Combining PV and CSP technologies in this way facilitates power plant efficiency with an estimated 50% relative gain in overall solar-to-energy conversion. Applications: 1) Concentrated solar power Plants 2) photovoltaic power Plant 3) solar Modules


1) Effective – Higher energy conversion efficiency than stand-alone PV or CSP systems and leading hybrid PV/CSP systems. 2) Practical– Maximizes energy absorption of PV cells while also converting the remaining part of the electromagnetic spectrum into dispatchable energy. 3) Versatile – Customizable to any combination of PV cell and CSP technology. 4) Retrofit – Can be applied to existing CSP systems with little modification.

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