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464 PHOTOVOLTAIC CONCENTRATORS<br />

Figure 11.7 Drawing of Intersol second-generation module [14]. Reproduced with permission by<br />

Sandia National Laboratories<br />

Linear Fresnel<br />

lens<br />

Aluminum<br />

sheet housing<br />

Air-cooled<br />

photovoltaic<br />

receiver<br />

Figure 11.8 Cutaway view of the Entech domed Fresnel module [17]. Reproduced with permission<br />

by Sandia National Laboratories<br />

four beneficial effects. First, it minimizes chromatic aberration caused by the index of<br />

refraction variation throughout the solar spectrum. Second, the angle of deflection of the<br />

ray is independent to the first order of the orientation of the prism. This minimizes the<br />

required tolerances in lens shape and minimizes the impact of lens deformation. Third, it<br />

minimizes the overall loss in transmission due to reflection. Finally, the nonplanar domed<br />

shape makes for a more rigid, self-supporting lens structure. 3M developed a roll forming<br />

process for the manufacture of Fresnel lenses that provided for a high speed, low-cost

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