Recent developments in nonimaging secondary concentrators for linear receiver solar collectors

摘要

The energetic and economic attractiveness of linear solar concentrators can be significantly improved by the use of properly secondary non-imaging (CPC-type) concentrators. Two specific illustrative cases are analyzed. One is the optical re-design of a commercial two-stage solar concentrator which generates process steam at 150$DGR@C. The primary is a linear Fresnel reflector with one-axis horizontal tracking. The receiver is a stationary, non- evacuated, glazed tubular receiver with secondary CPC. We have re-designed the initial, manufacturer-designed secondary so as to noticeably improve collector thermal output. Details of secondary design and system performance are presented. The other is a new concept in secondary CPC-type concentrators for parabolic trough collectors with tubular receivers and large rim angles (typically 80$DGR@-120$DGR@). It had been though that such large-rim- angle concentrators could not benefit from secondary concentrators, since the second-stage concentration boost goes as 1/sin(rim angle). However, by introducing multiple asymmetric CPC-type devices, we can increase the geometric concentration of a 90$DGR rim angle parabolic trough by roughly a factor of 3. Furthermore, certain secondary designs can be accommodated within the annulus of currently-manufactured evacuated receiver tubes, and still offer a flux concentration improvement of about a factor of 2.5. Examples of the new secondary designs, and achievable concentration gains, are presented.