Beyond the 2D limit: étendue-squeezing line-focus solar concentrators

Line-focus solar concentrators are commonly designed by extruding a two-dimensional concentrator in the third dimension. For concentration in air, these concentrators are, by the nature of their design, limited by the two-dimensional solar concentration limit of 212×. This limit is orders of magnitude lower than the 45000× concentration limit for three-dimensional solar concentrators. Through the use of étendue squeezing, we conceptually show that it is possible to design line-focus solar concentrators beyond this 2D limit. This allows a concentrator to benefit from a line focus suitable for heat extraction through a tubular receiver, while reaching concentration ratios and acceptance angles previously unseen for line-focus concentrators. We show two design examples, achieving simulated 75× concentration and 218× concentration ratios, with a ±1^◦ acceptance angle. For comparison, the 2D concentration limit is 57× at this acceptance angle. Étendue-squeezing line-focus solar concentrators, combined with recent developments in tracking integration, may enable the development of a new class of concentrated solar power systems.