Concentration ratio for a circular trough with flat receiver

TL;DR

This paper derives an analytical formula for the geometric concentration ratio of a circular trough solar concentrator with a flat receiver, revealing two regimes and equating to parabolic troughs in one.

Contribution

It introduces a simple formula for the concentration ratio of circular troughs with flat receivers, identifying two regimes and linking to parabolic trough performance.

Findings

Two concentration ratio regimes identified

Exact equivalence to parabolic troughs in rim ray regime

Formula fills a gap in concentrator design literature

Abstract

We present a simple analytical formula for the geometric concentration ratio of a circular trough optical concentrator coupled to a flat (planar) receiver. The receiver is sized to achieve full collection (no spillage) for any combination of acceptance and rim angle. The development reveals the existence of two concentration ratio regimes, one controlled by the edge ray caustics, and the other controlled by the intersection of the edge rays from the rim alone. Notably, we show that in the latter rim ray regime, the circular trough achieves the exact same geometric concentration ratio as a parabolic trough. The provided formula fills a gap towards the development of a complete catalogue of concentration ratio formulas for different concentrator/receiver geometries.