Building integrated concentrating solar systems - Solar Energy Sciences and Engineering Applications - page 560

r

CPC axis

2a

z

θ

CPC

Parabola axis

Figure 17.2.3 The angle θ used in the parametric equations of the CPC.

extreme
ray

(x L ,y L )

vertical
line

left parabola L

aperture (A)

axis of R truncation line

extreme
ray
axis of L

l

( x,y )

2 θ a

φ r
φ l

h

right parabola R

F R

F L

absorber

Figure 17.2.4 Asymmetric CPC with half acceptance angle 2 θ a = φ l + φ r .

b) Asymmetric compound parabolic concentrator (ACPC)
The foci and end points of the two parabolas of an ACPC make different angles with
the absorber surface, as shown in Figure 17.2.4. A is the aperture of the concentrator,
R is the right parabola, L is the left parabola, F R is the focus of R and F L is the focus
of L. For the ACPC, effective concentration ratio varies with the angle of incidence
(Rabl, 1976b).