Solar energy conversion with thermal cycles - Solar Energy Sciences and Engineering Applications - page 435

Figure 14.3.12 Characteristic angles of Fresnel collectors at 0 ◦ incidence angle.

or (ii) by reducing the concentration ratio. As a drawback, both solutions increase the
cost of the solar field.
For this reason, when developing a Fresnel technology, it is not correct to focus
on only one parameter, but the minimization of the cost of electricity must be the final
target.
Moving to yearly optical efficiency, the IAM for the linear Fresnel concentrators
will now be discussed. The starting point is that LFR requires two projections of the
incidence angle: one on the longitudinal plane and the other on the transversal plane
(see Figure 14.3.13): θ ||

is defined as the angle between the vertical axis and the beam
vector projection on the longitudinal plane, and θ ⊥ is defined as the angle between the

vertical axis and the beam projection on the transversal plane. In addition, another
characteristic angle,

i , can be defined as the angle between the sunray vector and its
projection on the transversal plane. This angle corresponds to the above-described inci-
dence angle of PT technology. Relations between angles are summarized in Equation
14.3.10 to 14.3.12:

θ

θ ⊥ = arctan( | sin( γ ) | tan( θ z )) (14.3.10)

θ || = arctan(cos( γ ) tan( θ Z )) (14.3.11)

θ i = arcsin(cos( γ ) sin( θ z )) (14.3.12)

where γ is the azimuth angle and θ Z is the zenith angle.
The incidence angle modifier which is a function of the zenith and azimuth angle
includes the cosine effect, the primary mirrors mutually blocking and shading, the sec-
ondary reflector and support shading, variation in optical properties and modification
of the interception factor.