Environmental Engineering Reference
In-Depth Information
the application of LFR technology since it is considered promising, with potential
economic advantages for the following reasons: (i) ground-based mirrors allow the
adoption of lighter structures thanks also to reduced wind drag effect; (ii) land area
is minimized due to reduced shading between collector rows; (iii) the receiver is fixed
and tracking energy consumption is decreased; (iv) the absence of ball joints lowers
pumping losses; and (v) ground-based mirrors are easier to clean.
Moreover, the concentration ratio (CR) of LFR can be higher than with parabolic
troughs since it is not limited by parabola aperture width. The adoption of more
mirrors would not change the wind drag effect, hence the same structure can be kept.
The CR for LFR is defined in Equation 14.3.8
7
.
aperture width
adsorber diameter
=
n
W
D
abs
·
CR
=
(14.3.8)
where
D
abs
[m] is the absorber diameter,
n
is the number of primary mirrors and
W
[m]
is the aperture of each mirror.
The aperture width in this case is the aperture width of each mirror times the
number of mirrors. Commercial LFRs have a concentration ratio of about 160 (which
is about twice that of parabolic trough systems).
LFRs can have a secondary reflector which collects solar radiation from the pri-
mary mirrors to the absorber tube. The concentration ratio definition for this case is
given in Equation 14.3.8; the only difference is that the solar radiation can be subjected
to multiple reflections. The HCE can be the same as for parabolic trough, while the
glass tube can also be absent where there is a secondary receiver.
The first application of LFR was in direct steam generation plants (DSG, see Section
14.5 for a detailed discussion of this technology) with saturated steam. In order to
increase the conversion efficiency of collected heat in the power section, the production
of superheated steam in the solar field was recently investigated (Novatech biosol,
2012), as was the adoption of molten salts as HTF (Areva CSP).
At the time this chapter was written (end of 2012), there are just a few solar plants
in operation based on LFR technology. The most important is Puerto Errado 2, built
by Novatec Solar with a 30 MW electric power output (Puerto Errado 2). In this plant,
saturated steam at 55 bar and 270
◦
C is produced in the solar field. Other operating
plants, though with significantly lower power output, are the Kimberlina solar thermal
power plant (Kimberlina Solar Plant) and the Liddel plant by Areva, formerly Ausra,
(Liddel Solar plant).
In terms of size, a commercial Fresnel linear collector has a width of about 16.6 m
and a height of 7-8 m. In general, the width affects the concentration ratio, while the
height affects optical efficiency. This part will be discussed in detail later.
The next section describes the main components of Fresnel collectors. The LFR
structure is not treated in detail for the sake of brevity, and because Fresnel mirrors
are ground-based with consequent less complexity than parabolic trough reflectors.
7
As for parabolic troughs, there is a debate on how to define the concentration ratio. Some
authors prefer to adopt the receiver diameter instead of the circumference, as in this work.
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