Environmental Engineering Reference
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Figure 14.3.21 Principal components and tracking mechanisms adopted in a solar dish system:
(a) turntable ring - Eurodish (Schlaich, 2001) and (b) pedestal based mechanism (Stirling
Energy Systems, 2013).
temperatures (ranging from 300 C to 800 C) and the type of receiver. As a general
consideration, cavity receivers will probably have a higher efficiency than external
tubular receivers, but they will probably be penalized from an optical point of view.
To give an idea of a real application, the thermal efficiency of the PS-10 is 92% at
nominal rated operation, while the yearly average reduces to 90.2%.
14.3.16 Solar dish
A solar dish system is composed of a reflector obtained by a solid of revolution surface,
namely a paraboloid, and a receiver positioned at the focal point of the reflector.
The solar collector is oriented towards the sun by a rotational movement along two
orthogonal axes by a two-axis tracking system. A thermal engine is placed at the top
of the receiver with working fluid heated by the concentrated radiation.
Parabolic dish systems are generally characterized by high efficiency, modularity
and flexibility. Another advantage is that the conversion process does not consume
water, as with most thermal-powered generating systems. Actually, the highest solar-to-
electricity conversion efficiency among solar technologies (31.25%) has been achieved
by a solar dish Stirling collector (Stirling Energy Systems) tested at Sandia National
Laboratories in the United States.
However, these systems are still experiencing relatively high specific costs and some
reliability issues, related to the receiver/engine block working at high temperature. It
should be noted that, in relation to costs, there is the potential for economies of
scale with mass production in the future, especially where large industrial production
volumes are concerned.
The parabolic dish can be manufactured by discrete elements (facets) that approx-
imate the geometry of a paraboloid or by a continuous reflector made with metal
membranes or glass mirrors approaching the ideal geometry. Figure 14.3.21 shows the
two typical structures of solar dish with tracking mechanisms based on a turntable or
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