Page 92 - RSE - Results of the Apollon Project

g

Research Areas to be Further Addressed

(RSE, ASSE, CPpwer)

As far as the MB technology developed under APOLLON is concerned, several improvements are possible to
increase the performance and reduce the cost. Module effciencies of 34% or better are reachable through a better
control on the shape of the primary mirror, improvements in mirror positioning and orientation, improvements in
the refective secondary optics (so far made manually) and by considering solar cell with effciency higher than 42%.
Improvement in the AR-coating of the glass window (wavelength optimization with mirror and cell) by exploiting
nanostructured coating can also produce a further increment of one or two points in module effciency.
The prototype modules have been designed for manual assembly, the future task is to redesign the prototypes,
converting them into commercial modules suitable for automated production.
In the current prototype, the thermal design of the receiver was not optimal. The choice of the thermal adhesive
has to be reassessed and the process of adhesive-application has to be optimized. In addition an attempt should be
made to further integrate heat-sink, receiver-support and module housing in order to improve cell cooling.
Here follow some general considerations for a successful implementation of future projects on CVP.

1. Off-axis mirror-based technology is claimed to be preferred over a spatial spectrum splitting technology. Both
technologies have been developed in the context of the Apollon project, however, as evaluated by CPower, the
spatial spectrum splitting technology has costs that are 0.15 euros/Wp higher than mirror bases technology.

2. Off-axis mirrors offer some important advantages with respect to on-axis mirror. The former have the potential
advantage of giving the possibility to maximize the area from which sunlight is collected. With on-axis mirrors
there is always a small portion of this area that is obscured by the cell, the heat sink or a secondary optics.
Modules with off-axis mirrors have irregular shapes however (trapezoidal rather than rectangular cross section)
and this tends to lead to a more inactive window area (higher glass and housing costs). On future HCPV mirror-
based products, a careful assessment has to be made to reduce the inactive window area.

3. Fresnel-lens-based technologies can be competitive with mirror-based technologies. This statement is also
supported by the fact that both systems commercially exist. Each of the two technologies has its advantages
and drawbacks. Fresnel-lens based systems potentially have lower optical operating effciency due to intrinsic
losses on the lens (which depends on temperature) and due to chromatic aberration, but they seem to be
constructively easier to assemble and they seem to be more tolerant to precision errors. Mirror-based technology
has the potential for higher optical effciency but requires a high precision in mirror shaping, surface quality
and positioning, and orientation of the mirrors. Mirror-based systems also seem to have the tendency to have
higher mismatch losses between the receivers of a module. Therefore the utilization of DC/DC converter should
be further implemented.

4. Throughout the holistic approach followed under APOLLON it was possible to increase the competitiveness of
CPV technology, by tackling several aspects that hindered its market penetration. In the coming years, it will be
useful to maintain such approach to increase the system performances and competitiveness.

5. In order to support a faster deployment of CPV technology, it is important to highlight the most important
parameters which infuence the system cost. For this purpose, it is very useful to consider the simplifed economic
analysis as reported in chapter 3 (Crystalline Si and III-V high effciency solar cells), which is better explained
herebelow, in particular regarding the initial assumptions. The equation (1), reported in this paper, was indeed
based on the following hypothesis:

91