Page 36 - RSE - Results of the Apollon Project

Results of the APolloN PRoject ANd coNceNtRAtiNg PhotovoltAic PeRsPective

tABLE 5. Simulated optical acceptance angles

1 Receiver 2 Receiver
st
nd
Ang. Acceptance along x-axis (°) +2.8, -3.0 +1.2, -1.3
Ang. Acceptance along y-axis (°) ±2.9 ±1.4

CPower Mirror-based spectrum-splitting (MBS ) prototype modules have been manufactured (see Figure 34) and
2
their electrical performance was measured. On a single unit, optical effciency was approximately 70%.

FiguRE 34. N.3 (left) and N.15 (right) series connected mirror based units for the C Power module prototypes

The performance of the prototype modules was lower than expected: the overall effciency was approximately
15-16%; the losses in the performance were mainly due to optical and mechanical mismatches. In spite of the
possibility to improve the module performance, the high complexity of such a system penalized its competitiveness
in the short term. On the other hand, theoretical calculations (see chapter 10) showed the possibility of reaching 32%
effcient modules by means of a “simpler” mirror based solution that should attain better economic competitiveness
by removing the extra costs coming from the additional materials necessary for the spectrum-splitting operation.

development of Second generation Mirror-based Optic Without Spectrum Splitting

Under the APOLLON Project, a second generation point focus concentrator has been developed by CRP and RSE.
The concentrator is composed of two optical stages: an off-axis parabolic primary mirror and an homogenizer with
the input window placed at its focus.
2
The PV cell (a 5.5x5.5 mm multi-junction device) is mounted in correspondence with the secondary output
aperture. A glass protective window, coated on both sides with nanostructured antirefection layers, is put on the
top of the concentrator. Several optical simulations have been carried out to optimize the components shape and
the system geometry while, at the same time, improving two main parameters: optical effciency and acceptance
angle. A novel pyramid homogenizer has been developed by RSE: it uses a novel design of its input cross-section
to improve, with respect to the standard solution, the angular acceptance of the concentrator, by taking advantage
of the optical aberrations produced by the primary optical element. Both primary and secondary optical elements
are refective and have been created with silver coated aluminium sheets so as to provide the highest possible
refectivity. For the selected optical confguration a patent application was submitted.
36 Results of the APOLLON project and Concentrating Photovoltaic perspective
FiguRE 35. Sketch of the whole concentrator system (left) and a detail of the developed homogenizer (right)

Cover glass

Primary
mirror

Secondary optic
(refective)
Solar cell
Figure 35. Sketch of the whole concentrator system (left) and a detail of the developed homogenizer
(right). 35

The simulated performance of the mirror based concentrator are reported in Table 6.

Table 6. Simulated performances of 2nd generation concentrator

Optical Angular Average Maximum
efficiency acceptance concentration concentration

84.1% ±0.86° 847X 1500X

A prototype of this mirror based concentrator has been realized by ASSE and it was tested by using the ENEA optical
bench for measuring its optical performances.

Optical acceptance angle
100%
95%
) ( % 90%
c y n 85%
f f i c i e 80%
e e t i v
l a e R 75%
70%
65%

-1.2 -1 -0.8 -0.6 -0.4 -0.2 60% 0 0.2 0.4 0.6 0.8 1 1.2
Misalignment (°)
METALCO MIRO 4 MIRROR "TIPO 3" MIRROR "TIPO 2"
MIRROR "METALCO MS2"
MIRROR "METALCO M2702AG"
MIRROR "TIPO 1"
Figure 36. Prototype of the concentrator under testing (left) and the measured angular acceptance
curve (right).

The experimental results are reported in Table 7: