Category Solar Collectors and Panels, Theory and Applications

Light collection and image size of the plastic lens

Sunlight collection efficiency was assessed on twenty samples of plastic collector production, randomly selected from available lenses. The optical tests were performed on a white light collimator, which reproduced the solar light divergence, examining collection efficiency E and focal distance f The efficiency of sunlight collection [14] is measured as a ratio between the light focused within the nominal image and the light entering in the lens EPD (enter pupil diameter). The nominal image of the lens is the image obtained from a ray tracing simulation using the optical project of the lens: it had approximate diameter 1.2mm. The E values are obtained with a possible error of ±2%...

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Collectors and fibres for the museum plant

For more than a decade our laboratory has studied sunlight collectors comparing the optical performance of different configurations to concentrate sunlight into an optical fibre [12­14]. Collection efficiency assessment and optical characterisation were carried out on samples of Paraboloids, Mangin collectors and a specially designed concentrator called Catadioptric Concentrator Monoblock (CCM). The Cassegrain collector CCM, presented in Sect. 2.3, was realised in quartz (Silica) and in plastic (polymethylmethacrylate PMMA): the plastic version has considerably reduced dimension, weight and cost, maintaining good collection efficiency.

Finally, to obtain the collector for the museum demonstrator, the optical project of the plastic CCM was adapted to provide collectors that could be mass p...

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The application to internal museum illumination

The possible applications of this innovative solar device were room illumination, water heating or energy supply for domestic devices. For this latter use a photovoltaic panel provides the conversion into electric energy, which can be stored for later use. However the most promising application of these systems appeared to be the illumination of buildings, in particular for artistic purposes such as in museums or in special uses requiring solar light (colour rendering and colour recognition). In these cases the low power level reached by the system is an advantage, because the lighting of artworks has illuminance restrictions for their conservation...

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Motorised frames holding 1 tile or 9 tiles

Suitable mechanical and electronic systems were developed to support and move the optics. The equatorial structure included two motors, one for the temporal axis and one for the declination axis. Optical collector movement was performed by a double guiding system: preliminary orientation by a passive system driving the motors to correctly orient the optics on a daily basis, then fine positioning and adjustments using an optical sun pointer. These electro-mechanical structures were necessary to perform field test, with direct exposition to the sun of the collectors. To test in operative conditions the realised collectors, two different moving frames were realised. The first (Frame A) supported a single tile of four collectors: in Fig. 13a it mounts Cassegrain C1 collectors...

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The tile with 4 Mangins and 4 Cassegrains

Mangin and CCM Cassegrain concentrators were mounted on tiles of four collectors, as shown in Fig. 12a and 12b, respectively. The use of a small tile facilitates the alignment operations and improves the possibility of its massive reproduction, so the tile dimensions were 14cm x 14cm. Reduced size of the tile and system geometry makes it adaptable to the available space and to specific architectural requirements.

image016

(a) (b)

Fig. 12. (a ) Tile of 4 Mangins.(b) Tile of 4 CCM Cassegrains.

Fig. 12a presents the tile with 4 Mangin60 collectors made of glass. The housing for the single collector is a metallic support of diameter 64 mm, which also holds the mirror. The fibre holder with its focusing adjustment is placed in the centre of the metallic support...

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Sun tracking systems to support and orient the collectors

1.2 Sun tracking method

The sun tracking technique was studied [15], experimented and tested under working conditions. Suitable mechanical systems, to support and move the optical system, were
designed and built. The movements to align the optical collectors in the sun direction were performed in two directions by using an equatorial configuration: the directions being on the temporal axis and on the declination axis.

The methodology to track the sun position employed a double guiding system that uses two complementary procedures. The first one provides the preliminary orientation, then the second realises the fine positioning and adjustments. The first tracking system is of a passive type and drives the motors to correctly orient the collectors every day of the year...

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Plastic collector development

The successive step was the development of plastic optical components, which reduced the realization costs. Collector C1 was realized both in Silica (quartz) and in PMMA (plastic); it is important to note that the optical project of C1 ought to be redesigned for the realization

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4

5

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9

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Layout and realisation

Max. enter Focal pupil diam. length (mm) (mm)

f/#

number

Imag

e size

(mm)

Rms

spot

diam.

(mm)

Total spot Collector Total size (5+6) efficiency efficienc (mm) factor y factor

Effectiv e area

(mm2)

Output

power

(W)

C1 in Fused Silica

56.0

55.0

0.98

0.480

0.054

0.534

0.73

0.64

2082

1.15

C1

realised in Quartz

56.0

55

0.98

0.8

0.66

0.54

2082

0.97

C2 in PMMA (pla...

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Experimental tests on realised samples

Several samples of concentrators in Tab. 1 were realised as discussed in Sect. 2 and we experimentally measured the performance of the realised collectors coupled to an optical fibre. The experimentation included laboratory tests and field measurements with direct explosion to the sun. The tests in laboratory were performed using an optical system reproducing the solar divergence [14]; while the field tests require the employment of tracking systems to correctly orient the concentrators (discussed in Sect. 4).

Only B1 of Tab. 2 was available as commercial product, while the other samples were optically manufactured by Italian firms on the base of the optical designs in Sect. 2...

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