PHOTOVOLTAIC MODULES OF "KVANT" WITH IMPROVED OPTICAL AND ELECTRICAL CHARACTERISTICS

Dimensions, mm

Marlem Kagan, Valery Nadorov, Victor Rjevsky, Vadim Unishkov The State Research-Production Enterprise "WANT", 129626, the 3-d Mytishchinskaya Street, 16,

Moscow, Russia

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970x440~38

ABSTRACT

White roof Sandy ground Near white walls

Power output, W 58.5 53.6 57.8

Current at Pmax, A 3.44 3.25 3.4

17.0 16/5 17.0

This paper presents the results of the development of photovoltaic modules with bifacial sensitivity as well as modules with improved optical and electrical characteristics. Such modules have bifacial sensitivity due to the special design of solar cells. The paper presents experimental results on estimating the net gain in the rated module's output power under various operating conditions. It was shown as a result that an additional output power was obtained (compared to Conditions when only the front face is illuminated). Replacement of the frontal glass by the fluorosopolymeric filrn has allowed to minimise optical bases of the module.

Module inclination angle

45

EXPERl M ENTAL. I INVESTIGATIONS

The paper presents the results of the study of photovoltaic modules that have improved output characteristics due to the bifacial sensitivity as well as modules with improved optical characteristics.

At present the efficiency of monocristalline silicon solar cells manufactured by the SRPE "KVANT" is 13- 15%. Photovoltaic modules with power output from 10 to IOOW based on these cells have been developed and put into production. These modules can be easily assembled into arrays with large surface area. Such modules have the bifacial sensitivity due to the special design of solar cells. These modules allow to obtain a considerable gain in the output power due to conversion of scattered and reflected light falling on the reverse side of the module. Table 1 shows characteristics of a modlule made of 36 cells connected in series (surface area of one cell is 95,6

cm2) measured at standard conditions AM 1.5, 1000W/m2, T=25"C.

Table 1

Parameter

Short circuit current, A

Open circuit voltage, V 21.34

I Current at Pmax, A I 3.1 I 2.2

I Output power, W I 50.5 I 36.0

Table 2

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0-7803-3166-4/96/$5.00 0 1996 IEEE

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25th PVSC; May 13-17, 1996; Washington, D.C.

it was shown as a result that in each of the above trials an additional output power was obtained (compared to conditions when only the front face is illuminated). The magnitude of this additional power lies within 10-15% of the rated power output of the module. In the conditions of six hour's daylight the module with parameters indicated in the Table 1 will provide additionally 30-45 W-h. Another important problem is minimisation of optical losses caused by reflection of radiation from the

surface of the glass and its absorption by the glass. In conventional designs when the front face glass is directed to the sun (version 1) total losses may reach 6-8%. The authors have suggested and tested a version of design in which toughened glass is just a bearing surface on which the cells are fixed and the front face is manufactured as a packet made of fluorosopolymeric film and EVA-type film (version 2).

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For the each version two BSR-10 modules have been manufactured comprising 36 series-connected solar cells with size 50x50 and their basic electrical characteristics have been measured under standard conditions. The measurement results are presented in the Table 3. As it is seen from the Table 3 the output characteristics of the version 2 module are better than those of the version 1 module by 10-15%.

To explain this fact the separate SC with close initial characteristics have been investigated. Their spectral sensitivity was measured before and after lamination in the packet according to the two versions mentioned above. The measured characteristics are shown in the Fig. 1.

The replacement of the frontal glass by a fluorosopolymeric film laminated in a packet with metallic grid allowed to obtain the surface structure in the form of small lenses able to focus the light into the solar cell base. It results in localising the minority carriers generation in the solar cell base and thereby in reducing the influence of surface and bulk recombination velocity on quantum efficiency. The reflection curves of SC ( R l ) and packets of version 1 ( R 2 ) and version 2 (R3) are shown in the Fig. 1. Although these reflection characteristics differ from one another the difference has no essential influence on the electrical characteristics of SC.

The test run on such a module confirmed its resistance to climatic and mechanical effects.

1. The photovoltaic modules based on silicon solar cells with bifacial sensitivity have been developed. At certain orientation of their back side these modules provide additionally 10-1 5% of rated output power.

2. The new version of module design has been developed and tested. In this module toughened glass serves as a substrate on which the solar cells are fixed and the front face is manufactured as a packet of fluorosopolymeric film and an EVA-type film. As a result the module's nominal power equal to 11.59W increased by 1.24W.

3. The analysis of improvement of the spectral characteristics of the laminated packet the front face of which has a fluorosopolymeric film with the surface structure in the form of small lenses in comparison to those of a solar cell has revealed that this effect is due to the reduction of the influence of recombination characteristics on the quantum efficiency.

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Solar cell

Version 2

100

O B I I I I I I I I 400 500 600 700 800 900 1000 1100 1200

Wavelength, nm

Fig:l Spectral sensitivity and reflection curves of solar cell, versions 1 and 2.

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