1. Introduction

At the present stage of science and technology, solar radiation can be converted into thermal energy by thermal collectors and into electrical energy by solar cells. The physical basis and technology for photothermal and photovoltaic solar energy conversion is well known and is described in many physical and solar energy publications (1–5). In order to convert solar energy simultaneously into thermal and electrical energy, we have constructed the thermoelectriccollector with a-Si solar cells on glass substrate, and measured the thermal end electrical characteristics.
 
 

2. Experiments

Thermoelectric collector consists of a collector case, thermoinsulation, cover glass, and thermoelectric absorber. The collector case is made of electrochemically colored Al (99,5) profiles. Thermoinsulation is accomplished with 4 cm wide glass wool. The thickness of the cover glass is 4 mm. Thermoelectric absorber consists of Al lamellas having the Cu tubes which are mechanically connected to the upper side of a–Si solar panels. Al lamellas are produced by the method of Al (99,5) pressing. After having the Al lamellas pressed, the Cu tubes are inserted into the bottom apertures of the lamellas. The Cu tubes are further mechanically expanded and are fitted tightly to the Al lamellas. Al lamellas are mutually connected by buckling male and female extensions over the lamellas’ edges. Due to the insulation of Al lamellas, the insulating paper is pasted over them, and in other cases, lamellas are covered by varnish. Thermoelectric collector contains six solar panels all of which feature the following dimensions: 91.5 × 30.5 cm². Solar panels are interconnected parallel.

The a–Si solar panels are made of glass substrate onto which the transparent SnO₂ electrode, photoconversion a–Si:H (n–i–p) layers, Al electrode, and back protection coatings are deposited. The transparent SnO₂ electrode was 0.35 mm thick, a–Si:H layers 0.8 mm and Al electrode about 0.2 mm thick. The solar panel efficiencies were >5%. Solar panels have been produced by Chronar Co. in Princeton (U.S.A.) and thermoelectric collector in Nissal Co., Nis (YU). Technical characteristics of a-Si solar panels with dimensions 91.5× 30.5× 0.3 cm³, on solar radiation AM1, G=1000 W/m², t=25^oC are: V_m=13.5V, I_m=880mA, P_m=12W, V_oc=20V and I_sc=1080mA. The overall dimensions of the collector are: 1960 × 950 × 80 mm³ and the total mass 60 kg.

With solar radiation intensity of I=923 W/m² it is possible to heat up the 80l of water to 50 ° C during the day, and to achieve the short circuit current of I_sc=4,7A and open circuit voltage of U_ok= 16,4 V. The nominal electric power of the collector is P_n= 28 W, current I_n= 3,11 A and voltage U_n= 9 V. The heated water is transported to the solar boiler via the thermosiphonic way or via the circulatory pump. Electricity is directed to the batteries (accumulator) over the charging regulator, and then directly or through the AC/DC converter to the consumer.
 

Fig.2. Thermal efficiency of thermoelectric collector	Fig.3. I–U characteristic of thermoelectric collector

Thermoelectric collector can be applied in industry and private households for heating the sanitary water and for production of electrical energy. Heated water may find many different applications, while produced electrical energy may be used for lighting purposes, air conditioning, telecommunication devices such as radio or TV and for other appliances.

3. Conclusion

On the basis of presented results, the following conclusions can be drawn:

• Thermoelectric collector consists of classical thermal collector box and thermoelectric Al(Cu)/glass–a–Si absorber.
• Thermoelectric collector heats water up to 65^oC and gives DC current with maximum open circuit voltage of 16V.
• The thermoelectric collector can be used in households, hospitals, hotels, and other purposes.

1. Lalovi} B., Kiss Z., Weakliem H.: A hybrid amorphous silicon photovoltaic and thermal solar collector, (1986-1987), Solar Cells 19, 131
2. Lalovi} B. et al.: The application of hybrid a-Si:H PV and thermal collectors for different usages, Proceedings of the International Photovoltaic Solar Energy conference, Florence, (1988), 280
3. Bosanac M., Pavlovi} T., Petkovi} Z.: Performance of thermoelectric solar collector, Sun?eva energija, v.10, 1, (1989), 17
4. Pavlovi}T.: Development of thermoelectric collector as alternative source of electric and thermal energy, Proceedings of scientific project, Faculty of Philosophy, Niš, (1989), 203