Soiling is a term used to describe the deposition of dust (dirt) on the solar modules, which reduces the amount of solar radiation that reaches the solar cells. This can cause a more difficult operation of the entire photovoltaic system and therefore generation of less electric energy. This paper presents the results of the influence of various pollutants commonly found in the air (carbon, calcium carbonate ? CaCO3, and soil particles) on the energy efficiency of solar modules. Scanning electron microscope investigation of carbon powder, CaCO3, and soil particles which were applied to solar modules showed that the particles of carbon and CaCO3 are similar in size, while the space between the particles through which the light can pass, is smaller in carbon than in CaCO3. Dimensions of soil particles are different, and the space between the soil particles through which the light can pass is similar to CaCO3. Solar radiation more easily reaches the surface of solar modules soiled by CaCO3 and soil particles than the surface of the solar modules soiled by carbon. The efficiency of the module soiled by carbon on average decreases by 37.6%, the efficiency of the module soiled by CaCO3 by 6.7%, and the efficiency of the module soiled by soil particles by 6.8%, as compared to the clean solar module. The greatest influence on reducing the energy efficiency of solar modules by soiling exerts carbon, and the influence of CaCO3 and soil particles is similar.

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Spectra of possible phonon states, as well as thermodynamic characteristics of nanocrystals (ultrathin film and quantum wire) of simple cubic crystalline structure are analyzed in this paper, using the method of two-time dependent Green functions. From energy spectra and internal energy of the system the thermal capacitance of these structures in low temperature region is found. The temperature behavior of specific heat is compared to that of corresponding bulk structure. It is shown that at extremely low temperatures thermal capacitance of quantum wire is considerably lower than the thermal capacitance of film as well as the bulk sample. Consequences of this fact are discussed in detail and its influence to thermodynamic properties of materials is estimated.

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Dispersion laws and states (i.e. probability of finding) of Frankel excitons in ultra-thin molecular films are found using a well-known method of Green’s functions. Space boundaries and changes of energetic parameters on boundaries are considered as perturbations. The cubic crystalline system with complex cell consisted of two molecules (a and b), i.e. bimolecular film, was analyzed in harmonic approximation, and then compared with the results obtained for simple cubic cell systems (i.e. monomolecular film). In both cases the energy spectra show sharp discrete levels, although the energy spectra of bimolecular films split into two zones with discrete levels. Probability of finding exciton in the mono- or bimolecular ultra-thin films is significantly influenced by the perturbation and the values of on-site energies of molecules a and b. Obtained conditions of the existence of localized exciton states at boundaries are of special interest.

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In this paper the results of theoretical and experimental investigation of electrical energy generated with differently oriented PV modules used as facade elements, are presented. It was found that in 2013, optimally oriented monocristalline solar module of 60 Wp generated 62.9 kWh; horizontal module 58.1 kWh; vertical module oriented toward the South 43.9 kWh; vertical module oriented toward the East 25.7 kWh, and vertical module oriented toward the West 22.9 kWh of electrical energy. Also it was found that optimally oriented Building Integrated PV system (BIPV) of 1.2 kWp can produce 1081.6 kWh/year; horizontal, vertical oriented toward the South, vertical oriented toward the East and vertical oriented toward the West can generate 7.6%, 30.2%, 59.2% and 63.6 less electrical energy, respectively. The greenhouse-gas payback periods (GPBP) for the optimally oriented and horizontal BIPV systems were estimated to be 7.8 and 8.5 years, respectively. The obtained results can be applied in designing residential, commercial and other buildings with BIPV systems in Serbia. [Projekat Ministarstva nauke Republike Srbije, br. TR 33009]