The article deals with practical application of photovoltaic cells in a variety of connecting options. For maximum efficiency of photovoltaic installations is necessary to take account of all the peculiarities of their work. As the title implies the article describes the peculiarities of photovoltaic cells in parallel and mixed commutation in uniform and non-uniform solar radiation, arising as a result of partial shading or soiling. It is given the theoretical explanation of the causes of the decrease of energy efficiency photovoltaic cells with the above commutation. It is represented experimental confirmation of this fact by the example of industrial plants using photovoltaic panels PS-250 and the single-crystal transformers produced by company "KVAZAR". Results of the research will be useful in the developing and design of photovoltaic installations, especially those with probable partial shading.