Vol 53, No 1 (2017)

Photovoltaic and thermal characteristics of a photovoltaic converter are studied. The power losses in photovoltaic conversion and the optimal power, current, and voltage and efficiency limit of the converter are determined. A theoretical model is presented for calculating the photoinduced current, reverse saturation current density, diffusion factor, lifetime, and current–voltage characteristic (CVC). The limiting idle voltage, efficiency, and CVC filling factor are determined for various temperatures.

The thermoelectric effect, i.e., appearance of thermally stimulated current and voltage during uniform heating in a temperature range from 30 to 250°C, is studied. It is shown that greatest values of the current and voltage appear when maximum band gap difference is observed.

It is shown in the paper that the reliability and efficiency of self-draining systems of the drainback syphon type depend on the atmospheric pressure and heating temperature of the heat carrier in the solar collectors, which affect the value of the allowable drop of the atmospheric pressure in the upper point of the system after it is filled with the heat carrier and achieves the specified heat operation mode. In such systems, the drop of the atmospheric pressure and growth of the heating temperature of the heat carrier lead to an increase in the power consumption for the heat carrier circulation owing to the interruption of the jet in the syphon because of boiling of the heat carrier. An improved structure of the self-draining solar circuit with an active element in the form of a Venturi tube was developed in which there are no such drawbacks under atmospheric pressure, and as compared to the common self-draining system of the drainback syphon type, the power consumption for the heat carrier circulation is reduced to 65–80%. The calculated dependences are given to define the necessary degree of the flow contraction in the Venturi tube and its resistance coefficients.

Solar power is an unlimited source of power in theory when compared to the needs of the planet, however, in practice it is still a source of power convertible to electrical energy on a limited basis. In this context, efficiency of this energy conversion by photovoltaic panels has a great importance. Panel surface taking a sufficient amount of light at the right angle has a direct effect on efficiency. This is related to keeping the panel surface as clear as possible of dust and similar objects which can be reflective and absorptive. The contamination of photovoltaic panels has a negative effect on the energy production of panels. In this study, the effect of panel surface contamination, one of the most important factors affecting panel efficiency, was investigated. The investigation was conducted by comparing data from two panel strings standing very close to each other in a plant, one of which was cleaned regularly and the other left contaminated.

An algorithm for calculating the solar radiation flux on the receiving surface of a nontracking parabolic trough concentrator with a louvered heliostat is presented. Cylindrical geometry of the concentrator and shape and arrangement of mirror lamellae of the heliostat make it possible to consider sunlight passage across the mirror system of the module as a whole band, which significantly increases the computational efficiency of the algorithm proposed.

Powerful solar stations of tower and modular types include from hundreds to thousands of concentrators and heliostats; thus, there occurs the problem of their control and maintaining the rotations of the concentrator following the apparent motion of the Sun. The optical tracking systems (TS) perform the task of tracking, but maintaining them requires wired or wireless connection with the control panel. The necessity of such a connection makes it possible to consider the problem of program tracking. Unlike optical TS, the accuracy of program tracking is affected by a number of factors, in particular, by nonverticality of the azimuthal axis of the concentrator. Therefore, the program tracking algorithm should include a block that takes into account and compensates for the nonverticality of the azimuthal axis. We have obtained a system of equations that forms the algorithm to account for the nonverticality of the azimuthal axis of the concentrators and estimated the influence of these inaccuracies. It has been shown that an increase in the Sun’s altitude (height) significantly influences the azimuthal angles on axes of rotation, while zenithal corrections are within the range of inaccuracies of the azimuthal axis alignment.

High-precision modern sensors for measuring the solar resources operating in six regions of the Republic of Uzbekistan are studied. The data on incoming solar energy obtained by the ground and satellite stations are analyzed.

The existed combined power and cooling cycle operates with ammonia–water mixture as working fluid having low cooling due to the vapor at the inlet of evaporator. It also demands high ammonia concentration at turbine inlet to get cooling and suitable only at low sink temperature (10–12°C). A new cooling cogeneration cycle has been proposed and solved to generate more cooling with adequate power generation from single source of heat with two options in working fluids i.e. ammonia–water mixture and LiBr–water mixture. The results show that an increase in cycle maximum temperature is only supporting the power but not the cooling. A suitable range for separator temperature has been developed and optimized to maximize the total output. From this study, the resulted specific power, specific cooling, cycle power efficiency, cycle coefficient of performance (COP) and cycle energy utilization factor (EUF), plant EUF, and specific area of solar collector are 0.008 kW/m², 0.11 kW/m², 2%, 0.28, 0.3, 0.13 and 8 m²/kW for ammonia–water cycle and 0.04 kW/m², 0.3 kW/m², 9.5%, 0.7, 0.8, 0.37 and 3 m²/kW for LiBr–water mixture plant respectively.

The main areas of large-scale development of solar energy are: —conversion of solar energy into low-grade heat, and using the latest in heating systems of residential, municipal facilities, public and industrial buildings that consume energy such as temperature capacity; —conversion of solar energy into electricity through photovoltaic and thermodynamic converters. This report provides short information of the dynamics of the creation and operation of solar power plants (SPP) with the thermodynamic conversion, and the criteria for reducing cost of electricity produced from them.