Cogenerative PV Thermal Modules of Different Design for Autonomous Heat and Electricity Supply

Cogenerative PV Thermal Modules of Different Design for Autonomous Heat and Electricity Supply

DOI: 10.4018/978-1-5225-3867-7.ch004
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Solar energy is used for electricity production by means of photovoltaic modules and for heat supply by means of solar water-heating collectors. In recent years, combined cogeneration photovoltaic thermal modules which work out at the same time both electricity and thermal energy began to be applied actively. The chapter includes consideration of the main types of cogenerative photovoltaic thermal modules of different design such as planar liquid devices as well as devices with concentrator of solar radiation. The advantages and disadvantages of each type are presented. Main directions for improving the efficiency of converting solar energy into thermal and electricity are offered. The description of the offered construction of the module, and also results of theoretical and pilot studies of the module is provided in full-scale conditions. Installation for such tests is described as well. Testing photovoltaic thermal modules with planar and concentrator design are presented in the chapter.
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The energy of the Sun is one of the most common and most widely used sources of energy. The amount of energy coming from the Sun to the Earth exceeds the global consumption and for many years remains an inexhaustible source of energy for mankind. The scale of this energy source is very well illustrated by the figure 1.

Figure 1.

Annual world energy consumption in comparison with the solar energy amount coming to Earth throughout the year

Source: Fortov & Popel, 2011

Solar power is used in practice for obtaining thermal energy in the form of hot water through solar water heating collectors and for electricity generation through photovoltaic converter (solar cells) which switched in modules and batteries.

Photovoltaic (PV) System. Solar PV generation based on photovoltaic transformation of solar radiation into electricity. Due to efficient improvement of PV technology it is used as for electricity production at big solar power plants as well in small solar power installation for local energy supply of stand-alone remote objects. The last one is the most interesting area from the point of view of this book. PV generation is preferred worldwide as Distributed Energy Resources (DERs) now. The major advantages of a PV system are the sustainable nature of solar energy, positive environmental impact, longer life time and silent operation.

Solar collectors. The thermal energy in the form of hot water generates in the solar collectors of various types which the most widely used are flat-plate collectors.

Widespread liquid flat solar collector is a heat-absorbing panel (absorber), which consists of channels (tubes) for circulating the coolant. Above the absorber (with a certain gap) is located the transparent and insulating layer. The whole structure is placed in a housing, bottom and side parts of which are equipped with insulating material.

The principle of operation of the solar collector is based on the ability of glass to pass short-wave solar radiation and to hold long-wave radiation of the heated surface (absorber) – a phenomenon called the “greenhouse effect.” As a result of this selective transmittance of solar radiation absorbed by the panel absorbers will be emission of the long-wave radiation. And, thanks to the ability of glass to hold long-wave radiation, there is a significant increase in temperature inside the space confined by glass.

Application field of flat solar collectors is quite extensive. They are used for example in heating systems of residential and industrial buildings, hot water systems, as well as in the number of special energy plants.

For integrated power supply of the above objects, as a rule, the system is installed consisting of collectors as well as a set of power solar modules.

Attempts were made to implement these two processes in a single device later.



The principle of formation of a single device, providing at the same time electrical and thermal energy is illustrated at the figure 2.

Figure 2.

Principle of formation of the photo-electric thermal module. 1 - PV module; 2 - solar collector; 3 - PV Thermal module


In this case, the PV Thermal (PVT) module creation is provided by placing solar cells on the heat absorbing surface of the flat solar collector. PV panel has different efficiency which depends on the type of used solar cells which converts solar radiation into electricity and the remaining solar energy converts into heat. The absorber in this design performs a dual function. First, it cools the PV panel, removing the excess energy that is not involved in the generation of electricity, thereby increasing its efficiency, and secondly, produces heat energy. Even in the case of use a flat collector it is necessary to solve some technological problems in order to the PVT module ha a high efficiency. The issue of creating a design of PVT module with higher efficiency in details will be considered below.

Key Terms in this Chapter

Optimum Inclination Angle of the Receiving Surface: Inclination angle of the receiving surface relative to the horizon, which allows obtaining the maximum solar radiation flux on its surface for a given period of time.

Geographical Coordinates: Angular values – latitude and longitude, which determine the position of objects on the earth's surface and on the map.

Receiving Surface: The surface of the photoelectric device/photovoltaic part of the device, which receives solar radiation.

Actinometrical Data: Results of long-term meteorological observations at weather stations processed and systematized by specialized organizations in the form of climate reference books and databases.

Standard Conditions for Testing the Solar Cell: Test conditions, regulated by the density of the solar energy flux of 1000 W/m 2 and the temperature of photovoltaic solar cells of 25 °C.

Solar Radiation Intensity: The density of solar radiation (energy illumination), coming per unit area of the photoelectric module.

Verification of Data: Verification of theoretical results by comparing them with experimental data.

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