PV/T Technology

1.1. Advantages of PV/T technology

PV/T technology combines photovoltaic (PV) generation of electric current and thermal (T) conversion of solar energy. In accordance with the laws of engineering system [1] evolution of a technical system life can be represented as S-shape curve (Fig.1). The curve S shows the most important technical parameters Ps (output power, efficiency, cost, life time etc.) depending on time.

The different technical systems certainly have individual peculiarities, but generally we can see three main areas. In “childhood” the systems are developed quite slowly. Then in maturity technical system’s parameters are improved very fast, the mass production begins and financial investments usually facilitate improving the systems. The third low growing and saturating area corresponds to aging of systems, where physics and technical limiting factors are practically

achieved. A new technical system should appear to achieve better parameters (Sn curve on Fig. 1). In our case, for example, photovoltaic (PV) system after achieving the limiting parameters can be improved only on jumping to a new approach, for instance, using multiplayer solar cells (SC) instead of one p-n junction in SC, or developing combined PV/T systems. Now it is possible to have efficiency already close to 40 % for multiplayer SC if to use only PV conversion. Total efficient of PV/T systems can be even much higher. Sometimes after saturation on the third stage of elaborating a certain degradation of output parameters can be observed (dashed line, Fig.1).

One example from solar engineering can illustrate this evolution behaviour of technical production. You can buy multi colored solar cells, but they cost more and deliver a little less energy. However, architects prefer them for aesthetic reasons. Even such decreasing of output parameters is patented. The invention [2] provides a colored solar cell unit where the application of the color need not be at the expense of the solar cell unit’s output.

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Fig.1. Evolution of a technical system.

 

The main advantage of PV/T hybrid systems is their high total efficiency. A logic of developing new solar systems demands both types of solar conversion.

That is why more and more publications are devoted to combined PV/thermal systems last years (see, for example, following references from [3, 4]).

Co-generation of heat and electricity is a good factor for integrating solar energy systems into buildings. Our analysis shows a general tendency of integrating of different solar energy technology. Chart at Fig.2 reflects this tendency of integrating classical solar energy technologies with modern ones [3].