Amongst the activities being carried out at CIDEMCO’s Area of Energy Efficiency are numerous research projects in the field of renewable energies, including photoelectric solar energy, thermal solar energy, solar refrigeration and biofuels. CIDEMCO’s research activity into photoelectric solar energy is currently targeting, on the one hand, the integration of photoelectric solar energy in buildings and, on the other, the optimisation of processes for the conversion of sunlight into electricity at an atomic level. This last involves the use of both theoretical and experimental techniques well known in the field of nanoscience and nanotechnology.
At a theoretical level, using advanced methods of computational simulation based on quantum physics, an attempt is being made to develop new semiconductor materials with a structure of optimised energy levels for the generation of photoelectric electricity. These materials are known as intermediate band semiconductors and can give rise to new, high-efficiency photoelectric cells.
Intermediate band semiconductors have an additional energy level within their structure of energy levels or band structure in such a sway that the sunlight photons, which otherwise would not be taken advantage of, is used to generate electricity. This enhanced use of solar photons would result in, in the case of a material of such characteristics, a significant increase in the efficiency of the conversion of solar to electrical energy. Theoretically, this type of cell can attain up to 63% efficiency.
Thus, what is being put forward is basically research aimed at developing new semiconductor materials that can be used as a basis for a new generation of photoelectric solar cells which have considerably greater efficiencies to those currently available on the market.
At the same time, and more experimentally focused, is the work on enhancing the key components for the photoelectric sector: the glass that covers the photoelectric panels and the ethylene-vinyl-acetate copolymer (EVA) used for encapsulation. This work is carried out in close collaboration with an important enterprise in the glass sector and the main EVA manufacturer and distributor in Europe. The scientific work, moreover, is undertaken in an ongoing collaboration with a number of universities.
In general the solar cells have a glass-EVA-semiconductor-EVA-back lamina structure. The glass usually used for the photoelectric panels is an extra-clear tempered one – with low iron salts content – reaching a 91% transmission index and of 3-4mm thickness and textured to minimise the reflection of light and favour transmission to the semiconductor material. The encapsulating EVA, apart from being optically transparent, is stable at high temperatures and when subjected to high doses of ultraviolet radiation.
The aim is to incorporate active components into the glass and the EVA that are capable of enhancing the response of the cell to the incident radiation. To this end, the analysis of optimum materials, by means of spectroscopy, is being worked on at a basic research level with the Universities of Cantabria and the Basque Country. At the same time, enterprises carry out the task of studying the optimum implementation of these materials and the possible interactions with the rest of the components, especially in the case of the EVA copolymer. At CIDEMCO the behaviour of these components integrated into the modules is studied and their efficiency evaluated.
Moreover, what is involved is the study of the behaviour of the new systems with concentrated sunlight. Given that the processes of electronic transition involved are strongly non-lineal, what is expected is a significant increase in the efficiency obtained by using concentrated sunlight.
This is why at CIDEMCO they are developing a system of sunlight concentration that will enable the opportune trials to be carried out and will be the basis for new projects.
Amongst the advantages of this proposed focus, special mention can be made of the fact that, once the materials with the properties being sought are identified, they can be used in the glass that covers the cells or adhere directly to the semiconductor material by means of the EVA, without any modification to the photoelectric material. Technically, it means an improvement over other methods, for example, in terms of the introduction of defects in the silica which, in some cases, may induce a deterioration in the efficiency of the cell. The method can be extrapolated to other types of cell (CIGS, CdTe, AsGa, etc.), undertaking new research into active components.
By means of this process of research, the aim is to gain a significant increase in the efficiency of current silicon-based photoelectric cells – in the region of 2-3 % -; this would have enormous repercussion in the photoelectric industry at national and international levels. Given that the effect would be integrated both in the glass and in the EVA in a simple manner and amortization of photoelectric systems, the conclusions of the Project will be used as a launchpad for the optimised development of both products (glass and EVA) and a large-scale production process and marketing by the participating enterprises.
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