A major problem of solar panels manufactured from monocrystalline, polycrystalline or amorphous silicon is their low efficiency and large decrease of this efficiency with increasing temperature. Due to this fact follows the most suitable certain geographic locations to place photovoltaic silicon power plants - especially areas whe is a low circumambient temperature and many sunny days. Obversely areas around the equatord appears to be innapropriate for silicon power plant because the is during the day high circumambient temperature.
Maximum efficiency is approx. 21 % (Sanyo) which has been achieved int the laboratory conditions for silicon technology, whereas in real conditions is neccessary to expect with the efficiency up to one third less due to thermal dependence. Other disadvantage of silicon solar panels is that for production of high quality panel with high efficiency is necessary large amount of highly pure silicon. The production is very energetically arduous and uneconomical. Especially from above mentioned reasons is getting the concentrated photovoltaics to the frontground - alias CPV (concentrated photovoltaics), where the main idea constists in the concetration of solar energy into a small point by dint of optical concentrator.
Into focus point of the system is placed a small photovoltaic chip - based on compounds of GaAs produced by epitaxial technology MOVPE1. The point´s diameter where are concentrated sunrays is typically range from 2 to 10 mm. Optical concentrator is usually solved by burning glass or mirror. Value of optical concetration is a ratio of lens´surface and the chip, whereas the typical values are in the range 200-1000 times. This concetration ratio is also known as number of suns, where the value of 500 means that area of the lens is 500 times larger than area of the photovoltaic chip.
Efficiency of solar cells based on GaAs is approx. double silicon cells efficiency in laboratory conditions - so about 42 %. Loss in efficiency compared with silicon cells is approx. half. Concentrated photovoltaics is particularly suitable on places where you can not use silicon photovoltaic due to high circumambient temperature, thus areas located in the subtropical and tropical zone.
Results of development in ELCERAM and TTS
During the four years of research and development has been designed, constructed and tested solar cell ELC 38 with corundum pad base. From these solar cells were constructed 6 solar panels ET - CPV 125. From solar panels was assembled solar system with 750 W output ath the intensity of 850 W/m2 of flatling beaming. Part of the solar system is a monitoring device that measures actual intensity of flatling beaming and from this information is calculated the whole systems´ efficiency.
More information about CPV:
Technical documentation about solar cell ELC 38 and solar system can be downloaded here.