The objective of the project is to combine existing industrial technologies and optimise them in a PV concentrator device which has the economic potential to produce bulk electrical power at the low cost required to justify its integration in a utility grid in Southern Europe (Spain, Italy, Portugal, Greece, South of France).
The existing industrial technologies to be assembled and optimised are the following:
(a) A concentrator providing 1000 suns on the solar cell whilst still allowing an angular acceptance of + 1,5 degrees to produce more than 95% of the maximum power. This later feature has never been used before in a PV system.
(b) Liquid Phase Epitaxy GaAs cells developed by a cheap technology similar to the one used in European optoelectronic industry. Also GaAs cells deriving from recent industrialisation in Europe of thin space solar cells by MOCVD epitaxy. Two substrate options will be evaluated: GaAs and germanium.
(c) Bonding and packaging technology already developed for common optoelectronic commercial devices (LED's, photodiodes, etc.) which are of similar dimensions to the GaAs solar cells envisaged.
The technological targets to be achieved by the concentrator device are the following:
(a) Conversion efficiency range 20-22% (@ Tcell=25 C);
(b) GaAs cell efficiency 24-26% (@ 1000 suns and Tcell=25 C) with a cell diameter in the range 0.5-2 mm,
(c) optical efficiency greater than 85%,
(d)concentrator aperture 18-70 mm,
(e)total concentrator thickness from 0.3 to 0.4 times the concentrator aperture diameter,
(f) an angular acceptance not smaller than + 1.5 degrees between incidence angl for which the output power is 95% of the maximum power, and + 2.5 degrees for 5 (of power), and
(g) a heat sink producing a cell temperature not greater than 40ºC above the am temperature.
GaAs cells have already proved to be efficient at irradiances above 1000 suns and one of the partners (IES-UPM) has achieved 23% at 1300 suns (confirmed by the Fraunhofer Institute in Freiburg). Three innovations will be explored in this project with respect to the GaAs cell and the cost objectives of the concentrator device:
l) A semiconductor structure similar to the one obtained by MOCVD (i.e., contac layer, window layer, pn junction and BSF layer) but grown up by Liquid Phase Epitaxy with a new low temperature process developed by one of the partners (IOFFE Institute) which allows layer growing rates as low as one nanometer/s (500-700º).
2) A semiconductor structure as described above, but grown on a germanium substrate which is less expensive and may have better thermal properties because of its thickness being less than half of that of GaAs substrate with equivalent industrial production yields.
3) A small area GaAs cell. The small area has several advantages in this project: Production yield increases; heat extraction is easier because perimetric heat spread contribution becomes important, etc. On the other hand, for a given module power, the number of operations associated to a single cell or to a single concentrator increases, but these operations van be highly automated based on the existing tools and equipments developed for the optoelectronics industry.
One of the partners (TEMIC) has a broad experience in this field and a leader position in the market.
The optical concentrator, called RXI and which is one of the main innovations of the project, was designed according to a new method developed by Minano et al. at IES-UPM. It has two features which make it particularly intersting for the project. 1) a very wide acceptance angle (+1.5 degrees for C=1200) and a very compact aspect ratio (concentrator thickness/aperture diameter < 0.3).
Funding SchemeCSC - Cost-sharing contracts
194021 St. Petersburg