- CPV Research at BGU’s National Solar Energy Center
Concentrator Photovoltaics (CPV) is a technique that allows one to employ concentrated sunlight to increase the electrical power output per square centimeter of PV material by typically three orders of magnitude. It is consequently expected that by thus reducing the size of what has hitherto been the most expensive component of a PV system, solar-generated electricity costs should become competitive with those of fossil-generated power, without the need for subsidies.
High concentration of sunlight (typically 500-15,000X) is achieved via appropriately designed optical concentrators – mirrors or lenses. Such optical design is one of our specialties. Depending upon system design, the CPV cells may be actively cooled or passively cooled. The heat transfer considerations of CPV receiver design is another of our specialties.
Conventional silicon PV cells cannot be employed at high levels of solar concentration because their internal resistance is too large. CPV cells have accordingly to be specially designed both vis-à-vis materials and internal geometry. The physical properties of CPV cells at high solar intensities is another of our specialties, which enables us to work closely with all the principal CPV cell designers.
Unique equipment we have for CPV cell and module characterization are: (a) PETAL – a 26 m diameter parabolic dish capable of producing concentrated sunlight up to approximately 10,000X at power densities of up to approximately 400 kW/m2 [Fig. 1] (b) an indoor test facility, employing an outdoor mini-dish and fiber-optic cables, that can characterize small CPV cells up to solar concentrations of approximately 10,000X [Fig. 2]; (c) an indoor solar furnace, fed by an outdoor heliostat, that can achieve optical concentrations up to approximately 15,000X on larger area CPV cells [Fig. 3].
Commercial CPV companies that have resulted from our research include Solfocus (USA) and Zenithsolar (Israel). The former company’s system employs mini-dishes and passively-cooled CPV cells [Fig. 4], whereas the latter company’s system employs large dishes with actively-cooled CPV cell modules [Fig. 5].
:The PETAL dish being used to test a water-cooled CPV module.
This facility characterize large modules at solar concentrations up to 10,000X
Figure 2: Apparatus for characterizing CPV cells indoors with concentrated sunlight supplied from an outdoor mini-dish via an optical fiber. This facility can characterize small solar cells up to optical concentrations of 10,000X.
Test facility for characterizing large CPV cells at solar concentrations up to 15,000X. A collimated light beam, from an outdoor heliostat, enters horizontally from the left; is directed vertically upward by a diagonal plane mirror; is concentrated and re-reflected vertically downward by a concave mirror; passes through an orifice in the diagonal mirror and illuminates the target cell beneath.
The passively-cooled Solfocus CPV system at ISFOC, Spain.
Figure 5: The actively-cooled Zenithsolar CPV system at kibbutz Kvutzat Yavneh, Israel.
Aplanatic optics for CPVProfs Gordon and Feuermann
have developed specialized aplanatic optics for compact concentrating PV devices. These optics are dual mirror designs that remove both spherical and coma aberrations and therefore permit a ‘tighter’ focus than conventional optics such as lenses or paraboloidal mirrors.
They permit either higher concentration – closer to the thermodynamic limit of concentration – or laxer optical and tracking tolerances, reducing manufacturing costs of the system.
The design has been motivated by industry and is being produced commercially for high performance concentrating photovoltaics (see http://www.solfocus.com/en/index.php
High-temperature material synthesis for novel inorganic fullerenes.A collaboration between Weizmann Institute of Science
(Profs. Reshef Tenne and Moshe Levi) and BGU (Profs.Jeffrey Gordon, Eugene Katz, and Daniel Feuermann).
The aim is to generate photo-thermal ablation and/or drive chemical reactions that are commonly the domain of high-power pulsed lasers, at potentially far lower cost and energy consumption by using highly concentrated solar radition. Furthermore, the distributed high-temperature annealing conditions achievable in reactors driven with ultra-bright non-coherent radiation could prove superior to those with oven-enhanced laser ablation methods in the sense of producing a wider variety of nanostructures, including nanotubes and fullerenes (closed-cage structures) at the fundamental limit of molecular stability. The optic at the right concentrates solar radiation by a factor of 30,000. The optic was designed by Gordon and Feuermann and is unique in its capability to concentrate direct sunlight.
Photothermal coatings based on nano-materials for the efficient conversion of the solar energy.
A collaboration between Hebrew University (Profs. Mandler and Magdassi), Tel Aviv University (Prof. Kribus and Steinberg), and BGU (Prof. Feuermann).These coatings have the purpose of being highly absorbing in the solar spectrum while having low emission in the far infrared, thus reducing heat losses by radiation. In this work, we design and develop selective coatings based on CERMET coating (silica, alumina, titania). We prepare and study their intrinsic optical properties. We also combine a reflective and anti-reflective layer to achieve the desired spectral selectivity.
Projects at the Ben-Gurion National Solar Energy Laboratory.
Ministry of Energy and Water Resources – all started Jan. 2012:
Accurate Monitoring of direct normal irradiance (DNI) on a one-second time scale for smart grid purposes. – through Dec. 2013
The data base that is being compiled will be useful inter alia for studying the transient effects that the fluctuating output of photovoltaic systems may be expected to exert on the electricity grid.
Experimental Investigation of a 5 KW Vanadium Redox Flow Battery (VRB) – through Dec 2014
The research results from this project will enhance our understanding of how to get the maximum amount of photovoltaic power into the grid from PV systems of various sizes.
Technical and Economic Study of combining Israeli know-how in the long-term program of the IEA PVPS (IEA), – through Dec 2014.
The research aspect of this project studies the technical and economic feasibility of constructing so-called Very Large Scale Photovoltaic (VLSPV) – namely, GW-scale – power plants in the world’s deserts.
EU 7th Framework: ECOSOLE project. - a 3-year project which started August 2012.
This project will study and demonstrate all aspects of designing and manufacturing a commercially viable high-concentration Concentrator Photovoltaic System. Our part of the project is to develop outdoor test methods for characterizing the performance of components (modules) and entire systems.
BIRD: project in collaboration with the US company Southwest Solar Technologies. – an 18-month project which started February 2013.
This project is similar in scope to the EU project, excerpt that, in contrast to the latter’s passively-cooled parquet of CPV cells, here the receiver’s dense-array of CPV cells is actively cooled.
German PV Industry: funding, via the Fraunhofer Institute ISE: Outdoor Weathering (OWT III) 3-year project which started in 2012.
This third 3-year project quantifies the degradation of various solar collectors under the extreme climatic conditions of Sede Boqer.
Soitec (formerly Concentrix) funded Grid-connected CPV project. – October 2011 – September 2014.
This project studies and quantifies the performance of a grid-connected, passively-cooled Concentrator Photovoltaic system. Part of the research was to develop a formula that would enable the prediction of system performance under any (non-hostile!) climatic conditions.
EU 7th Framework. Elevated concentration PV solar energy generator and fully-automated machinery for high throughput manufacturing and testing (ECOSOLE). Aug 2012 – July 2015
Siemens/Solel: Parabolic trough solar-thermal projects - through Dec 2017.
Our role is to offer miscellaneous technical advice and services to the operator of the systems.