Toward high-efficiency hybrid (electricity and heat) high concentration photovoltaic systems

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Photovoltaic power generation is a growing renewable primary energy source, expected to assume a major role as we strive toward fossil fuel free energy production. However, the rather low photovoltaic efficiencies limit the conversion of solar radiation into useful power output. Hybrid systems extend the functionality of concentrating photovoltaics (CPV) from simply generating electricity, to providing simultaneously electricity and heat. The utilization of otherwise wasted heat significantly enhances the overall system efficiency and boosts the economic value of the generated power output. The system presented in this lecture is the outcome of collaborative research in my research group, with the IBM research lab in Zurich and the Fraunhofer Institute for solar energy systems in Freiburg, Germany. It consists of a scalable hybrid photovoltaic-thermal receiver package, cooled with an integrated high performance microchannel heat sink we initially developed and optimized for the efficient cooling of electronics. The package can be operated at elevated temperatures due to its overall low thermal resistance between solar cell and coolant. The effect of the harvested elevated coolant temperature on the photovoltaic efficiency is investigated. The higher-level available heat can be suitable for sophisticated thermal applications such as space heating, desalination or cooling (polygeneration approaches). A total hybrid conversion efficiency of solar radiation into useful power of 60% has been realized. The exergy content of the overall output power was increased by 50% through the exergy content of the extracted heat.dc201

Operation & maintenance - the key for reliable performance in a CPV power plant

The 44.19 MWp concentrator photovoltaic (CPV) power plant CPV 1 in Touwsrivier, South Africa is three years in operation. Lessons learnt for optimizing the power production are presented. The plant configuration is described and the key steps for reliable and efficient operation and maintenance are discussed. By introducing structured operation and maintenance procedures, the produced energy of the plant could be significantly increased. Without these new maintenance procedures the power plant output was less than originally predicted. Eventually, after introducing the proper maintenance concept in July 2017 for the first time, the total produced energy cumulated over a 12 month period was above the predicted modelled energy. This proves the importance to develop and apply site specific structured operation and maintenance procedures

Pushing Energy Yield with Concentrating Photovoltaics

A 4J CPV module achieving 41.4 % efficiency at CSTC is presented in this paper. The high efficiency is enabled through the combination of high quality achromatic full-glass lenses with high efficiency 4J solar cells. This module has been built to demonstrate the potential of CPV module technology when improving the efficiency of the optical elements as well as the solar cell performance by integrating more junctions. The characteristics of the full-glass lens module are compared to a conventional Fresnel lens module. High efficiency is one of the keys to increase the energy yield of CPV power plants and to make the technology more competitive. Another aspect is the use of diffuse, scattered and albedo light resources which is typically not converted in high-concentration PV modules. Hybrid CPV modules combine high concentration PV with a flat-plate technology like silicon to push the energy yield even further. In this work, we present latest developments of our EyeCon hybrid module technology at Fraunhofer ISE and demonstrate the potential of a bifacial submodule (136 cm2) consisting of one silicon solar cell on which six concentrator cells are mounted. The technology has significant potential to extend the application area where CPV technology can compete with conventional flat plate PV

Worldwide Energy Harvesting Potential of Hybrid CPV/PV Technology

Hybridization of multi-junction concentrator photovoltaics with single-junction flat plate solar cells (CPV/PV) can deliver the highest power output per module area of any PV technology. Conversion efficiencies up to 34.2% have been published under the AM1.5g spectrum at standard test conditions for the EyeCon module which combines Fresnel lenses and III-V four-junction solar cells with bifacial c-Si. We investigate here its energy yield and compare it to conventional CPV as well as flat plate PV. The advantage of the hybrid CPV/PV module is that it converts direct sunlight with the most advanced multi-junction cell technology, while accessing diffuse, lens-scattered and back side irradiance with a Si cell that also serves as the heat distributor for the concentrator cells. This article quantifies that hybrid bifacial CPV/PV modules are expected to generate a 25 - 35% higher energy yield with respect to their closest competitor in regions with a diffuse irradiance fraction around 50%. Additionally, the relative cost of electricity generated by hybrid CPV/PV technology was calculated worldwide under certain economic assumptions. Therefore, this article gives clear guidance towards establishing competitive business cases for the technology

Outdoor experimental characterization of novel high-efficiency high-concentrator photovoltaic (HCPV) modules using achromatic doublet on glass (ADG) Fresnel lenses as primary optics

In this paper we present a comprehensive outdoor experimental characterization of the first modules assembled using the Achromatic Doublet on Glass (ADG) Fresnel lens technology. First, only the elementary units comprising one lens and one cell are investigated: the electrical performance is measured varying the cell-lens distance in order to identify the optimal focal distance. Second, a mono-module (module composed of one lens and one solar cell) has been assembled and installed on a two-axis tracker where it has been continuously measured between June and October 2018. Also, a monomodule including conventional Silicone on Glass (SoG) Fresnel lenses has been assembled and used as benchmark. Results demonstrated that the achromatic design of the ADG lenses used as Primary Optical Elements (POE) provides a significantly reduced temperature dependency of the module performance. The performance is maintained constant throughout the whole measurement period enhancing the energy output over time

ALCHEMI - a low cost, high efficiency, optoelectronic HCPV module for 1000× operation

This paper summarizes the current status of the ALCHEMI project, a European collaborative undertaking under the Solar-Era.Net co-fund scheme. The project’s aim is to develop novel, low cost, HCPV modules that operate at ∼1000 suns, and demonstrate a DC module efficiency of >37% under Concentrator Standard Test Conditions (CSTC), and a manufacturing process that will achieve costs <€0.9/Wp (<$1/Wp) in large volumes. Novel refractive optics have been designed and manufactured, and a bespoke high concentration solar cell grid design developed and applied to state-of -art commercially available multi junction solar cells. A significant contribution to cost reduction of the modules will be achieved by implementing assembly processes using surface mount technology and pick and place (PnP) tools as in the LED industry. The modules will be characterized on sun for an extended period in Cyprus, and CSOC (Concentrator Standard Operating Conditions) and CSTC (Concentrator Standard Test Conditions) power ratings will be determined, allowing a comparative analysis against conventional PV technologies installed side-by-side in the same location

Update on project ALCHEMI - A low cost HCPV module for 1000 sun operation

Project ALCHEMI is a Solar Era.Net funded European collaborative project, which is developing a low cost, high efficiency HCPV module using a previous design developed by Fullsun PV. In this project, the 625 sun Gen 1 module has been redesigned to operate at 1000 suns and further improved by the utilization of state of the art 3 junction solar cells from three different vendors. Through use of ~42% efficient cells, it is expected to achieve module efficiencies of <37%. This paper describes the cell and module test and assembly process and initial evaluation of how the next generation of module will be improved still further through another iteration of the design of the secondary optical element (SOE)