Concentrated photovoltaic (CPV) technology has always s been the flagship for record efficiencies. The CPV stream represents the topmost recorded conversion efficiency of 46% for a PV device. This highest efficiency has been attained at the cell level by a joint research group from the Fraunhofer Institute of Solar Energy Systems (ISE) in association with its French partners Soitec and CEA Leti in 2014. On Feb. 23, the Freiburg based research center even announced a 43.4% efficiency for a mini-module comprised of four-junction solar cells and high efficiency optics. However, ISE will reveal the details about its innovation at a later date and a more appropriate platform – the CPV12 International Conference on Concentrator Photovoltaic Systems, which will take place from April 24 to 27, 2016. Nevertheless, a joint report (Current Status Of Concentrator Photovoltaic (CPV) Technology; Authors: Simon Philipps et al.) prepared by ISE in cooperation with National Renewable Energy Laboratory (NREL) published in February 2016 provides some insight about this record level performance as well as latest updates about the CPV segment.
Basics of CPV
The fundamental principle of CPV is to use optics to concentrate the sunlight hitting a solar cell, which enables to reduce the solar cell area dramatically. This allows employing high efficiency, but the cost of the solar cells are rather expensive. The cells used in a CPV module is determined by the concentration factor. Concentrating the sunlight between 300 to 1000 times, generally termed as high concentration photovoltaics (HCPV), typically employ multi-junction solar cells based on lll-V semiconductor materials. Low concentration (LCPV) design with a concentration factor of less than 100 times generally use crystalline silicon cells. ISE's record module is designed for HCPV consisting of a single full glass lens and a wafer bonded multi-junction solar cell. The cell is based on a four-junction configuration: GaInP/GaAs//GaInAsP/GaInAs.
HCPV has several advantages: The cells have higher efficiencies and have lower temperature coefficients than traditional crystalline cells. The later is beneficial when the operating temperatures are high. These PV systems are equipped with trackers that allows stable electricity production throughout the day. According to the above mentioned study, the CapEx requirement can be lower for CPV compared to a standard flat PV panel. A 2014 analysis (A Bottom-up Cost Analysis of a High Concentration PV Module, Presenters: Kelsey Horowitz) by NREL for a specific HCPV system with a Fresnel lens primary optic and refractive secondary lens revealed that the total capex for cells and modules of a vertically integrated company is around $0.55 per W (DC), with a possibility to further lower this level by varying the design. The joint report of ISE and NREL underscores that most HCPV companies have their optics and cells manufactured by a third party, which reduces the CapEx burden considerably.
Competitive LCOE?
However, CPV is not strong at all when it comes to commercial activities. According to the latest update report, only 360 MW of total CPV capacity was installed by by the end 2015. Worldwide manufacturing capacities strongly decreased in 2015 due to two leading CPV producers – Soitec and Suncore – closed their manufacturing facilities. The main standing block for this stream of PV is the difficulty to compete with traditional mainstream crystalline silicon technology, especially tremendous progress it made in reducing module costs by taking advantage of its manufacturing scale. However, CPV supporters claim to be competitive on the levelized cost of electricity ground in sunny areas with higher proportions of direct sunlight. According to a 2013 study from ISE on Levelized Cost of Electricity – Renewable Energy Technologies (Authors: Christoph Kost et al.), which also evaluated CPV, the price of a CPV solar park with a 10 MW installed capacity was in the range of €1,400 to €2,200 per kW. This translates to electricity generation costs of €0.10 to €0.15 per kWh at locations with a DNI of 2,000 kWh/(m²a) and €0.08/kWh to €0.12/kWh with 2,500 kWh/(m²a).
The same report highlights that CPV has a potential to reduce costs with continued development. It anticipates that if installations grow further by 2030, system costs would decrease to €700 to €1,100 per kW and the corresponding generation costs would go down to €0.045 to €0.075/kWh.
High efficiency is the key driver for cost reduction in CPV. The best lab cell efficiency has already reached 46% and the top efficiency for a large area module is 38.9%. Looking at previous progression of CPV, commercial cell efficiencies quickly follow the levels attained in the lab. In this context, ISE's announcement of attaining 43.4% efficiency for a mini-module has a lot of significance.
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