Wednesday at the PVSC was somewhat different than the other days with the poster session in the morning before the close of the exhibit hall and also beginning early with the 5k fun run. It was an excellent day though with many good interactions, talks, and posters.
In the Concentrator Cells, Modules, and Systems session at 8 am, John Lasich of Solar Systems reported on the final 140 kWp Heliostat PV concentrator systems, which showed DC efficiencies ranging from 24-26%. The session also took note of the fact that ~1 MW of dish systems using III-V multi-junction solar cells are deployed in the field.
The morning poster session included many interesting posters. Several posters concerning quantum III-V quantum dots in a III-V matrix material grown epitaxially described how growth conditions and materials selection can affect the performance of resulting devices.
In the Area 9 posters Chris McDermott whose company owns and leases commercial warehouse space in the NY-NJ area purchases and installs PV on their facilities. The lack of available performance data prevents making informed purchasing decisions. The decision to invest in PV makes sense in the NJ market, due to NJ’s solar RECs market. Drew Torbin described ProLogis’ business model for installing PV on the warehouse and distribution facilities. In the U.S., ProLogis enters into an arrangement with the local utility. The utility owns the PV and compensates ProLogis for the use of the roof. Considering the magnitude of warehouse roof space across the country, this could be a promising market for PV.
In the afternoon in Area 4 Dr. Henley of Silicon Genesis described impressive waftering methods that can yield (111)-oriented wafers without kerf losses. A talk by Tim Van der Wood provided an overview and description of the use of Raman spectroscopy through a confocal microscope to characterize Si solar cell materials. In characterization of a laser drilling experiment, results showed that a short etch will remove all of the strained material created by the drill hole. J. Kraiem of Apollon Solar spoke about the progress in use of metallurgical grade Si in solar cells.
Presentations in the Area 6 session included Art Cornfeld, described an inverted metamorphic (IMM) solar cell by Emcore, with close to 33% AM0 efficiency and a high specific power of 3.6 W/g. The IMM cell is particularly suited for flexible lightweight satellite solar panels. Ben Cho discussed the AIAA S-111 qualification testing of Emcore's 29.5% AM0 efficient GaInP/.GaInAs/Ge ZTJ solar cell, which exhibits high radiation hardness (84% power @ 1E15 1MeV e-) and excellent resistance to reverse bias breakdown (avg -33.5V). P. Stella of JPL described a power analysis tool to provide accurate power analyses and have been responsible for the rovers to exceed their original 90 day mission lifetime. In a later talk the use of PV to power missions to two asteroids was described in which it was emphasized that the amount of power available greatly affects the number of experiments that can run as well as providing power to ion thrusters. P. Jenkins described a 1 year mission plan to evaluate a variety of cells in high radiation environments.
In the Area 9 panel there was a lively discussion of challenges to deeper utility grid penetration of distributed PV and novel incentive policies such as solar renewable energy credits (SREC's) clearly indicate that state policies remain as important as federal to the acceleration of PV adoption. Michael Winka, NJ Board of Public Utilities, is the man most responsible for designing NJ’s solar RECs market and the suite of public policies that make NJ one of the top two best markets for PV in the U.S. He says that NJ decided to create a solar RECs market in order to pay for the investment over time and minimize ratepayer impact. Kathleen Weiss, First Solar’s Vice President for Government Affairs, proclaimed NJ’s public policies aimed at growing facilitating the PV market among the best in the nation, along with CA. She said First Solar expects to reach its goal of $1/watt by 2012. John Baker, Chief Strategy Officer of Austin Energy, described the utility’s plans to incorporate 300 MW of distributed PV on their system. He also stated the City’s goal of powering city government buildings 100% by renewable energy by 2020.
In the later afternoon Area 3 session Spectrolab reported a cumulative production of 680 kW of multijunction cells for space and 27 MW for CPV applications. They have reduced costs by 20% in the last year, mostly through automation, and expect to reduce cost by another factor of 2 by 2011. Three years field experience of multijunction cells operating under high concentration at Solar Systems shows no measurable degradation. Instituto Energia Solar reported a two-junction GaInP/GaAs record efficiency of 32.9% at 500-1000X and 31.1% at 2900X.
In the Area 2 session Robert Collins' invited review provised a comprehensive introduction and overview of the power of real time CdS/CdTe growth monitoring with modern spectroscopic ellipsometry. Collins talk provided an insight into the power of optical spectroscopy, specifically spectroscopic ellipsometry, to provide an in situ, on-line, monitor for the PV community to use in research deposition systems as well as solar module production systems. Dave Albin presented data on the use of two different bilayer TCOs for CdS/CdTe growth: cadmium stannate/zinc stannate and SnO2:F/SnO2. He showed that the ZTO was susceptible to interdiffusion from CdS during damp heat stressing and suggested that this deterioration mechanism can be improved with processing adjustments to control strain in the CTO/ZTO layers. The damp heat data of Albin and C-V measurements also pointed to the role of positive Cu ions electromigrating under the influence of the collection field near the junction. Victor Plotnikov, grad student, presented a detailed study of achieving good cell performance with the thinnest possible CdTe layers. He achieved 9.7% efficiency with only 0.5 microns of CdTe and 6.8% with only 0.3 microns. Bifacial J-V analysis helped identify the limiting mechanisms and point toward further improvements. In a talk by Dr. Sampath of Colorado State made the point that the CdCl2 is critical to the stability of CdTe/CdS solar cells in accelerated lifetime tests. At the end of the session Dr. Ayodhya described >10% efficient CdTe cells on flexible substrates on polyimide.
In Area 5 a unified view was presented of the wide range of silicon-hydrogen microstructure defects. A novel glass/seed layer method was also described for growth of thin (8 micron) c-Si devices with a PV conversion efficiency of ~ 8% without light trapping. Applied Materials first substantial paper was presented describing a 5.7 m2 tandem micromorph modules with an ~8% efficiency.
For Area 4 Jan Schmidt described lifetimes in specialized Al-doped Si and showed a 1000x improvement in lifetime compared to Al-doped Czochralsky wafers. A contribution from REC Wafer described 17% efficient multicrystalline Si devices with reduced dislocation densities.
