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United States of America Photovoltaic technology status and prospects Ward Bower, Sandia National Laboratories1, Albuquerque, New Mexico |
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The U.S. Department of Energy's (DOE) Office of Energy Efficiency and Renewable
Energy directed the U.S. PV Program through its Office of Solar Energy Technologies
in the U.S. and was part of an overall Solar Energy Technology Program. The “Office
of Solar Energy Technologies” refocused all of its renewable energy work into
a systems-driven approach strategy whereby the market needs now have greater influence
in determining priorities for future research and development (R&D). The U.S.
DOE was the primary funding source for PV research and development in 2004, and
it directed the resources of its national laboratories to assist in the PV industry's
applied research and development activities. The Office of Energy Efficiency and
Renewable Energy led the national laboratories to develop a comprehensive operating
plan based on a strategic, multiyear technical plan that responds to the broad
policies for energy R&D determined by the executive and legislative branches of
the federal government. The National Center for Photovoltaics (NCPV) continued
working with the PV industry through various cost-shared programs to develop and
improve component designs, device manufacturability and systems components and
systems. Education, technical transfer, technical assistance and competitive contracts
were used extensively to accomplish the work in 2004. Photovoltaic-related activities
were allocated to PV cell and module development, manufacturing processes, balance-of-system
and system technology categories. The U.S. Department of Energy web site http://www.eere.energy.gov/
solar provides up-to-date information on and links many of the PV activities in
the United States.
The "U.S. Photovoltaics Industry Roadmap," was updated in September 2004, and continues to unify the vision, long-term strategies and goals for the PV industry through 2030. The vision goals are geared toward the electrical/energy consumer, competitive and environmentally friendly energy products, and services from a thriving U.S.-based solar electric power industry. The “DOE Solar Energy Technology Program - Multi-Year Technical Plan 2003-2007 and Beyond” (MYTP) remained in concert with the “Industry Roadmap” to help guide the National PV Program activities to reflect a systems-driven approach (SDA) to R&D.
The NCPV, an alliance of technical organizations, continued to
serve as the focal point for the nation's capabilities in PV. The R&D goals and strategies were formulated in concert with the “Industry Roadmap” and through the NCPV “Annual Operating Plan.”
The “Annual Operating Plan” was coordinated with the MYTP and
focused on the Systems-Driven Approach. It is also used to
coordinate work for PV and “Solar Thermal” technologies.
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The National PV Program research is focused on increasing domestic capacity by
lowering the cost of delivered electricity from PV and improving the efficiency
of PV modules and systems. Laboratory and university researchers worked with industry
on high-volume, low-cost manufacturing, such as increasing deposition rates to
grow thin-film layers, improving materials utilization, reducing cost, improving
reliability and using in-line monitoring to increase yield and performance.
Specific goals were not changed in 2004 and were to:
These National PV Program R&D activities were directed through the U.S. Department of Energy with headquarters in Washington, DC, and by research centers at the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (Sandia). Overreaching goals of the U.S. PV activities were the “acceleration of the development of PV as a national and global energy option,” “assurance of the technology” and “global market leadership for the nation.” The dissemination of information pertaining to PV technologies is handled through printed reports, web sites, conferences and workshops. Two such SDA direction-related workshops for inverters and energy storage were held in 2004. The National Solar Program shared the costs in areas of fundamental research, technology development and advanced materials and devices. The authorized funding for PV was categorized into three major areas for FY2004. They were as shown in the following.
The FY2004 federal budget for the Photovoltaic component of the National PV Subprogram totaled USD 76,5 M. Additional funding for PV-related R&D was administered through state and local governments, partnerships, and through PV industry cost sharing.
The NCPV relies on the core expertise of NREL and Sandia National
Laboratories to create, develop, and deploy PV and systems-related
technologies. Other national PV resources that the NCPV draws
on are Brookhaven National Laboratory, two Regional Experiment
Stations (the Florida Solar Energy Center and the Southwest
Technology Development Institute), and U.S. DOE Centers of
Excellence at the Georgia Institute of Technology and the University of Delaware (Institute of Energy Conversion). In addition, more than 90 university, industry and utility research partnerships across the country are linked together. The NCPV awards most of its federal funds through competitive procurements requiring cost sharing to industry, and through contracts to universities, and other research facilities.
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Major advancements were achieved in first-time manufacturing of three thin films (CIS, CdTe, and a-Si), taking fiscal year US productions levels up from about 12 MW in FY2003 to about 20 MW in FY2004:
Significant progress has been made in the area of thin-film CIS and related materials. For example, for small laboratory devices, totalarea conversion efficiency of 19,5 % has been achieved by NCPV scientists. Using a ZnS buffer layer, a total-area conversion efficiency of 1,4 % has also been achieved by NCPV scientists.
Phase II of the DOE “High reliability Inverter Initiative” began late in 2003. Three contractors were selected to complete Phase II projects aimed at developing a prototype; finalizing development of new inverter designs; assess, test and validate new designs; and validate compliance to utility-interconnection standards. All manufacturers are working to assure UL listing, quality control programs and highly accelerated life testing.
The R&D for Phase II resulted in:
Phase III is scheduled to be conducted with at least two contractors. It will be structured to refine prototypes into commercial products. Final products will be validated through laboratory evaluations, UL listings, environmental testing, and long-term evaluation. Issues pertaining to environment, safety and health remained an essential aspect of working with the balance-of-system industry, and are included in all work sponsored by the National Solar Program.
To accomplish HiPerf's objective, the National Center for Photovoltaics (NCPV) directed in-house and subcontracted research through the "High Performance PV-Exploring and Accelerating Ultimate Pathways" solicitation in high-performance polycrystalline thin films and multi-junction concentrators. Two specific objectives of this research included bringing efficiencies for thin-film cells toward 25 %, (for modules toward 20 %) and creating 33 %-efficient multijunction concentrators. The objectives were met by achieving a record efficiency of 37,3 % for a 3-junction terrestrial concentrator cell, and working toward the design of a high-concentration module with efficiency greater than 33 %. It is expected that the project's three phases will steer high-efficiency technologies toward commercial, prototype products. Each phase of the project focuses on a specific approach to solving the problems associated with high efficiencies. Phase IB is a continuation of Phase I and addresses exploring and accelerating ultimate pathways to reach the project's long-term goals.
Other areas of crystalline R&D included large-scale PV module manufacturing using ultra-thin polycrystalline silicon solar cells, innovative approaches to low-cost module manufacturing of stringribbon silicon PV modules, EFG technology and diagnostics R&D for large-scale PV manufacturing, and development of an in-line minority-carrier lifetime monitoring tool for process control during fabrication for crystalline silicon solar cells.
In an effort to accomplish the objectives, renewal for active “In-Line Diagnostics and Intelligent Processing” contracts was completed. Also completed were the “Letters-of-interest” review, source selection, and initiated awards under the “Large-Scale Module and Component Yield, Durability and Reliability” solicitation.
Sandia also urged industry to participate in “Highly Accelerated Life Tests (HALT™)” and “Highly Accelerated Stress Screens (HASS™)” to improve quality and reliability of hardware. The test facilities at Sandia and NREL continued to contribute significantly to all of the reliability-improving programs.
Sandia and NREL conducted PV module performance and durability studies for manufacturers. For new PV modules, or for those that have operated in the field for years, researchers collect data on electrical performance, physical properties, integrity of solder joints, and properties of encapsulants. Evaluations included outdoor electrical performance, dark current/voltage (I-V), infrared (IR) imaging, ultraviolet (UV) inspection, solder-joint metallurgy, and ultrasonic characterization, as well as destructive testing for specific failure modes.
The inverter test facility at Sandia continued to provide critical characterization, benchmarking, surge testing and accelerated life testing. The 30-kW hybrid test bed for inverters, designed for grid-connected or stand-alone PV systems was in operation as the Distributed Energy Test Laboratory (DETL). It included a complete mini-grid control unit and a 75-kVA micro turbine; a 90-kVA diesel; and load banks that are resistive, inductive, and capacitive in nature. The DETL was used to verify tests and procedures called out in standards, and to aid a certification test protocol for inverters.
Sandia National Laboratories' Distributed Energy Technologies Laboratory (DETL) performed numerous evaluations and performance studies of PV inverters ranging in size from 100Wac to 75kWac. Inverter evaluations involve two types of products (readily available and developmental prototypes). Standardized test protocols were developed at the DETL. The DETL grid-tied test protocol included tests for compliance to today's standards. Examples are IEEE Std. 519 for harmonic distortion, FCC Part 15 for radio-frequency emissions, and IEEE/ANSI 62,41 for surge voltages in low voltage ac power circuits.
NREL maintained the Outdoor Test Facility (OTF) to test performance and reliability of solar cells, modules, and small (1-5 kW) systems. The OTF also calibrated primary reference cells for use in-house, by other national laboratories, by industry, and by universities. Researchers at the OTF measured performance in actual outdoor tests and using solar simulators indoors. Indoors at the OTF, modules were tested for failure and performance in conditions of high voltage, high heat, high humidity, flexing, static loading, and simulated hail strikes. Outdoors, the test beds at the OTF measured long-term performance and stability. Two test beds performed stress tests of modules under accelerated conditions of high voltage and high sunlight concentration.
Sandia's “PV System Reliability Plan,” drafted in consultation with industry, continues to guide hardware and system development. The plan recommends continuation of several activities such as developing a reliability database to improve understanding of the performance of real systems; examining PV systems and components after extended operation in the field to identify sources of performance degradation or failures that could be prevented by changes in manufacturing; modeling system performance to identify fault-tolerant designs, sensitivities to component failure, cost-effective component replacement strategies; and working with industry and users to resolve technical or institutional barriers to system reliability.
As more installations of PV systems occur, the electrical and personnel safety of the systems are undergoing more thorough examinations by designers, installers, inspectors and users. Vital utility and industry issues, such as codes and standards, were continuing activities in the National Solar Program. The program supported work to provide a consensus of industry input into the National Electrical Code® (NEC®), listing and certification standards, and numerous standards activities in both the domestic and the international arenas. Sandia National Laboratories led Industry Forum work for the 2005 National Electrical Code (NEC) with proposals and balloting processes for PV system installation updates. The 2005 NEC was published in September 2004.
Sandia National Laboratories led efforts to draft a “Performance Test Protocol for Evaluating Inverters Used in Grid-Connected Photovoltaic Systems.” The document, while still being refined is now being considered by several state-supported incentive programs as new trends toward performance based incentives are emerging.
The IEEE 1547 “Standard for Interconnecting Distributed Resources with Electric Power Systems” is being incorporated in utility interconnect guidelines. Four additional tasks for the standard continued to be developed. Underwriters Laboratories continued new updates for the UL1741 "Standard for Static Inverters and Charge Controllers for Use in Photovoltaic Power Systems" and expanding the standard to include inverters for all distributed generation.
The “National Voluntary Certification Program” for PV installers was developed with the support of the U.S. DOE PV Program and was launched in 2003. The North American Board of Certified Energy Practitioners (NABCEP) now certified over 200 installers. NABCEP testing is conducted twice a year.
The quantity of PV modules produced in the United States in 2004 reached 135 MW
and grew at more than 30 % in 2004. Photovoltaic installations in the U.S. grew
to more than 85 MW. The U.S. PV applications in 2004 involved virtually all market
sectors with the exception of the central power application. The majority of the
growth was in the grid-connected sector.
The U.S. now installs more than 50 MW per year of grid-connected systems. Approximately 25 MW of small, 2- to 4-kW roof-mounted systems are installed on private residences. The systems use all types of PV modules and are sometimes connected to a multiple mode inverter that permits the PV system to first serve the building's load and then to send excess power to the utility grid. When the grid power is not available, the inverter may be designed to switch to “standby” and power the local load from energy stored in a battery bank.
There are several mainstay inverter manufacturers serving the U.S.
market today. Many new inverter manufacturers emerged in 2004
and those new products continue to be listed for safety and were
being commercialized in 2004.
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Working with the states and supporting the North American Board of Certified Energy Practitioners for a “Voluntary National Certification Program for Practitioners” remained important activities for the IREC program in 2004. IREC sponsored numerous workshops and special sessions at PV conferences.
International work included continuation of the Mexico Renewable Energy Program that was sponsored by the U.S. Agency for International Development (USAID) and supported by the U.S. Department of Energy, to institutionalize the use of renewable energy technologies. This program had been honored as one of the most successful renewable energy programs for USAID and continues to serve as a model for increasing the use of PV in other parts of the world. The projects were implemented in partnership with local Mexican organizations in each geographical or political area to purchase, finance, install and maintain the sustainable systems. This program is resulting in wide-ranging system replication, through increased awareness of the benefits of renewable energy technologies, and improved private sector capacities to serve the market.
The NCPV support, such as training and technical assistance in Bolivia, Brazil, China, Ghana, Guatemala, Honduras, India, Indonesia, Kenya, Mexico, Morocco, Nigeria, Pakistan, the Philippines, Russia, South Africa, and Venezuela, has helped U.S. companies continue to make inroads into the international market.
The U.S. DOE Million Solar Roofs (MSR) Initiative promoted the use of PV and solar thermal to reduce the energy demands of buildings.
It enabled businesses and communities to install solar systems on
one million rooftops across the U.S. The Million Solar Roofs Initiative was designed to support states and local communities as they developed a strong commitment to the sustained deployment of solar energy technologies. Fifteen new MSR State and Local partnerships during FY2004 were added, bring the total to 89. In addition, 125 businesses, electricity providers, organizations, and agencies joined Partnerships, bringing the national total of participants to 822 MSR was awarded USD 1,6 M in State and Local Partnership grants - combined with USD 767 K in cost-share - to support localized efforts to remove barriers and develop local markets for solar energy technologies. Finally, MSR initiated/funded a telecommunications study involving Bell South, Verizon, and Emerson to explore opportunities for solar on switching stations to support their operations.
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The U.S. Department of Energy, in partnership with its national laboratories,
will continue with important PV initiatives through the DOE Solar Energy Technologies
Program. The “Industry Roadmap” and an updated “DOE Solar Energy Technology Program
- Multi-Year Technical Plan 2003-2007 and Beyond” will guide the work using a
“Systems-Driven Approach” to determine priorities based on market needs. The research
and development and technical advances will include all of the components, interconnects,
and materials needed for a viable PV industry. PV materials, advanced cells, improved
manufacturing processes, advanced balance-of-system hardware, higher reliability,
high-tech inverter/BOS/systems development, fire and personnel safety, codes,
& standards, hardware certification and practitioner certification will remain
vital elements in the program.