Direct conversion of solar energy to electricity by photovoltaic devices (solar cells) offers what may be the most promising of nearterm solutions to our energy problems. The federal government has been pushing the commercialization of photovoltaics by funding research on new materials and manufacturing processes.
Earliest commercialization is expected in residential systems where the power grid provides the backup. The Florida Solar Energy Center has been operating a 5 kw experimental residential facility for several months with encouraging results. Although the present payback rate is not attractive, the system is reliable and has produced 500 to 600 kilowatt- hours of energy in the poorer winter months at Cape Canaveral

Beach, Charles D.

Litka, Arthur H.

English

Embry-Riddle Aeronautical University

The Space Congress® Proceedings 1981 (18th) The Year of the Shuttle Apr 1st, 8:00 AM Photovoltaics, The Solar Electric Solution Charles D. Beach Florida Solar Energy Center Arthur H. Litka Florida Solar Energy Center Follow this and additional works at: https://commons.erau.edu/space-congress-proceedings Scholarly Commons Citation Beach, Charles D. and Litka, Arthur H., "Photovoltaics, The Solar Electric Solution" (1981). The Space Congress® Proceedings. 2. https://commons.erau.edu/space-congress-proceedings/proceedings-1981-18th/session-3/2 This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact commons@erau.edu. PHOTOVOLTAICS, THE SOLAR ELECTRIC SOLUTIONDr. Charles D. Beach Division Director, R&DMr. Arthur H. LitkaManager, Photovoltaic ApplicationsFlorida Solar Energy Center300 State Road 401 Cape Canaveral, Florida 32920ABSTRACTDirect conversion of solar energy to electri­ city by photovoltaic devices (solar cells) offers what may be the most promising of near- term solutions to our energy problems. The federal government has been pushing the com­ mercialization of photovoltaics by funding research on new materials and manufacturing processes.Earliest commercialization is expected in residential systems where the power grid provides the backup. The Florida Solar Energy Center has been operating a 5 kw experimental residential facility for several months with encouraging results. Although the present payback rate is not attractive, the system is reliable and has produced 500 to 600 kilo­ watt-hours of energy in the poorer winter months at Cape Canaveral.INTRODUCTIONSince the 1973 fuel shortages, there has been a steadily mounting interest in solar energy as an alternative to imported oil. In particu­ lar, attention has focused strongly on the photovoltaic (PV) solar cell technology—direct conversion of sunlight to electricity,A practical photovoltaic system was used to power a telephone relay system in 1955. The use of silicon solar cells in space began in 1958 with the launch of Vanguard 1. Hundreds of PV-powered spacecraft have a few thousand years of cumulative operational experience in space. No space flight has ended because of solar cell failure. In- addition to space applications, many remote terrestrial power applications, such as communication repeater stations, have been operated by private and governmental organizations for up to 10 years at power levels from one to several hundred watts.Photovoltaic energy systems provide a clean,simple method for direct conversion of sun­ light to electrical energy. They require no complex machinery, heat engine cycle, or intermediate conversion to heat; in addition, photovoltaic systems are silent. Since they are intrinsically modular, photovoltaic sys­ tems are potentially cost effective on a small scale.The systems are extremely flexible with re­ spect to system size (modularity) and siting, and they are reliable and safe. Their fuel source is non-depletable and secure, and silicon cell production is not limited by the availability of raw materials.The most significant drawbacks of PV systems are: (1) high cost of production, which re­ sults partly from their low efficiency (re­ quiring large collection surfaces), and partly from the current methods of production and deployment; and (2) the intermittent nature of the solar resource.Photovoltaic applications are frequently classified in four user categories:Stand-alone Systems for Remote ApplicationsThese are often the relatively small systems for telemetry, communication, lighting, and other utility purposes for which the site is manned or unmanned. The space systems are, of course, among the earliest applications but terrestrial uses include railroad signals, highway emergency telephones, and data collec­ tion from ocean buoys to mountaintops. Usu­ ally these systems are designed for inter­ mittent duty and have battery storage to supply the back-up power needed at night or during bad weather.Dispersed Grid-connected Residential SystemsOne of the most attractive PV applications is residential. Such systems could be designed to stand alone by using a large battery3-36storage bank or a small gasoline or diesel generator, but there is an economic advantage to using the power grid to supply the back­ up they need.Intermediate-load Centers.Commercial, institutional, community and in­ dustrial PV systems can provide for on-site power needs, and the excess energy produced can be supplied to the power grid. The loads on commercial and industrial systems occur primarily during daytime hours, so they are especially well matched to the PV system's output.Large-scale Central Station SystemsUtilities are accustomed to working with cen­ tral systems. However, a photovoltaic sys­ tem, because its output is proportional to the area used for collection, does not pro­ vide the usual economies of scale. With large central systems some savings can be achieved in balance-of-plant costs (the cost of hardware between the solar collectors and the load) and in operation and maintenance costs, if not in collector costs.FEDERAL PHOTOVOLTAIC PROGRAMThe Solar Photovoltaics Energy Research, De­ velopment, and Demonstration Act of 1978 (Public Law 95-590) provides for "an accel­ erated program of research, development and demonstration of solar photovoltaic energy technologies leading to early competitive commercial applicability of such technol­ ogies..." with the long-term objective of producing "electricity from photovoltaic systems cost competitive with utility-gen­ erated electricity from conventional sources." To achieve this objective, re­ search on advanced technologies, as well as technology development and cost reduction of baseline technologies, must be vigorously pursued.It is quite certain that this effort will be hindered by the present administration's budget reduction moves. Even so, under rea­ sonable circumstances photovoltaic systems could ultimately supply as much as 30 percent of the total U.S. consumption of electricity. For example, if electricity consumption in the year 2020 demanded the use of 80 quads* thermal, PV could displace approximately 25 quads.The principal numerical goal established by Congress is a system price goal of $1 perpeak watt (Wp)* in 1988 based on a PV cell cost of $0.50/Wp (Figure 1). If the goal is defined more precisely by specifying it in 1980 dollars, the $l/Wp target becomes $1.40/ Wp (1980$).To allow for some of ttie differences in ex­ pected readiness dates, the price goals could be refined by setting separate targets at $1.60/Wp for distributed (grid-connected) systems to be achieved in 1986, and $1.10 to $1.30/Wp for central station systems to be achieved in 1990, both expressed in 1980 dollars. The actual year of achievement is, of course, dependent upon many unpredictable factors.Another numerical goal is that 90 percent of all photovoltaic systems produced in 1988 be purchased by private buyers. The goal, as set by Congress, is not compatible with large government purchases, such as defense related purchases, purchases by federal utilities (TVA and Bonneville) or by state and local government entities (municipal utilities, schools, hospitals). However, large govern­ ment subsidized purchases may be the only way to effect the increased production needed to reduce cell cost by the target dates.The underlying philosophy of the federal government's photovoltaic program is to de­ velop and promote photovoltaic systems and technology to facilitate a healthy, self- sustaining, private market supplying competi­ tively priced electricity to grid-connected systems by 1986. The earliest target market ts in residential dispersed systems, an area wfiich will have a major impact on utilities, labor unions and financial and legal institu­ tions.Market stimulation is not the only tactic be­ ing employed to reduce PV cell costs. Several promising technological approaches have the potential to lower PV system prices enough to compete with conventional electricity sources. Research and development programs address both new materials and techniques for photovoltaic conversion and new approaches to high volume production of silicon cells.Various means of photovoltaic conversion are under investigation, such as luminescent dye concentrators, chalcogenide glasses, thermo- photovoltaics, multi-junction cells, and amorphous silicon. The two materials compet­ ing with silicon that are closest to commer­ cial readiness are cadmium-sulflde (CdS) andA quad is 10 (one quadrillion) Btu.The peak watt (Wp) rating is the power de­ livered under typical midday clear sky condi­ tions; a solar illuminance of 1000 watts per square meter.3-37gallium arsenide (GaAs). The CdS and related materials are suited to a high rate of appli­ cation to substrates, but they have lower efficiency than silicon; on the other hand, the GaAs cells will probably always cost more than silicon, but they offer higher efficiency and are amenable to use under concentrated solar radiation.There are several approaches under develop­ ment for low-cost production of photovoltaic collectors. Automation, mass production scale economies, and low-cost, high-volume process­ ing with inexpensive materials form the basis for manufacturing equipment development. Intensive efforts have been underway for several years to develop such production equipment and facilities for the baseline collector concepts (single-crystal silicon, both Czochralski (Cz) and ribbon, and some PV concentrators). These efforts have shown some very promising results.Although silica (SiO?) is the most abundant of all materials, one potentially important obstacle to photovoltaic industrial growth is the possibility of a severe shortage of refined, semiconductor grade, polysilicon material. Some polysilicon is produced by wafer manufacturers, but most is supplied to them by chemical firms.Polysilicon and photovoltaic industries anti­ cipate that a shortage will arise in the early to mid-1980's because of the unique situation current polysilicon producers face. The current refinement technology is capital and energy intensive, and it takes 3 to 5 years to bring new capacity on line. How­ ever, new technologies for refinement, de­ veloped both in the private sector and in the federal PV program, are nearing readi­ ness for scale-up to commercial production. These processes could reduce the cost of polysilicon refinement by a factor of six, and allow much greater refinement capacities. Thus, producers are reluctant to install con­ ventional refinement capacity that could be­ come obsolete.Several oil companies have recently acquired silicon module manufacturers. This is pre­ dictable, given the long-term nature of photo­ voltaic investments and the general compati­ bility between oil company corporate strategy and the promise of photovoltaic energy mar­ kets. The trend currently shows no signs of causing adverse effects on industry struc­ ture or on photovoltaic markets and prices. In fact, oil and electronic companies can be an important source of investment capital to PV firms. The health of the photovoltaic industry is good and should eventually im­ prove as prices fall and volume expands.RESIDENTIAL SYSTEMSThe earliest significant market penetration for PV systems is expected in the dispersed, grid-connected residential systems because of several factors, both technical and societal.o Power grid back-up provides for a reliable electrical system without storage costs.o A large market is present where even a small penetration can have a significant effect in terms of fuel savings.o Roof tops are available to avoid land cost, and eventually solar cells may be manufac­ tured directly on roofing material and thereby reduce system costs.o Tax credits are available at least for a limited time, giving a greater benefit to homeowners than they do to commercial and industrial users.o Residential systems are more amenable to de­ sign and size standardization than are sys­ tems for other applications, and unlike many electrical generating systems, small systems are just as efficient as larger ones.o A highly dispersed solar energy source pro­ vides a better hedge against the effects of bad weather than does a large central sys­ tem.On the other hand, residential loads profiles generally are not as well matched to PV output as are some applications. In Florida and other areas that have high air-conditioning loads, utilities are able to benefit from the contribution of PV systems during the day even though their peak loads may extend two or three hours beyond the daylight hours.Many complex problems are associated with the utility interconnection. From the utility perspective the attractiveness of distributed PV systems supplying electricity to the grid depends on pricing policies of the regulating authorities, the need for daytime power gen­ eration sources and the ability to maintain, control and operate the grid safely and reli­ ably.In 1980 the Florida Solar Energy Center began to promote the commercialization of residen­ tial photovoltaic systems by building a full- scale experimental photovoltaic residential facility on FSEC grounds. (Figure 2) Al­ though primarily built with state funds, Florida Power and Light Company and MIT's Lincoln Laboratory (administering DOE funds) have contributed some financial and technical support to assist FSEC with hardware and data acquisition.3-38This conventionally structured, energy-effi­ cient, load-controlled and fully instrumented facility is providing the Center with valu­ able experience in PV residential applica­ tions. The system employs 5,000 Wp of stand­ off-mounted PV roof modules which are inter­ faced to the utility through a line-synchro­ nous inverter. Interconnection of the solar panels to the 220 vac supply is shown in Figure 3. The line-synchronization requir­ ed by the inverter means that if the ac line is shut down, no power, ac or dc, comes out of the inverter.Approximately three full months of operating data have been collected on the PV house. During that time the only operating appli­ ances in the house were the heat pump serv­ ing to heat and cool the house and a small dedicated heat pump used to heat household water. Most of the energy supplied by the PV system during that time has been trans­ mitted out of the house (running the kilowatt- hour meter backward) and used by other loads throughout the Center.During the initial data collection period, December 1980 through February 1981:o Average solar irradiance on the 62.5m panels was 264 kilowatt-hours/day, very close to the December-February average of the past three years at FSEC.o Overall system conversion efficiency is about seven percent; that is, 1651 kilowatt- hours were delivered by the system. This is an average of 18.3 kilowatt-hours/day.o The inverter operates with an ac output/ dc input efficiency of 85 to 90 percent, depending on input levels.This experiment will continue with data to be collected on the operation of the system into various typical household loads. Different inverters will be used in the system to com­ pare their relative efficiencies and power quality. These technical performance data will be used to verify design and simulation techniques as they are developed.Three interrelated areas of technical assess­ ment are being investigated in the PV resi­ dence :1. Residential PV design2. Subsystem integration3. System analysis verification through operations performance.The close relationships of system design and subsystem integration are being fully address­ ed with this facility. Overall design con­ siderations, such as optimum array sizing and interconnection, have been studied throughthe facility, as well as the procedures nec­ essary to mechanically, electrically and aesthetically integrate the PV array modules onto the roof structure. Other areas of subsystem integration assessment have includ­ ed the power conditioning/utility interface equipment, lightning protection equipment, possible on-site storage options and perfor­ mance optimization equipment (i.e., maximum power trackers and peak electrical demand controllers). Concurrent with the above, maintenance requirements and durability per­ formance are continually being monitored by FSEC personnel.With this operational experience, the facil­ ity will provide the technical support to those industries, professions and trade groups which must necessarily be involved to achieve widespread commercialization of PV systems. These groups include the scientific and engineering community, academic institu­ tions, architectural and building trades associations, the utility companies and the legal and financial communities. Local, state and federal officials and various special interest organizations should also benefit by this effort.BIBLIOGRAPHYSelected U.S, Department of Energy Reports:Watktns, 6, A, et al, Photovoltaic Institu­ tional Issues Study, SAND 79-7054 Sandia National Laboratories, (April 1980).Jet Propulsion Laboratories, Photoyolta ic Program, Systems Development Plan 5240-5 (August 1980).Burt Hill Kosar Rittelmann Associates, Resi­ dential Photovoltaic Module and Array Re­ quirements Study Final Report DOE/JPL/955149-1 (June 1979).U.S. Department of Energy,Photovoltaic Sys­ tems Program Summary DOE/ET-0019/2 (December 1978).PRC Energy Analysts Co., Solar Photovoltaic Applications Seminar; Design, Installation and Operation of Small Stand-alone Photovol­ taic Power Systems DOE/CS/32522-T1 (July 1980),Jet Propulsion Laboratory, Federal Policies to Promote the Widespread Utilization of Photovoltaic Systems DOE/CS-0014/1 (February 1980).3-39201975 DOLLARS PER PEAK 15 WATT @28°C10 8 6 4 2 046 130 200 kW kW kW (FLAT-PLATE ARRAY PURCHASES)"| | (CONCENTRATOR ARRAY PURCHASES)I I 25° 1 1 kW KEYI i T- 1 H AVERAGE OF MULTIPLE BUYS (ACTUAL) ± | | D SINGLE BUY (ACTUAL) ~ 1 • 1 • GOAL- 4 \|1 \ INTRODUCTION OF AUTOMATION D \ NEW MANUFACTURING TECHNOLOGY• \($7) ($8) •I 1 1 1 1 1 1 1 ?~" 1 •1976 1978 1980 1982 1984 1986FIGURE 1. U.S. Department of Energy photovoltaic price goals compared to historical trend.FIGURE 2, Florida Solar Energy Center's experimental photovoltaic-powered house (rear1 view),340Power GridAC Power Flow to and from Utility House LoadsLine Synch. InverterDC from Solar PanelsFIGURE 3. Diagram of the photovoltaic system's DC to AC interface through a line-synchronous inverter.3-41

Photovoltaics, The Solar Electric Solution

https://commons.erau.edu/cgi/viewcontent.cgi?article=2540&amp;context=space-congress-proceedings

Photovoltaics, The Solar Electric Solution

Abstract

Similar works

Full text

Available Versions

Embry-Riddle Aeronautical University