Optics and Photonics Essential Technologies for Our Nation (2013) / Chapter Skim
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5 Energy
5 Energy
Pages 127-162
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From page 127... ...
: "Solar energy could potentially produce many times the current and projected future U.S. electricity consumption."1 Inertial confinement fusion is a potential optical technique that could generate abundant energy in the future2,3 A recent article discusses the National Ignition Facility, which has a near-term goal of achieving ignition (defined as 1-MJ [megajoule]
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From page 128... ...
Concentrated photo voltaic (CPV) power generation involves the use of solar cells after the incoming light is concentrated.
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From page 129... ...
With CPV, higher-cost, and more efficient, solar cells can be used. The cost of the concentrators will be the main issue, as stated in the NAS-NAE-NRC report Overview and Summary of America's Energy Future: Technology and Transformation published in 2010: "In general, nearly all of the costs involved in using renewable energy for power generation are associated with the manufacturing and installation of the equipment."7 For high-concentration CPV, more concentrating options are available for larger electric plants, and so CPV may favor utility-scale plants over the smaller plants used by an individual.
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From page 130... ...
Solar cells have become common in applications for which grid power is not ac cessible (see Figure 5.1) or convenient, such as powering remote devices or small handheld electronics.
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From page 131... ...
. This is a more realistic cost for an investor to use when comparing a solar plant to other potential electricity generation alternatives.
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From page 132... ...
SunShot Initiative is a collaborative national initiative to make solar energy cost competitive with other forms of energy by the end of the decade. Reducing the installed cost of solar energy systems by about 75 percent will drive widespread, large-scale adoption of this renewable energy technology and restore U.S.
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From page 133... ...
With current solar cells, the temperature of the cells must be kept near room temperature in CPV in order to maintain high efficiency, and so an efficient heatremoval process must be used. CPV solar cells have been measured at 1,000 Suns concentration and 43 percent efficiency,13 and it is anticipated that at least 2,000 Suns concentration can be used, although it may cost some conversion efficiency.
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From page 134... ...
There will be installation costs and possible cost of land use for electric plants. As with all methods of generating electricity, there will be environmental considerations, such as the impact on a desert when large areas are covered by reflectors or solar cells.
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From page 135... ...
Investor literature for major solar cell manufacturers does promise reaching the cost parity level of $1.00/W for installed cost around 2015.17,18 Obviously investor literature may be optimistic, but major PV solar cell companies at least have plans on how to meet the dollar per watt cost goals. The LCOE of photovoltaics continues to drop due to manufacturing infrastructure improvements and more advanced technologies becoming available.19 Figure 5.4 shows installed cost LCOEs for a number of installed projects based on a very recent National Renewable Energy Laboratory article.20 17 More information on the First Solar corporate overview, third quarter, 2011, is available at http:// www.firstsolar.com/.
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From page 136... ...
Solar Energy Materials and Solar Cells 90(18-19)
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From page 137... ...
Production of first-generation solar cells is highly competitive, with no single company holding a market share substantially larger than 10 percent, and different companies leading in each geographic region.24 The focus for advancing first-generation solar cells is on reducing manufacturing costs. It is not expected that this technology will be capable of being produced for less than $1.00/W installed cost.
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From page 138... ...
FIGURE 5.6 Eighty-megawatt thin-film cadmium telluride (CdTe) -based solar plant in Canada.
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From page 139... ...
2011. "27.6% Conversion Efficiency, a New Record for Single-Junction Solar Cells Under 1 Sun Illumination." 37th IEEE Photovoltaic Specialists Conference 000004-000008.
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This has some similarities to concentrated solar power, discussed below. The low-concentration systems typically use conventional single-junction solar cells and rely on the optics being inexpensive enough that the reduced PV material required justifies the added cost of concentrating.
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Energy 141 FIGURE 5.7 A high-concentration photovoltaic panel using Fresnel lens optics and III-V solar cells. SOURCE: Courtesy of Amonix.
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North America and Europe are expected to maintain dominance in this market, with the rest of the world gaining some market share. The best 35 Frost and Sullivan Research Service.
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FIGURE 5.9 Expected installed capacity of concentrated solar power market divided regionally, and compound annual growth rate; 2010 is the base year. SOURCE: "Global Solar Power Market." Frost and Sullivan analysis.
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From page 144... ...
This larger temperature difference allows more ef ficient electricity generation than the common trough technology, with conversion efficiencies in the range of 20 to 35 percent.41 Power tower systems offer a much more efficient alternative to the parabolic troughs that currently dominate the CSP landscape. In addition to the greater conversion efficiency, the power towers make more efficient use of the land, and the heliostats are less expensive to manufacture and maintain than the parabolic 37 Frostand Sullivan Research Service.
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FIGURE 5.11 Eleven megawatt Solar Power Tower near Seville, Spain. SOURCE: Courtesy of Abengoa Solar.
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A reflective parabolic dish tracks the Sun and focuses onto a small power-conversion unit. A heat-transfer fluid is heated several hundred degrees Celsius and is subse FIGURE 5.12 A dish solar thermal power generation module test unit in Phoenix, Arizona.
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From page 147... ...
This waste heat can either be recycled to generate more electricity or can serve a variety of other uses, such as the heating of water.43 The primary difficulty is that most PV chips become less efficient as they increase in temperature. Wide-bandgap materials will work better for solar cells at higher temperatures, but there will still be a loss of efficiency.44 Researchers at Stanford University are conducting research on a "photovoltaic-like" device that becomes more efficient at higher temperatures, which would be ideal for integration into a hybrid system.45 The Stanford approach, also discussed in a paper by Andrews et al.,46 has calculated efficiencies for an idealized device, which can exceed the theoretical limits of single-junction photovoltaic cells.
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From page 148... ...
It would be possible to make a system optimized for CSP, operating at high temperatures, and then to add high-temperature solar cells to it to boost efficiency. Alternately it would be possible to design an optimum CPV system with high PV efficiency, and then to add whatever power could be generated using a lower-temperature, and therefore less efficient, heat cycle ap proach to generate electricity.
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From page 149... ...
of disruptive research and development, but it shows that many solar technologies have the potential to compete with conventional energy sources. The same graph also depicts the LCOE for natural gas, which was at $0.10/kWh in 2010 and was predicted to steadily increase to about $0.14/kWh in 2020, a point at which it is possible that many of the solar technologies will be at a lower LCOE.
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Research to advance artificial photosynthesis is being carried out at the Joint Center for Artificial Photosynthesis in California.51 SOLID-STATE LIGHTING Incandescent lightbulbs have been in use for well over 100 years. English chem ist Humphry Davy demonstrated the first electrically driven incandescent light in 1802.
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From page 151... ...
They are significantly more efficient then incandescent bulbs, but they contain mercury, a hazardous material.54 Compact fluorescent bulbs fitting most lamps started to be commercially available in 1985.55 Fluorescent lights take minutes to come to full brightness, which makes some people avoid these lights despite their higher efficiency as compared with incandescent bulbs.56 Color balance can also be an issue for fluorescents, depending on the phosphors used. Mercury vapor and sodium vapor lamps are another available lighting option.
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From page 152... ...
A typical 100-W incandescent bulb puts out about 1,500 lm, or 15 lm/W per watt of electricity. Lower-wattage incandescent bulbs are even less efficient.
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From page 153... ...
Traffic lights were another early use, as the long lifetime helped reduce the labor cost of replacing bulbs. LEDs are widely used in cars and are making an entry to headlights as well, although attaining the required brightness for headlights is difficult with LEDs.61 LEDs are frequently used in brake lights owing to the faster turn-on time of LEDs; replacing incandescent bulbs with LEDs in brake lights results in a faster turn-on time by almost 0.2 second.
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From page 154... ...
Solid-state lighting is used now in locations with inconvenient access due to the long lifetime, often from 30,000 to 80,000 hours. This is an advantage over the nominal 1,000-hour lifetime of incandescent bulbs.
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From page 155... ...
If the efficiency of all blue, green, and red LEDs is as high as that of blue LEDs, theoretically about 20 percent higher efficiency can be gained using RGB color rendering compared to blue + phosphor LED due to the narrowband spectra, and another 20 percent can be gained in efficiency because there is no Stokes loss in the phosphor. RGB color rendering is theoretically the most efficient.
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From page 156... ...
The L Prize competition is the first government-sponsored technology competition designed to spur development of ultra-efficient solid-state lighting products to replace the common light bulb." (See Figure 5.3.1.) FIGURE 5.3.1 Webpage showing the "L Prize" World Wide Web page (July 2, 2011)
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From page 157... ...
SOURCE: Courtesy of Cree, Inc. TABLE 5.3 Top-10 High-Brightness LED M anufacturers, by Revenue in 2010 2010 Ranking Company Name 1 Nichia 2 Samsung LED 3 Osram Opto Semiconductors 4 Philips Lumileds Lighting 4 Seoul Semiconductor 6 Cree 6 LG Innotek 8 Sharp 9 Everlight 9 Toyoda Gosei NOTE: Companies have the same ranking when the difference in revenue is within the margin of error.
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From page 158... ...
This makes GaN on Si a promising approach for lowering costs. Recently Bridgelux showed cool-white LED efficiencies as high as 160 lm/W at a correlated color temperature of 4350 K, and warm-white GaN on Si LEDs delivered 125 lm/W at a color temperature of 2940 K and CRI of 80.73 As an alternative to a sapphire substrate, at least one company, Cree, uses SiC.
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From page 159... ...
It is the opinion of the committee that development of cost-competitive solar power for utility-scale application over the next decade is feasible, and in fact likely. Major solar cell providers have plans to reach cost parity by about 2015.
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From page 160... ...
Today, it is not known how to achieve this cost parity with current solar cell technologies. Additionally, it is important to recall the statement made in 2010 by the America's Energy Future Panel on Electricity from Renewable Resources in the report Electric ity from Renewable Resources: Status, Prospects, and Impediments.
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From page 161... ...
Develop high-temperature solar cells suitable for use in conjunction with CSP systems. These solar cells can provide sunlight conversion to electricity in addition to the CSP thermal conversion.
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From page 162... ...
162 Optics and Photonics: Essential Technologies for O u r N at i o n Recommendation: Governmental land use planning bodies should consider the potential impacts of a significant increase in land use associated with solar electric power plants. Recommendation: The DOE and electric utilities should evaluate the electric grid for power movement across multiple time zones and evaluate whether changes should be made to support the period of time when grid parity is reached for solar power.
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