Chapter 4: Solar Energy Capture

 (Draft date:  February 14, 2008)

Author's note:  This is a preliminary draft and a work in progress.  (Further explanation.)

“I’d put my money on the sun and solar energy.  What a source of power!  I hope we don’t have to wait until oil and coal run out before we tackle that.”  -Thomas Edison, 1931

-----------------------------

The potential for solar energy generation in the U.S. is tremendous.  According to the National Renewable Energy Laboratory (NREL), the solar resource of Alaska is equivalent to that of Germany, which is the largest installed solar market in the world today.  Worldwide, scientists estimate that 600 terawatts of solar energy could be captured worldwide through through passive solar heating and cooling of buildings, solar hot water heating, and solar electricity generation.

Section 1: Photovoltaic Electricity Generation

Modern solar cell technology was developed at Bell Laboratories in the U.S. in the 1950s. Research and development has greatly reduced the cost of solar pholtovoltaic electricity from several dollars per kilowatt-hour in 1980 to less than 25 cents currently.  By developing better manufacturing techniques: fabrication techniques which use polysilicon more efficiently, developing thin film cells that can be made from amorphous silicon and other low-cost materials, achieving manufacturing economies of scale, developing higher efficiency solar devices (see below for examples) and new solar nanomaterials (see below for descriptions), NREL and the industry project that the cost of producing solar photovoltaic electricity will be down to 4-6 per kilowatt-hour by 2025.  From 1992 to 2004 the cost of generating electricity with photovoltaics dropped an average of 58 percent.  In 2006, researchers at the University of Johannesburg and at Nanosolar, a private Palo Alto company, announced their major breakthrough in production costs for solar cells.  Their technology reduces solar cell production costs by a factor of 4-5 times <www.energybulletin.net/19262.html>.  In 2007 over a dozen companies including Miasole, Nanosolar, and Ovonics are scaling up production of thin-film-based low-cost solar modules which can be churned out like rolls of plastic.

In December, 2007, Nanosolar shipped their first thin film photovoltaics to Beck Energy for installation at an East German 1 megawatt solar electric plant.  In May 2007 Popular Science awarded the Nanosolar “PowerSheet” product line their Top Innovation of the Year award for 2007.  In the award, they predicted the cost of the Nanosolar PowerSheet thin film photovoltaics would drop to $0.99 a watt, one-third of cost per watt in 2004 and 3.3 percent of the cost in 1975.

For photovoltaics as an electricity source on the national energy grid, he effect of intermittency is determined by the ratio between the output of a widely-spread group of photovoltaic installations and their peak output.  With average insolation over the United States, photovoltaics can supply 14 percent of the block of electricity determined by their collective peak output.

In 2007 the Prometheus Institute of Cambridge, MA, and Worldwatch Institute published a study which predicted the rapid decline in photovoltaic costs they predicted would make solar electricity a mainstream power option in the next few years.  The growth of photovoltaic manufacturing has been constrained by a worldwide shortage of manufacturing capacity for purified polysilicon.  Within the next two years over a dozen companies in Europe, Japan, China and the U.S. will bring unprecedented levels of polysilicon production capacity.  Prometheus estimates this increase in polysilicon supply will bring photovoltaic costs down by 40 percent.

Global production of photovoltaic cells reached an estimated 1,200 megawatts in 2004, representing a 58 percent increase over 2004 levels and a doubling of production in two years.  In 2006, global production of photovoltaic cells grew 41 percent and manufacture of photovoltaics accounted for over half of the world use of polysilicon for the first time.  Production of photovoltaics jumped to 3,800 megawatts in 2007, an increase of about 50 percent over 2006.

Production growth rates have averaged 48 percent per year since 2000, driven by strong pro-solar policies in a handful of industrial countries.  Cumulative production of photovoltaic cells worldwide since 2000 total 12,400 megawatts as of the end of 2007, an average increase of megawatt capacity of 48 percent from 2002-2007, or roughly doubling every two years,  making photovoltaics the world’s fastest-growing energy source.  The photovoltaic industry supports more than 25,000 jobs worldwide; 2005 sales were $11.5 billion.  Analysts expect PV sales to reach $30 billion by 2010.  The consulting firm Clean Edge projects $51 billion in sales by 2015. Globally, module costs have dropped from about $30 per watt in 1975 to close to $3 per watt in 2004.  Advanced photovoltaic technologies under development are expected to cut costs further, making PV-generated power fully competitive with fossil and nuclear fuel-generated power.  The U.S. Department of Energy has launched the Solar America Initiative which aims to bring solar energy systems to cost-competitiveness by 2015 for residential, commercial, and utility applications.  The Initiative will focus on improving installed cost and performance of solar systems through refinements in technology and manufacturing processes.

Initiatives to Reduce Photovoltaic Installed and Production Costs

Flat-screen TV maker Applied Materials is applying the technology it used to bring the cost of manufacturing flat-screen TV displays to photovoltaic production.  Growth in Applied Materials’ core business, chip manufacturing, has slowed, and the flat-screen TV market has plateaued.  Defining their core technology as “We apply nanomanufacturing technology to improve the way people live” and “we deposit very thin films,” Applied Materials entered the solar market in 2006 and has already developed a process of layering thin film photovoltaic silicon onto glass or other low-cost support material.  The company’s business plan is to bring solar photovoltaic costs down from $4 to $1 per watt by 2009, and then down to 70 cents by 2010.

Nanosolar is building the world’s largest photovoltaic power plant near Silicon Valley.  With financing from Google founders Larry Page and Sergey Brin and other venture capitalists, the plant will have 430 megawatts per year production (total existing U.S. production is 153 megawatts per year).  The new technology used prints a copper-based medium on flexible plastic or foil sheets in a process much like printing newspapers.  The printed sheets are then cut up into cells approximately 6 inches square for wiring into arrays.  The prototypes developed over four years are as efficient as silicon-based photovoltaic cells and cost one-fifth as much to manufacture.  The copper-based cells are flexible and can be formed into shapes to fit on building surfaces including roofs and arches.  Google also announced plans to install 9,200 solar photovoltaic panels at its Mountain View headquarters in 2007.  These 12.8% efficient panels, made by Sharp, are projected to meet 30% of Google’s peak energy needs in summer.

In December, 2006, Boeing-Spectrolab announced they have created a solar cell with 40.7% sunlight-to-energy conversion efficiency.  The multiple-junction solar cell (0.26685 square centimeters) consists of germanium and several layers of gallium arsenide; each of the 20-30 layers responds to different wavelengths of light in sunlight concentrated by lenses or mirrors on the cell, producing an output of 2.6 watts.  The maximum concentrated solar output in watts from these cells is 24 watts per square centimeter.  The cell was developed with Department of Energy grant funding, and the efficiency of the cell was independently confirmed by the DOE’s National Renewable Energy Laboratory in Golden, Colorado.  In 1954, 4% efficiency was state of the art; contemporary commercial photovoltaic cells range from 12-18% efficient, with high cost units used in satellites attaining 28% efficiency.  Spectrolab believes the new cell can be mass produced at a cost comparable to contemporary commercial photovoltaics, which would make solar power from it at 8-10 cents per kilowatt hour cost-competitive with off-peak grid electricity in all markets.

Ted Sargent, Professor of Electrical and Computer Engineering at the University of Toronto has developed a solar cell technology based on “quantum dots.”  The quantum dots are made from semiconductor crystals only a few nanometers in size.  They can be tuned to absorb particular frequencies of light and then stacked together to capture the broadest possible spectrum of sunlight.  Current solar cells capture light only in the visible spectrum, while half of solar energy is in the infrared.  By capturing energy across the solar spectrum, Sargent’s quantum dots can achieve 30 percent sunlight-to-energy conversion efficiency while being dispersed in a solvent and painted onto some backing like clothing or a house wall.

Already available commercially from Open Energy Corp. is the SolarSave Roofing Membrane that features high-efficiency monocrystalline PV cells mounted in a completely waterproof base which requires no roof penetrations.  They also make SolarSave Roofing Tiles which incorporate the same cells into a roofing material designed to match commonly used cement tiles.  Finally, SolarSave makes Architectural PV Glass in different sizes, shapes and power configurations where the photovoltaic cells are built into the glass itself and capture some of the sun energy coming through, acting as a shading medium in certain light wavelengths.

 International Trends in Photovoltaic Installation

 Japan is the world leader in PV, accounting for over 50 percent of 2004 PV production.  A six-year government initiative there has encouraged the installation of 1,000 megawatts of capacity, and 160,000 Japanese homes are now PV-powered.  The Japanese government’s policy is to install 4,820 megawatts of PV capacity by 2010 and produce 10 percent of Japan’s total electricity from photovoltaic solar by 2030.  The average price for Japanese residential PV systems has declined by more than 80 percent since 1993.

In 2006 China’s production of photovoltaic cells passed that in the U.S., making China the world’s third-largest producer of solar cells after Germany and Japan.  China’s leading PV manufacturer, Suntech Power, climbed from the world’s eighth largest producer in 2005 to fourth in 2006.

Europe produced 27 percent of new solar cells in 2004 and passed Japan in annual installations that year.  Germany installed 300 megawatts of new solar capacity, bringing the nation’s total to 700 megawatts.

The United States is a declining solar producer in the world economy, going from 44 percent in 1996 to 11 percent in 2004.  U.S. cumulative installed solar capacity reached 277 megawatts at the end of 2003.

An estimated 62 percent of new photovoltaic installations in 2004 were grid-connected, versus just 3 percent in 1994.  System costs are now low enough that photovoltaic electricity cost per watt is competitive at peak demand times in California and at all times in Japan.  In 2006, grid-connected photovoltaic capacity increased 50 percent to 5,000 megawatts.

The Las Vegas-based Powered by Renewables Corporation and a Baltimore firm are building a $115 million 18-megawatt photovoltaic plant in southern Nevada to sell power to the military.  The largest existing photovoltaic plant in the world is a 10-megawatt facility in Germany.

A.  Examples of Installed Photovoltaic Generation:

1.         In 2006 the tenth Utah state park installed a solar energy system.  Goblin Valley, Cleveland Lloyd Dinosaur Quarry, and Yuba State Parks are 100 percent solar-powered.  In the other seven parks small systems power picnic areas, restrooms, shade areas and sheds which are remote from power grid connections.

2.         Brockton Brightfield is a 425-kilowatt photovoltaic system located on 3.7 acres in Brockton, Mass.  A “brightfield” is a rehabilitated “brownfield” transformed into a solar-energy-generating station.  The system comprises 1,395 SCHOTT ASE 300 modules and generates an estimated 535 megawatt-hours of electricity annually.  The City of Brockton expects the system to pay for itself in 15-20 years, in addition to the value of having a contaminated, abandoned industrial site put back into taxbase economic productivity.

B.  Examples of increased cost-efficiencies in technology in photovoltaics:

1.         SunPower introduced its new high-power, high-efficiency solar panel on October 16, 2006.  The SPR-15 utilizes 22 percent efficient Gen 2 solar cells.  With a rated output of 315 watts, it permits customers to generate up to 50 percent more power per square foot of roof area with half as many panels, says SunPower <Error! Hyperlink reference not valid.

 2.

Section 2 Concentrating solar electricity generation

Concentrating solar power (CSP) currently costs about 11 cents per kilowatt-hour to produce and is becoming less expensive.  Deployed in utility-scale steam plants in the Southwest, it can provide dispatchable electricity by virtue of its ability to utilize low-cost thermal storage or make use of natural gas to heat steam when sun is not available.

Demonstration plants utilizing concentrated solar-thermal technology were originally created by the Department of Energy and National Renewable Energy Laboratories in California.  In 2000, the National Research Council concluded that these solar-thermal power plants worked as commercially-competitive grid electric generating facilities.  A DOE-funded cost analysis by a commercial consulting firm found that, produced in quantity, solar-thermal plants would be profitable at about 6 cents per kilowatt-hour.  In 2002, the National Research Council concluded that with further government funding, solar-thermal power generation could be brought to market.  As California, Nevada, and other states began to adopt renewable energy portfolios requiring a certain percentage of all electricity sold by utilities come from renewable sources, commercial power producers finally began to show interest in building concentrating solar power plants.

CSP plants totaling 354 megawatts capacity have been reliably operating in the Mohave Desert in California for 20 years, and a new 64-MW plant is under construction in Nevada, with many more CSP plants planned around the world.  Solar thermal electric generation can exceed 35 percent efficiency in converting solar radiation to electric power.

Section 3: Solar Heat Generation

The global market for solar thermal collectors grew some 50 percent between 2001 and 2004.  About 18 million square meters of capacity were added in 2004, bringing estimated global installation to 150 million square meters of collector.  About 73 percent of this total heats water and building space, meeting the needs of more than 32 million households worldwide.  The remaining capacity heats swimming pools.

China accounts for 55 percent of world solar collector installations, when pool installations are excluded, or 52 million square meters of collectors.  The Chinese government target call for four times that area installed by 2015.  Japan, Europe, and Turkey each account for 10 percent of installed collector capacity.

 Despite the fact that a home solar hot water heating system will pay for itself in the United States through fuel savings in four to eight years, 98 percent of U.S. solar collector systems heat swimming pools, not building space or culinary hot water.

Section 4: Combined Solar Electric and Heat Production

Conserval Systems, Inc., had developed the SolarWall transpired solar heat collector.  They now sell the SolarWall PV/T  photovoltaic thermal system which delivers both heat and electricity to a building on which it is installed by installing PV modules over transpired solar collectors.  In the winter, the excess heat from the PV modules is drawn through the transpired collector into a space between the building and the SolarWall and is used to warm ventilation air.  In the summer, the air used to cool the PV modules is directed by dampers outside the building while only ambient-temperature air is allowed into the ventilation intakes.  Conserval claims the combined system is 50 percent efficient.

Section 5: Photocatalytic Hydrogen Production

Al Herring writes that elemental hydrogen, which is not found in nature, should be classified as a storage medium for energy, not as an energy source.  Herring says it takes 1.4 units of energy to produce one unit of hydrogen energy; he is obviously assuming the hydrogen is being produced by electrolysis of water by direct current, where this is the energy value of the electricity used to the energy value of the hydrogen generated.  However, if the energy used to generate the hydrogen is captured directly from solar photons, the hydrogen becomes an energy source since to energy which could be applied to other loads was used to generate it.  If hydrogen is generated by electrolysis powered by wind- or photovoltaic-generated electricity, then a forty percent loss of generated energy is sustained in converting that electricity to a storable fuel form: hydrogen.  If the hydrogen is generated directly in a device by energy transfer directly from photons, then hydrogen becomes a solar energy source which is a storable, transportable fuel, and there is no energy efficiency cost consideration.  Happily, three different technologies which generate hydrogen directly from energy from solar radiation in nanotubes, solar cells, or ceramic heat exchangers are under development.

A.  Using nanotubes of titanium dioxide

 Scientists have turned to nanotubes of titanium dioxide to address the efficiency problem with prior photocatalysts which split water into hydrogen and oxygen with the energy of solar radiation striking the catalyst.  Existing photocatalysts can only use ultraviolet light which comprises about 4 percent of total sunlight energy.  Materials that can photocatalyze using the visible spectrum of light tend to break down in water.  The tube form of titanium dioxide is five times more efficient than film forms in splitting water molecules because the tubular shape permits electrons to stay free longer after being “knocked loose” by photons, increasing the probability the electron will split a water molecule.  Pennsylvania State University researchers have pushed ultraviolet-to-hydrogen efficiencies beyond 12 percent using six-micron-long titanium dioxide nanotubes, generating 80 milliliters of hydrogen per hour per watt of ultraviolet light.

University of Texas at Austin researchers have found how to add carbon to the titanium dioxide nanotubes to shift the spectrum of light they absorb to the visible spectrum.  Under an artificial mix of ultraviolet and visible light spectra these modified nanotubes were twice as efficient at splitting water.  The researchers are now working on how to shift the nanotubes’ sensitivity entirely into the pure visible light spectrum.

The teams are aiming to boost the nanotubes’ water-splitting efficiency in visible light above the Department of Energy’s 2010 goal of 10 percent.  If the average U.S. rooftop was covered with a visible-light, 12 percent-efficient photocatalyst, it would generate the hydrogen energy equivalent of about 11 liters of gasoline a day.

B.  Using doped iron oxide with cobalt

Michael Grätzel, chemistry professor at the Ecole Polytechnique Fédérale de Lausanne in Switzerland has grown nanostructured thin films of iron oxide that convert sunlight into the electrons needed to form hydrogen from water in a solar cell.  Iron oxide has long been an appealing material for hydrogen generation in solar panels because it holds up well in water and emits electrons when struck by photons.  In ordinary iron oxide, the resulting charge carriers do not escape the material and so recombine, canceling each other out before electrolyzing water.  Grätzel and his colleagues discovered that, by doping the rust with silicon, the material could be coaxed to form cauliflower-like structures with extremely high surface area, ensuring that a large part of the atoms in the material were in contact with water molecules.  They also discovered that doping with cobalt catalyzes the electrolysis reaction.  In trials, the new iron-oxide films converted 42 percent of ultraviolet photons in sunlight to electrons and holes.  The system’s overall efficiency is so far only 4 percent because iron oxide does not absorb all parts of the solar spectrum.  However, Grätzel’s careful observations of the results of iron oxide film variations (published in the Journal of the American Chemical Society)  have led Hydrogen Solar of the U.K. to work on developing mass-produced panels, aiming at reaching a 10 percent solar efficiency level (20 percent efficiency with iron oxide is theoretically possible) by adjusting the amount and arrangement of silicon and cobalt to improve the functional structure of the films.

If consumers and businesses were able to use solar panels on site to generate hydrogen, rather than getting hydrogen shipped in from a large facility, it would cut out the cost of shipping hydrogen.  Solar-to-hydrogen panels would be more efficient than small electrolysis machines.

C.  Thermochemical cycle using ceramic heat exchangers

Sandia National Laboratories is working on the high-temperature decomposition of sulfuric acid in ceramic heat exchangers heated by concentrated solar energy (or other heat source, e.g., nuclear).  The technology developed in 2006 is now being used in international sulfur-iodine experiments.  A scale-up demonstration of hydrogen production using the technology is proposed for Sandia’s Solar Tower facility.

Chapter 4: Solar Energy Capture

 (Draft date:  February 14, 2008)

Author's note:  This is a preliminary draft and a work in progress.  (Further explanation.)

“I’d put my money on the sun and solar energy.  What a source of power!  I hope we don’t have to wait until oil and coal run out before we tackle that.”  -Thomas Edison, 1931

-----------------------------

The potential for solar energy generation in the U.S. is tremendous.  According to the National Renewable Energy Laboratory (NREL), the solar resource of Alaska is equivalent to that of Germany, which is the largest installed solar market in the world today.  Worldwide, scientists estimate that 600 terawatts of solar energy could be captured worldwide through through passive solar heating and cooling of buildings, solar hot water heating, and solar electricity generation.

Section 1: Photovoltaic Electricity Generation

Modern solar cell technology was developed at Bell Laboratories in the U.S. in the 1950s. Research and development has greatly reduced the cost of solar pholtovoltaic electricity from several dollars per kilowatt-hour in 1980 to less than 25 cents currently.  By developing better manufacturing techniques: fabrication techniques which use polysilicon more efficiently, developing thin film cells that can be made from amorphous silicon and other low-cost materials, achieving manufacturing economies of scale, developing higher efficiency solar devices (see below for examples) and new solar nanomaterials (see below for descriptions), NREL and the industry project that the cost of producing solar photovoltaic electricity will be down to 4-6 per kilowatt-hour by 2025.  From 1992 to 2004 the cost of generating electricity with photovoltaics dropped an average of 58 percent.  In 2006, researchers at the University of Johannesburg and at Nanosolar, a private Palo Alto company, announced their major breakthrough in production costs for solar cells.  Their technology reduces solar cell production costs by a factor of 4-5 times <www.energybulletin.net/19262.html>.  In 2007 over a dozen companies including Miasole, Nanosolar, and Ovonics are scaling up production of thin-film-based low-cost solar modules which can be churned out like rolls of plastic.

In December, 2007, Nanosolar shipped their first thin film photovoltaics to Beck Energy for installation at an East German 1 megawatt solar electric plant.  In May 2007 Popular Science awarded the Nanosolar “PowerSheet” product line their Top Innovation of the Year award for 2007.  In the award, they predicted the cost of the Nanosolar PowerSheet thin film photovoltaics would drop to $0.99 a watt, one-third of cost per watt in 2004 and 3.3 percent of the cost in 1975.

For photovoltaics as an electricity source on the national energy grid, he effect of intermittency is determined by the ratio between the output of a widely-spread group of photovoltaic installations and their peak output.  With average insolation over the United States, photovoltaics can supply 14 percent of the block of electricity determined by their collective peak output.

In 2007 the Prometheus Institute of Cambridge, MA, and Worldwatch Institute published a study which predicted the rapid decline in photovoltaic costs they predicted would make solar electricity a mainstream power option in the next few years.  The growth of photovoltaic manufacturing has been constrained by a worldwide shortage of manufacturing capacity for purified polysilicon.  Within the next two years over a dozen companies in Europe, Japan, China and the U.S. will bring unprecedented levels of polysilicon production capacity.  Prometheus estimates this increase in polysilicon supply will bring photovoltaic costs down by 40 percent.

Global production of photovoltaic cells reached an estimated 1,200 megawatts in 2004, representing a 58 percent increase over 2004 levels and a doubling of production in two years.  In 2006, global production of photovoltaic cells grew 41 percent and manufacture of photovoltaics accounted for over half of the world use of polysilicon for the first time.  Production of photovoltaics jumped to 3,800 megawatts in 2007, an increase of about 50 percent over 2006.

Production growth rates have averaged 48 percent per year since 2000, driven by strong pro-solar policies in a handful of industrial countries.  Cumulative production of photovoltaic cells worldwide since 2000 total 12,400 megawatts as of the end of 2007, an average increase of megawatt capacity of 48 percent from 2002-2007, or roughly doubling every two years,  making photovoltaics the world’s fastest-growing energy source.  The photovoltaic industry supports more than 25,000 jobs worldwide; 2005 sales were $11.5 billion.  Analysts expect PV sales to reach $30 billion by 2010.  The consulting firm Clean Edge projects $51 billion in sales by 2015. Globally, module costs have dropped from about $30 per watt in 1975 to close to $3 per watt in 2004.  Advanced photovoltaic technologies under development are expected to cut costs further, making PV-generated power fully competitive with fossil and nuclear fuel-generated power.  The U.S. Department of Energy has launched the Solar America Initiative which aims to bring solar energy systems to cost-competitiveness by 2015 for residential, commercial, and utility applications.  The Initiative will focus on improving installed cost and performance of solar systems through refinements in technology and manufacturing processes.

Initiatives to Reduce Photovoltaic Installed and Production Costs

Flat-screen TV maker Applied Materials is applying the technology it used to bring the cost of manufacturing flat-screen TV displays to photovoltaic production.  Growth in Applied Materials’ core business, chip manufacturing, has slowed, and the flat-screen TV market has plateaued.  Defining their core technology as “We apply nanomanufacturing technology to improve the way people live” and “we deposit very thin films,” Applied Materials entered the solar market in 2006 and has already developed a process of layering thin film photovoltaic silicon onto glass or other low-cost support material.  The company’s business plan is to bring solar photovoltaic costs down from $4 to $1 per watt by 2009, and then down to 70 cents by 2010.

Nanosolar is building the world’s largest photovoltaic power plant near Silicon Valley.  With financing from Google founders Larry Page and Sergey Brin and other venture capitalists, the plant will have 430 megawatts per year production (total existing U.S. production is 153 megawatts per year).  The new technology used prints a copper-based medium on flexible plastic or foil sheets in a process much like printing newspapers.  The printed sheets are then cut up into cells approximately 6 inches square for wiring into arrays.  The prototypes developed over four years are as efficient as silicon-based photovoltaic cells and cost one-fifth as much to manufacture.  The copper-based cells are flexible and can be formed into shapes to fit on building surfaces including roofs and arches.  Google also announced plans to install 9,200 solar photovoltaic panels at its Mountain View headquarters in 2007.  These 12.8% efficient panels, made by Sharp, are projected to meet 30% of Google’s peak energy needs in summer.

In December, 2006, Boeing-Spectrolab announced they have created a solar cell with 40.7% sunlight-to-energy conversion efficiency.  The multiple-junction solar cell (0.26685 square centimeters) consists of germanium and several layers of gallium arsenide; each of the 20-30 layers responds to different wavelengths of light in sunlight concentrated by lenses or mirrors on the cell, producing an output of 2.6 watts.  The maximum concentrated solar output in watts from these cells is 24 watts per square centimeter.  The cell was developed with Department of Energy grant funding, and the efficiency of the cell was independently confirmed by the DOE’s National Renewable Energy Laboratory in Golden, Colorado.  In 1954, 4% efficiency was state of the art; contemporary commercial photovoltaic cells range from 12-18% efficient, with high cost units used in satellites attaining 28% efficiency.  Spectrolab believes the new cell can be mass produced at a cost comparable to contemporary commercial photovoltaics, which would make solar power from it at 8-10 cents per kilowatt hour cost-competitive with off-peak grid electricity in all markets.

Ted Sargent, Professor of Electrical and Computer Engineering at the University of Toronto has developed a solar cell technology based on “quantum dots.”  The quantum dots are made from semiconductor crystals only a few nanometers in size.  They can be tuned to absorb particular frequencies of light and then stacked together to capture the broadest possible spectrum of sunlight.  Current solar cells capture light only in the visible spectrum, while half of solar energy is in the infrared.  By capturing energy across the solar spectrum, Sargent’s quantum dots can achieve 30 percent sunlight-to-energy conversion efficiency while being dispersed in a solvent and painted onto some backing like clothing or a house wall.

Already available commercially from Open Energy Corp. is the SolarSave Roofing Membrane that features high-efficiency monocrystalline PV cells mounted in a completely waterproof base which requires no roof penetrations.  They also make SolarSave Roofing Tiles which incorporate the same cells into a roofing material designed to match commonly used cement tiles.  Finally, SolarSave makes Architectural PV Glass in different sizes, shapes and power configurations where the photovoltaic cells are built into the glass itself and capture some of the sun energy coming through, acting as a shading medium in certain light wavelengths.

 International Trends in Photovoltaic Installation

 Japan is the world leader in PV, accounting for over 50 percent of 2004 PV production.  A six-year government initiative there has encouraged the installation of 1,000 megawatts of capacity, and 160,000 Japanese homes are now PV-powered.  The Japanese government’s policy is to install 4,820 megawatts of PV capacity by 2010 and produce 10 percent of Japan’s total electricity from photovoltaic solar by 2030.  The average price for Japanese residential PV systems has declined by more than 80 percent since 1993.

In 2006 China’s production of photovoltaic cells passed that in the U.S., making China the world’s third-largest producer of solar cells after Germany and Japan.  China’s leading PV manufacturer, Suntech Power, climbed from the world’s eighth largest producer in 2005 to fourth in 2006.

Europe produced 27 percent of new solar cells in 2004 and passed Japan in annual installations that year.  Germany installed 300 megawatts of new solar capacity, bringing the nation’s total to 700 megawatts.

The United States is a declining solar producer in the world economy, going from 44 percent in 1996 to 11 percent in 2004.  U.S. cumulative installed solar capacity reached 277 megawatts at the end of 2003.

An estimated 62 percent of new photovoltaic installations in 2004 were grid-connected, versus just 3 percent in 1994.  System costs are now low enough that photovoltaic electricity cost per watt is competitive at peak demand times in California and at all times in Japan.  In 2006, grid-connected photovoltaic capacity increased 50 percent to 5,000 megawatts.

The Las Vegas-based Powered by Renewables Corporation and a Baltimore firm are building a $115 million 18-megawatt photovoltaic plant in southern Nevada to sell power to the military.  The largest existing photovoltaic plant in the world is a 10-megawatt facility in Germany.

A.  Examples of Installed Photovoltaic Generation:

1.         In 2006 the tenth Utah state park installed a solar energy system.  Goblin Valley, Cleveland Lloyd Dinosaur Quarry, and Yuba State Parks are 100 percent solar-powered.  In the other seven parks small systems power picnic areas, restrooms, shade areas and sheds which are remote from power grid connections.

2.         Brockton Brightfield is a 425-kilowatt photovoltaic system located on 3.7 acres in Brockton, Mass.  A “brightfield” is a rehabilitated “brownfield” transformed into a solar-energy-generating station.  The system comprises 1,395 SCHOTT ASE 300 modules and generates an estimated 535 megawatt-hours of electricity annually.  The City of Brockton expects the system to pay for itself in 15-20 years, in addition to the value of having a contaminated, abandoned industrial site put back into taxbase economic productivity.

B.  Examples of increased cost-efficiencies in technology in photovoltaics:

1.         SunPower introduced its new high-power, high-efficiency solar panel on October 16, 2006.  The SPR-15 utilizes 22 percent efficient Gen 2 solar cells.  With a rated output of 315 watts, it permits customers to generate up to 50 percent more power per square foot of roof area with half as many panels, says SunPower <Error! Hyperlink reference not valid.

 2.

Section 2 Concentrating solar electricity generation

Concentrating solar power (CSP) currently costs about 11 cents per kilowatt-hour to produce and is becoming less expensive.  Deployed in utility-scale steam plants in the Southwest, it can provide dispatchable electricity by virtue of its ability to utilize low-cost thermal storage or make use of natural gas to heat steam when sun is not available.

Demonstration plants utilizing concentrated solar-thermal technology were originally created by the Department of Energy and National Renewable Energy Laboratories in California.  In 2000, the National Research Council concluded that these solar-thermal power plants worked as commercially-competitive grid electric generating facilities.  A DOE-funded cost analysis by a commercial consulting firm found that, produced in quantity, solar-thermal plants would be profitable at about 6 cents per kilowatt-hour.  In 2002, the National Research Council concluded that with further government funding, solar-thermal power generation could be brought to market.  As California, Nevada, and other states began to adopt renewable energy portfolios requiring a certain percentage of all electricity sold by utilities come from renewable sources, commercial power producers finally began to show interest in building concentrating solar power plants.

CSP plants totaling 354 megawatts capacity have been reliably operating in the Mohave Desert in California for 20 years, and a new 64-MW plant is under construction in Nevada, with many more CSP plants planned around the world.  Solar thermal electric generation can exceed 35 percent efficiency in converting solar radiation to electric power.

Section 3: Solar Heat Generation

The global market for solar thermal collectors grew some 50 percent between 2001 and 2004.  About 18 million square meters of capacity were added in 2004, bringing estimated global installation to 150 million square meters of collector.  About 73 percent of this total heats water and building space, meeting the needs of more than 32 million households worldwide.  The remaining capacity heats swimming pools.

China accounts for 55 percent of world solar collector installations, when pool installations are excluded, or 52 million square meters of collectors.  The Chinese government target call for four times that area installed by 2015.  Japan, Europe, and Turkey each account for 10 percent of installed collector capacity.

 Despite the fact that a home solar hot water heating system will pay for itself in the United States through fuel savings in four to eight years, 98 percent of U.S. solar collector systems heat swimming pools, not building space or culinary hot water.

Section 4: Combined Solar Electric and Heat Production

Conserval Systems, Inc., had developed the SolarWall transpired solar heat collector.  They now sell the SolarWall PV/T  photovoltaic thermal system which delivers both heat and electricity to a building on which it is installed by installing PV modules over transpired solar collectors.  In the winter, the excess heat from the PV modules is drawn through the transpired collector into a space between the building and the SolarWall and is used to warm ventilation air.  In the summer, the air used to cool the PV modules is directed by dampers outside the building while only ambient-temperature air is allowed into the ventilation intakes.  Conserval claims the combined system is 50 percent efficient.

Section 5: Photocatalytic Hydrogen Production

Al Herring writes that elemental hydrogen, which is not found in nature, should be classified as a storage medium for energy, not as an energy source.  Herring says it takes 1.4 units of energy to produce one unit of hydrogen energy; he is obviously assuming the hydrogen is being produced by electrolysis of water by direct current, where this is the energy value of the electricity used to the energy value of the hydrogen generated.  However, if the energy used to generate the hydrogen is captured directly from solar photons, the hydrogen becomes an energy source since to energy which could be applied to other loads was used to generate it.  If hydrogen is generated by electrolysis powered by wind- or photovoltaic-generated electricity, then a forty percent loss of generated energy is sustained in converting that electricity to a storable fuel form: hydrogen.  If the hydrogen is generated directly in a device by energy transfer directly from photons, then hydrogen becomes a solar energy source which is a storable, transportable fuel, and there is no energy efficiency cost consideration.  Happily, three different technologies which generate hydrogen directly from energy from solar radiation in nanotubes, solar cells, or ceramic heat exchangers are under development.

A.  Using nanotubes of titanium dioxide

 Scientists have turned to nanotubes of titanium dioxide to address the efficiency problem with prior photocatalysts which split water into hydrogen and oxygen with the energy of solar radiation striking the catalyst.  Existing photocatalysts can only use ultraviolet light which comprises about 4 percent of total sunlight energy.  Materials that can photocatalyze using the visible spectrum of light tend to break down in water.  The tube form of titanium dioxide is five times more efficient than film forms in splitting water molecules because the tubular shape permits electrons to stay free longer after being “knocked loose” by photons, increasing the probability the electron will split a water molecule.  Pennsylvania State University researchers have pushed ultraviolet-to-hydrogen efficiencies beyond 12 percent using six-micron-long titanium dioxide nanotubes, generating 80 milliliters of hydrogen per hour per watt of ultraviolet light.

University of Texas at Austin researchers have found how to add carbon to the titanium dioxide nanotubes to shift the spectrum of light they absorb to the visible spectrum.  Under an artificial mix of ultraviolet and visible light spectra these modified nanotubes were twice as efficient at splitting water.  The researchers are now working on how to shift the nanotubes’ sensitivity entirely into the pure visible light spectrum.

The teams are aiming to boost the nanotubes’ water-splitting efficiency in visible light above the Department of Energy’s 2010 goal of 10 percent.  If the average U.S. rooftop was covered with a visible-light, 12 percent-efficient photocatalyst, it would generate the hydrogen energy equivalent of about 11 liters of gasoline a day.

B.  Using doped iron oxide with cobalt

Michael Grätzel, chemistry professor at the Ecole Polytechnique Fédérale de Lausanne in Switzerland has grown nanostructured thin films of iron oxide that convert sunlight into the electrons needed to form hydrogen from water in a solar cell.  Iron oxide has long been an appealing material for hydrogen generation in solar panels because it holds up well in water and emits electrons when struck by photons.  In ordinary iron oxide, the resulting charge carriers do not escape the material and so recombine, canceling each other out before electrolyzing water.  Grätzel and his colleagues discovered that, by doping the rust with silicon, the material could be coaxed to form cauliflower-like structures with extremely high surface area, ensuring that a large part of the atoms in the material were in contact with water molecules.  They also discovered that doping with cobalt catalyzes the electrolysis reaction.  In trials, the new iron-oxide films converted 42 percent of ultraviolet photons in sunlight to electrons and holes.  The system’s overall efficiency is so far only 4 percent because iron oxide does not absorb all parts of the solar spectrum.  However, Grätzel’s careful observations of the results of iron oxide film variations (published in the Journal of the American Chemical Society)  have led Hydrogen Solar of the U.K. to work on developing mass-produced panels, aiming at reaching a 10 percent solar efficiency level (20 percent efficiency with iron oxide is theoretically possible) by adjusting the amount and arrangement of silicon and cobalt to improve the functional structure of the films.

If consumers and businesses were able to use solar panels on site to generate hydrogen, rather than getting hydrogen shipped in from a large facility, it would cut out the cost of shipping hydrogen.  Solar-to-hydrogen panels would be more efficient than small electrolysis machines.

C.  Thermochemical cycle using ceramic heat exchangers

Sandia National Laboratories is working on the high-temperature decomposition of sulfuric acid in ceramic heat exchangers heated by concentrated solar energy (or other heat source, e.g., nuclear).  The technology developed in 2006 is now being used in international sulfur-iodine experiments.  A scale-up demonstration of hydrogen production using the technology is proposed for Sandia’s Solar Tower facility.