Solar Resources

This section discusses solar resources in the United States and world.

In the first to fourth centuries, the Greeks and the Romans began using solar energy. The Roman’s began to use solar heat energy because the burning of wood was reducing the forests around Rome. The Romans built their bathhouses with large south facing windows to let in the sun’s warmth. The Greeks also began using sunlight to heat their homes. The homes were built so that the windows to the main rooms of the house faced south while the northern side of the home was protected from cold winds. The Greeks also provided for shade in the summer by using eaves on the windows of the southern side of the residence.


In the sixth century, sunrooms on houses and public buildings were so common that the Justinian code from the Byzantine empire initiated “sun rights” to ensure individual access to the sun.


In the Classic Pueblo Period, 1100 – 1300 A.D., the Anasazi community built dwellings in the side of a cliff. The Anasazi community occupied what is now the four corners of Utah, Arizona, New Mexico, and Colorado. This area is full of horizontal mesas “capped” by sedimentary formations. Wind and water erosion in the area have created steep walled canyons out of the sandstone. The layers of sandstone and limestone are more resistant to erosion than the layers of shale. The sandstone and limestone strata form overhangs over the shale strata. The Anasazi community built homes and other buildings into the cliff overhangs. Dwellings opened to the South West to absorb the most sunlight while the back of the cliff protected them from the cold northern winds. Cliff overhands let the winter sun in but also shaded villagers from the intense summer sun. The power of the sun played such an important role in the Anasazi community that eleven of the major buildings are oriented to the sun and moon. Additionally, every major building has an internal geometry that corresponds to the relationships of the solar and lunar cycles. Anasazi community


In the 1830s, Antoione-Cesar Becquerel, a French physicist, found that certain materials produce a small amount of electric current when exposed to light. This effect is referred to as the photovoltaic (PV) effect. Although the effect was observed, Becquerel could not explain the cause. Becquerel


In the 1860s, August Mouchout patented a design for a motor running on solar energy because he believed coal supplies would eventually run out. First, Mouchout developed the first solar dish collector. Then, after receiving funds from a French monarch, he designed a machine that turned solar energy into mechanical steam power and it soon operated the first steam engine. Mouchout’s funding was cut short when the French renegotiated a cheaper deal w/ England for the supply of coal and improved their transportation system of coal. Mouchout


A decade later, William Adams wrote a book on Solar Energy in which he introduced his idea to use mirrors to power a steam engine. This design is now known as the Power Tower and the technology is still used today. The tower used rows of small, flat mirrors on a rack. The rack rolled around a semi-circular track, reflecting sunlight onto a boiler. The tower could power a 2.5 horsepower steam engine. However, it could not compete with wood or coal.


Also in the 1870s, selenium’s sensitivity to light was discovered by Willoughby Smith, an English electrical engineer. Smith developed a method to continually test an underwater cable as it was being laid. In this test, he needed a semi-conducting material with a high resistance and he selected selenium rods for the testing. selenium discovery


In the 1880s, Charles Fritts, an American, invented the first solar cells from selenium wafers. Fritts hoped his selenium wafers would compete with Edison’s coal-fired plants, however, the selenium wafers had a less than 1% efficiency of converting sunlight into energy. wafers


In the early 1890s into the early 1900s, the first solar energy companies were born. Aubrey Eneas formed the First Solar Energy Company – The Solar Motor Company. Eneas saw opportunity in the American southwest, eventually moving the company from Boston to Los Angeles. Eneas marketed machine for steam-powered irrigation. Eneas first experimented w/ a device using a parabolic, trough-shaped reflector but it only heated one side of the boiler. Eneas then decided to use Mouchout’s conical reflector to heat the boiler more evenly and efficiently, resulting in a greater volume of steam production. Eneas then chopped the bottom end of the cone off and made the side more upright. This change in design increased the amount of sunlight heating the boiler raising the temperature on average to 1,000 degrees Fahrenheit. Eneas believed this temperature was enough to produce steam at industrial levels. The delicate design of the machine left it vulnerable to inclement weather. The Solar Motor Company sold their 1st Solar Energy system to a doctor but it was destroyed less than a week later by a windstorm. The piece holding the boiler gave way, sending the heavy tube crashing down onto the mirrored cone. Its 2nd system was destroyed by a hailstorm less than a week after it was sold and a 3rd was destroyed by a “dust devil” – mini tornado common to Arizona, in a similar fashion to the 1st machine.


In the 1880s, Swiss inventor John Ericsson built another version of the solar parabolic trough. He also was convinced coal sources would run out and there was a need for an alternative energy source. The trough resembles an oil drum cut in half with a reflective surface on the inside. The reflector focuses the sunlight onto a pipe carrying a fluid. The temperature of the fluid increases as it flows throw the pipe. The trough was cheaper than Mouchout’s dish-shaped reflector but could not produce higher temperatures than the reflector.


1901 – Ostrich Farm (yes, ostrich!) in southern California was a swanky tourist resort. It housed over 1,000 ostriches and patrons would come to see and feed them as well as watch farm hands ride the large animals bare-back. On the ostrich farm was a giant, concentrating solar motor – “the only machine of it’s kind in the work in daily operation.” This machine was invented by Aubrey Eneas, the same man who co-founded the Solar Motor Company of Boston, and was monstrous in size. It weighed 8,300 pounds and featured a conical reflector consisting of more than 1,700 mirrors. The mirrors focused sunlight onto a long cylindrical boiler in the center. This mirrored cone had over 700 surface feet and measured 35 feet across at its wide end. The device was connected to a track that ran the length of the a vertical, lightweight steel tower. The steel tower allowed a clock mechanism to keep the mirrors angled toward the sun throughout the day. The tourists to the Ostrich Farm were amazed that the device was powered on sunlight only yet was able to pump more than 1,400 gallons of water per minute. This water was used to transform the area from a dry, dusty farm to a lush garden full of flowers.


In 1941, Russel Ohl, an American, invented the selenium solar cell. Ohl was a researcher for Bell Labs and was researching silicon samples when he noticed his sample had a crack in it. Electricity flowed through the cracked sample when it was exposed to light. Ohl accidentally made a “p-n junction,” the basis of a solar cell. Excess positive charge builds up on one side of the junction while excess negative charge builds up on the other side of the junction. This creates an electric field and when the cell is hooked up in a circuit, an incoming photon hits the circuit. When the photon hits the cell, it can give an electron a kick and start an electric current. This solar cell was only about 1% efficient. silicon discovery , silicon discovery


1953 - Calvin Fuller, Gerald Pearson, and Daryl Chaplin of Bell Labs created the first practical solar cells. Daryl Chapin, an engineer, was trying to develop a source of power for telephone systems in dry, humid locations because the dry cell batteries degraded too quickly. Chaplin decided solar power was the option with the most potential. He tried selenium solar cells but they weren’t efficient enough. Meanwhile, Calvin Fuller, a chemist, and Gerald Pearson, a physicist, were working on controlling semiconductors’ properties by introducing impurities. Fuller gave Pearson a piece of silicon containing gallium impurities. Pearson dipped it in lithium which created a “p-n junction.” Pearson then hooked it up an ammeter to the silicon and shined a light on it. The ammeter jumped significantly. Pearson, aware of Chapin’s project, notified him of the silicon discovery. The three scientists worked together making silicon solar cells and even created a “silicon battery” by linking several silicon solar cells together. The silicon solar cells were about 6% efficient. Bell Labs



Major New Projects

Before diving into the major new projects, it should be at least noted that all projects must go through an environmental assessment and be approved by multiple state and federal agencies. This Environmental Progress Meter for one of the proposed projects, gives at least a little insight into what all must be accomplished before a project can even think about construction.

All new major solar projects begin with the same premise and the same technology that originally jumpstarted the solar energy field. Therefore, it is necessary to describe the basics before diving into the new solar power plants. Solar energy can be converted into electricity by using Photovoltaic Devices, or Concentrating Solar Power Plants.

Photovoltaic Devices
Photovoltaics, or solar cells are electricity-producing devices made of semiconductor materials, like crystalline silicon. The photovoltaic cell is used to convert solar energy into electrical power. Sunlight is composed of photons (particles of solar energy) and these photons carry different amounts of energy. When photons strike the photovoltaic cell, the photons reflect, pass through, or absorb; however, only absorbed photons are able to be utilized to generate electricity because the absorbed photons provide energy to the cell. When enough energy is absorbed the by the semiconductor material, the electrons are dislodged from the material of the semi-conductors atoms. When the electrons are dislodged spaces are created, and when enough electrons, each carrying a negative charge, travel to the front surface of the photovoltaic cell the resulting imbalance creates a voltage potential. To increase the power output of the cells, because one cell only produces about 1 to 2 watts of energy, the cells are electrically connected into modules. The modules can then be further connected to form an array if more power output is desired. The number of modules connected together to form an array will depend on the amount of power output needed or necessary. The photovoltaic cells generate direct current, which is used for small loads like your batteries, or telephones. Therefore, when photovoltaic cells are to be used for commercial purposes, or sold to electric utilities, the direct current must be converted to alternating current in order to connect to the grid.


Since its development, photovoltaic technology has been applied to a variety of uses including, space satellite radios, space and telecommunication satellites, household appliances, and homes. However, since the 1980’s it has been used as an electrical power provider and in 1982 the first photovoltaic megawatt-scale power station went on-line in Hisperia, California. It had a capacity of 1 MW. However, for many years thereafter, the global growth in photovoltaic technology was primarily sustained by small and medium-sized installations with an output below 1 MW. But, since 2007 this has changed substantially. Falling technology prices and the instability and rising costs within the fossil fuel industry has made solar parks increasingly attractive. The large photovoltaic power plants are generally fed into a medium voltage grid, and are almost exclusively free standing.

The large-scale grid-connected photovoltaic power plants usually operate at the megawatt-scale, and the industry is dominated by the use of crystalline silicon and cadmium telluride cells. These two semiconductors have remained dominate because there is a lack of experience using new types of semi-conductor material and solar cells. Therefore, financial entities are cautious to provide financing for their use. Crystalline silicon cells are by far the most mature and extensive technology. Crystalline silicon cells require a smaller surface area, and consequently, less support structure and cabling. Additionally, they have roughly seventeen to twenty percent efficiency (when efficiency is discussed, it refers to the amount of electrical power created and capable of use as output). Cadmium telluride requires a significantly greater surface area to achieve the same output which increases the cost of installation. Further, Cadmium telluride is considerably less efficient than crystalline modules, at only eleven percent efficiency rates; however, these thinner cells are considerably less expensive. As far as energy payback time is concerned, the payback period for the cadmium telluride cells is also quite a bit lower than crystalline silicon cells. Energy payback refers to how much time is required for producing the amount of energy spent for manufacturing the technology. For cadmium telluride cells the payback period is often less than one year, but crystalline silicon is typically between one and four years. However, both cells have a lifetime of about twenty to thirty years, so both are net energy producers because they generate much more energy over their lifetime than the energy that was expended in producing them.

Five Largest Photovoltaic Power Plants
1.) Sarnia Photovoltaic Power Plant
2.) Olmedilla
3.) Solarpark Strasskirchen
4.) Solarpark Lieberose
5.) Puerollan

Sarnia Photovoltaic Power Plant
This plant is located in Sarnia, Ontario Canada and was built by First Solar. First Solar is a major manufacturer of photovoltaic cells, and is involved in most new developments. The Sarnia facility is located on 950 acres and provides a total capacity of 80 MW of power; the facility generates approximately 120,000 MWh per year (or 13.69 MW=120,000/8760). Therefore, its capacity factor would be 17.5% (17.5%=13.69/80) (capacity factor is the ratio of the actual output of a power plant over a period of time and its output if had operated at capacity the entire time), and its power density is (13.69 MW/384 ha (acres—hectares)) 3.5 W/m2. This power output puts Sarnia as the largest photovoltaic power plant in the world. Cadmium telluride photovoltaic modules were used for the more than 1.3 million panels employed. With an 80 MW capacity, it can provide power for about 12,800 homes (it is common in articles for the worth of the MW to be described in terms of how many homes that would power). The complete system came on-line on August 20, 2010. No waste is produced, and the panels will be recycled after their useful lifespan.


Olmedilla Photovoltaic Power Plant
Built in Olmedilla de Alarcon, Spain and was completed in 2008. Olmedilla uses 162,000 flat crystalline silicon panels on 266 acres, and has a capacity of 60 MW. The actual production is 85,000 MWh/year (9.7 MW); therefore, it has a capacity factor of about 16%, and a power density of (9.7 MW/108 ha) 9 W/m2. The entire plant cost $530 million and was completed in fifteen months.


Solarpark Strasskirchen
This facility is located in Bavaria Strabkirchen, Germany. It has an installed capacity of 54 MW and was completed in 2009. The actual production is roughly 57,000 MWh/year (6.5 MW). Therefore, it has a capacity factor of 12%, and a power density of (6.5 MW/ 34 ha) 19 W/m2 . The total farm is comprised of 225,000 solar modules and covers about 86 acres (34 ha) of land.


Solarpark Lieberose
The facility is located in Turnow Preilack, Germany and has a capacity of 53 MW. The actual production is 53,000 MWh/year (6.05 MW). Therefore, it has a capacity factor of 11%, and a power density of (6.05 MW/162 ha) 3.7 W/m2. The plant was completed in 2009. The total park is comprised of 700,000 solar modules and comprises about 402 acres (162 ha) of land.


Puertollan Photovoltaic Solar Park
This solar farm was completed in 2008. It has 476 facilities with individual power of 100 KW, Therefore, the facilities total rated power is 47.6 MW. The actual production for this facility could not be found. The facility uses a total of 231,653 panels and is built on 241 acres of land.


Recently Approved Photovoltaic Power Plants

Power Plants in the Development and Planning Stages
Currently, there are a number of large photovoltaic power plants in the planning or development stages. The amounts of power a few of these new proposed plants are estimated to put out will significantly dwarf the previously listed top five. This is primarily due to the falling solar module prices and because First Solar has significantly lowered the production costs of thin-film cells which has helped the photovoltaic power plants overcome the lower efficiencies and become competitive.

Topaz Solar Farm
Will be located on the northwestern corner of Carrisa Plains, in San Luis Obispo County, California and has a capacity of 550 MW. The actual production will be approximately 1,100,000 MWh/year (125 MW); therefore, its capacity factor would be about 23%, and its power density would be (125 MW/1821 ha) 7 W/m2. The facility will be located on approximately 4,500 acres (1821 ha) of land and create 400 jobs. The location was selected due to the available solar resource, its proximity to existing electrical transmission lines, current land uses, and environmental sensitivities. Topaz Solar Farm has yet to receive final approval, but has secured a purchase power agreement with PG&E.


Desert Stateline and Sunlight
First Solar and Southern California Edison have agreed to build two large-scale photovoltaic projects in southern California. Desert Sunlight will be located in Riverside, and Desert Stateline will be in San Bernardino County. The entire project is to be located on 4,410 acres of public land. Desert Sunlight is poised to produce 250 MW of power, while Desert Stateline will have a capacity of 300 MW for a combined output of 550 MW. Desert Sunlight will have a nominal production of about 571,000 MWh/year (65 MW), and Desert Stateline will and actual production of about 673,000 MWh/year (76.8 MW). Therefore, Desert Sunlight will have a capacity factor of 26%, and Desert Stateline will have a capacity factor of 25%. The entire project will have a power density of (142 MW/ 1784 ha) 8 W/m2. Both projects still need approval from the BLM for permitting, but construction is scheduled to begin in 2012 for Desert Sunlight and 2013 for Desert Stateline. Both are expected to be completed by 2015. Additionally, a Power Purchase Agreement was approved by the California Public Utilities Commission on September 2, 2010. Desert Sunlight is seeking American Recovery and Reinvestment Act of 2009 (ARRA) funding and is listed as a ‘fast-track’ project for BLM permitting. A fast-track project are those where the corporations involved have demonstrated that they have made adequate progress to start the environmental review and public participation process to potentially be cleared for approval by 2010. If you are approved by 2010, this allows the corporation to be eligible for stimulus funding under ARRA. Desert Stateline is not currently pursuing ARRA funding.


Needle Mountain Power
The project is to be located on about 10,300 acres of privately owned and debt free land in western Mohave County, Arizona. The facility would require 8,200 acres for the solar generating facility and another 2,100 acres for industrial and commercial use. If all goes as planned, Needle Mountain Power plans to provide 1,200 MW of generation. However, Needle Mountain may find an issue with transmission line availability. Two large power lines, operated by the Department of Energy, cross the property and can interconnect with markets in Arizona, California and Nevada. However, these lines, currently can only hold about 400 MW, but if the lines are improved as is being discussed, then they could be capable of facilitating the full 1,200 MW of power. The total cost of construction is $4 billion, but developers are hopeful that financial incentives—tax credits, loan guarantees, state property tax reductions—could improve the overall economic and financial viability of the project. On March 9, 2010, Arizona Governor Jan Brewer offered her support for the development. Up next for the project is issuing the Environmental Impact Statement.

Agua Caliente
Located on 2,400 acres of farmland in Yuma County, Arizona the facility will provide 290 MW of power. On June 3, 2010 the California Public Utilities Commission approved the Power Purchase Agreement with PG&E. Additionally, no new transmission lines are required for this facility, and on July 07, 2010 FERC accepted the Interconnection Agreement and established an effective date of July 28, 2010. Additionally, this October AguaCaliente submitted their Environmental Assessment as required by the National Environmental Policy Act (NEPA).

Chevron Lucerne Valley Solar Project
The facility will be located in the Mojave Desert, approximately eight miles east of Lucerne Valley in San Bernardino County, California. It has a proposed capacity of 45 MW and when fully built will consist of 40,500 panels and cover about 422 acres of BLM-managed public land. On October, 5, 2010, Secretary of the Interior, Ken Salazar, approved the project. This is another ‘fast-track’ project seeking ARRA funding. It is still not determined if additional transmission capacity would be required for this project to connect to the grid.

Concentrated Solar Power
The other type of technology that can be used to harness solar energy is Concentrated Solar Power. The basic premise of concentrated solar power involves the conversion of solar radiation to thermal energy which is then used to run a conventional power system from steam. Concentrated solar power plants can be composed of either parabolic trough concentrating collectors, power tower/heliostats, or parabolic dish collectors. The important aspect of concentrated solar power is its thermal storage capabilities. The mirrors focus solar energy onto a receiver which heats the heat transfer fluid. Then to produce electricity immediately, the heated fluid transfers its heat energy to water creating steam. The steam is then used for the conventional turbine and generator to create electricity. However, this heat energy in the fluid can also be stored and used at a later time to generate electricity which makes solar energy more cost-competitive and a realistic option for clean, renewable energy.


Parabolic Trough
This is the simplest form of a concentrated solar power system. The solar collector field is composed of rows of trough-shaped solar collectors (usually mirrors), which contain an integral receiving tub. The entire solar field is usually composed of several parallel rows of the trough-shaped solar collectors; the collectors tilt with the sun to ensure that the sun is continuously focused on the receiver. The receiver is a tube containing the heat transfer fluid, usually oil or water. This fluid is heated as the sunlight shines down; the fluid circulates through the pipes to create steam, and this steam is in turn used for the turbine and generator.

Parabolic Dish
The parabolic dish uses mirrors to direct and concentrate sunlight onto an engine which produces electricity. The dish collects the solar energy coming from the sun, and the resulting concentrated sunlight is reflected onto a thermal receiver that absorbs the solar energy; the parabolic dish also tracks the sunlight continuously throughout the day. The thermal receiver then converts the collected solar energy into heat and transfers the heat to the generator. The most common type of generator used in parabolic dish systems is the Stirling engine. The Stirling engine uses the heated fluid to create mechanical power, and then this work drives and produces the electrical power. The parabolic dish produces small amounts of electricity as compared with other concentrated solar power technology. However, the units of dishes can be combined for a greater output of energy.


Power Tower/Heliostats
Numerous large, flat mirrors (heliostats) track the sun and focus sunlight onto a receiver at the top of a tall tower. The heat transfer fluid is heated in the receiver which is used to generate steam, and this steam is in turn used in a conventional turbine genitor to produce electricity. Some use water/steam as the heat transfer fluid, but some advanced designs are starting to use molten nitrate salt because of its energy-storage capabilities and its superior heat-transfer characteristics.


First Commercial Operation
Concentrated Solar Power plants first came onto the grid in the mid 1980’s via nine Solar Energy Generating Systems (SEGS) which utilized the parabolic trough technology. The nine SEGS are located in California in the Mojave Desert. Their total capacity equals 384 MW of energy. The nine plants still reliably operate today, and have produced more than fifty percent of all solar electricity in the world. The total land area for these nine plants comprises 2,314,678 square meters. Each of the SEGS received federal and state tax incentives as well as all have power purchase agreements with Southern California Edison.

Recently Approved Concentrated Solar Power Plants

The President, on July 3, 2010, announced a conditional commitment of $1.45 billion dollars for Abengoa Solar, Inc. to build Solana Solar facility seventy miles southwest of Phoenix, Arizona. The plant is said to have a capacity of 250 MW, and will employ molten salt thermal energy storage with a six hour storage capacity. The large buildings containing the molten salt will be located next to the steam boilers of the CSP plant. At select times, like when the sun is not shining, instead of creating steam, the heat transfer liquid will heat the molten salt. Then the fluid can be heated by running it through the hot salt instead of through the mirrors, and generate electricity in this manner. With a capacity of 250 MW, the Solana plant will be the largest concentrated solar power plant in the world, but only temporarily. The plant will utilize 2,700 parabolic trough collectors and cover approximately 1,920 acres. Solana is currently in the advanced stage of permitting and has received most of its authorizations from local, county, and state authorities. Additionally, Abengoa Solar has entered into a purchase power agreement with APS to sell energy produced for thirty years.


Imperial Valley Solar Project
A concentrated solar power facility proposed on approximately 6,140 acres of federal land managed by the BLM and approximately 300 acres of privately owned land. The generating facility will have the capacity to produce roughly 750 MW of solar power. On October 5, 2010 the BLM gave final clearance for the project to begin construction. State approval occured the previous week. This is the first solar project to ever be approved for construction on public lands. The project is to be constructed in two phases with the first phase employing 12,000 SunCatchers with a capacity of 300 MW, and the second phase employing 18,000 SunCatchers with a total capacity of 750 MW. The SunCather is a privately manufactured and developed parabolic dish technology. Essentially, however, the SunCatcher performs and generates electricity in the same way as any other parabolic dish.

The project plans also include the construction of a new 230 kV substation (area where voltage is transformed from high to low or the reverse using transformers) approximately in the center of the project site. For the first phase of the project to be completed, this is the only transmission line that needs to be constructed. However, for the second phase of the project to be able to come on-line and deliver power to San Deigo, the Sunrise Powerlink Transmission line project proposed by SDG&E would need to be completed. The Sunrise Powerlink is essentially a 500 kV transmission line that runs from Imperial County to San Diego with a 1,000 MW capacity. The total cost of the new transmission line is $1.883 billion dollars. The Sunrise Powerlink was approved by the California Public Utilities Commission in December 2008, the BLM in January 2009, and the U.S. Forest Service in July 2010. Additionally, SDG&E was given the green light to start construction by the Forest Service on October 15, 2010 when it affirmed the agency’s Record of Decision.

The Imperial Valley Solar Project incurred a setback on October 29, 2010 when the Quechan Indian tribe filed suit to stop construction arguing the installation would cause damage to cultural and biological resources of significance.


Blythe Solar Power Project
The project is a joint operation between Solar Millennium and Chevron Energy Solutions. It is a concentrated solar thermal electrical generating facility using parabolic trough technology. There will be four adjacent, independent, and identical solar plants each with a capacity of 250 MW. Therefore, the entire facility will have a 1,000 MW capacity, and will need about 7,025 acres of land. The project is to be located primarily on public lands in Mojave Desert. For all four solar plants to be completed it will take at least six years and at least $6 billion dollars. On October 25, 2010 the Secretary of the Interior, Ken Salazar approved this plant and gave it the final clearance for construction to begin..


The proposed project would consist of three solar thermal power plants near Ivanpah Dry Lake, in San Bernardino County, California on BLM land. The three plants would be constructed in three phases with two 100 MW phases and one 200 MW phase. The technology to be used in each of the three facilities is power towers with heliostats. Each 100 MW site would require about 850 acres and would be comprised of three tower receivers and arrays, while the 200 MW site would require about 1600 acres and have four tower receivers and arrays. On October 07, 2010 Ivanpah received all of its final permits and was given the go-ahead to begin construction, and on October 27, 2010 ground was broken for the Ivanpah solar facilities.


This list does not begin to cover all of the utility-scale solar energy projects currently under development or in operation. The Solar Energy Industries Association provides a more comprehensive list that is updated reguarly.

Power Densities
Traditonal power sources have much higher power densities than all renewable sources. Natural Gas has a power density between 200-2000 W/m2, and coal has a power density between 100-1000 W/m2. Solar, as discussed earlier, has a power density of between 4-10 W/m2. Therefore, a new energy infrastructure dependent upon renewables will have to have an increase in fixed land requirements, and if solar is used, this will preempt any other land use in areas devoted to photovoltaic cells, troughs, dishes, or power towers. Additionally, for renewable energy to come onto the grid, more land would have to be secured for the addition of more extensive transmission lines and transmission rights-of-way to transport the electricity from remote sunny areas to the population centers.



Good solar resources website. The website an independent, non-commercial site where individuals can go to obtain information about photovoltaics, economics, large scale, books, etc….


New self-assembling photovoltaic technology can keep repairing itself to avoid any loss in performance.
September 7, 2010
David L. Chandler, MIT News Office

Constant exposure to sunlight causes gradual degradation. In conventional silicon-based photovoltaic cells, degradation has not been a problem, but the new systems being developed do experience a degradation in efficiency. When operation exceeds 60 hours, efficiency falls to 10 percent of was observed.

Plants avoid this degradation of their systems because the molecules involved in photosynthesis constantly break down and are reassembled so that they are continually brand new. During photosynthesis the reactive form of oxygen produced by sunlight causes plant proteins to fail in a very precise way and then those same proteins are quickly reassembled to restart the process.

Associate Professor Michael Strano and his team at MIT have created a set of molecules that mimics the self-assembling properties of chloroplast proteins, called the photoelectrochemical cell. These molecules can turn sunlight into electricity molecules and can be repeatedly broken down and then reassembled quickly, just by adding or removing an additional solution.


The MIT team “produced synthetic molecules called phospholipids that form disks; these disks provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light. The disks, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes — wire-like hollow tubes of carbon atoms that are a few billionths of a meter thick yet stronger than steel and capable of conducting electricity a thousand times better than copper. The nanotubes hold the phospholipid disks in a uniform alignment so that the reaction centers can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.”

The synthetic system will under the right conditions spontaneously assemble into a light-harvesting structure that produces an electric current. When a surfactant is added to the mix, the seven components all come apart and form a soupy solution. Then, when the researchers removed the surfactant by pushing the solution through a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell.

The individual reactions of these new molecular structures in converting sunlight are about 40 percent efficient. Theoretically, the efficiency of the structures could be close to 100 percent.

Nanoscale layers promise to boost solar cell efficiency
December 18, 2008

Operation of a PV cell, A n-type Silicon, B p-type Silicon How PV systems work.

When photons strike a material, electrons absorb energy and jump from their low-energy “ground” state to their high-energy “excited” state. That process leaves holes where electrons are missing. The electrons and holes remain loosely bound. In a solar cell, the ectrons and holes are separated created so the electrons can flow through an external circuit.

That separation is generally achieved by using a second type of material whose energy level is lower. Arriving at the interface between the materials, the electrons see an opportunity to lose some of their extra energy, so they move into the second material. Over time, holes accumulate in the first material and electrons in the second. Connect the outside edges of the two materials by a loop of wire and the electrons will flow back to the first material, powering a light bulb or other device along the way.


There are two approaches to material selection that can help optimize the process just described. One key is choosing the correct difference, or “offset,” between the energy levels of the electrons in the two materials. This means reducing the amount of energy the electron leaves behind when it jumps to the next level. Any dissipation above the amount necessary to move the electron to the next level reduces the energy available for power. So fine-tuning the energy offset at the interface between the two materials is one means of increasing efficiency.

Another means is to choose the correct “band gap” for each material, that is, the difference in energy between the electrons’ ground and excited states. The band gap determines what color light, or wavelength, the material will absorb and emit.

Silicon PVs are optimized to respond to the sun’s broad visible light spectrum and are not very good at converting ultraviolet light or infrared light. Ultraviolet light is strongly absorbed but also strongly reflected by the silicon PV surface. Infrared light simply passes through. The opportunity to fine tune PV performance with respect to converting ultraviolet and infrared light presents an opportunity to improve output.

The idea is to combine the silicon solar cell with additional PV cells made from materials that can absorb those poorly utilized wavelengths thereby capturing and converting more of the energy in sunlight.

“The first step in making a good solar cell is to get the right spacing between energy levels within the individual materials and the right positions with respect to the neighbor’s energy level.

Moungi G. Bawendi, Lester Wolfe Professor in Chemistry is an expert in creating nanomaterials with specially tuned band gaps and energy levels. Bawendi’s specialty is the quantum dot, a tiny bit of material that is just a dozen or so atoms across. Because the particle is so small, electrons are unable to move around as much as they’d like and they become more energetic. The energy levels and band gap are determined by the exact size of the particle. “So with a quantum dot, you can fine-tune its band gap over a very broad range simply by varying the size of the material. Bawendi’s group can make nano-crystals that are precisely tuned to absorb a particular color.

The quantum dots —or polymers, organic molecules, metal oxides, or other nanoscale materials—must be depsited so that they work together to capture as much of the solar spectrum as possible and to separate the photogenerated electrons and holes efficiently.

Instead, of just mixing it all up into an emulsion and spreading it as a thin film the researchers have developed a layering technique that results in a stacked nanostructured PV. The nanomaterials can be layerred on flexible substrates such as rollable plastic or metal foils, or deposited on conventional silicon-based PVs to form “tandem” structures with boosted efficiency. Nanomaterials work better than silicon because, unlike silicon, they are created in an optically active form before being deposited on the silicon. This researchers can use simple room-temperature processes, such as printing of nanostructured inks, stamping, or silk screening.

According to Bulović, “first-principles calculations suggest that if they do everything exactly right using a single nanostructured layer on top of silicon, they should achieve 15 percent efficient conversion—somewhat better than today’s commercial PVs.” Theoretically they should be able to achieve 25% power conversion if they combine multiple layers that are good at absorbing differing parts of the spectrum.

So far, that efficiency has not yet been achieved. But Bulović is optimistic, “we just need to understand the detailed physical phenomena that govern the operation these nanostructured photovoltaics.”

Solar funnel

New antenna made of carbon nanotubes could make photovoltaic cells more efficient by concentrating solar energy.
September 13, 2010
Anne Trafton, MIT News Office

Using carbon nanotubes, hollow tubes carbon atoms, to form antennas that capture and focus light energy, could potentially allow much smaller and more powerful solar arrays.

“Instead of having your whole roof be a photovoltaic cell, you could have little spots that were tiny photovoltaic cells, with antennas that would drive photons into them,” says Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering and leader of the research team.


The antenna consists of a fibrous rope about 10 micrometers (millionths of a meter) long and four micrometers thick, containing about 30 million carbon nanotubes. Strano’s team built, for the first time, a fiber made of two layers of nanotubes with different electrical properties — specifically, different bandgaps.

The inner layer of the antenna contains nanotubes with a small bandgap, and nanotubes in the outer layer have a higher bandgap. That means the excitons in the outer layer flow to the inner layer, where they can exist in a lower (but still excited) energy state.

When light energy strikes the material, all of the excitons flow to the center of the fiber, where they are concentrated. Strano and his team have not yet built a photovoltaic device using the antenna, but they plan to. In such a device, the antenna would concentrate photons before the photovoltaic cell converts them to an electrical current. This could be done by constructing the antenna around a core of semiconducting material.

The interface between the semiconductor and the nanotubes would separate the electron from the hole, with electrons being collected at one electrode touching the inner semiconductor, and holes collected at an electrode touching the nanotubes. This system would then generate electric current.

Solar cells that incorporate carbon nanotubes could become a good lower-cost alternative to traditional silicon solar cells, says Arnold. “What needs to be shown next is whether the excitons in the inner shell can be harvested and converted to electrical energy,” he says.

Strano’s team is now working on ways to minimize the energy lost as excitons flow through the fiber, and on ways to generate more than one exciton per photon. The nanotube bundles described in the Nature Materials paper lose about 13 percent of the energy they absorb, but the team is working on new antennas that would lose only 1 percent.

New Nanotechnology Breakthrough Could Drastically Reduce Solar Costs

Scientists at the Massachusetts Institute of Technology (MIT) have successfully coated paper with a solar cell. PaintOnSolar.png This breakthrough could lead to layers of these materials essentially being sprayed using different manufacturing techniques to make a thin-film solar cell on a plastic, paper, or metal foils.

This technology has the potential to result in drastic solar cost reductions, lower the weight of solar panels, installation with a staple gun.

For more information.

Hybrid Solar Panels Convert ‘Heat Stress’ to Hot Water

A new design by Solimpeks Solar Energy Corp. that improves solar PV panel efficiency by turning “heat stress” into hot water.

As PV panels become hotter the efficiency lowers and that directly affects power output.

A test to determine how much is lost as a result of heat stress showed that above 42 degrees Celsius or 107.6 degrees Fahrenheit panels lost about 1.1 percent of their energy for every degree of temperature added.

Solimpeks, Solar energy Corp., which makes the Volther Powervolt 175/460 and the Powertherm 155/680 (which features extra solar glass and greater long-term efficiency), offers both solar PV electricity generation and solar hot water by using between one and two liters of water to absorb the extra heat that prevents panels from performing in their optimum range.


According to Inhabitat, the water-cooled PV panels are reported to deliver efficiencies of up to 28 percent while also providing 140 to 160 °F water. This falls well within and even hotter than the typical hot water temperature range which is usually between 120 °F and 140 °F. Solar PV efficiencies in the laboratory setting are approaching the theoretical limit, 25 percent; but in the real world, efficiency reaches about 22 percent, and like everything else in this world you get what you pay for. Of course the added benefit is that while cooling the panels with water extends the life of the panel it also reduces the costs of producing hot water.

Solar Integrated Windows

Developed by Kyosemi Corporation, Sphelar solar cells are a glimpse of how windows in buildings might be used to collect solar power in the not-so-distant future.

Sphelar cells are solidified silicon drops measuring 1.8 mm in diameter and are 20 – 80% transparent. It is their transparency that allows for use in glass to create a transparent solar cell window, capable of absorbing light from any direction or angle. Both sides of the glass can collect light, both sides generate electricity wherever the light source is located.

The cells can be embedded in flexible surfaces and so can be formed into a variety of shapes from curved surfaces to pliable sheet.

Based on Sphelar® technology, Kyosemi provides small-sized solar modules. Six different voltage choices are offered which range from 0.48 to 6 (V) and 1.25-1.38 mA.
A spherical micro solar cell moulded in a plastic case captures the light from all directions. Range from 0.481 -0.484 Vpm.


Small-size Sphelar® dome products to have an output power of 40-100mW (Vpm: 3.8-5.8V), they are suitable as energy harvestors for WSN (Wireless Sensor Network).

Meet Eleanor
MIT won 2nd place

Eleanor is a great step forward in the electrical system that is crucial to any high performance solar racer. Using top of the line mono-crystalline silicon cells, Eleanor uses less power than a hair dryer, but manages to travel at highway speeds of over 55 mph.

The solar array is managed by 98% efficient maximum-power-point-trackers (MPPTs), modules that act as an interface between the battery pack and the solar array, which ensure the cells are operating at their peak power. A CAN network provides the team and the drivers with a constant data flow about the status of the battery pack and the solar array, allowing the team to optimize their speed in real-time.

With generous help from sponsors, SEVT recently constructed its most energy-dense battery pack yet, one of the highlights of the electrical system. The battery pack monitors voltage and temperature of 600 cells, and has safeguards to protect against damage.

The NGM motor, a high efficiency direct-drive motor, specifically tailored to high efficiency vehicles such as solar racers. Because Eleanor uses battery power slowly the she can cruise for two hundred miles without recharging. Together with the solar array and the battery, Eleanor can cruise under full sunshine almost indefinitely.

Solar on water

[ Tamarack Lake solar electric boat Solar Watercraft


Solar wifi


International prize for solar cooker

One Earth Designs, a company created by an MIT student team to produce a low-cost portable solar cooker for use in developing countries, won top prize last week in the Netherlands Green Challenge.


The solar cooker is made of yak wool and a thin reflective coating and is expected to sell for about $13. In addition to cooking food and boiling water, the portable device can be folded up and carried in a canvas bag, can be used to provide home heating and to generate power for lights or cellphones.

Solar Planes
The Solar Impulse, made its maiden voyage April 7, 2010 in Switzerland.

The flight only lasted 87 minutes, but the Solar Impulse is designed to be able to fly around the world without stopping, simply relying on solar power. The plane held an array of 12,000 solar panel cells and reached an altitude of 4,000 feet.

The founder of Solar Impulse, Bertrand Picard, felt the solar plane test to be a crucial step in his goals of circumnavigating by air on solar power.

KYOCERA Solar Module First in the World to Pass Major Testing of TUV Rheinland's Independent ‘Long-Term Sequential Test’

October 14, 2010
Kyocera Corporation (President: Tetsuo Kuba) announced today that its main 210-watt solar module is the first in the world to have passed the major sub-tests of the new “Long-Term Sequential Test” performed by TUV Rheinland Japan Ltd. which independently evaluates solar module quality and reliability.

Technology trends
IEA PV Roadmap
Flat Plate Technology
Increasing efficiencies

c-Si, crystalline silicon PV modules 15-18%
improve efficiency and effectiveness of resource consumption through
materials reduction
improved cell concepts
automation of manufacturing

sc-Si, sgl crystalline 14-20%
mc-Si, multi-crystalline modules 14%

PV cells made from ribbons 14%


Thin film - 7 % to 13 %. Thin film materials commercially used are amorphous silicon (a-Si), cadmium telluride (CdTe), and copper-indium-gallium-diselenide (CIGS).

CIGS: Copper indium gallium (di)selenide
CdTe: Cadmium-telluride

Another option being researched is HIT: Heterojunction with Intrinsic Thin layer cells to improve efficiency. A crystalline silicon cell coated with a supplementary amorphous PV cell to increase the efficiency.

Emerging technologies

1. Advanced inorganic thin film technologies (Si, CIS).
2. Organic cells – made from plastic instead of silicon
Dye sensitized solar cell – hybrid approach of an organic cell retaining an inorganic compound.

Novel Concepts – aim at achieving ultra-high efficiency solar cells by developing active layers which best match the solar spectrum or which modify the incoming solar spectrum.

Concentrator technologies (CPV)

Projected efficiency increases


Batteries - Storage

CSIRO - UltraBattery

The UltraBattery is a hybrid energy storage device that integrates a supercapacitor with a lead acid battery in one unit cell.
This unique design harnesses the best of both technologies to produce a battery that can provide high power discharge and charge with a long, low-cost life.

UltraBattery technology is being developed for two major applications: low emission transport, specifically hybrid electric vehicles (HEV), and renewable energy storage from wind and solar sources.

Concentrating solar thermal technologies

Three main technologies:
1. Central recievers
2. Parabolic trough
3. Paraboloidal dishes

Ceramic receiver technology
Advance solar volumetric air receiver for commercial solar tower power plants.
Advantage over metallic mesh is that ceramic has a better resistance to high temperature and weathering,

Reducing the costs of dish/Stirling systems
Focus on the optical dish design, the supporting structure the Stirling engine and control system developed by EURODISH.

High flux solar facilities SOLFACE PROJECT
Offers high quality research into nano-tech & nano-science
solar photo excitation.
solar photoluminescence of gaseous species.

Energy Storage for Direct Steam Solar Power Plants
Storage media based on the micro encapsulation of PCM (phase change materials) in a matrix of expanded graphite.
Select most efficient storage configuration for high efficiency internal charging/discharging heat transfer.

Advances in solar thermal electricity technology

Solar thermal electricity – process of collecting solar energy and converting it to heat through the use of some heat to electricity conversion device. Usually a heat engine, other options consist of a thermoelectric pile converter or a fan converter as in solar chimneys.

Single axis tracking

A technology where relatively long and narrow reflectors are tracked about a single axis to keep the sun’s image in focus on a linear absorber or receiver. The receiver is usually a tube or series of tubes which contain a heat transfer fluid.

Parabolic trough technology

Large fields of parabolic trough collectors are used supply the thermal energy needed to produce steam for a Rankine steam turbine/generator cycle.

The reflectors curve around one axis and the heat transfer fluid travels along the center of the inner curve. The parabolic shape collects rays along a single line focus with radiative losses of only a few percent. Before it went out of business LUZ International put into operation LS-1 and LS-2 trough technology.


• LS-1 optical concentration 19:1, it and the LS-2 used black chrome selective coatings
• LS-3 – last collector design by LUZ

  • represents state of the art in parabolic trough,
  • optical concentration 26:1, metal ceramic coatings,
  • not market competitive w/o substantial env. subsidy,
  • industrial groups backing this believe large production w/result in electricity generation costs of .055/kWh in areas of high insolation,

companies now –
- mirrors – Pilkington Solar Int’l,
- HCE receiver tube technology sold to SOLEL Solar sys. ltd. Jerusalem, Israel.
Disadvantages of the linear fresnel systems are that the collectors must be positioned at a distance from each other to avoiding shading and because there is only one absorber on a single linear tower there is not choice about the direction of orientation of a given reflector.

Mills calculates that the solar thermal plants currently in operation that incorporate operation and maintenance improvements and collector design could produce power for about 10-12 cents/kWh. If a US$25/tone carbon credit is put into the calculation the cost for electricity drops to US$0.032 – 0.043/kWh, not included in this price is the value of local environmental improvements.

Improving linear fresnel reflector technologies

Compact linear Fresnel reflectors (CLFR)

In the CLFR the system uses parallel rows of mirrors underneath an elevated thermal absorber. The mirrors are slightly curved and the rows are moved by a central motor. The reflectors can be positioned close together because the parabolic shape is flattened. This eliminates the shading problem found in previous LFR systems. The closely positioned reflectors have the option of directing the reflected solar radiation to at least two absorbers. The CLFRs are mounted close to the ground, this avoids wind problems and reduces structural costs.


D. Mills Advances in solar thermal electricity technology



The Solarmundo does not use intermeshed tower arrays like the CFLR. The LFR employed by Solarmundo uses a reflector inside the cavity and single tubular absorber and glass secondary reflector that operates at high temperatures. More of the sunlight is captured for heating the absorber. The absorber moves under thermal expansion and is contained by a U-shaped tower structure and moving supports.

The company claims beam to electric efficiency between 10% - 12% on an annual basis which is lower than the trough system which achieves between 14% and 16% efficiency.

Transporting and exporting electricity from CSP

When distance is greater than a few hundred kilometres, economics favour high voltage direct-current (HVDC) technology over alternative-current technology. HVDC lines of gigawatt capacity can exceed 1,000 km and can be installed across seabeds and they also have a smaller environmental footprint. Electricity losses are 3% per 1,000 km, plus 0.6% for each conversion station (as HVDC lines usually link two alternative-current areas). This creates opportunities for CSP plant operators to supply a larger range of consumers.

Duke Solar Power Roof

The Power Roof(trademark) is a roof integrated, single axis tracking moving absorber stationary reflector system provides heat and power to a single building. The system includes a high temperature solar collector system, a natural daylighting system, a radiant barrier, an insulating system, an optional means to capture passive solar heat in the winter, an infiltration barrier, the building roof structure, and a waterproof guaranteed roofing system.” The collected thermal energy can be used for industrial processes, absorption cooling, desalination, water purification, secondary space heat and for domestic hot water purposes.

Two axis tracking technologies

Paraboloidal dish technology
ANU (Australian National University dish technology. These are big structures and the emphasis is on developing a lightweight, stiff structure. ANU’s SG3 dish is 25m in diameter, it consists of 54 triangular mirror panels, made of thin glass with a foam and metal laminate backing developed by ANU. As of the publication of this article no commercial array has been constructed taken place, but two have been built, one in Canberra and one which was sent to Israel to be used by the Weizman Institute.

The Weizman dish, called PETAL was installed at Sede Boquer in Israel. has been installed for high concentration experiments and is operating well. Steam is collected across the field and run through large steam turbines.

Boeing SES dish

In the United States Phase II of the Boeing/Stirling Energy Systems Dish Engine Critical Components (DECC) has delivered 10,000 hours of operation, claims a daily conversion of solar beam to electricity of 24%, peak efficiency of 29.4%, peak solar power generation of 24.9 kW and a solar availability of 96%. It uses a Kockums 4-95 Kinematic Stirling engine which operates at 720 degrees Celsius. Next stage field trials.

Current Boeing/SES dish/stirlingdesign.

Pictured below is the SAIDC/STM joint venture. It uses a STM generation III 4-120 kinematic stirling engine operating at 720 degrees Celsius. Annual solar efficiency is reported as 18% and the peak efficiency, 23%. The dish can be operated using natural gas. Two have been built and are in Golden, Colorado and Phoenix, Arizona.


In Europe, SBP and DLR (Deutsches Zentrum fuerrorr Luft- and Raumfahrt e.V. have been running three DISTAL I systems with a rated power of 9kW in Spain for more than 20,000 hours with 90% availability. They have achieved an effective radiant flux concentration of more than 3500 and a peak solar to electric conversion 20%.

DLR is developing and testing a hybrid version of the heat pipe receiver with an integrated gas burner. Currently being tested is a new 8.5 m diameter DISTAL II dish with higher concentration, sunrise to sunset tracking operation, and it uses a reworked SOLO 161 Stirling engine.

One disadvantage faced by Stirling engine users are the high costs, estimated by Mills at over US$7 ppW, he anticipates a shift to solarised Brayton micro-turbines which he expects to be available at US$1 ppW range. The advantage of the Stirling engine is that the best of the Stirlings deliver 42% efficiency as compared to the Brayton at 25-33%. Larger Braytons reach a peak efficiency of 40% but are too large for dishes.

Spectrolab makes GaAs tandem cells for use in space. When paired with the Boeing dish it can obtain 40% efficiency, comparable to the Stirling system.

Single tower to multi-tower arrays
Solar tower technology has been dominated by the configuration of the array around a central large tower receiver. Early plants in Genoa and Sicily used water/steam HTF and eutectic salt storage, in 1981 in Spain, the first grid connected plant using sodium HTF and sodium heat storage, in Japan a water/steam HTF, in France the Themis plant used salt heat transfer fluid (HTF) and 2-tank molten salt heat storage, in the U.S., Solar One used water/steam and oil storage, in 1985 a Crimean plant used water and saturated steam HTF and pressurized water storage. In the 1990s Solar One was converted to Solar Two and used molten salt heat storage allowing for operation during cloudy days and evenings.

In 1999, the Spanish government began planning for two more commercial central receiver tower projects. The field is required to incorporate 16 hours of full power storage. Molten nitrate salt is used for both heat transfer and storage. The molten salt flows through pipes illuminated at the top of the tower providing the turbine with steam at a temperature close to the peak salt temperature of 565 degrees Celsius.

Another Spanish project involves a consortium consisting of CIEMAT, DLR, FICHTNER and run by an IPP called Sanlucar Solar. This tower will use a volumetric air receiver operating at 680 degrees Celsius at the top of a 90m tower and a conventional steam turbine. The heliostats themselves are 91 m2 and will span 500,00 m2 and incorporates short term storage made of alumina saddles that will provide power for one hour.

The trend of implementing distributed generation of fossil fuels has infiltrated the solar energy sphere of thinking as well. One idea put forth by Romero is a modular integrated utility systems (MIUS). The idea is to use a 26m tower, a heliostat area 6624m2 tower using a Brayton 1.36 MW(e).

The Schelde Heron turbine has a peak efficiency using solar energy of 39.5% higher than the 25-34% typical of smaller turbines. The waste heat from the turbine is significant but can be used for process heat near the plant site.

In Australia the multi-tower solar array (MTSA) allows extremely closely spaced reflectors capturing over 90% of the solar beam radiation falling on the area, multiple receivers of radiation use advanced thermal and photovoltaic absorber technology, and the receivers can be place above the reflector field between 8m – 12m high.

The MTSA splits the incoming solar beam between the photovoltaic receiver and the Brayton microturbine. The efficiency of the photovoltaic receiver is boosted to 35-37% because it is sent the green to red portion of the visible and very near infrared energy that most closely matches its requirements and the rest is sent to the Brayton microturbine which can achieve 25% efficiency. Again waste heat from the turbine can be used for thermal purposes or air conditioning chillers. According to Mills if advanced microturbines and GaAs tandem PV cells are used the system could realize over 40% efficiency. Deploying a highly efficient microturbine like the Schelde Heron without PV and with a single large Rankine cycle second stage turbine would allow electrical conversion efficiencies close to 50%.


Low temperature technologies

Enviromission LTD
• Evacuated tubes
o two types: all glass and flat metal absorber in glass type,
o most tube production takes place in China,
o and most of the tubes are used for solar hot water production.

Now tubes are being used in higher temperature production. Selective coatings increase the temperature of the hot water produced to 185 degrees Celsius and can be used with the new generation of organic Rankine cycle (ORC) turbines.

Now tubes are being used in higher temperature production. Selective coatings increase the temperature of the hot water produced to 185 degrees Celsius and can be used with the new generation of organic Rankine cycle (ORC) turbines.

A closed loop of working fluid is heated to the point at which it produces vapour. The vapour drives a micro turbine and then condenses back to liquid and the cycle repeats itself. Overall efficiency is a not so very impressive 10-13%, but the system is a 24 hour delivery system and the overall cost of the system will probably go down.

Mills notes that the main problem is the costs of the ORC engines are high, almost as high as PV panels, but the differences between the two systems weighs in favor of foreseeing that future costs of energy from evacuated tube technology will be lower. The cost of the engine can be spread over the hours of operation, larger production of tubes will cause the price to drop, simple and cheaper seasonally adjusted evacuated tube collectors designed for higher temperatures may allow improved engine efficiency and lower panel ppW costs, using pentane heat transfer fluid operating at 200 degrees Celsius, pressurized water or thermal oil can be used as the transfer fluid and as the storage medium avoiding battery costs

Solar Chimney
• Chimney – air is heated underneath a large glass structure of about 5 km in diameter and passes up a large chimney through a wind turbine near the base as it rises.
• The chimney for a 200 MW(e) tower would be the tallest structure in the world.

Structural cost reduction
The Eurotrough project developed a cheaper box section support system for the trough reflectors.

Direct steam generation
Direct Steam Generation in parabolic trough, DISS
Tilting the trough for some of the time illuminates the top of the absorber tube containing vapour phase which is poorly conductive. This can cause stratification of the flow, tube overheating and pipe bending under the temp difference that arise across the pipe cross section.

To resolve: LS-4 technology. The German DLR Direct Steam Generation in Parabolic Troughs (DISS) project. The liquid is circulated in “an evaporating portion of the array at saturated steam conditions and the steam is taken off with a steam separator to a separate part of the array for superheating.” The increased parasitic parasitic energy costs are offset by the ability for controllability of superheated steam parameters and the fact that stratification is impossible.

New plants, using current technology with these proven enhancements, could produce power today for about US$0.10–0.12/kW h. With an environmental subsidy based upon carbon trading, a World Bank funded study (Enermodal Engineering Ltd., 1999) suggests that in large production this technology would be competitive against fossil fuel, with the cost of electricity under a US$25 per tonne carbon credit between US$0.032 and $0.043/kW h, lower than conventional generation. This does not include any local environmental improvement which might be valued.

Solar Parabolic Trough

generate high-pressure superheated steam. The superheated steam is then fed to a conventional reheat steam turbine/generator to produce electricity. The spent steam from the turbine is condensed in a standard condenser and returned to the heat exchangers via condensate and feedwater pumps to be transformed back into steam. Condenser cooling is provided by mechanical draft wet cooling towers. After passing through the HTF side of the solar heat exchangers, the cooled HTF is recirculated through the solar field.


The ISCCS is a new design concept that integrates a parabolic trough plant with a gas turbine combined-cycle plant. The ISCCS has generated much interest because it offers an innovative way to reduce cost and improve the overall solar-to-electric efficiency. The ISCCS uses solar heat to supplement the waste heat from the gas turbine in order to augment power generation in the steam Rankine bottoming cycle. In this design, solar energy is generally used to generate additional steam and the gas turbine waste heat is used for preheat and steam superheating. Most designs have looked at increasing the steam turbine size by as much as 100%. The ISCCS design will likely be preferred over the solar Rankine plant in regions where combined cycle plants are already being built.

Hydrogen production
Using solar to split hydrogen. Zero emission production of hydrogen using solar.
Long-term scenarios for energy and environment: Energy from the desert with very large solar plants using liquid hydrogen and superconducting technologies
L. Trevisani *, M. Fabbri, F. Negrini
Department of Electrical Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy
Received 1 May 2005; received in revised form 29 June 2005; accepted 16 September 2005

The system proposed in this paper resorts to the use of liquid hydrogen (LH2) for energy storage, and to the combined transport of electric energy and LH2 with a MgB2 superconducting line. The system allows flexible delivering of energy in electric and chemical form, depending on end-users demands.

A pilot plant for the transport of electric energy and hydrogen through the Gibraltar’s strait is proposed. The plant is limited in power to 100 MW, but is designed to be extensible up to 12 GW in future, as a large power link between the European and the North African nets. The location choice is based on following characteristics:
• limited length of the stretch;
• expected increase of energy transport demand in the area,
• assuring grids stability;
• great renewable energy resource availability in North Africa.

US industry currently produces 9 Mtons/year of hydrogen for use in chemicals production, petroleum refining, metals treating, and electrical applications. In the US 700 km of pipeline exist. The primary combustion product from hydrogen is water, when solar is used for electrolysis the plant would be a zero emission plant.

Hydrogen has more energy per unit mass than any other fuel, higher heating value of 141.9 Mj/kg, the lowest density and low volumetric energy content (25% less than natural gas). For storage it can be compressed, 14.5 kg/m3 at 20 MPa and 288K, or liquefied, 70.8 kg/m3 at 0.1 Mpa and 20.4 K.

The proposed system, schematically represented in Fig. 1, is aimed at providing a solution for large RES power transport and delivery regulation. When there is RES power availability in excess of grid demanding, the system produces hydrogen by water electrolysis, which can be cooled down to 20.4 K for liquid storage. The stored hydrogen can be reconverted into electric energy in periods of RES shortage. The exceeding part can be transported through a cryogenic pipeline, acting at the same time as the cryogen of a MgB2 superconducting DC line for the concurrent transport of electric energy and LH2. A similar line, but powered by nuclear power plants, was proposed for the American SuperGrid. Assuming that LH2 is required for energy storage at the plant location and for end-users delivering, the system has been shown to be energetically more efficient than competing systems based on conventional technologies (GH2 pipeline or electric line) in the case of a reference solar plant of 500 MWp and 10 km line length.

Ammonia Storage
Developing ammonia based thermochemical energy storage for dish power plants.
Lovegrove, Luzzi, Soldiani, Kreetz

Solar thermal power station using thermochemical energy storage.

Developing ammonia based thermochemical energy storage for dish power plants.
The solar thermal group at the Australian National University has been working for over two decades on a system for dissociating ammonia with concentrated solar energy so that the products can be stored and recycled through a conventional ammonia synthesis converter to achieve 24 h power production.

Closed loop thermochemical storage of solar energy using ammonia.

The Solar Thermal Group at the Australian National University has completed an experimental solar-driven ammonia-based closed-loop thermochemical energy storage system. The system uses a cavity receiver containing 20 reactor tubes filled with iron based catalyst material, which collects the radiation from a 20 m2 dish solar concentrator and dissociates ammonia with concentrated solar energy so that the products can be stored and recycled through a conventional ammonia synthesis converter to achieve 24 h power production. Reliable operation over a range of conditions including cloud transients has been demonstrated.


Production of ammonia is one of the world’s largest chemical process industries, with in excess of 125 million tonnes produced annually (Appl, 1999). In a modern ammonia plant the exothermic reaction heat from ammonia synthesis converters is routinely converted to superheated steam suitable for electric power generation in conventional Rankine cycle systems.

Design of the cavity receiver with 15 kWsol solar ammonia dissociation reactor and its assembly on ANU’s 20 m2 dish without insulation fitted.

The receivers of the LS3 Luz collectors used in the SEGS plants operate at around 400 degree Celsius, the ammonia cycle is possibly the only practical thermochemical cycle that can operate with energy input at this temperature. As well as the advantages of energy storage and transport free from thermal loss, the ammonia cycle offers other potential advantages to a trough based system. A major advantage is that heat recovery can be achieved at a consistent high temperature in the region of 450 degree Celsius irrespective of the operating temperature of the receiver.


15 kWsol ammonia dissociation receiver reactor in operation on the ANU 20 m2 dish.


Rapid solar-thermal dissociation of natural gas in an aerosol flow reactor

Jaimee K. Dahl, Karen J. Buechler, Ryan Finley, Timothy Stanislaus, Alan W. Weimer, Allan Lewandowski, Carl Bingham, Alexander Smeets, Adrian Schneider
A solar-thermal aerosol flow reactor process is being developed to dissociate natural gas (NG) to hydrogen (H2) and carbon black at high rates. Concentrated sunlight approaching 10 kW heats a
9:4 cm long x 2:4 cm diameter graphite reaction tube to temperatures ~2000 K using a 74% theoretically efficient secondary concentrator. Pure methane feed has been dissociated to 70% for residence times less than 0.1 s. The resulting carbon black is 20–40 nm in size, amorphous, and pure. A 5 million (M) kg/yr carbon black/1.67 M kg/yr H2 plant is considered for process scale-up. The total permanent investment (TPI) of this plant is $12.7 M. A 15% IRR after tax is achieved when the carbon black is sold for $0.66/ kg and the H2 for $13.80/GJ. This plant could supply 0.06% of the world carbon black market. For this scenario, the solar-thermal process avoids 277 MJ fossil fuel and 13.9 kg-equivalent CO2/kg H2 produced as compared to conventional steam-methane reforming and furnace black processing.

Currently, hydrogen is produced through the steam reforming of natural gas and carbon black is produced by the furnace black process. In steam reforming, steam is reacted with methane over a reforming catalyst to ultimately produce hydrogen and carbon dioxide (a greenhouse gas). For the furnace black process, a mixture of liquid fuel and NG is fed to the combustion zone of a reactor. The feed is partially combusted with air to provide the energy needed for the process. Energy released from the partial combustion dissociates the remaining feed mixture to carbon black and hydrogen. The products of these reactions are carbon black, hydrogen, carbon monoxide, carbon dioxide, and water. Large quantities of NOx and SOx are produced. According to Spath and Amos, fossil energy use and emissions from a large-scale steam reforming plant are 183 MJ fossil fuel and 11.85 kg-equivalent CO2/kg H2 produced.

For solar-thermal processing, where carbon black is sold, fossil energy usage and emissions are actually avoided ( – 94 MJ/kg H2; 2.07 kg-equivalent CO2/kg H2). This is because the solar thermal process avoids the energy and pollution normally associated with carbon black production. Then, in comparing the co-product solar-thermal processing to conventional steam reforming, the overall avoided fossil fuel usage and CO2-equivalent emissions are – 277 MJ and – 13.9 kg-equivalent CO2/kg H2 produced.

A potential issue is that at some point the demand for H2 will be so great that the co-produced carbon black via this process will eventually saturate the market.

Solar-thermal co-product plant for hydrogen and carbon black.

Click on the pdf image below to obtain a list of solar start-ups.
Disclaimer: this list does not pretend to be comprehensive, this is an ever changing field.

Politics and Economics

This section looks at the political implications of solar energy—support for and opposition of, as well as looks at the economic feasibility of transitioning to a solar-based energy policy for the United States and the world.


Several key pieces of legislation have recently been passed to promote renewable energy, including solar energy.

The American Recovery and Reinvestment Act of 2009

The ARRA created a Treasury Grant Program. Under this program, any owner of commercial solar energy property is eligible to apply for a grant worth 30% of the property’s value. By taking this grant, the owner is waiving his/her right to receive a solar energy tax credit for that year.

ARRA also appropriated $6 billion dollars for a Department of Energy Loan Guarantee Program that would provide loan guarantees for an estimated $60 billion worth of generation, manufacturing, and transmission facilities. Unfortunately, almost $3.5 billion, or 58% of the original appropriations, has been cut to provide for other unrelated programs, such as “Cash for Clunkers” and FAA programs.

In 2009, Sen. Dianne Feinstein introduced an [h amendment] to the ARRA that would promote solar energy by, mainly, granting a tax credit for up to 30% of any amounts paid to purchase two sections of high solarity disturbed private land. The amendment defines high solarity disturbed private land:

• Located in the United States
• Was acquired in units that average less than 100 contiguous acres from any private person
• Is in a location identified on the July 2007 Concentrating Solar Power Resources Map
• Having a solar resource of 7 kwh per meter2 or higher, at 3% or less grade
• Outside of a sensitive environmental or urban area

The amendment is currently buried in the Senate Finance Committee.

The Solar Manufacturing Jobs Creation Act
Senate Bill 2755 and House Resolution 4085 would extend the 30% tax credit to all equipment used to create solar energy property. Both versions are currently in their respective chamber’s committee, the House Energy and Commerce Committee and the Senate Finance Committee.

In addition to federal legislation, the [ Database for State Incentives for Renewables and Efficiency] is a comprehensive source for legislation and policies enacted on the local, state, and federal level to promote solar energy.

Some key legislation enacted across the country includes:

• More than half the states allow for the creation of solar easements.
• More than 20 states have solar access laws (laws that prohibit Homeowner Associations or municipalities from banning solar energy equipment, etc.)
• 39 states have developed interconnection standards to better deliver solar energy to individuals.

Most states began enacting pro-solar energy legislation in the mid-to-late 1990s.


A key factor in the analysis of solar energy is whether it is affordable, cost efficient, or even economically possible.

According to the National Renewable Energy Laboratory, the average overnight capital cost of the average Solar PV plant with an average capacity of 25% is $6000 (calculated in 2006 dollars/kW). Fixed Operating and Maintenance Costs average out to be between $10-30/kW)

Since solar energy does not utilize any fuel, the levelized cost would be calculated from its capital cost and operational and maintenance costs.

According to the EIA, the average cost of generating electricity by conventional standards is between 5-18 ¢/kWh and is averaging 17 ¢/kWh by solar energy. In most places, it is around 10¢/kWh by conventional standards. Worldwide consumption is roughly:
• in 2009, the United States had a net consumption of 3741.485 billion kWh
• in 2008, Europe had a net consumption of 3361.281 billion kWh
• The Middle East had a net consumption of 629.743 billion kWh
• Asia and Oceania had a net consumption of 6151.475 billion kWh

Therefore, there would be a net increase of $49 billion in cost of electricity generation in the United States alone.

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The Solar Energy Task Force of the Western Governors’ Association has reported that a decrease in the average cost from solar production to 10 ¢/kWh is feasible in the next few years.


An additional hurdle to a solar-based energy policy is the delivery of the electricity and thermal energy to the consumer. As noted above, many states have adopted interconnectedness standards and legislation; however, policies and delivery systems differ from state to state. The Interstate Renewable Energy Council has issued a set of model interconnection procedures to help resolve this issue.

As well, the Bureau of Land Management describe link has available 23 million acres [or 93 million hectares] of land available that is solar-energy feasible in the United States. (see map above)

With a power density of between 4-10 w/m2, the available land is not enough to produce enough energy to meet the United States 122 quadrillon btu/year consumption. If all 23 acres produced with a power density of 4 the total is only 361,200 MW.

Combine that lack of power generation with the loss of energy of 3%/1000 km when transporting as well as .6% loss at each connecting station.


A full-disk multiwavelength extreme ultraviolet image of the sun taken by SDO on March 30, 2010. False colors trace different gas temperatures. Reds are relatively cool (about 60,000 Kelvin, or 107,540 F); blues and greens are hotter (greater than 1 million Kelvin, or 1,799,540 F). Credit: NASA/Goddard/SDO AIA Team.

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