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America's Solar Energy Potential

Every hour, the sun radiates more energy onto the earth than the entire human population uses in one whole year.

The technology required to harness the power of the sun is available now. Solar power alone could provide all of the energy Americans consume — there is no shortage of solar energy. The following paragraphs will give you the information you need to prove this to yourself and others. You do not need advanced math skills to follow and perform the arithmetic examples shown below. Anyone who can balance a checkbook or calculate the total square feet of floor space in his or her home, and understand why an area measuring 10 yards by 10 yards equals 100 square yards, can perform the following arithmetic examples and prove that American energy independence could be achieved with solar energy alone.

Science tells us that every square meter of the earth's surface, when exposed to direct sunlight, receives about 1000 watts (1 kilowatt) of energy from the sun's light. Depending on the angle of sunlight, which changes with the time of day, and the geographical location [see map below], the power of the sun's light will be somewhat more or less than 1 kilowatt-hour per hour for every square meter of the earth's surface exposed to the sun.

USA solar map On average, and particularly in the Sunbelt regions of the Southwestern United States, every square meter area exposed to direct sunlight will receive about 1 kilowatt-hour per hour of solar energy. However, scientists estimate that sunlight will provide useful solar energy for only about 6 to 7 hours per day because during the early hours and late hours of the day the angle of the sun's light is too low. So, for example, if the sun's light provides 6 productive hours of solar energy per day, then a square meter of land in direct sunlight will receive about 6 kilowatt-hours of solar energy during the course of a day.

Scientists like to measure things using the metric system. However, most Americans are unfamiliar with the metric system. (Europeans use the metric system.) It is easier for Americans to think in square feet and square yards because feet and yards are common lengths in the United States. So, for the sake of clarity and because this is written for an American audience, all measurements will be converted from meters to yards.

A meter is just a little longer than a yard (about 3 and ¼ feet to a meter, compared with 3 feet to a yard). There are 10.8 square feet in a square meter. There are 9 square feet in a square yard (3x3=9). A simple calculation can accomplish the conversion from square meters to square yards. A square yard is 83.33 percent of a square meter. Prove this by multiplying 10.8 (the number of square feet in a square meter) by 83.33%. The answer is nine (the number of square feet in a square yard). If you perform the calculation you will see that the answer is slightly less than the whole number 9 (but close enough for our purpose). Using this conversion, we can say that a square yard of land in direct sunlight receives 1000 x 83.33% = 833 watts of solar energy. This calculation can also be used in reverse to convert yards to meters, simply divide by .8333 (833 divided by .8333 = 1000 rounded).

Every square yard of land, if exposed to direct sunlight, receives about 833 watts of solar energy [NOTE: see the map above, and adjust the estimated amount of solar energy accordingly]. Therefore, a one square yard area exposed to continuous direct sunlight [in an optimal geographical location] for six hours will have received 6 hours x 833 watts = 4,998 watt-hours of solar energy during the course of a day. In round numbers, a one square yard area will receive about 5000 watt-hours (5 kilowatt-hours) per day of solar energy. Another way to obtain this result would be to take the 6 kilowatt-hours per meter (explained above in the third paragraph) and apply the conversion calculation (6 x 83.33% = 5 rounded).

Americans can assume, at least in the Sunbelt regions of the southwestern United States, that every square yard of land exposed to direct sunlight will receive about 5 kilowatt-hours per day of solar energy.

With the above information in mind, perform the following exercise: Measure an area ten yards long and ten yards wide. That would be thirty feet by thirty feet. Take a good look at the size of it. You are looking at an area covering 100 square yards. If that area were in direct sunlight all day it would receive about (5 x 100) 500 kilowatt-hours per day of solar energy. Now go look at your home electric bill. Your electric company calculates your home electric bill based on how many kilowatt-hours of electrical energy you use. Find the total amount of electricity that you have been billed for (given in kilowatt-hours). The amount of kilowatt-hours on your bill is for an entire month. If your home is a typical residential electric customer, you and your family consume between 500 and 1000 kilowatt-hours of electricity per month. Compare the quantity of electric energy your home consumed in one month with the quantity of energy the sun gives freely to a 100 square yard area exposed to direct sunlight. One hundred square yards of sunshine provides as much energy in 1 to 2 days as an average family uses in an entire month!

It would be great if 100% of the sunshine became electricity, but solar energy and electricity are not the same. Technology accomplishes the conversion of solar energy to electricity. Several different technologies are used; perhaps the one that most people have heard of is the solar panel, made from photovoltaic cells called PV.

For a detailed explanation of photovoltaic cells there is a very good article on the Internet located at:
www.howstuffworks.com/solar-cell.htm, it is well written and easy to read.

Conversion of one form of energy to another always causes a loss of energy. In other words, the new form of energy will be less than the original. Efficiency is the word scientists use to describe the difference in power resulting from the conversion of one form of energy to another. The efficiency of commercially available solar panels (PV) is about 15%. This means that when a solar panel converts the sun's light to electricity, only about 15 percent of the energy in the sunlight becomes electricity. The same thing is true of gasoline in your car. Your car's engine can only convert about twenty-five percent of the energy in gasoline to mechanical energy that turns the wheels.

With an average efficiency of 15 percent, a square yard of solar photovoltaic cells (PV) would produce (5 kilowatt-hours of solar energy multiplied by 15% =) .75 kilowatt-hours of electric energy per day. Solar panels (PV) covering an area ten yards by ten yards (100 square yards or 900 square feet) would produce 100 x .75 = 75 kilowatt-hours of electricity per day.

Seventy-five kilowatt-hours per day is a lot of electricity for a single-family home. If part of the electricity is stored in a home battery, or is used to electrolyze water for producing hydrogen gas, and the gas is stored for use by a fuel cell when needed, then 100 square yards covered with solar panels would provide an average family with energy independence. Most detached family homes have more than 100 square yards (900 square feet) of roof, or that much space around their homes where solar panels could be installed.

In the Southwest, if you look at any commercial or industrial park, or any typical mall or supermarket you will see that most of the buildings have flat roofs. Those roofs require insulation to lower the cost of air conditioning on hot days. If those roofs where covered with solar panels the sun would provide electricity for the air conditioning and save businesses millions of dollars per month that would otherwise be paid to the utility companies.


Another technology, Concentrated Solar Power (CSP), takes a different approach to harnessing the power of the sun. Unlike photovoltaic cells, CSP uses mirrors to concentrate the sunlight on a focal point, which magnifies the suns heat. Similar to holding a magnifying glass in the sun, focusing the light onto a piece of paper until the paper catches on fire.

CSP technology has more than one form. Troughs, dishes and towers are the different forms available today. A CSP dish or tower looks like a modern glass sculpture and contributes aesthetically to the landscape. CSP systems can achieve 30 percent efficiency, or about twice the efficiency of standard photovoltaic cells (2 x .75 = 1.5 kilowatt-hours per square yard per day).

Large Concentrating Solar Power plants create the thermal energy equivalent to conventional fossil fuel power plants. After the sun sets, CSP plants generate electricity from cost-effective thermal storage, providing 24-hour service to the power grid.

Consider the solar energy potential of one acre of land. There are 43,560 square feet in an acre. Divide the number of square feet in one acre by 9 (the number of square feet in one square yard) and you find that there are 4,840 square yards in one acre of land. A CSP dish, tower, or trough receiving an acre of sunshine would yield about (1.5 kilowatt-hours per square yard times 4,840 square yards per acre) 7,260 kilowatt-hours of electricity per day, at 30% efficiency. One acre has enough solar energy potential to yield 7.26 megawatt-hours of electricity per day, using technology that exists now. (Each thousand kilowatts is one million watts. A million watts is a megawatt.)

Consider the solar energy potential of one square mile of land. A square mile is 640 acres. One square mile of sunshine has the potential of providing (640 acres x 7.26 megawatt-hours) 4,646 megawatt-hours per day of electricity using existing CSP technology at 30% efficiency.

Ten thousand square miles is a plot of land 100 miles long by 100 miles wide. Multiply 640 acres by 10,000 square miles equals 6,400,000 acres. With a yield of 7.26 megawatt-hours of electricity per day per acre, a CSP system receiving 6,400,000 acres of sunshine would produce about 46,464,000 megawatt-hours of electricity per day.

What does this mean?

The entire State of California uses about 50,000 megawatt-hours of electricity per hour at peak time, and much less during off-peak hours: Sweltering California declares power emergency —Cal ISO expects record demand at 52,336 megawatts.
www.energy.ca.gov/electricity/2004-07-08_SUMMER_DEMAND.PDF size: 68 Kb
www.energy.ca.gov/electricity/2003-01-28_OUTLOOK.PDF size: 170 Kb
www.energy.ca.gov/electricity/peak_demand/2002-07-10_CHART.PDF size: 20 Kb

Suppose that California uses an average of 38,000 megawatt-hours of electricity per hour over a 24-hour period, then 24 hours x 38,000 megawatts = 912,000 megawatt-hours per day, multiplied by 365 = 333,880,000 megawatt-hours per year. This supposed average is too high because in 2005, California actually consumed 288,245,000 megawatt-Hours (MWh) for the entire year: www.energy.ca.gov/electricity/gross_system_power.html

A CSP farm large enough to capture the solar energy radiating on an area of land 100 miles long by 100 miles wide can produce about 50 times more electricity in a day than California consumes in a 24-hour period. For example, 50 x 912,000 = 45,600,000 megawatt-hours per day.

Imagine driving your car 100 miles along one side of the CSP farm, then turn 90 degrees right and drive 100 miles along another side, then turn 90 degrees right again and drive another 100 miles, then make another 90 degree right turn and drive another 100 miles to complete driving a 100 mile square. Inside that area is 10,000 square miles or 6,400,000 acres.

A 10,000 square mile solar energy farm that produces 46,464,000 megawatt-hours of electricity per day would produce 365 x 46,464,000 = 16,956,360,000 megawatt-hours of electricity per year or about 17 trillion kilowatt-hours, which is 17,000 terawatt-hours or 17 petawatt-hours.
Tera- (symbol: T) is a prefix in the SI system of units denoting 1012, 1 Trillion or 1,000,000,000,000 (1 million million) therefore, 1 terawatt = 1 Trillion watts.
In physics and mathematics, peta- (symbol: P) is a prefix in the SI (system of units) denoting 1015, 1 Quadrillion or 1,000,000,000,000,000 (one billion million) therefore, 1 petawatt = 1 Quadrillion watts.


The CSP examples above assume 30 percent energy conversion efficiency and 100 percent land use. In a practical application, not all of the land area will be used. This is because of unfavorable terrain and the need for service roads and land for plant facilities. And, the solar collectors must be individually positioned for optimal orientation to the angle of sunlight and given enough space between collectors to prevent a collector from casting a shadow on adjacent collectors; the result is unused space between the collectors. For these reasons, actual electricity production will be less than the numbers shown in the examples. However, the desert regions of the southwestern United States will easily produce 7 hours of productive sunlight per day, and often exceed 1 kilowatt of solar energy per square meter, so in that respect the above calculations are conservative.

All of California's electricity can be produced from 200 square miles of sunshine; 128,000 acres of desert land. Lake Mead, behind Hoover Dam, covers more than 200 square miles. Given an area the size of Lake Mead, for the production of electricity from solar energy, California would be energy independent.

CSP plants seem to use a lot of land, but in reality, they use less land than hydroelectric dams for generating an equivalent electricity output, if the size of the lake behind the dam is considered. The same is true for coal plants. A CSP plant will not use any more land than a coal power plant if the amount of land required for mining and excavation of the coal is taken into consideration.


If the sunshine radiating on the surface of an area 100 miles wide by 100 miles long would provide all of the electricity that America needs, every day, why would Americans hesitate to use it? There are millions of open acres in the deserts of America, where the sun's energy does nothing more than heat rocks and sand.

In 1942, General Patton established a training area in the deserts of the southwestern United States to train and prepare American soldiers to fight in the deserts of North Africa during World War II. Patton's original training area was 18,000 square miles, and then expanded to 87,500 square miles (350 miles x 250 miles), an area stretching from Boulder City, Nevada to the Mexican border and from Phoenix, Arizona to Pomona, California. One million soldiers trained in this area using tanks, artillery and aircraft. The desert is very resilient, there is little evidence today of injury to the desert ecosystem.
www.militarymuseum.org/CAMA.html

The point being, the federal government can “borrow” public land from the National and State desert Parks for the purpose of building a national solar energy system. The system would only be needed until fusion energy, or something like it, is developed, then the land would be returned to nature in the care of the public parks service. Time, sand and the desert wind would gradually remove all evidence of technologies brief occupancy. In the meantime, the lizards, turtles, snakes and scorpions would hide and sleep in the shade under the giant mirrors and troughs.

The reason why solar energy has not been development on a large scale is the cost. Not the cost of sunshine, that is free. Private investors resist putting their money into solar energy projects because of the high upfront capital investment required for plant and equipment. The initial investment is what causes the price per kilowatt-hour for electricity from solar energy to be higher than the price of electricity generated from natural gas or coal. The estimated kilowatt-hour rates assigned to solar energy are not based on the cost of electricity generation, they are based on the cost of the investment capital and the requirement to earn a return on investment, or pay back the loan for the investment. Remember, the solar fuel is free.

Solar energy would not be expensive if the cost of the initial capital investment is not factored into the price per kilowatt-hour.

With the obvious enormous public benefit a national solar energy system would provide, why is the government holding back? Should solar energy be a public works project? We have a good example that may help answer that question. Southern California, as it is seen today, would not exist without Hoover Dam and the Colorado River Aqueduct, because without the Colorado River water the current population of Southern California would never have happened. Southern California does not have enough natural water to support the demand of a small fraction of its current population. The federal government funded Hoover Dam and the Colorado River Aqueduct. The economy of Southern California, having grown because of that funding and other public investments, has returned more in tax revenue than was spent building the dam and aqueduct, plus the sale of water and electricity has earned enough to pay the federal government back the amount of the original funding, with interest.

The Following is quoted from the Executive Summary of a report by Sargent & Lundy engineering, titled: Assessment of Parabolic Trough and Power Tower Solar Technology Cost and Performance Forecasts, delivered to the U.S. DOE National Renewable Energy Laboratory:

Based on this review, it is S&L’s opinion that CSP technology is a proven technology for energy production, there is a potential market for CSP technology, and that significant cost reductions are achievable assuming reasonable deployment of CSP technologies occurs. S&L independently projected capital and O&M costs, from which the levelized energy costs were derived, based on a conservative approach whereby the technology improvements are limited to current demonstrated or tested improvements and with a relatively low rate of deployment.

The projections for electrical power consumption in the United States and worldwide vary depending on the study, but there will be a significant increase in installed capacity due to increased demand through 2020. Trough and tower solar power plants can compete with technologies that provide bulk power to the electric utility transmission and distribution systems if market entry barriers are overcome:

  • Market expansion of trough and tower technology will require incentives to reach market acceptance (competitiveness). Both tower and trough technology currently produce electricity that is more expensive than conventional fossil-fueled technology.
  • Significant cost reductions will be required to reach market acceptance (competitiveness). S&L focused on the potential of cost reductions with the assumption that incentives will occur to support deployment through market expansion.

For the more technically aggressive low-cost case, S&L found the National Laboratories' "SunLab" methodology and analysis to be credible. The projections by SunLab, developed in conjunction with industry, are considered by S&L to represent a "best-case analysis" in which the technology is optimized and a high deployment rate is achieved. The two sets of estimates, by SunLab and S&L, provide a band within which the costs can be expected to fall. The figure and table below highlight these results, with initial electricity costs in the range of 10 to 12.6 /kWh and eventually achieving costs in the range of 3.5 to 6.2 /kWh. The specific values will depend on total capacity of various technologies deployed and the extent of R&D program success. In the technically aggressive cases for troughs / towers, the S&L analysis found that cost reductions were due to volume production (26%/28%), plant scale-up (20%/48%), and technological advance (54%/24%).

EXECUTIVE SUMMARY:
www.nrel.gov/docs/fy04osti/35060.pdf size: 589 Kb
Downloads a 47 page Adobe PDF document.

Solar Energy R&D:   Solar cost decreases 10% per year


Solar Energy News:
•   Solar at the cost of Coal — Welcome to the Revolution — “How can solar energy–with its reputation for high cost–compete with baseload coal, still the dominant fuel for U.S. electric power generation? ... I truly believe it’s doable, ... I believe it’s even doable without assigning a cost to carbon. .. Seen in that light, solar at the cost of coal may not be so far-fetched after all.”
•   Artificial Photosynthesis - U.S. Department of Energy — “After nearly 3 billion years of evolution, nature can effectively convert sunlight into energy-rich chemical fuels using the abundant feedstocks of water and carbon dioxide. All fuels used today to power vehicles and create electricity, whether from fossil or biomass resources, are ultimately derived from photosynthesis... plants and photosynthetic microbes were not designed to meet human energy needs - much of the energy captured from the sun is necessarily devoted to the life processes of the plants. Imagine the potential energy benefits if we could generate fuels directly from sunlight, carbon dioxide, and water in a manner analogous to the natural system, but without the need to maintain life processes. The impact of replacing fossil fuels with fuels generated directly by sunlight would be immediate and revolutionary.”
•   Turning sunlight into liquid fuels — Using the energy of sunlight to produce pure hydrogen and oxygen from water molecules without electrolysis
•   Inspired by the photosynthesis performed by plants —MIT Scientists mimic essence of plants' energy storage system
•   Harnessing sunlight on the cheap —MIT student project aims to develop cost-efficient solar power
•   Solar farm to rise over 3 square miles in Arizona —Spanish company to build, operate $1 billion plant based on mirrors, turbine
•   Solar farms to rise on California rooftops
    —Southern California Edison Co. plans to build the nation's largest solar energy installation—an array of collector cells covering two square miles of rooftops that could power about 162,000 homes.
•   The Solar America Initiative
•   Silicon Nanocrystals for Superefficient Solar Cells
•   Storing Solar Power Efficiently —Thermal-power plants that store heat for cloudy days could solve some of the problems with solar power
•   Sunlight used to smelt zinc
•   High-schoolers finish solar car race
•   One man's castle runs on hydrogen
•   Solar power boom comes with pains
•   Honda Entering Solar Cell Market for Homes and Vehicles
•   BP, Caltech team up on solar power —Silicon in nanorods could open door to radical breakthrough
•   New World Record Achieved in Solar Cell Technology  •December 2006
    —New Solar Cell Breaks the 40 Percent Efficient Sunlight-to-Electricity Barrier: Boeing [NYSE: BA] today announced that Spectrolab, Inc., a wholly-owned subsidiary, has achieved a new world record in terrestrial concentrator solar cell efficiency. Using concentrated sunlight, Spectrolab demonstrated the ability of a photovoltaic cell to convert 40.7 percent of the sun's energy into electricity. The U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in Golden, Colo., verified the milestone.
“This solar cell performance is the highest efficiency level any photovoltaic device has ever achieved,” said Dr. David Lillington, president of Spectrolab. “The terrestrial cell we have developed uses the same technology base as our space-based cells. So, once qualified, they can be manufactured in very high volumes with minimal impact to production flow.”
High efficiency multijunction cells have a significant advantage over conventional silicon cells in concentrator systems because fewer solar cells are required to achieve the same power output. This technology will continue to dramatically reduce the cost of generating electricity from solar energy as well as the cost of materials used in high-power space satellites and terrestrial applications.
“These results are particularly encouraging since they were achieved using a new class of metamorphic semiconductor materials, allowing much greater freedom in multijunction cell design for optimal conversion of the solar spectrum,” said Dr. Richard R. King, principal investigator of the high efficiency solar cell research and development effort. “The excellent performance of these materials hints at still higher efficiency in future solar cells.”
 Spectrolab high-efficiency multijunction solar concentrator cells
    —Boeing Spectrolab

•   Cheap, Superefficient Solar  —Solar-power modules that concentrate the power of the sun are becoming more viable.
•   Cheaper, More Efficient photonic crystals  —A new type of material could allow solar cells to harvest far more light.
•   Solar Power at Half the Cost  —A new roof-mounted system that concentrates sunlight could cut the price of photovoltaics.
•   Supplying the World's Energy Needs with Light and Water  —A new roof-mounted system that concentrates sunlight could cut the price of photovoltaics. A leading chemist says that a better understanding of photosynthesis could lead to cheap ways to store solar energy as chemical fuel.

Solar Energy Storage:
Nanowire battery can hold 10 times the charge of existing lithium-ion battery December 18, 2007 “Stanford researchers have found a way to use silicon nanowires to reinvent the rechargeable lithium-ion batteries. The new technology, developed through research led by Yi Cui, assistant professor of materials science and engineering, produces 10 times the amount of electricity of existing lithium-ion, known as Li-ion, batteries. A laptop that now runs on battery for two hours could operate for 20 hours.”
Interview with Dr. Cui, Inventor of Silicon Nanowire Lithium-ion Battery Breakthrough

High-Voltage Direct Current (HVDC) Transmission:
GE HVDC technology
ABB HVDC technology
High-Voltage Transmission Lines
Superconducting Transmission Lines
Nanotechnology leads to discovery of super superconductors

High-Voltage Composite Electricity Transmission Lines:
Composite Technology Corporation
Composite-Reinforced Aluminum Conductor (CRAC)
CRAC-TelePower: Electricity and Data over the same line
Produced by the California Energy Commission
The 44 page report is a 238 KB Adobe PDF document.

Reference links:
Power from the sun
CSP - How it Works
Concentrating Solar Power
Frequently Asked Questions
Boeing Spectrolab Solar Cells
The Solar Tres power tower plant
Solar Tres Project - solarpaces.org
Thermal solar power tower - history
Solar Radiation Resource Information
The National Solar Thermal Test Facility
TroughNet - Parabolic Trough Solar Power
Thermal Storage Research and Development
The El Paso Salinity Gradient Solar Pond (SGSP)
Parabolic Trough Power Plant System Technology
Solar Two Demonstrates Clean Power for the Future
Advantages of Using Molten Salt for thermal storage
Frequently Asked Questions about Photovoltaics (PV)
Download SunLab Solar Energy Technology White Papers
Report to Congress: 1,000 megawatts of Solar power by 2006 size: 956 Kb
U.S. Department of Energy's Solar Energy Technologies program
NREL and Research Partners Work to Trim Solar Electricity Costs
Research and Development Advances in Concentrating Solar Power
Lunar Solar Power System by Professor of Physics David Criswell
Assessment of Parabolic Trough and Power Tower Solar Technology Cost and Performance size: 589 Kb
The Centre for Sustainable Energy Systems (CSES) at the Australian National University (ANU)

FRESNEL LENS:
Green Power Science
When placed in the sun, a fresnel lens will act as a giant magnifying glass and concentrate light to a very small point. Most large fresnel lenses will concentrate several square feet of sunlight to less than an inch resulting in a hot spot over 2000 degrees Fahrenheit. This will cause wood to instantly catch on fire or zinc and copper metal to melt in a few seconds or even burn and vaporize. We have boiled 12 oz. of water in a dark glass bottle in 90 seconds and burned a hole in a stainless steel bowl.. One gallon of water was boiled in 30 minutes.

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