Concentrated Solar Power (CSP)
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 perday.
What does this mean? The entire State of California uses about 50,000 megawatt-hours of electricity perhour 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. Thissupposed 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 17,000terawatt-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.
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%).
www.nrel.gov/docs/fy04osti/35060.pdf size: 589 Kb
Downloads a 47 page Adobe PDF document.
- Hits: 376