Article: A parabolic trough is a type of solar thermal collector that is straight in one dimension and curved as a parabola in the other two, lined with a polished metal mirror. The energy of sunlight which enters the mirror parallel to its plane of symmetry is focused along the focal line, where objects are positioned that are intended to be heated. For example, food may be placed at the focal line of a trough, which causes the food to be cooked when the trough is aimed so the Sun is in its plane of symmetry. Further information on the use of parabolic troughs for cooking can be found in the article about solar cookers.
For other purposes, there is often a tube, frequently a Dewar tube, which runs the length of the trough at its focal line. The mirror is oriented so that sunlight which it reflects is concentrated on the tube, which contains a fluid which is heated to a high temperature by the energy of the sunlight. The hot fluid can be used for many purposes. Often, it is piped to a heat engine, which uses the heat energy to drive machinery or to generate electricity. This solar energy collector is the most common and best known type of parabolic trough. The paragraphs below therefore concentrate on this type.
Efficiency
The trough is usually aligned on a north-south axis, and rotated to track the sun as it moves across the sky each day. Alternatively, the trough can be aligned on an east-west axis; this reduces the overall efficiency of the collector due to cosine loss but only requires the trough to be aligned with the change in seasons, avoiding the need for tracking motors. This tracking method approaches theoretical efficiencies at the spring and fall equinoxes with less accurate focusing of the light at other times during the year. The daily motion of the sun across the sky also introduces errors, greatest at the sunrise and sunset and smallest at solar noon. Due to these sources of error, seasonally adjusted parabolic troughs are generally designed with a lower concentration acceptance product.
Parabolic trough concentrators have a simple geometry, but their concentration is about 1/3 of the theoretical maximum for the same acceptance angle, that is, for the same overall tolerances of the system to all kinds of errors, including those referenced above. The theoretical maximum is better achieved with more elaborate concentrators based on primary-secondary designs using nonimaging optics which may nearly double the concentration of conventional parabolic troughs and are used to improve practical designs such as those with fixed receivers.
Heat transfer fluid (usually thermal oil) runs through the tube to absorb the concentrated sunlight. This increases the temperature of the fluid to some 400 °C. The heat transfer fluid is then used to heat steam in a standard turbine generator. The process is economical and, for heating the pipe, thermal efficiency ranges from 60-80%.
The overall efficiency from collector to grid, i.e. (Electrical Output Power)/(Total Impinging Solar Power) is about 15%, similar to PV (Photovoltaic Cells) but less than Stirling dish concentrators.
Design
A parabolic trough is made of a number of solar collector modules (SCM) fixed together to move as one solar collector assembly (SCA). A SCM could have a length up to or more. About a dozen or more of SCM make each SCA up to length. Each SCA is an independently tracking parabolic trough.
A SCM may be made as a single-piece parabolic mirror or assembled with a number of smaller mirrors in parallel rows. Smaller modular mirrors requires smaller machines to build the mirror, reducing cost. Cost is also reduced in case of the need of replacing a damaged mirror, like after a object hit (during bad weather or other causes).
In addition, V-type parabolic troughs exist which are made from 2 mirrors and placed at an angle towards each other.
In 2009, scientists at the National Renewable Energy Laboratory (NREL) and SkyFuel teamed to develop large curved sheets of metal that have the potential to be 30% less expensive than today's best collectors of concentrated solar power by replacing glass-based models with a silver polymer sheet that has the same performance as the heavy glass mirrors, but at a much lower cost and much lower weight. It also is much easier to deploy and install. The glossy film uses several layers of polymers, with an inner layer of pure silver.
As this renewable source of energy is inconsistent by nature, methods for energy storage have been studied, for instance the single-tank (thermocline) storage technology for large-scale solar thermal power plants. The thermocline tank approach uses a mixture of silica sand and
quartzite rock to displace a significant portion of the volume in the tank. Then it is filled with the heat transfer fluid, typically a molten nitrate salt.
Variations Enclosed trough
The enclosed trough architecture encapsulates the solar thermal system within a greenhouse-like glasshouse. The glasshouse creates a protected environment to withstand the elements that can negatively impact reliability and efficiency of the solar thermal system.
Lightweight curved solar-reflecting mirrors are suspended within the glasshouse structure. A single-axis tracking system positions the mirrors to track the sun and focus its light onto a network of stationary steel pipes, also suspended from the glasshouse structure. Steam is generated directly using, oil field-quality water, as water flows from the inlet throughout the length of the pipes, without heat exchangers or intermediate working fluids.
The steam produced is then fed directly to the field’s existing steam distribution network, where the steam is continuously injected deep into the oil reservoir. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up as a result from exposure to humidity. GlassPoint Solar, the company that created the Enclosed Trough design, states its technology can produce heat for EOR for about $5 per million British thermal units in sunny regions, compared to between $10 and $12 for other conventional solar thermal technologies.
Early commercial adaption
In 1897, Frank Shuman, a U.S. inventor, engineer and solar energy pioneer built a small demonstration solar engine that worked by reflecting solar energy onto square boxes filled with ether, which has a lower boiling point than water, and were fitted internally with black pipes which in turn powered a steam engine. In 1908 Shuman formed the Sun Power Company with the intent of building larger solar power plants. He, along with his technical advisor A.S.E. Ackermann and British physicist Sir Charles Vernon Boys, developed an improved system using mirrors to reflect solar energy upon collector boxes, increasing heating capacity to the extent that water could now be used instead of ether. Shuman then constructed a full-scale steam engine powered by low-pressure water, enabling him to patent the entire solar engine system by 1912.
Shuman built the world’s first solar thermal power station in Maadi, Egypt between 1912 and 1913. Shuman’s plant used parabolic troughs to power a 45-52 kilowatt (60-70 hp) engine that pumped more than 22,000 litres of water per minute from the Nile River to adjacent cotton fields. Although the outbreak of World War I and the discovery of cheap oil in the 1930s discouraged the advancement of solar energy, Shuman’s vision and basic design were resurrected in the 1970s with a new wave of interest in solar thermal energy. In 1916 Shuman was quoted in the media advocating solar energy's utilization, saying:
We have proved the commercial profit of sun power in the tropics and have more particularly proved that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the sun.
Commercial plants
List of solar thermal power stations
Most commercial plants utilizing parabolic troughs are hybrids; fossil fuels are used during night hours, but the amount of fossil fuel used is limited to a maximum 27% of electricity production, allowing the plant to qualify in the US as a renewable energy source. Because they are hybrids and include cooling stations, condensers, accumulators and other things besides the actual solar collectors, the power generated per square meter of area varies enormously.
As of 2014, the largest solar thermal power systems using parabolic trough technology include, the 354 MW SEGS plants in California, the 280 MW Solana Generating Station that features a molten salt heat storage, the 250 MW Genesis Solar Energy Project, that came online in 2014, as well as the Spanish 200 MW Solaben Solar Power Station, the 200 MW Solnova Solar Power Station, and the Andasol 1 solar power station, using a Eurotrough-collector.
See also Parabola Parabolic reflector Solar cooker
List of solar thermal power stations
References Bibliography
Solar Engineering of Thermal Processes http://books.google.com/books?id=UtZSAAAAMAAJ
Boca Raton London New York Washington, D.C. http://books.google.com/books?id=8aQDw14fQnkC
External links
Kramer Junction Solar Power Plants, satellite image, Google Map.
ParabolaTool - Tool for calculating the shape of a parabolic trough |
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More information Solar EOR PetroWiki Jump to navigation Jump to search
Solar enhanced oil recovery, or solar EOR, is a form of thermal
enhanced oil recovery (EOR)
, a technique applied by oil producers to extract more oil from maturing oil fields. Solar EOR uses
CSP
to use the sun’s energy to heat water and generate steam. The steam is injected into an oil reservoir to reduce the viscosity, or thin, heavy crude thus facilitating its flow to the surface. Thermal recovery processes, also known as
steam injection
, have traditionally burned natural gas to produce steam. Solar EOR is proving to be a viable alternative to gas-fired steam production for the oil industry. Solar EOR can generate the same quality steam as natural gas, reaching temperatures up to 750˚F (400˚C) and 2,500 PSI.
Contents 1 Types 1.1 Central tower 1.2 Enclosed trough 2 Projects 2.1
21Z in McKittrick, California
2.2
Coalinga in Coalinga, California
2.3 Petroleum Development Oman 3 References 4
Noteworthy papers in OnePetro
5 External links 6 See also Types Central tower
Originally designed electricity generation, central tower, or power tower technology, uses a field of large tracking mirrors, called heliostats, to concentrate the sunlight on a boiler filled with water that rests on a central tower. The sun’s energy is reflected on the boiler to produce steam, which is used to turn a traditional turbine and create electricity. For EOR, the process ends at steam production. High-temperature steam made from demineralized water in the tower receiver passes through a heat exchanger, generating lower temperature steam from high-contamination oilfield feedwater. The steam is then fed into distribution headers which lead to injection wells, conveying steam into the oil-bearing formation.
Enclosed trough
The enclosed trough architecture encapsulates the solar thermal system within a greenhouse-like glasshouse. The glasshouse creates a protected environment to withstand the elements that can negatively impact reliability and efficiency of the solar thermal system.
Lightweight curved solar-reflecting mirrors are suspended within the glasshouse structure. A single-axis tracking system positions the mirrors to track the sun and focus its light onto a network of stationary steel pipes
[1]
, also suspended from the glasshouse structure. Steam is generated directly using, oil field-quality water, as water flows from the inlet throughout the length of the pipes, without heat exchangers or intermediate working fluids.
The steam produced is then fed directly to the field’s existing steam distribution network, where the steam is continuously injected deep into the oil reservoir. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up as a result from exposure to humidity. The company states its technology can produce heat for EOR for about $5 per million British thermal units in sunny regions, compared to between $10 and $12 for other conventional solar thermal technologies.
According to research analysts at Raymond James, solar EOR can be done more cost effectively than using gas, even as current depressed prices. Steam represents as much as 60 percent of the production cost for heavily oil extraction.
[2]
In addition to being cost competitive with gas, solar EOR provides a hedge against long-term gas price escalation. Long-term price projections put natural gas at $5.00/Mcf, considerably higher than the 2011 forecast of $3.75/Mcf. When an oil producer invests in a solar EOR system, all costs are upfront and the standard life of the equipment is 30 years.
Projects
21Z in McKittrick, California
GlassPoint Solar partnered with Berry Petroleum, California’s largest independent oil producer, to deploy the world’s first commercial solar EOR project. Commissioned in February 2011, the project is located on a 100-year old McKittrick Oil Field in McKittrick, California. Coined the Kern County 21Z Solar Project, the system spans roughly one acre and will produce approximately one million Btus per hour of solar heat, replacing natural gas used for steam generation. The solar EOR project was constructed in less than six weeks and is the first installation of GlassPoint's enclosed trough technology in an oil field.
[3]
Coalinga in Coalinga, California
In October 2011, Chevron Corp. and BrightSource Energy revealed a 29-megawatt solar- to-steam facility at the Coalinga Oil Field in Fresno County, California. The Coalinga solar EOR project spans 100 acres and consists of 3,822 mirror systems, or heliostats, each with two 10-foot (3-meter) by 7-foot mirrors mounted on a 6-foot steel pole focusing light on a 327-foot solar tower.
[4]
BrightSource was contracted to provide the technology, engineering and production and construction services, and Chevron Technology Ventures will manage operations of the project. The facility began construction in 2009. It was reported that Chevron spent more than its $28 million on the contract, and BrightSource has lost at least $40 million on the project and disclosed it will lose much more.
[5] Petroleum Development Oman
In May 2013, GlassPoint Solar and Petroleum Development Oman (PDO) commissioned the Middle East's first solar EOR project.
[6]
PDO is a joint venture between the Sultanate of Oman, Shell and Total. The 7 MW solar EOR facility produces a daily average of 50 tons of emissions-free steam that feeds directly into existing thermal EOR operations at PDO's Amal West field in Southern Oman. The system in 27 times larger than GlassPoint's first installation at Berry Petroleum's 21Z oil field.
[7]
Reports by Petroleum Development Oman indicate that the pilot was delivered on-time, under-budget, and above contract output specifications, with zero lost time injuries. In the first year of operations, the fully automated system successfully exceeded all performance tests and production targets. The system recorded a 98.6% uptime, significantly exceeding PDO’s expectations. Even during severe dust and sandstorms, the system has proven to maintain regular operations.
References ↑
Goossens, Ehren. 2011. Chevron Uses Solar-Thermal Steam to Extract Oil in California. Bloomberg,
http://www.bloomberg.com/news/2011-10-03/chevron-using-solar-thermal-steam-at-enhanced-oil-recovery-plant.html.fckLR↑ http://www.cnbc.com/id/101995330# . ↑
David, Javier E. "Strange Bedfellows: Solar Power Meets Oil Drilling." CNBC. N.p., 14 Sept. 2014. Web. 09 June 2015. <
http://www.cnbc.com/id/101995330# >. ↑
Molchanov, Pavel, 2011. Solar EOR Keeps Advancing: Oman to Build First System In Mid-East. Raymond James Energy Report,
http://www.glasspoint.com/media/2012/12/Raymond-James_Oman-+-solar-EOR.pdf . ↑
Helman, Christopher. 2013. Oman Project Is A Step Toward "The Ikea Of Solar". Forbes,
http://www.forbes.com/sites/christopherhelman/2013/05/21/oman-project-is-a-step-toward-the-ikea-of-solar/ . ↑
Hussain, Emran. 2011. World's First Commercial Solar EOR Project Begins. Arabian Oil and Gas, [
http://www.arabianoilandgas.com/article-8545-worlds-first-commercial-solar-eor-project-begins/ . ↑
Gilbert, Daniel. 2011. Drilling for Crude Goes Solar. The Wall Street Journal,
http://online.wsj.com/news/articles/SB10001424052970203405504576602891728012656 . ↑
Mahdi, Wael. 2013. GlassPoint Solar Sees Interest from Middle East Oil Firms. Bloomberg,
http://www.bloomberg.com/news/2013-05-21/glasspoint-solar-sees-interest-from-middle-east-oil-firms.html .
Noteworthy papers in OnePetro
Agarwal, A. and Kovscek, A.R. 2013. Solar-Generated Steam for Heavy-Oil Recovery: A Coupled Geomechanical and Reservoir Modeling Analysis. Presented at the SPE Western Regional & AAPG Pacific Section Meeting 2013 Joint Technical Conference, Monterey, California, USA, 19-25 April. SPE-165329-MS.
http://dx.doi.org/10.2118/165329-MS .
Cochevelou, G. 2005. Solar Power: Ready For Take-off! Presented at the 18th World Petroleum Congress, Johannesburg, South Africa, 25-29 September. WPC-18-0945.
https://www.onepetro.org/conference-paper/WPC-18-0945 .
Palmer, D. and O'Donnell, J. Construction, Operations and Performance of the First Enclosed Trough Solar Steam Generation Pilot for EOR Applications. Presented at the SPE EOR Conference at Oil and Gas West Asia, Muscat, Oman, 31 March-2 April. SPE-169745-MS.
http://dx.doi.org/10.2118/169745-MS .
van Heel, A.P., Van Wunnik, J.N.M., Bentouati, S. et al. The Impact Of Daily And Seasonal Cycles In Solar-Generated Steam On Oil Recovery. Presented at the SPE EOR Conference at Oil & Gas West Asia, Muscat, Oman, 11-13 April. SPE-129225-MS.
http://dx.doi.org/10.2118/129225-MS . External links GlassPoint Solar Website GlassPoint Solar Videos
Wikipedia: Solar thermal enhanced oil recovery
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