Moss Landing Power Plant
|Moss Landing Power Plant|
The Moss Landing power plant, with its highly visible stacks
|Location||Moss Landing, California|
|Thermal power station|
|Primary fuel||Natural gas|
|Nameplate capacity||1060 MW|
The Moss Landing Power Plant is natural gas powered electricity generation plant located in Moss Landing, California, at the midpoint of Monterey Bay. The plant's large stacks are landmarks, visible throughout the Monterey Bay Area. The plant is owned and operated by Houston-based Dynegy and currently has a generation capacity of 1020 MW (net) from its two combined cycle generation units. The plant was once the largest power plant in the state of California with a generation capacity of 2560 MW before its two large supercritical steam units were taken offline.
In 1949, Pacific Gas & Electric (PG&E) began construction on the Moss Landing Power Plant. Five natural gas and oil powered steam units were built during the 1950s. Producing 613 MW, commercial generation started in 1950.
In 1964, the construction of two additional units began (6 and 7), with two new 500-foot (150 m) stacks. These two units produce 750 MW each for a total of 1500 MW, with boilers that are 180 feet (55 m) tall. They employ a newer technology using supercritical steam at 3,600 psi (25 MPa).
In 1995, the original 5 units were retired, and in 1997 PG&E let the permits lapse for these units.
As part of the Deregulation of Utilities in California, PG&E sold the plant to Duke Energy (DENA) in 1998. To comply with more restrictive pollution regulation, units 6 and 7 were upgraded in 1998 with a selective catalytic reduction unit and digital control systems.
Starting in 2000, the eight 225-foot (69 m) stacks and 19 fuel oil storage tanks were removed, and two new units were built on the former site. The new units 1 and 2 were brought online in 2002. They are combined cycle units, 50% more efficient than the other units, because they use two turbines: first, a pair of 170 MW gas turbines, then a 190 MW steam turbine, for a total of 530 MW each. When completed in 2002, the plant was the largest power plant in California by Capacity at 2560 MW. 
In 2006, having invested over half a billion dollars in upgraded capacity, efficiency and emission control, Duke Energy sold the plant to LS Power Equity Partners. Dynegy then purchased the plant in April 2007 along with other assets of LS partners.
On December 31, 2016, Dynegy retired supercritical steam units 6 & 7 as they were no longer economically competitive. Dynegy continues to maintain the permit on these units, however.
On June 29, 2018, Vistra Energy , which merged with Dynegy on April 9, 2018, announced that it will develop a 300 MW / 1,200 MWh energy storage system to be located at Moss Landing, using the existing turbine building and existing interconnection from units 6 & 7. Vistra Energy expects the energy storage system to begin commercial operation by the end of 2020, pending receipt of approval from California Public Utilities Commission (CPUC). This would be the largest lithium-ion battery energy storage system in the world.
Pacific Gas & Electric (PG&E) asked CPUC to approve four energy storage projects located at Moss Landing including another large lithium-ion battery storage system of 182.5 MW / 730 MWh to be provided by Tesla and owned and operated by PG&E. PG& E said it expects the Tesla system will begin commercial operation by the end of 2019. 
In February of 2017, independent power producer Dynegy, Inc. announced that it may close the plant, due to market conditions resulting from a glut of wholesale electricity in California making it difficult to operate profitably.
The glut in wholesale prices is partially a result of policies which guarantee utilities like Pacific Gas and Electric Company (PG&E), (a regulated monopoly), return on investment for building new power plants, even when they are not needed. Independent power producers like Dynegy, on the other hand, do not have a guaranteed return on their investment.
The plant has power lines that connect it to Path 15 and interconnections like Path 26 and Path 66 that allow power to flow to far-away regions. The plant is also connected to local loads and the San Jose region by transmission lines.
Both the supercritical units and the combined cycle units use once-through cooling. The supercritical units have a cooling requirement of 600,000 US gallons (2,300 m3) per minute, and the combined cycle units a requirement of 250,000 US gallons (950 m3).
Supercritical Steam Units 6 & 7
The generation process for units 6 and 7 starts with natural gas injected at one end of the boiler to be burned. Primary water is injected at the other end of the boiler to receive the heat produced. The gas simply comes from a natural gas pipeline, and combustion products go up the stack and into the atmosphere.
Water has a much more complicated path, and consists of two distinct systems: coolant water and primary (steam-generating) water. Cooling water is pumped out of the Monterey Bay or the nearby Elkhorn Slough. Then it is purified, used to cool down the water coming from the turbines, and discharged into the ocean. Steam for the turbines is created from the primary water flow, which is preheated before entering the boiler. From the boiler, the superheated steam is directed into a first turbine working at high pressure, then into a low pressure turbine. The turbines drive the generators.
At the end of their life, units 6 & 7 were typically operated as peaking units when demand for electricity was highest. In 2016, they only operated approximately 3% of the time.
Combined Cycle Units 1 & 2
Combustion products drive the gas turbines directly. First, air is drawn from the air intake to the compressor (driven by the turbine axle), then it is burned with natural gas in the combustion chamber. The hot combustion gasses then go through the actual turbine (driving the axle). From a thermodynamic standpoint, this is the standard Brayton cycle. Because the gas turbine does not transfer energy from the combustion process to the turbine via steam, it avoids the cost, energy loss and environmental impact of the primary water cycle.
At the output of the gas turbines, some of the remaining energy (heat) in the exhaust gas is recovered through a heat exchanger and transferred to water that feeds a steam turbine, similar to units 6 and 7.
On a smaller scale than the supercritical units, units 1 and 2 are also more flexible, with a start-up time of only an hour, against 24 hours for units 6 and 7.
- ""Dynergy Generating Assets"" (PDF). February 2018. Retrieved May 28, 2018.
- "Final Staff Assessment- Moss Landing Power Plant Project" (PDF). California Energy Commission. June 2000. Retrieved May 28, 2018.
- "Duke Energy Breaks Ground on Moss Landing Modernization Project". Duke Energy. November 16, 2000. Archived from the original on July 2, 2004.
- "Duke Energy Completes Sale of Wholesale Generation Assets to LS Power". press release. May 4, 2006. Archived from the original on September 27, 2011. Retrieved February 16, 2011.
- "LS Power Closes Deal for Duke Assets". press release. May 4, 2006. Retrieved May 28, 2018.
- "Dynegy Announces Completion of LS Power Transaction". press release. April 2, 2007. Retrieved May 28, 2018.
- "Moss Landing power plant's tall twin towers are off, but permits remain". Monterey County Weekly. February 23, 2017. Retrieved May 28, 2018.
- "Vistra / Dynegy Merger - Vistra Energy". Vistra Energy. Retrieved 2018-07-03.
- "Vistra Energy to Develop 300-Megawatt Battery Storage Project in California". investor.vistraenergy.com. Retrieved 2018-07-03.
- "Advice Letter 5322-E from PG&E to CPUC" (PDF). Retrieved July 3, 2018.
- "Tesla strikes another mammoth energy storage deal in California". Ars Technica. Retrieved 2018-07-03.
- Penn, Ivan; Menezes, Ryan (2017-02-05). "Californians are paying billions for power they don't need". Los Angeles Times. Archived from the original on 2017-02-22. Retrieved 2017-12-30.
California has a big — and growing — glut of power, an investigation by the Los Angeles Times has found. The state’s power plants are on track to be able to produce at least 21% more electricity than it needs by 2020, based on official estimates. And that doesn’t even count the soaring production of electricity by rooftop solar panels that has added to the surplus.
Utilities are typically guaranteed a rate of return of about 10.5% for the cost of each new plant regardless of need. This creates a major incentive to keep construction going: Utilities can make more money building new plants than by buying and reselling readily available electricity from existing plants run by competitors.
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