1

World's Largest Solar Thermal Power Plants

Pamela Simamora

Washington University in St. Louis

June 14, 2016

MEMS 5422

2

I. TABLE OF CONTENT 1. Table of Content .............................................................................................................2 2. Abstract .............................................................................................................3 3. Introduction .............................................................................................................4 4. Project .............................................................................................................5 5. Conclusion ...........................................................................................................13 6. References ...........................................................................................................14

3

II. ABSTRACT

As unlimited resources, sunlight can be a key to overcoming climate change. The sun irradiance onto Earth is adequate to provide the world energy needs for an entire year. Despite its abundant potential, the solar energy only provides less than one-tenth of one percent of global energy use. This untapped potential will bring an enormous impact both on the environment and the economy if used effectively.

The solar energy can be harvested with photovoltaic technology and solar thermal energy technology. The concentrated solar power (CSP) has been mainly used in the solar thermal energy technology. The concentrated solar power (CSP) types that have been used in the power plant projects around the world are the parabolic trough, solar power tower, Fresnel reflectors, and dish Stirling. This paper will explore some of the largest CSP plants in the world.

Keyword: solar thermal energy, concentrated solar power, parabolic trough, solar power tower, Fresnel reflectors, dish Stirling.

4

III. INTRODUCTION

As an unlimited resource, sunlight can be a key to overcoming climate change. The sun irradiance onto Earth is adequate to provide the world energy needs for an entire year. Despite its abundant potential, the solar energy only provides less than one-tenth of one percent of global energy use. This untapped potential will bring an enormous impact both on the environment and the economy if used effectively.

Most of the people are familiar with the photovoltaic solar panel. These photovoltaic cells are made of semiconductors that can generate electricity when the sun ray knocks the electrons from their atoms. The electrons then will go through the cell to produce electricity.

Besides the PV solar panel, the solar energy can also be harvested by using the concentrated mirrors as used in the solar thermal power plants. The mirrors are used to concentrate sunray to the receiver above the mirrors or in the tower to heat the Heat Transfer Fluids (HTF) flowing inside. The heated fluid then will drive the turbine to produce electricity and transmit it to the grid. The HTF used in this technology range from oil to water and molten salt. The molten salt is usually used as the storage system.

There are several types of concentrated solar power (CSP), the parabolic trough, solar power tower, Fresnel reflectors, and dish Stirling. In this paper, the author will explore some of the largest CSP plants in the world associated with each of CSP types mentioned before.

5

IV. PROJECT

In this chapter, we are going to explore some largest solar thermal projects around the world.

1. Ivanpah Concentrated Solar Power

Ivanpah CSP is a concentrated solar thermal plant located in San Bernardino, California, USA. This power plant can produce 392 MW electricity used to serve 140,000 homes. This capacity suffices to make the Ivanpah CSP plant as the world's largest flat mirrors CSP plant (solar tower). The plant uses more than 300,000 software-controlled flat mirrors or heliostats that cover 3,500 acres of land.1 The mirrors can track the sun, and the sunlight is focused to the three 459 ft solar power towers where the boilers are put to generate the high-temperature steam that can spin the conventional steam turbine to produce electricity.

Figure 1 - Ivanpah CSP plant (Source: BrightSource Energy1)

Figure 2 - Ivanpah CSP plant (Source: BrightSource Energy1)

6

Unfortunately, this clean energy is not one hundred percent clean, as it requires the natural gas to preheat the boiler in each morning. The media has criticized this natural-gas use as the Ivanpah CSP generated 46,000 tons of CO2 emissions in its first-year operation.2 This number is predicted to increase as Ivanpah filed a petition for the natural-gas-use increment to the California Energy Commission.

The BrightSource Energy, one of the stakeholders of Ivanpah CSP plant, argues that the natural gas is used to maximize the power generation from the sun, as it will accelerate the power plant startup and increase the amount of electricity production from sunlight. Further, the BrightSource Energy explains that the weather condition in Ivanpah is worse than projected on a historical average basis, which leads to bad performance of the power plant. In order to maintain the system output, the natural gas is then used to heat the auxiliary boilers that will generate steam used to preheat the receiver.3

In May 2016, one of the solar towers in the Ivanpah CSP plant was forced to shut down as the misaligned heliostats reflected the sunlight to the steam ducts and water pipes and caused a fire at the power plant.4 This accident demands the substantial improvement of the sun tracking system used in the CSP power plants.

In term of technology, the Concentrated Solar Power (CSP) system is different with the Photovoltaic system, as the mirrors used in the CSP system cannot generate electricity like the PV solar panel does. The mirrors only act as the medium to transfer the energy or heat from the sun to the fluid inside the boiler. In a more advanced technology as used in the Crescent Dunes Solar Energy Project in Las Vegas, it is possible for the CSP power plant to keep generating the electricity several hours after the sun goes down as the CSP plant uses the molten salt as the heat transfer and thermal energy storage medium.

This molten salt is pumped up to the boiler in the tower. After heated in the boiler, the molten salt will flow to the hot storage tank before flowing to the heat exchanger where the heat transfer from the hot salt to the water occurs. As the molten salt temperature decreases, the water temperature increases and let the water become steam. The steam will be used to spin the conventional turbine to generate the electricity that will be transmitted through the power grid. Meanwhile, the low-temperature molten salt flows back to the cold storage tank. The molten salt inside the hot storage tank can keep its heat while being stored at later times.

Figure 3 - Solar Tower configurations (Source: U.S. Department of Energy5)

7

2. Noor Ouarzazate Solar Complex

Noor Ouarzazate Solar Complex is the world's largest parabolic trough solar power plant located in Morocco, on the edge of Sahara desert. The complex that consists of three Concentrated Solar Plants (CSP) plus one Photovoltaic solar plant called as Noor 1, Noor 2, Noor 3, and Noor 4 will generate up to 580 MW of electricity when finished. The construction has begun since May 2013 and is expected to fully operate in 2018. The complex requires 3,041 ha of land. Noor 1 will be able to produce up to 160 MW of electricity with three hours storage. This plant uses half a million parabolic troughs that cover 450 ha (1,112 acres) of land. Noor 2 will produce up to 200 MW of electricity using the parabolic trough with minimum seven hours storage. Noor 3 will produce 150 MW of electricity using CSP tower with minimum seven hours storage. Noor 4 will produce 50 - 70 MW of electricity using PV panels.6,7,8

Figure 4 - Noor 1 Ouarzazate Solar Complex (Source: NPR.org9)

Figure 5 - Noor 1 Ouarzazate Solar Complex (Source: Moroccan Agency for Solar Energy (MASEN)10)

8

The Noor Ouarzazate Solar Complex uses two kinds of Concentrated Solar Power technology; the parabolic trough and solar tower. The solar tower used in Noor 3 uses the molten salt as the transfer fluid and thermal energy storage medium. The technology is the same with the technology utilized in the Crescent Dunes Solar Energy Project, Las Vegas explained in the previous part of this paper.

Meanwhile, the Noor 1 and Noor 2 power plants use the parabolic troughs, which are parallel rows of single axis tracking parabolic collectors. The parabolic trough can track the sunlight to reflect the optimum heat to the receiver tube placed at the focal line of the parabolic mirrors. The synthetic oil that used as the HTF then will be heated up and flow to the solar preheater where the water is preheated, then to the steam generator where the water is evaporated, and finally to the solar superheater where the water is superheated. This superheated steam then is used to spin the steam turbine (Rankine cycle) for electricity generation. The heat from the HTF is also transferred to the molten salt that will be used as the thermal energy storage. An expansion vessel is required to buffer the volume changes caused by the thermal expansion and contraction of synthetic oil. Meanwhile, the HTF heater is used to heat up the oil in the morning and help produce minimum steam to start the turbine and ensure the HTF’s temperature above its minimum operating temperature. The parabolic trough can reach 14% of efficiency.7

Figure 6 – Noor 1 and Noor 2 configurations (Source: World Bank11)

The gas-fired backup system can keep the CSP plant generating electricity after the sun goes down and when the sunlight is not sufficient to cover the peak demand. The amount of gas used is limited to 25% of thermal energy generation. 12

3. Puerto Errado

Puerto Errado is the largest Fresnel lens solar thermal power plant in the world. Located in the Region of Murcia of Spain, Puerto Errado consists of 2 solar power plants, Puerto Errado 1 and Puerto Errado 2. The Puerto Errado 1 was the first utility-scale Fresnel lens solar thermal power plant with 1.4 MW-capacity. It has operated since 2009 by covering 5 hectares of land. The Puerto Errado 2 then started to run in 2012 with the capacity of 30 MW. It has 28 rows of mirrors that cover an area of 70 hectares. 13

9

Figure 7 - Puerto Errado power plant (Source: Tubosol14)

Figure 8 - Puerto Errado power plant (Source: Tubosol14)

The Fresnel reflector systems are working by using flat or curved mirrors mounted on trackers. These mirrors then reflect sunray to the receiver tube above the mirrors. Sometimes the systems have a small parabolic mirror above the receiver to get more focused sunray.

10

Figure 9 - Fresnel lens solar thermal power plant (Source: Energy.gov15)

Figure 10 - Fresnel lens solar thermal power plant configurations (Source: Tubosol14)

This plant is using water as the HTF. The water from the feed water pump flows to the Fresnel reflector systems to be heated to generate steam that will be separated from water in the steam drum separator. This steam then will be stored in the storage before being used to spin the steam turbine/generator to produce electricity. The output steam from the turbine then will be condensed in the air-cooled condenser before going back to the feed water tank.

4. Maricopa Solar Project

The Marico Solar Plant is a dish Stirling CSP plant located in Peoria, Arizona, USA. The plant has a capacity of 1.5 MW. The Maricopa Solar Plant is the first commercial project using SunCatcher or dish Stirling technology in the world. The power plant uses sixty-concentrated solar power dishes with each dish can generate up to 25 kW electricity.

11

Figure 11 – Maricopa Solar Power Plant (Source: CSPworld.org16)

The dish is 38ft-wide and equipped with an automatic tracker and mirrors that capture and concentrate the solar energy onto a Power Conversion Unit (PCU). This PCU will convert the solar energy into grid-quality electricity. Unlike the other CSP technologies, this SunCatcher technology does not use water to produce the electricity.

Figure 12 - Stirling CSP plant (Source: energy.gov17)

The dish Stirling system uses parabolic dishes to focus the sunray onto a receiver mounted at the focal point of the dish. The dish consists of small mirrors set into circular arrays to concentrate the sunray onto a receiver. The receiver that includes a Stirling engine and generator uses the heat from the sunray to vary the pressure of the hydrogen-filled sealed chamber. These different pressures will drive pistons to generate the mechanical power. This mechanical work is in the form of rotation of the engine's crankshaft. This rotation then will drive the generator to produce electricity. A high efficiency can be achieved as the system gets a high level of solar concentration at the focal point.

12

Figure 13 - Source: Mechanical configurations for Stirling engines (Source: OMSOP18)

Unlike the other CSP technologies, the dish system cannot store the solar energy in the form of heat, and they cannot be integrated to the gas-fired system. That means this technology is less able to provide the dispatchable power. The amount of electricity produced by dish system is smaller than other CSP technologies, typically in the range of 3 to 25 kilowatts.17

13

CONCLUSION

• There are four types of concentrated solar power (CSP) used to harvest the solar thermal energy: flat mirrors CSP plant (solar tower), parabolic trough, Fresnel lens, and dish Stirling

• The Concentrated Solar Power (CSP) system is different with the Photovoltaic system as the mirrors only act as the medium to transfer the energy or heat from the sun to the fluid inside the receiver/boiler

• The CSP power plant can keep generating the electricity several hours after the sun goes down if the CSP plant uses the molten salt as the transfer fluid and thermal energy storage medium

• The parabolic trough is a solar technology that uses parallel rows of single axis tracking parabolic collectors to reflect the optimum heat to the receiver tube located at the focal line of the parabolic mirrors

• The Fresnel reflector systems are working by using flat or curved mirrors mounted on trackers that will reflect sunray to the receiver tube above the mirrors

• The dish Stirling system uses parabolic dishes of mirror to focus the sunray onto a receiver mounted at the focal point of the dish

• The Ivanpah Concentrated Solar Power is the world's largest flat mirrors CSP plant (solar tower) by producing 392 MW

• The Noor Ouarzazate Solar Complex is the world's largest parabolic trough solar power plant with capacity reaches 360 MW

• The Puerto Errado is the largest Fresnel lens solar thermal power plant in the world by generating 31.4 MW

• The Marico Solar Plant is world's largest dish Stirling CSP plant by generating 1.5 MW

14

REFERENCES

1. BrightSource. Ivanvah Project Facts: A BrightSource Energy Concentrating Solar Power Project. (accessed June 10, 2016).

2. http://www.renewableenergyworld.com/articles/2015/11/if-a-solar-plant-uses-natural-gas-is-it-still-green.html (accessed June 10, 2016).

3. http://www.brightsourceenergy.com/the-top-five-things#.V1-U6eYrKRs (accessed June 10, 2016).

4. http://www.computerworld.com/article/3073569/sustainable-it/cause-of-blaze-at-solar-power-plant-under-investigation.html (accessed June 10, 2016).

5. U.S. Department of Energy. 2014: The Year of Concentrating Solar Power. 2014. (accessed June 12, 2016).

6. https://www.technologyreview.com/s/600751/moroccos-massive-desert-solar-project-starts-up/#/set/id/600752/ (accessed June 12, 2016).

7. Wuppertal Institute and Germanwatch. Social CSP; Energy and development: exploring the local livelihood dimension of the Noor I CSP project in Southern Morocco. 2015. (accessed June 12, 2016).

8. African Development Bank. Ouarzazate Solar Complex Project – Phase II (Noor II and Noor III Power Plants); Project Appraisal Report. 2014. (accessed June 12, 2016).

9. http://www.npr.org/sections/thetwo-way/2016/02/04/465568055/morocco-unveils-a-massive-solar-power-plant-in-the-sahara (accessed June 12, 2016).

10. Moroccan Agency for Solar Energy (MASEN). The Moroccan Experience - Noor Plan. 2015. (accessed June 12, 2016).

11. The World Bank. International Bank for Reconstruction and Development Project Appraisal Document on a Proposed Loan: To The Moroccan Agency for Solar Energy with Guarantee from The Kingdom of Morocco for The Noor-Ouarzazate Concentrated Solar Power Plant Project. 2014. (accessed June 12, 2016).

12. Günther, Matthias; Joemann, Michael; Csambor, Simon. Advanced CSP Teaching Materials: Chapter 5; Parabolic Trough Technology. (accessed June 12, 2016).

13. https://en.wikipedia.org/wiki/Puerto_Errado (accessed June 13, 2016). 14. Tubosol PE2. Puerto Errado 2: Two Years of Operation. 2014. (accessed June 13,

2016). 15. http://energy.gov/eere/energybasics/articles/linear-concentrator-system-basics-

concentrating-solar-power (accessed June 13, 2016). 16. http://www.cspworld.org/cspworldmap/maricopa-solar-project (accessed June 13,

2016). 17. http://energy.gov/eere/energybasics/articles/dishengine-system-concentrating-

solar-power-basics (accessed June 13, 2016). 18. Optimised Microturbine Solar Power System (OMSOP). Project Deliverable:

D3.4 Report on State-of-the-art Dish-Engine Applications. 2013. (accessed June 13, 2016).