BrightSource Energy Frequently Asked Questions | Concentrating Solar Power


Company Overview

  1. 1. When was the company founded?

    BrightSource Energy was founded in 2006. 

  2. 2. Where is the company located?

    Headquartered in Oakland, Calif., BrightSource Energy also has offices in the China, Europe, Israel and South Africa.

  3. 3. How is BrightSource Energy financed? Who are BrightSource Energy’s investors?

    To date, BrightSource Energy has raised more than $530 million in private financing from blue chip investors including VantagePoint Venture Partners, Alstom, Morgan Stanley,, BP Alternative Energy, StatoilHydro Ventures, Chevron Technology Ventures, Black River, Draper Fisher Jurvetson, and DBL Investors (a spin-off from JP Morgan), and the California State Teachers’ Retirement System.

  4. 4. How many employees work at BrightSource?

    As of May 2012, more than 400 employees work for BrightSource around the world.

  5. 5. What does BrightSource do?

    BrightSource Energy designs, develops and deploys concentrating solar thermal technology to produce high-value steam for electric power, petroleum and industrial-process markets worldwide. BrightSource combines breakthrough technology with world-class solar power plant design capabilities to generate clean energy reliably and responsibly. BrightSource’s solar thermal systems are designed to minimize impact to the environment and help customers reduce their dependence on fossil fuels.

  6. 6. What markets does BrightSource compete in?

    Our primary market is electricity generation. Our technology can also be used in petroleum and industrial applications, like enhanced oil recovery.

  7. 7. What is BrightSource’s US project portfolio?

    We currently have approximately 100,000 acres under control – the equivalent of approximately 9 GW of power.

  8. 8. Who are BrightSource’s current customers in the U.S.?

    We currently have one of the largest solar pipelines in the US – approximately 2,400 megawatts with Pacific Gas & Electric (PG&E) and Southern California Edison.  We also built and supplied the technology for a 29 megawatt (thermal) solar-to-steam facility for Chevron to support enhanced-oil recovery at their Coalinga, CA oil field.

  9. 9. Is BrightSource looking to expand within the US?

    In the US, we are currently focused on the Southwest – California, Arizona, New Mexico, Nevada, etc. 

  10. 10. Is BrightSource looking to expand outside the US?

    We plan to partner with blue-chip development, finance and EPCs within each international market we enter. For example, we are currently partnered with Alstom in markets where they are strong in the Mediterranean, Australia, and Southern and Northern Africa.


  1. 1. How does BrightSource Energy’s technology work?

    BrightSource Energy’s proven solar thermal tower technology produces electricity the same way as fossil fuel power plants – by creating high temperature steam to turn a conventional turbine. However, instead of using fossil fuels to create the steam, BrightSource uses the sun.

    At the heart of BrightSource’s proprietary solar thermal system is a state-of-the-art solar field design, optimization software and a control system that allow for the creation of high temperature steam. Thousands of software-controlled mirrors track the sun in two dimensions and reflect the sunlight to a boiler that sits atop a tower. When the concentrated sunlight strikes the boiler’s pipes, it heats the water to create superheated steam. The steam is either piped from the boiler to a conventional steam turbine to produce electricity, where transmission lines will carry the power to homes and businesses, or the steam is used in industrial process applications such as thermal EOR.

    By integrating conventional power block components, such as turbines, with our proprietary technology and state-of-the-art solar field design, electric power plants using our systems can deliver cost-competitive, reliable and clean power when needed most.

    The company can also integrate proven molten salt storage or hybridize with a fossil fuel, further increasing output and reliability, and significantly reducing energy costs.

  2. 2. Is BrightSource’s technology proven?

    BrightSource’s technology has been operating at the company’s demonstration facility, the Solar Energy Development Center (“SEDC”) since June 2008. The SEDC is the only known solar thermal facility in the world to have directly produced superheated steam at over 540°C on a continuous basis through technology that will be used on a utility scale. With more than three years of operations, the 6MWth facility provides unmatched operational and production data from its 1,641 heliostats, 12,000 square meters (130,000 square feet) of reflecting area and 60-meter (200 foot) receiver tower.

    Our technology is also being used in a commercial enhanced oil recovery facility owned by Chevron in Coalinga, California. The plant has been operating since October 2011. 

  3. 3. What are the basic advantages of BrightSource’s power tower technology?

    BrightSource’s proprietary solar thermal technology is significantly advancing the solar thermal industry. By using mirrors to directly heat water in the boiler, BrightSource’s plants are able to produce higher temperature and pressure steam. The ability to produce high quality steam allows for BrightSource’s systems to more efficiently produce power than competing solar thermal and photovoltaic technologies. 

    By reaching high temperature and pressure steam, BrightSource’s plants can also more cost-effectively incorporate storage or hybridize with fossil fuels in its plants, thereby increasing the amount of clean power it can produce and reducing the overall cost of energy.

    BrightSource’s innovation is a result of the technical team’s decades of unrivaled experience in the solar thermal industry. 

  4. 4. Do towers have a cost/performance advantage over troughs?

    Yes. Based on BrightSource’s own analyses as well as those in independent, externally published sources, the levelized cost of electricity from a tower system will be between 30% to 40% lower than with a trough system. The cost/performance advantage of tower systems is based on five key contributing factors: 

    • More efficient production of steam from solar radiation due to two-axis tracking
    • More efficient generation of electricity from steam due to higher temperature steam production
    • Less ‘parasitic’ energy usage for plant operation due to reduced movement of thermal mass
    • Higher capacity factor – more megawatt hours produced per megawatt of installed power equipment
    • Lower capital costs due to commodity-based inputs, no concrete foundations, and fewer pipes and cabling
  5. 5. How does a tower system produce steam more efficiently?

    Parabolic trough systems lose a relatively large proportion of heat, with about two-thirds of the losses occurring at the heat-collecting pipes in the troughs themselves and the remainder in the long pipes distributing the oil throughout the solar field. More energy is lost when reflected sunlight must pass through an evacuated glass tube in order to reach the heat-collecting pipe.

    Tower systems have much lower heat losses because their heat-collecting pipes are concentrated in the receiver and not dispersed around the solar field.

    Other factors are related to the geometry of the mirrors and their targets. For example, the mirrors in a tower system receive sunlight at a more advantageous angle than parabolic trough mirrors because they track the sun on two axes (i.e., in three dimensions) rather than on only one axis. The tracking advantage is particularly important when the sun is relatively low in the sky, such as in winter, or even in the early and late daylight hours at other times of the year. This means that a larger proportion of sunlight is reflected and ultimately utilized for electricity on a yearly basis.

  6. 6. How does a solar power tower system work and how is it different from parabolic trough systems?

    In a solar power tower system, computer-controlled mirrors track the position of the sun to reflect light onto a ‘central receiver’ or boiler sitting atop a tower. The boiler, containing water, is designed to be heated from the outside to produce superheated pressurized steam. The steam is then transported to a traditional steam turbine generator to produce electricity.

    By contrast, parabolic trough systems use synthetic oil as an intermediate ‘heat-transfer fluid’ to absorb heat, which is then pumped through heat-collecting pipes mounted in the focus of parabolic trough-shaped mirrors. The pipes pass through a heat exchanger to generate steam, which drives a turbine generator to produce electricity.

  7. 7. How does the “capacity factor” make tower systems more economical?

    The capacity factor of a power plant is simply the number of hours of electricity it produces divided by the number of hours in a year.

    During the winter, the poor angle of the sun onto horizontal troughs lowers system performance. But because the tower’s solar field can provide adequate electricity throughout the year, towers have a higher capacity factor.

    Furthermore, a tower system can be designed to work at peak output levels for more hours over the course of the year, simply by adding inexpensive heliostats to an existing array of tower, receiver and power equipment. In contrast, the investment in trough plants is more evenly distributed throughout the solar field, and the raising of capacity factor is far more costly.

  8. 8. Why is generation of electricity from steam more efficient in a tower system?

    New generations of turbines can convert supercritical steam to electricity at efficiencies of more than 50%. BrightSource’s tower systems take advantage of the most efficient steam turbine generators, and the company’s initial projects in California are rated at 540°C to 560°C and 140 to 160 bar with a net cycle efficiency of 40%. Future projects are planned to operate in the supercritical range of temperatures and pressures, with steam-to-electricity efficiency reaching 50%.

    Trough systems, on the other hand, cannot make use of the same advances in turbine technology to increase the efficiency of electricity generation because the synthetic oils used for heat collection are limited to temperatures of about 390°C. Based on currently available information, turbines serving parabolic trough systems are generally around 36% efficient.

  9. 9. What is ‘parasitic’ energy usage and why do tower systems use less?

    Parasitic energy is how much electricity the plant itself uses. For example, the pumps and motors of a solar field or receiver are examples of parasitic energy. The biggest use of parasitic energy in a parabolic trough plant is to pump the synthetic oil throughout the heat-collecting pipes throughout the field.

    Tower systems avoid this costly expenditure of energy simply by not circulating fluid – water – in the solar field. The water/steam circulation pump in a central receiver requires far less electricity, and as a result total parasitic energy usage in a tower system is at least 50% less than in a comparable trough plant.

    Typical parasitic energy values (including all solar field and heat exchange systems, the power block and balance of plant) are 12% to 14% of electricity produced for parabolic trough systems and 5% to 6% for a solar power tower plant.

  10. 10. How do the capital costs of towers and troughs compare?

    Towers have a unit capital cost advantage over troughs, which can be broken down into four distinct elements: 

    • Glass: Flat glass mirrors are less expensive than curved glass mirrors.
    • Structural steel: Tower heliostats are mounted singly or in pairs, creating a low wind load and therefore requiring far less structural steel per square meter of mirror.
    • Pipes: A tower system contains far fewer heat-collecting pipes in its boiler because of the higher sunlight concentration ratios. Furthermore, tower piping is installed only at the central tower and not distributed throughout the field. In addition, trough systems require kilometers of header pipes for distribution of cold and hot oil to and from the working collector assemblies.
    • Civil works: Trough assemblies require sizable concrete foundations, and trenching and cabling throughout the solar field to bring power to the drive motors. The compact heliostats in a BrightSource tower system do not require foundations and use minimal cabling.
  11. 11. Why are power tower systems easier to implement than parabolic trough systems?

    First, tower technology has surpassed solar plant topographic limitations: trough systems require extremely flat terrain with grades limited to <1%, while tower systems can be sited on terrain with grades of up to 5%.

    Second, tower technology does not face as many barriers in terms of field equipment. There are fewer manufacturers of curved glass appropriate for trough mirrors than manufacturers of simple flat glass mirrors. Furthermore, there are, at present, only two manufacturers of the specialized heat-collecting pipes used in parabolic trough systems.

    Third, the potential adverse environmental impacts of trough systems often require more intensive environmental scrutiny and longer permitting processes.

  12. 12. What is the history of the power tower technology?

    In the 1970’s Sandia National Laboratories in Albuquerque, New Mexico studied the power tower concept and proposed a test facility to investigate the concept and qualify components and systems for larger‑scale evaluation at a pilot plant.  As a result, the National Solar Thermal Test Facility (NSTTF) was built at Sandia in 1976. At NSTTF, 222 computer-controlled heliostats directed the sun into any of four test bays on a 205-foot (63-meter) tower to produce a total thermal capacity of 5 megawatts.

    The tower technology was first developed and made operational for electricity production in 1982 by the U.S. Department of Energy (U.S. DOE) working with an industry consortium to build a 10 megawatt project, known as Solar One, in Barstow, California.  Solar One produced over 38 million kilowatt-hours of electricity during its operation from 1982 to 1988.

    Between 1992 and 1999, Bechtel acted as program manager for U.S. DOE on the Solar Two project that enlarged and retrofitted Solar One to use molten salt for heat transfer and thermal storage. During its operational period from April 1996 to April 1999, Solar Two successfully demonstrated efficient collection of solar energy and dispatch of electricity, including the ability to routinely produce electricity during cloudy weather and at night. In one demonstration, it delivered power to the grid for 153 straight hours (nearly a full week) before extended cloudy weather interrupted 24 hours per day operation.

    More recently, the first commercial power tower – an 11 megawatt plant known as PS-10, was commissioned near Seville, Spain in March 2007. A 20 megawatt project known as PS-20 was completed adjacent to PS-10 in April 2009. In 2011, the 20 megawatt Gemasolar project went live with up to 24 hours of solar power production.

    BrightSource has also completed its demonstration facility, the Solar Energy Development Center (“SEDC”) in June 2008. The SEDC is the only known solar thermal facility in the world to have directly produced superheated steam at over 540°C on a continuous basis through technology that will be used on a utility scale.

    BrightSource’s technology is also being used in a commercial enhanced oil recovery facility owned by Chevron in Coalinga, California. The plant has been operating since October 2011. 


  1. 1. How Does BrightSource SolarPLUS™ plant with storage work?

    BrightSource’s SolarPLUS plant combines BrightSource’s high-efficiency solar thermal system with a proven two-tank molten salt storage medium.

    A traditional BrightSource solar thermal system uses a field of software-controlled mirrors called heliostats to reflect the sun’s energy to a boiler atop a tower to produce high temperature and high pressure steam. The steam is used to turn a conventional steam turbine to produce electricity.

    In BrightSource’s SolarPLUS plants, the steam is directed to a heat exchanger, where molten salts are further heated to a higher temperature, thus efficiently storing the heat energy for future use. Later, when the energy in storage is needed, the heat stored in the molten salts is used to generate steam to run the steam turbine.

  2. 2. What is the storage medium being used?

    BrightSource is implementing a proven two-tank molten salt system. The molten salt mix is composed of 60% by weight sodium nitrate (NaNO3) and 40% potassium nitrate (KNO3). This mixture is also known as “solar salts” because of its widespread use in the solar thermal industry.

  3. 3. What are the benefits of a BrightSource plant with storage?

    There are five main benefits of a BrightSource SolarPLUS plant:

    • Reducing the total energy costs by increasing a plant’s capacity factor – the amount of hours that a plant runs annually
    • Shifting electricity production to periods of highest demand
    • Providing firm capacity to the power system; replacing the need for conventional power plants as opposed to just supplementing their output
    • Providing ancillary services such as spinning reserves to help support a reliable grid
    • Avoiding the variability and integration costs that other renewable resources like photovoltaics (PV) and wind create for utilities and grid operators; reducing the need for additional fossil fuel units required to back up intermittent renewables that put a hidden financial burden on ratepayers
  4. 4. How does a SolarPLUS™ plant reduce energy costs?

    SolarPLUS plants reduce energy costs by increasing its capacity factor – how much power a plant produces – and through improved efficiencies of BrightSource’s solar thermal technology compared to competing commercial solar thermal technologies. These efficiency advantages are found in plants with standard solar and those with storage, and reduce costs by requiring less capital investment.   

  5. 5. What are the advantages of BrightSource’s storage approach vs other solar thermal technologies with storage?

    When compared to other commercialized solar thermal plants with storage, our primary advantage is in our solar thermal technology’s ability to reach higher temperature and pressure levels, which allows our plants to run more efficiently with or without storage capacity. These higher efficiency levels result in improved economics in solar and storage power production. 

Enhanced Oil Recovery

  1. 1. What is enhanced oil recovery?

    Thermal enhanced oil recovery (EOR) is used in “secondary” and/or “tertiary” phase oil fields where oil remaining in an underground reservoir is both too low-pressure, and too viscous, to freely flow to the surface. “Steam flood” thermal EOR manipulates oil production by “flooding” the reservoir, via a separate injection well, with very hot, high quality steam in order to increase reservoir pressure and reduce the viscosity of the resource.

    Thermal EOR is a significant industry in the US where, in 2006, operations produced approximately 500,000 barrels of oil per day. Thermal EOR requires a number of conditions: a high reservoir porosity, a field depth of 500-5000 meters, and most importantly, an oil ‘gravity’ less than 20. Steam itself must also be matched to a specific reservoir with an optimal pressure, temperature, and quality.

  2. 2. What are the benefits of using solar thermal technology for enhanced oil recovery?

    Thermal EOR helps avoid CO2 and other airborne particulates, creates new jobs, and frees up natural gas for other uses, providing a hedge against volatile natural gas prices.  

Cost & Value

  1. 1. How much does electricity from BrightSource’s plants cost?

    For competitive reasons, we do not disclose the exact cost of electricity produced at our projects. However, given our capacity factor and efficiency advantages, we believe that our projects are lower than other leading solar technologies and will continue to drop in cost through deployment with our US and international customers.

    The CSP industry has a history of significant cost reductions when introducing new technologies. The SEGS plants reduced costs by 50% over nine plants. With next generation technologies being deployed today, we believe that similar cost reductions can be achieved with power tower technology as well. 

  2. 2. How do you plan to reduce the cost of your plants?

    Cost reductions with BrightSource’s technology come from:

    • Economies of scale (larger plants)
    • Increasing steam temperature and pressure efficiencies
    • Increasing capacity factor through storage
    • Supply chain improvements
  3. 3. What value does a BrightSource solar thermal plant bring to a utility customer?

    Utilities value solar thermal plants as a reliable power source, much like a conventional power plant. Large solar thermal plants will continue to be highly attractive to utility customers because they can produce significant amounts of reliable, dispatchable electricity. Solar thermal with storage avoids the intermittency issues associated with photovoltaic solar and wind generation, which is a necessary power characteristic to maintain a stable grid for utilities and their customers. Solar thermal integrates more seamlessly into the transmission grid because it has similar flexibility as a conventional thermal plant. 

    As thermal energy storage is added to solar thermal power plants, solar thermal becomes even more valuable because stored energy can be used to accommodate the variability of other non-dispatchable renewable, including wind and PV. Stored energy can also be used to meet electricity demand in the late afternoon and early evening hours, after the sun has gone down and PV output drops. This extra generation is highly valued by utilities.  

Environmental Benefits

  1. 1. What are the environmental advantages of BrightSource’s technology?

    • Our pole-based heliostats avoids sensitive plant habitat and allow for building around the land’s natural contours, which requires less grading and the use of extensive concrete pads than other solar thermal technologies. For example, with our technology, we can place poles directly in the ground, without concrete pads, which allows for vegetation to exist within the field below the mirrors. We can also build on up to a 5% grade, meaning that we do not have to grade the site to achieve perfectly flat land, unlike PV and parabolic trough technologies. 
    • We use dry-cooling, despite its additional cost, to reduce water usage by more than 90% over competing technologies.  
    • Unlike trough technology, the power tower design does not require the use of oil or other synthetic chemicals to produce electricity.
    • Our plants are more land efficient than competing solar technologies.
  2. 2. How does BrightSource select the sites for its projects?

    When determining where to site our projects, we use a very stringent set of environmental and generation criterion including:

    • Sites with existing nearby transmission
    • Areas with high direct natural solar insolation, which decreases the amount of land required
    • Sites close to development or that have already had pre-existing human impact
    • Areas that do not contain any Desert Wildlife Management Area (DWMA), area of critical environmental concern (ACEC), Wildlife Habitat Management Areas (WHMAs), nor any other designated critical habitat
  3. 3. Do you work with environmental groups to develop your power plants?

    We work closely with a number of local and national environmental groups when planning and executing our solar thermal plants. Feedback from these groups is essential in designing and deploying a thoughtful utility-scale solar plant.

  4. 4. How does BrightSource’s technology reduce water use?

    We are setting the bar for very low water use. Our projects feature a dry-cooling technology, which allows the project to reduce water usage by more than 90% over competing solar thermal technologies using conventional wet cooling systems. For example, the water consumed on the Ivanpah project – roughly the equivalent of 300 homes’ annually – is for cleaning the mirrors, much like a PV plant of similar size.

  5. 5. Do you protect species found on your project sites?

    We go to great lengths to protect and care for the plant and animal species found on our solar power project sites. For example, at our Ivanpah project, we have a comprehensive desert tortoise protection program onsite, including a “Head Start” tortoise hatchery program. For more information on the “Head Start” program, please visit the following blog post

    We approach native plant life with the same level of care. In addition to allowing for trimmed vegetation to co-exist in the field of mirrors, we can also avoid areas of sensitive plant life. For example, at Ivanpah, we have a native plant nursery and have identified areas within the solar field, which we call “halos,” where we do not place heliostats. 

Species Protection

  1. 1. Is the desert tortoise an endangered species?

    The desert tortoise is federally-listed as a threatened species – not an endangered species. “Endangered” is a more serious designation within the Endangered Species Act, meaning that the species is currently on the brink of extinction. “Threatened” species do not currently face the same risk, although they are protected to help
    prevent their becoming endangered.

  2. 2. What steps are you taking to protect and repopulate the desert tortoise populations at Ivanpah?

    • Financial Investment: The Ivanpah project owners have to date spent approximately $22 million caring for the desert tortoises found on or near the site. In addition, we will spend up to $34 million to meet the project’s federal and state mitigation obligations.
    • Biologists: At any given time, there are dozens of trained, Agency approved (Bureau of Land Management, US Fish & Wildlife Service, California Department of Fish & Game and California Energy Commission) biologists on site to make sure that every tortoise on site is given the highest levels of care. At certain periods of construction, there have been over 150 biologists on the project.
    • Nurseries: The tortoises found on the project site were first moved to a designated nursery where biologists carefully recreated their burrows and provided food and water. While in the nursery, biologists ensured that there was no interaction between the tortoise and conducted the appropriate medical tests to ensure the animals were healthy and free of a respiratory disease common in the species.
    • Juvenile “Head-Start” Care Program:  All juvenile tortoises, classified as tortoise under 120mm in size including newborn hatchlings, will be provided specialized “head-start” care and protection for approximately the first five years of life, or until they are large enough to resist predation from ravens, kit foxes, and coyotes and other factors such as drought and disease. 
    • Translocation: Eventually, all of the tortoises cared for on the project site will ultimately be relocated back into their natural habitat nearby. The majority of the tortoise will remain within their original “home range” (unlike tortoises translocated long distances to unfamiliar habitat) and will have comparable plant diversity and richness as the Ivanpah site. Keeping the tortoise close to their original homes greatly increases the rate of success for translocation.
    • Long Term Monitoring: Biologists will track the tortoises that are translocated from the project site as well as the tortoises outside the project site within the “receiving” area for five years.  A total of 80 adult and sub adult tortoises were found on site, as well as 93 juvenile tortoises many thought too small to be detected.   An additional 53 tortoise were hatched in the tortoise nurseries in the fall of 2011. The biologists will use tracking information from nearly 400 tortoises, including those in nearby populations that are monitored as “controls” for tortoise found on-site, or in areas that will receive tortoises that are moved off-site, to ensure the safe integration and gather additional insights on the desert tortoise and its recovery.  
  3. 3. What is the natural survival rate of the desert tortoise?

    In its natural environment, only about 2% of desert tortoises survive to adulthood (reproductive age).  Tortoise care programs for hatchling (newborn) and juvenile tortoise provide a critical path for improving survival rates by providing support and protection from ravens, kit foxes, and coyotes and other factors such as drought and disease during approximately the first five years of life.

  4. 4. What can be done to help increase the survival rate of desert tortoise?

    In an effort to help facilitate the rebuilding of the desert tortoise population in the Ivanpah Valley area, we have developed a world-class juvenile “head-start” care program at the Ivanpah project.  Head-start care programs provide support and protection for hatchling and juvenile tortoise during approximately the first five years of life, or until they are large enough to resist predation and other factors such as drought and disease. 

    At the Ivanpah head start facility, we are currently caring for more than 100 juvenile desert tortoises, including 53 newborn hatchlings born in the fall of 2011. The facility includes highly secure, specialized juvenile tortoise pens that carefully protect from predators – which include ravens, raptors, ground squirrels and coyotes. Head start programs have been found to provide a critical avenue for enhancing repopulation of the desert tortoise.

  5. 5. How much land within the Mojave Desert is designated for desert tortoise habitat?

    Desert tortoise habitat is divided into six large areas, called “recovery units,” spanning tens of millions of acres across Arizona, California, Nevada and Utah. The Ivanpah site is within the approximately nine million-acre Northeastern Mojave recovery unit, comprising approximately four hundredths of one percent (0.04%) of the unit’s total acreage. 

    In the Ivanpah Valley alone, over 630,000 acres have been designated as Critical Habitat for desert tortoise. The Ivanpah site is not located within any defined Critical Habitat, and has been designated by the BLM as “Category 3” habitat – the “least important” category of habitat for the desert tortoise.  In total, over 6.4 million acres have been identified as critical habitat for the tortoise across the six recovery units, including 4.75 million acres in California.

  6. 6. How will your desert tortoise care and protection efforts affect the tortoise population long-term?

    As a result of our tortoise care and protection efforts, many more healthy tortoises will be returned to the Ivanpah Valley than would have survived had the Ivanpah project not been built.  Additionally, each of the translocated tortoises, their hatchlings living in the head-start program and the recipient tortoise population are being studied extensively by biologists.  The data gleaned at the Ivanpah project will help the desert tortoise biologist community learn more about the species and determine additional ways to help the population once again flourish.

  7. 7. Which public agencies do you consult with on your tortoise care efforts?

    We work extensively with government agencies such as the California Energy Commission, Bureau of Land Management, California Department of Fish and Game, U.S. Fish and Wildlife Service, Mojave National Preserve and the environmental community to develop a thoughtful and responsible tortoise care and mitigation strategy.  The project also underwent stringent California Environmental Quality Act and National Environmental Policy Act reviews.

Dry Cooling

  1. 1. How does BrightSource’s solar thermal technology conserve water?

    In BrightSource’s solar technology, we use water in two primary ways: to clean the heliostat mirrors and to produce steam for electricity generation. 

    Water is not consumed during power generation.  To produce steam from the sun, we use tens of thousands of computer-controlled mirrors to track the sun in two dimensions and reflect the sunlight to a water-filled boiler that sits atop a tower. When the concentrated sunlight strikes the boiler’s tubes, it heats the water to create superheated steam. This high-temperature steam is then piped from the boiler to a conventional steam turbine-generator where electricity is generated.  In order to conserve water, we use a dry cooling process to condense the steam back to liquid water, which is then cycled back to the boiler in a closed loop cycle. 

    The minimal amount of water consumed by a BrightSource power plant is used from the cleaning of heliostat mirrors, and even this water is made up of partially recycled boiler water.

  2. 2. How much water is used in a BrightSource Energy solar thermal plant?

    The amount of water used varies depending on the size of the plant.  For example, our 392 (gross) megawatt Ivanpah solar plant will use approximately 100 acre feet of water each year.  This is comparable to the amount of water used by 300 households annually, and less than the amount used to water two holes of the nearby 36-hole golf course. 

  3. 3. What is dry cooling?

    In thermal steam systems, the super heated steam inside the boiler pipes must be cooled and condensed back into water in a closed loop system.  Dry cooling, or air cooling, uses an air-cooled condenser comprised of many large fans to circulate air over the pipes to cool and condense the steam.  By comparison, a wet cooling system will circulate water across the pipes to cool and condense the steam. 

  4. 4. What are the benefits of dry cooling?

    There are a number of benefits to using a dry cool system.  The primary motivation to use dry cooling for BrightSource is to conserve scarce water resources in the arid desert climates where we build our plants.  Overly taxing an area’s water resources can very seriously damage the biological ecosystem of the area, negatively impacting both animal and plant species.  Dry cooling requires 90 percent less water than competing wet-cooled or hybrid dry-wet cooled systems.  By using dry cooling, we are also able to eliminate the need for evaporation ponds and extensive water treatment facilities, which provide us with greater flexibility on where we can site our solar power plants.

  5. 5. What are the drawbacks of dry cooling?

    The primary drawbacks of using a dry cooling system are the added cost and the loss of efficiency.  Power tower is the most cost-effective dry cooling plant because it produces more power, offsetting the additional cost per unit of electricity and has the ability to produce higher temperature steam, which results in a smaller efficiency loss when interfacing with dry cooling technologies.

    Studies from the National Renewable Energy Lab (NREL) show that air-cooled condensers can add about five percent to a plant’s capital costs and experience an efficiency loss that varies depending on the ambient air temperature.  By nature, dry cooling requires large fans to cool and condense the steam, and these fans require a significant amount of electricity to operate.  The electricity required to operate the fans takes away from the total amount of electricity that can be sold to a customer, referred to as “parasitic loss.” The warmer the ambient temperature, the larger the parasitic loss.

  6. 6. How does BrightSource’s technology overcome the challenges of dry cooling?

    BrightSource’s technology is designed to produce the highest temperature and pressure solar steam in the world.  We are able to heat water to over 550 degrees Celsius, or over 1000 degrees Fahrenheit.  Competing parabolic trough systems or molten salt tower systems are limited by temperatures that the heat-transfer medium such as molten salt or synthetic oils can reach.  This technological advantage lets us use more of the steam’s heat energy (enthalpy) to more efficiently power a steam turbine-generator.  As a result, our solar thermal power systems can produce more electricity than competing technologies. 

    Our ability to produce and sell more electricity makes dry cooling an economically viable choice.  It significantly reduces the cost implications of using a more expensive dry cooling system, and it also reduces the percentage of overall parasitic load. 

  7. 7. How does an air-cooled condenser work?

    An air-cooled condenser (ACC) condenses the steam by forcing ambient air over tubes that contain the steam that exits the turbine.  ACCs are typically comprised of modules arranged in parallel rows, with each module containing a number of finned tube bundles.  An axial flow, forced-draft fan located under each module forces the cooling air across the heat exchange area of the finned tubes.

  8. 8. What does an air-cooled condenser physically look like? What are the main components?

    The ACCs at Ivanpah provide a good example of the main components of an ACC and what the equipment looks like. The three ACCs at Ivanpah each have 15 modules, placed in a 3 x 5 arrangement, with overall plot area of ~ 242 ft L x 125 ft W x 97 ft H.  Each module has a 36 ft diameter fan, driven by a 200 HP motor.  The ACC is raised off of the ground to reduce the amount of dust and debris that enters the system.