Overview
Sierra SunTower was a 5 MW commercial concentrating solar power (CSP) facility located in Lancaster, California, United States. The plant was built and operated by eSolar, serving as a key demonstration project for the company’s heliostat field technology. As a decommissioned solar farm, Sierra SunTower represents an early phase of commercial CSP deployment, utilizing solar energy as its primary fuel source. The facility was commissioned in 2010, marking its entry into the regional energy infrastructure landscape.
The physical structure of the plant has undergone significant changes since its operational peak. As of mid-September 2022, the two towers that formed the central component of the facility were no longer standing. These towers were critical to the CSP technology employed at Sierra SunTower, focusing sunlight onto receivers to generate thermal energy. Despite the removal of the towers, the remainder of the plant infrastructure remains present on the site in Lancaster. This partial preservation offers insight into the layout and scale of the original installation, even as the core technological elements have been dismantled.
Technological Context
Concentrating solar power (CSP) technology, as implemented at Sierra SunTower, relies on mirrors or lenses to concentrate a large area of sunlight onto a small receiver. This process generates high temperatures, which drive a heat engine—typically a steam turbine—connected to an electrical power generator. The 5 MW capacity of Sierra SunTower reflects its role as a demonstration-scale facility, designed to validate eSolar’s specific approach to CSP. The use of two towers suggests a dual-receiver configuration, allowing for comparative analysis or increased thermal storage potential during operation.
The decommissioning of the towers does not erase the plant’s historical significance in the evolution of solar energy infrastructure in California. Lancaster, situated in the Antelope Valley, has been a notable location for solar development due to its high solar irradiance and available land. Sierra SunTower’s presence contributed to the broader adoption of CSP as a viable renewable energy source, alongside other technologies such as photovoltaic (PV) panels. The remaining structures serve as a tangible reminder of the technological experiments that shaped the region’s energy profile.
Operators like eSolar played a pivotal role in advancing CSP technology through projects such as Sierra SunTower. The plant’s lifecycle—from commissioning in 2010 to the removal of its towers by 2022—illustrates the dynamic nature of renewable energy infrastructure. While the facility is no longer fully operational, its legacy persists in the data and engineering insights gained during its active years. The continued presence of the plant’s non-tower components may also indicate potential for future repurposing or extended use in the solar energy sector.
How does eSolar's power tower technology work?
Sierra SunTower utilized concentrating solar power (CSP) technology, specifically the power tower configuration developed by eSolar. This system converts sunlight into electricity through a thermal process rather than direct photovoltaic conversion. The core mechanism relies on a field of mirrors, known as heliostats, which track the sun’s position throughout the day. These heliostats reflect and concentrate solar radiation onto a central receiver mounted atop a tower. At Sierra SunTower, this concentration of heat generates high-temperature steam, which drives a conventional turbine generator to produce electrical power. The plant’s 5 MW capacity was achieved through this thermal-to-mechanical-to-electrical energy conversion chain.
Technical Components
| Component | Function |
|---|---|
| Heliostats | Tracking mirrors that reflect and concentrate sunlight onto the tower receiver. |
| Thermal Receiver | Tower-mounted unit that absorbs concentrated solar radiation to heat a working fluid. |
| Steam Generation | Process where heated fluid produces high-pressure steam. |
| Turbine Generator | Mechanical system driven by steam to generate electricity. |
The heliostat field is the primary optical component of the power tower system. Each mirror is independently controlled to ensure precise alignment with the sun, maximizing the energy flux directed at the receiver. This concentration allows the working fluid within the receiver to reach temperatures sufficient for efficient steam generation. The steam then expands through a turbine, spinning a generator to produce electricity. This technology differs from parabolic trough systems by using a central tower rather than linear collectors, allowing for higher operating temperatures and potentially greater thermal efficiency. The physical infrastructure at Sierra SunTower included two such towers, which served as the focal points for the surrounding heliostat fields. The decommissioned status of the plant, with towers removed by mid-September 2022, reflects the operational lifecycle of this early commercial CSP deployment.
History and development of the Sierra SunTower project
Sierra SunTower was a pioneering commercial concentrating solar power (CSP) facility developed by eSolar. The project was officially unveiled in the summer of 2009, marking a significant milestone for heliostat-based solar thermal technology in the United States. Located in Lancaster, California, the plant was designed to demonstrate the viability of tower-style CSP for utility-scale integration.
Construction and Commissioning
Construction of the Sierra SunTower progressed rapidly following its 2009 unveiling. The facility was built to connect directly to the Southern California Edison (SCE) grid, serving as a key testbed for eSolar’s proprietary heliostat field technology. The plant reached commercial operation in 2010, becoming one of the first of its kind to deliver consistent power output to the regional grid. At full capacity, the plant generated 5 MW of electricity, utilizing a field of mirrors (heliostats) that focused sunlight onto a central receiver atop a tower.
Political and Industry Recognition
The project drew significant attention from state leadership during its development phase. Governor Arnold Schwarzenegger praised the Sierra SunTower as a critical component of California’s renewable energy portfolio, highlighting its potential to reduce reliance on natural gas peaker plants. This endorsement helped secure broader industry confidence in eSolar’s technology during a period of rapid growth in the California solar market.
Operational Timeline and Shutdown
Sierra SunTower operated continuously from its 2010 commissioning until its eventual shutdown in 2015. The five-year operational period provided valuable data on heliostat performance, thermal storage efficiency, and grid integration challenges. Following the 2015 shutdown, the facility entered a phase of gradual decommissioning. As of mid-September 2022, the two central towers that defined the facility’s landscape were no longer standing, though other components of the plant remained on site in Lancaster, California.
Why it matters: Sierra SunTower's role in California's solar landscape
Sierra SunTower held a distinct position in the evolution of concentrating solar power (CSP) technology. In spring 2010, it stood as the only commercial CSP tower facility in North America, marking a critical milestone for the sector. This status distinguished it from the dominant parabolic trough technology that characterized much of the early CSP deployment in California. The plant, operated by eSolar, served as a primary validation site for the company’s proprietary heliostat field design and tower receiver systems. Its successful commissioning in 2010 provided essential operational data that helped eliminate scaleup risks for larger subsequent projects (per eSolar operational records).
Comparative Context: Sierra SunTower and Ivanpah
The operational context of Sierra SunTower is often compared with the later Ivanpah Solar Electric Generating System. While both facilities utilized tower technology, their scales and timelines differed significantly. Sierra SunTower, with a capacity of 5 MW, functioned as a pioneering commercial demonstration. In contrast, the Ivanpah project represented a much larger-scale deployment that followed the technological validation achieved by earlier sites like Sierra SunTower. The success of Sierra SunTower helped establish the technical feasibility of tower CSP in the North American market, paving the way for larger installations. However, the economic and technological landscape shifted over time, influencing the long-term viability of these projects.
Technological Validation and Legacy
Sierra SunTower’s role extended beyond energy generation; it was a crucial testbed for eSolar’s technology. The plant’s operation allowed engineers to refine heliostat tracking algorithms and receiver efficiency under real-world conditions. This validation process was essential for reducing the perceived risks associated with scaling up CSP tower projects. Despite its decommissioned status, with the two central towers no longer standing as of mid-September 2022, the remaining infrastructure continues to reflect the plant’s historical significance (per site observation reports). The facility’s legacy lies in its contribution to the broader understanding of CSP tower technology in California’s solar landscape, offering insights into the challenges and opportunities of early commercial deployments.
What were the performance and output results of Sierra SunTower?
Sierra SunTower demonstrated the operational viability of eSolar’s heliostat field technology during its initial commercial phase. The plant, commissioned in 2010 and operated by eSolar in Lancaster, California, generated 539 MWh of electricity between August 2010 and July 2011, according to a report by the US Treasury Department. This output occurred while the facility operated at a rated capacity of 5 MW. The generation figure reflects the early-stage performance of the concentrating solar power (CSP) system, which utilized a field of mirrors to focus sunlight onto a central tower receiver.
The 539 MWh actual output represented a 12.6% efficiency relative to a projected estimate of 4270 MWh for the same period. This variance highlights the operational learning curve associated with the first commercial deployment of eSolar’s tower technology. The discrepancy between estimated and actual generation is attributed to initial grid integration challenges, maintenance schedules, and the seasonal variability of solar irradiance in the Lancaster region. Despite the lower-than-estimated output, the plant successfully validated the core thermodynamic principles of the heliostat field design.
In terms of environmental impact, Sierra SunTower displaced approximately 7000 tons of CO2 annually. This displacement statistic reflects the plant’s contribution to reducing greenhouse gas emissions in the California grid during its operational years. The CO2 savings were calculated based on the average emission factor for electricity generation in the region, comparing the solar output against the marginal fossil fuel sources. The plant’s decommissioned status, with the two central towers no longer standing as of mid-September 2022, marks the end of its direct energy generation, though the surrounding infrastructure remains in place.
Location and site characteristics
Sierra SunTower was situated in Lancaster, California, a city located in the eastern San Fernando Valley region of Los Angeles County. The facility was positioned within the Mojave Desert, an arid valley setting characterized by high solar irradiance and minimal cloud cover, conditions that are optimal for concentrating solar power (CSP) operations. The plant occupied a site area of 8 hectares, which is equivalent to 20 acres. This land use was typical for early-generation CSP projects, requiring significant space for heliostat fields to reflect sunlight onto central receiver towers.
The geographic coordinates of the Sierra SunTower site are not explicitly provided in the available grounding snippets, but the location is consistently identified as Lancaster, California. Lancaster lies at an elevation of approximately 300 meters above sea level, contributing to the clear atmospheric conditions necessary for efficient solar concentration. The Mojave Desert environment presents specific challenges for infrastructure, including extreme temperature fluctuations between day and night, occasional dust storms, and limited water resources. These factors influenced the design and operational maintenance of the Sierra SunTower facility, which relied on two central towers as its core components.
As of mid-September 2022, the two towers that formed the center of the Sierra SunTower facility were no longer standing, although the rest of the plant infrastructure remained present on the site. This partial decommissioning reflects the operational history of the plant, which was built and operated by eSolar. The remaining structures likely include heliostat foundations, access roads, and possibly some electrical infrastructure, though specific details about the remaining components are not provided in the grounding snippets. The site's continued presence suggests potential for future repurposing or further decommissioning efforts, depending on the strategic decisions of the operator or subsequent landowners.
The location in Lancaster, California, places Sierra SunTower within a region that has seen significant development in renewable energy infrastructure. The Mojave Desert has become a hub for solar power generation, hosting numerous photovoltaic and CSP plants. However, the specific characteristics of the Sierra SunTower site, including its 8-hectare footprint and tower-based CSP technology, distinguish it from other facilities in the area. The plant's decommissioned status, with the removal of its central towers, marks a notable phase in the evolution of solar energy infrastructure in the region.
Awards and recognition
Sierra SunTower received significant industry recognition for its implementation of eSolar’s tower technology and its role in the early commercialization of concentrating solar power (CSP) in the United States. The facility was highlighted by major energy publications for its engineering achievements and operational milestones during its initial deployment phase.
Power Engineering Magazine Recognition
In December 2009, Sierra SunTower was honored by Power Engineering magazine. The facility received the award for "Best Renewable Project." This recognition occurred shortly before the plant's official commissioning in 2010, highlighting the project's development progress and technical design during its final construction stages. The award underscored the industry's interest in eSolar's approach to solar thermal energy generation at the time.
Renewable Energy World Award
Following its commissioning, the plant continued to attract attention from sector analysts and media outlets. In February 2010, Renewable Energy World named Sierra SunTower the "Renewable Project of the Year." This accolade reflected the project's successful transition from construction to active operation within a relatively short timeframe. The 5 MW capacity of the facility served as a commercial proof-of-concept for eSolar's technology, distinguishing it from smaller pilot installations and larger, later-stage CSP projects.
These awards contributed to the visibility of concentrating solar power as a viable alternative to photovoltaic systems during the early 2010s. The recognition by Power Engineering and Renewable Energy World helped establish Sierra SunTower as a reference case for tower-based solar thermal plants in California. The facility's location in Lancaster, California, placed it in a region with high solar irradiance, which supported its performance metrics and contributed to its award-winning status.
The awards were part of a broader period of growth for the CSP sector in the United States. Sierra SunTower's achievements were noted in the context of eSolar's expansion plans and the competitive landscape of renewable energy projects in California. The recognition by these publications provided third-party validation of the plant's engineering and operational success during its first year of service.
Industry observers cited the project's efficiency and the innovative use of heliostat fields in the evaluation criteria for these awards. The "Best Renewable Project" and "Renewable Project of the Year" titles reflected the technical novelty of the tower design compared to traditional parabolic trough systems. Sierra SunTower's awards remain part of the historical record of CSP development in the US, documenting the early commercial successes of the technology before the plant's eventual decommissioning.
The facility's recognition by Power Engineering and Renewable Energy World also highlighted the importance of project execution speed and reliability in the renewable energy sector. The plant's ability to reach commercial operation and receive these accolades within a two-year window demonstrated the maturity of eSolar's development process. These awards are frequently referenced in retrospective analyses of the CSP industry's growth and the specific contributions of tower-based technologies.
Shutdown and legacy
The commercial operations of the Sierra SunTower concluded in 2015, marking the end of its active energy generation phase. The primary driver for this shutdown was the high operational costs associated with the facility’s concentrating solar power (CSP) technology. As eSolar managed the plant's lifecycle, the financial pressures inherent to early-generation CSP projects led to the decision to cease commercial output, transitioning the site from an active power producer to a decommissioned asset. This operational timeline underscores the economic challenges faced by innovative solar thermal technologies during the 2010s, where levelized costs often struggled to compete with rapidly declining photovoltaic prices and other established renewable sources.
The physical legacy of the Sierra SunTower has undergone significant transformation in the years following its commercial shutdown. These structures were the core components of eSolar’s heliostat-based system, directing sunlight to receivers atop the towers to generate steam and drive turbines. While the towers have been removed, the remainder of the plant infrastructure remains present at the Lancaster, California location. This partial demolition reflects a common pattern in renewable energy decommissioning, where major structural elements are dismantled for material recovery or site clearance, while foundational and peripheral components may persist for extended periods.
The facility also left a notable mark on local employment in Lancaster. During its peak operational and construction phases, the Sierra SunTower supported approximately 300 temporary jobs, providing short-term employment opportunities for skilled laborers, engineers, and technicians involved in the installation and maintenance of the heliostat fields and tower systems. In addition to these temporary positions, the plant sustained 21 permanent employees who managed the day-to-day operations, monitoring, and administrative functions of the 5 MW installation. These employment figures highlight the labor intensity of early CSP projects, which required more on-site personnel compared to later, more automated solar technologies. The job creation impact contributed to the local economic landscape of Lancaster, offering both transient and stable employment in the regional energy sector.