eSolar
Corporate brand
UnclaimedeSolar is a privately held American developer of modular concentrating solar power technology.
Last updated November 4, 2026
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Overview
eSolar is a United States solar-technology company associated with Idealab and focused on concentrating solar power (CSP), particularly modular power-tower systems. Founded in 2007 in Pasadena, California, the company sought to lower the cost of solar thermal electricity through a combination of compact heliostats, factory-oriented manufacturing, repeatable field modules, and software-controlled sun tracking. Its approach used arrays of mirrors to concentrate sunlight onto receivers mounted on towers, where the resulting heat could produce steam for a conventional turbine or heat molten salt for thermal storage and later electricity generation. The company’s technology strategy addressed several cost and deployment problems that had limited large-scale CSP. Rather than relying on unusually large, individually installed heliostats, eSolar designed smaller mirror units intended to be prefabricated, mass-produced, transported, and installed in regular field layouts. Its control software was designed to calibrate and monitor individual heliostats while maintaining accurate solar pointing. The company also promoted modular plant architecture, allowing capacity and expected operating characteristics to be adjusted by combining standardized solar-field and tower units rather than designing every project as a one-off facility. eSolar’s most visible demonstration was the 5 MW Sierra SunTower in Lancaster, California. Unveiled in 2009 and connected to the Southern California Edison grid, the plant used two solar modules, four heliostat subfields, approximately 24,000 mirrors, and two tower-mounted receivers. The receivers generated superheated steam that powered a refurbished General Electric turbine-generator. The project demonstrated commercial-scale operation and received renewable-energy certification, but its operating performance and economics also exposed the difficulties facing power-tower CSP. Treasury reporting cited in reference material recorded 539 MWh of generation for the August 2010–July 2011 period, substantially below the original estimate. The facility was shut down for commercial operation in 2015 because it was considered too expensive to operate except during the sunniest conditions. Alongside the direct-steam system demonstrated at Sierra SunTower, eSolar worked with Babcock & Wilcox Power Generation Group on a molten-salt design. The proposed architecture used multiple hexagonal heliostat fields and tower receivers to heat salt from approximately 285 °C to approximately 565 °C. Hot salt could be held in centralized storage and later used to generate electricity, enabling operation beyond periods of direct sunlight. The design was intended to support plants ranging from roughly 50 MW to 200 MW by replicating modules. The company pursued partnerships and licensing arrangements to commercialize its technology. In 2009, NRG Energy agreed to collaborate on projects with potential combined capacity of up to 500 MW in California and the broader Southwestern United States. In 2010, eSolar announced a major Chinese licensing and development arrangement with Penglai Electric, although the planned program does not appear to have progressed. Other announced relationships included Ferrostaal for international turnkey projects, General Electric’s strategic investment in 2011, and a 2014 commercial contract with Aalborg CSP connected to the expansion of Sundrop Farms in Port Augusta, Australia. The company attracted more than $182 million in reported investment from backers including Google.org, Oak Investment Partners, NRG Energy, ACME Group, Idealab, and Quercus Trust. It also received substantial recognition for its technology and demonstration plant, including World Economic Forum Technology Pioneer status, renewable-energy project awards, inclusion in the 2010 MIT Technology Review TR50, and recognition in The Wall Street Journal’s cleantech company survey. However, a 2017 GreenTech Media report suggested that eSolar had ceased business in late 2016. The available material does not establish a formal dissolution, acquisition, or continuing operating status, so the company’s present status remains uncertain.
History
eSolar was established in 2007 by Idealab, the Pasadena-based technology incubator founded by Bill Gross. Its business objective was to create a lower-cost alternative to fossil-fuel generation through concentrating solar power rather than photovoltaic panels. The company concentrated on solar power towers, in which fields of heliostats reflect sunlight toward a receiver positioned on a tower. Heat from the receiver can be converted into steam for a turbine or transferred to molten salt for storage and later power generation. A central element of eSolar’s design philosophy was the use of smaller heliostats than those commonly associated with large CSP facilities. The smaller mirrors were intended to support prefabrication, high-volume manufacturing, easier transportation, and faster installation. eSolar also developed software for calibrating the mirrors, tracking the sun, and monitoring field performance. The combination of standardized hardware and software-based control was intended to reduce field-construction complexity and improve pointing accuracy. The company organized its plants around repeatable modules. In a direct-steam configuration, a module used more than 20,000 square meters of heliostats arranged in north and south subfields around a tower-mounted receiver. A representative 46 MW unit was described as using 16 heliostat fields and towers connected to a single steam turbine-generator and condenser. In the proposed molten-salt configuration, a hexagonal field surrounded a tower receiver, and multiple modules could be combined to create larger plants with thermal storage and differing capacity factors. The Sierra SunTower provided the principal public demonstration of the technology. Construction took approximately 12 months and created more than 300 temporary jobs, while the operating facility employed 21 permanent workers. The 5 MW plant used two eSolar modules, four heliostat subfields, approximately 24,000 heliostats, and two receivers. Its direct-steam cycle drove a refurbished 1947 General Electric turbine-generator. The project was certified by the California Energy Commission and sold electricity to Southern California Edison under a power purchase agreement intended to provide renewable energy for up to 4,000 homes. Sierra SunTower received significant attention as a commercial CSP demonstration, but its operating results illustrated the challenges of the technology. Reference material reports 539 MWh of generation from August 1, 2010, through July 31, 2011, compared with an initial estimate of 4,270 MWh. The facility was ultimately shut down for commercial operation in 2015 because it was too costly to operate except during the most favorable solar conditions. The plant site remained, while the two central towers were reportedly no longer standing by August 2018. From 2009 onward, eSolar pursued commercial partnerships. NRG Energy agreed to work with the company on up to 500 MW of potential projects in California and the Southwestern United States and invested in equity and development rights. In 2010, eSolar announced a broad partnership with Penglai Electric to license its technology for a proposed 2,000 MW Chinese program. The program was described as potentially involving more than $5 billion in capital, but reference material indicates that it apparently did not progress. eSolar also partnered with Ferrostaal for possible projects in Spain, the United Arab Emirates, and South Africa. The company’s technology development continued beyond direct steam. With Babcock & Wilcox Power Generation Group and support from the United States Department of Energy, eSolar worked on modular molten-salt plants intended to scale from approximately 50 MW to 200 MW. In this concept, salt entered the receiver at about 285 °C and returned to storage at about 565 °C. General Electric made a strategic investment of up to $40 million in 2011. In 2014, eSolar won a contract from Aalborg CSP for a solar collector system supporting the expansion of Sundrop Farms in Port Augusta, Australia. The company attracted more than $182 million in reported investment from Google.org, Oak Investment Partners, NRG Energy, ACME Group, Idealab, and Quercus Trust. Its Sierra SunTower project and broader technology received awards and recognition from the World Economic Forum, Power Engineering, Renewable Energy World, MIT Technology Review, and The Wall Street Journal. Despite this visibility and financial backing, the commercial difficulties of CSP remained substantial. A 2017 GreenTech Media report suggested that eSolar had ceased business in late 2016. The available reference does not establish whether the company was legally dissolved, acquired, or retained assets or intellectual property, leaving its current status uncertain.
- 2017
Business closure reported
[1]A GreenTech Media report suggested that eSolar had stopped operating in late 2016.
- 2015
Sierra SunTower commercial shutdown
[1]The Sierra SunTower ceased commercial operation because its operating economics were unfavorable under less-than-ideal solar conditions.
- 2014
Sundrop Farms contract
[1]Aalborg CSP selected eSolar to supply a solar collector system for the Sundrop Farms expansion in Port Augusta.
- 2013
SCS5 heliostat design announced
[1]eSolar introduced the SCS5 heliostat design, emphasizing simplified construction and improved reliability.
- 2011
General Electric strategic investment
[1]General Electric announced a strategic investment of up to $40 million in eSolar.
- 2010
Penglai Electric licensing partnership
[1]eSolar announced a proposed Chinese CSP development and licensing program with Penglai Electric.
- 2010
Ferrostaal international partnership
[1]Ferrostaal partnered with eSolar to pursue turnkey solar thermal projects in several international markets.
- 2009
NRG development partnership
[1]NRG Energy partnered with eSolar on potential CSP projects totaling up to 500 MW in California and the Southwestern United States.
- 2009
Sierra SunTower unveiled
[1]eSolar unveiled its 5 MW Sierra SunTower facility in Lancaster, California.
- 2009
World Economic Forum Technology Pioneer recognition
[1]eSolar was selected as a 2010 Technology Pioneer by the World Economic Forum.
Products and positioning
A clean-energy technology developer positioned around lower-cost, scalable concentrating solar power using small prefabricated heliostats, software-enabled precision tracking, repeatable modules, and optional molten-salt thermal storage.
Concentrating solar power plant · 2009
Sierra SunTower
A 5 MW direct-steam solar power-tower facility in Lancaster, California. It used roughly 24,000 heliostats in four subfields, two tower-mounted receivers, and a refurbished General Electric turbine-generator. The project was designed as a commercial demonstration of eSolar’s modular CSP architecture and supplied electricity to the Southern California Edison grid under a power purchase agreement.
Heliostat and solar collector system · 2013
SCS5
A heliostat design announced by eSolar in 2013. The system was intended to simplify the mirror structure, improve reliability, and reduce the installed cost of the solar collector system by more than one-third compared with earlier designs.
Solar power tower technology
Modular direct-steam CSP system
A modular architecture in which standardized heliostat fields focus sunlight on tower-mounted receivers that boil water into steam. The steam drives a turbine-generator and is then condensed and returned to the receiver cycle. Modules were intended to be combined to meet different plant-size requirements.
Solar thermal generation and storage technology
Modular molten-salt CSP system
A proposed configuration developed with Babcock & Wilcox Power Generation Group using hexagonal heliostat fields, external tower receivers, and molten salt. The system was designed to heat salt to approximately 565 °C, store thermal energy centrally, and generate electricity when required. Multiple modules were intended to support plants from approximately 50 MW to 200 MW.
Brand decisions
2015
End commercial operation at Sierra SunTowerStrategyBackground
The demonstration facility’s operating economics were considered unfavorable except during the sunniest conditions, and reported generation was well below its initial estimate.
Action taken
Commercial operation of Sierra SunTower was discontinued.
Aftermath
The plant remained as a physical site and continued to illustrate both the potential and operational limitations of eSolar’s power-tower approach.
Electricity generation. 4270 MWh initial estimate → 539 MWh generated (August 1, 2010 to July 31, 2011)
2013
Introduce the SCS5 heliostat designProduct launchBackground
eSolar sought to reduce the capital and installation costs of its solar collector fields while improving field reliability.
Action taken
The company announced the SCS5 heliostat at the 2013 SolarPACES conference, presenting it as a simpler and more reliable collector design.
Aftermath
The design became part of eSolar’s effort to commercialize standardized modular CSP systems, although the available material does not document its subsequent scale of deployment.
Sources1 sources
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