BrightSource Energy has filed a registration statement on Form S-1 with the Securities and Exchange Commission (SEC) for a proposed initial public offering of shares of its common stock.

Goldman, Sachs & Co., Citi and Deutsche Bank Securities will act as book-running managers for the offering. The number of shares to be sold in the proposed offering and the offering price have not yet been determined. A copy of the prospectus relating to these securities may be obtained, when available, from: Goldman, Sachs & Co., Prospectus Department, 200 West Street, New York, NY 10282; Citi, Prospectus Department, Brooklyn Army Terminal, 140 58th Street, 8th Floor, Brooklyn, NY 11220; and Deutsche Bank Securities Inc., Prospectus Department, Harborside Financial Center, 100 Plaza One, Floor 2, Jersey City, New Jersey 07311-3988.

A registration statement relating to these securities has been filed with the Securities and Exchange Commission but has not yet become effective. These securities may not be sold nor may offers to buy be accepted prior to the time the registration statement becomes effective. This release shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of these securities in any State in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such State.

The guarantee will allow the company to borrow money to help build a 392MW solar farm called Ivanpah in California’s Mojave Desert. Investors in the project also include NRG Energy and Google, which is putting in $168 million. Last month, it completed a funding round of $201.7 million that included equity and options, according to its SEC filing. It raised about $176 million last year and was the center of speculations that it would go for an IPO soon.

The Ivanpah project is the first commercial solar farm for BrightSource, which has built a 6MW demonstration project in Israel. Lining up financing to build Ivanpah – and completing it – is critical to prove the company’s technology and ability to become a bona fide power plant developer. Founded in 2004, the company’s employees include some who worked on a series of solar thermal power plants in California in the 1980s.

The company uses mirrors called heliostats to concentrate the sun and direct the light to heat up water in a boiler located at the top of a tower. The heated water generates steam to run a turbine and generate electricity. This type of concentrating solar thermal technology is new and is also being developed by other companies such as SolarReserve and Abengoa Solar.

BrightSource Energy, Inc. designs, develops and sells solar thermal power systems that deliver reliable clean energy to utilities and industrial companies. The company has contracted to sell approximately 2.6 gigawatts of power to be generated using its proprietary solar thermal technology.

BrightSource’s LPT solar thermal technology generates power the same way as traditional power plants – by creating high temperature steam to turn a turbine. However, instead of using fossil fuels or nuclear power to create the steam, BrightSource uses the sun’s energy.

BrightSource’s LPT solar thermal system uses proprietary software to control thousands of tracking mirrors, known as heliostats, to directly concentrate sunlight onto a boiler filled with water that sits atop a tower. When the sunlight hits the boiler, the water inside is heated and creates high temperature steam. Once produced, the steam is used either in a conventional turbine to produce electricity or in industrial process applications, such as enhanced oil recovery (EOR). In order to conserve precious desert water, the steam is air-cooled and piped back into the system in a closed-loop process.

Their tracking mirrors, known as heliostats, are highly engineered and designed for accuracy, durability and longevity with minimal maintenance. The heliostat consists of two flat glass mirrors (supported by a lightweight steel support structure) that are mounted on a single pylon equipped with a computer-controlled drive system. This control system enables the heliostats to track the sun in two-directions, maximizing the collection of the sunlight while accurately aiming at the solar receiver. In the current system design, a 130 MW plant will utilize up to 60,000 heliostats, depending on land area and shape, and site-specific considerations. The low-impact design of the heliostat allows our solar plant sites to accommodate a slope of up to 5%, avoid areas of sensitive habitat and eliminate the need for the concrete pads used with other solar thermal technologies, reducing the system’s environmental impact.

BrightSource’s proprietary solar field optimization software is used during the system design phase to determine the optimal position of each heliostat to maximize output and meet the customer’s power production profile. The technology also provides considerable design flexibility, allowing projects to be built on sites with irregular topographies and shape. Using actual site conditions and custom-built meteorological datasets, the software produces precise GPS-ready mappings ready for download to solar field installation crews.

Their proprietary heliostat control software system, the Solar Field Integrated Control System (SFINCS), controls the heliostats arrayed in the solar field to track the sun and aim the sunlight onto the receiver. SFINCS performs a number of functions including:

Solar energy management, to focus the ideal amount of solar energy on the receiver at various times of the day to maximize electricity production while ensuring that the solar receiver’s flux and temperature limits are not exceeded.

Solar field control, to provide aiming points on the solar receiver surface for each individual heliostat, as well as facilitating start-up and shutdown.

Heliostat tracking maintenance, to calibrate the heliostats based on three-dimensional laser scanning and other photogrammetric methods.

At the core of the SFINCS are our proprietary algorithms that perform real-time optimization of the distribution of energy across our solar receiver using real-time, heliostat-aiming and closed-loop feedback systems. In addition, SFINCS can automatically configure the heliostats to protect them from inclement weather.

The solar receiver is a standard utility-scale industrial boiler designed to be heated from the outside using concentrated solar radiation reflected onto the boiler by the heliostats. The boiler is designed to withstand the rigors of the daily cycling required in a solar power plant over the course of its lifetime, and is treated with a proprietary solar-absorptive coating to ensure that maximum solar energy is absorbed in the steam.

In electricity generation applications, the high-temperature, pressurized steam generated in the solar receiver is piped to a conventional steam turbine generator. The electricity generated is then delivered to the transmission grid for consumption.

In a solar-to-steam application, such as thermal enhanced oil recovery, the process is similar to generating electricity. However, for solar-to-steam applications, saturated steam is piped from the receiver to a heat exchanger to generate the process steam.

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

What are the main advantages of solar power tower systems?

There are three primary advantages of tower systems over parabolic trough systems:
Significantly lower cost of producing electricity
Ease of implementation
More positive environmental impact

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.

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.

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.

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.

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.

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 systems do not require foundations and use minimal cabling.

BrightSource says that power tower systems are actually easier to implement than parabolic trough systems. Why is this?

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.

Aren’t all solar thermal technologies the same in terms of environmental benefits?

Some solar thermal technology components can have adverse environmental impacts of their own.  BrightSource decided to employ a more expensive dry cooling approach in its power plants, which greatly reduces the load on local water resources, including transportation and disposal of waste.

In addition, the potential for introducing hazardous materials into the environment is greatly reduced when the working fluid in a solar thermal system is water/steam and not the synthetic oil of trough systems, which is known to present issues in terms of hazardous waste, spill cleanup and fire hazards.