By Rikki Stancich

Tulip, the invention of Israeli concentrated solar power technology developer AORA, is being readied for its official European launch next week next week.

A pilot novel modular tower power hybrid system, designed to run 24 hours a day, was installed in China back in 2006, with the commercial prototype launched in Israel's Arava desert in 2009.

Now, the unique tulip tower has been installed at Spain’s Platforma Solar de Almeria (PSA), the world's largest science park dedicated solely to the research and development of solar-based power-generating systems.  

CSP Today speaks to Aora’s CEO Zev Rosenzweig to learn more about the system’s advantages over other concentrated solar power (CSP) tower technologies.

CSP Today: AORA will officially launch its first commercial European CSP installation in Spain in the first week February 2012. The micro solar-gas turbine is the first commercially available CSP-hybrid system, designed to run on 100% solar, with a fuel back-up. Can you provide more detail on the technology to be deployed?

Zev Rosenzweig: The technology is the same as the prototype in the Arava desert in southern Israel – a 100kw CSP tower unit, powered by a gas turbine running on hot air, with a minimal water requirement. It is a hybrid designed to run 100% on solar energy, partial solar, or on gas fuel (or alternatives, such as biodiesel or biogas) only.

In short, it is designed to provide continual power. The air is always routed through the combustion chamber on the way to the turbine. If the air temperature falls below a certain level  the fuel feed automatically kicks in to add heat and ensure the constant provision of electricity.

A solar receiver concentrates the solar energy and heats the air, which has been  compressed by the turbine . The air exits the solar receiver and if the temperature is lower than 950 degrees Celsius, the fuel feed kicks in.  Conversely, the fuel feed shuts off if the air temperature is at or above 950 degrees.

This means there is no fluctuation in power level, and that it can even run through the night using the same turbine but burning fuel.

Currently, it is the only technology that runs on 100% solar during solar hours, with fuel back-up to enable a system that runs constantly, 24/7.

CSP Today: What is the overall plant size and what is its footprint in terms of land requirement?

Zev Rosenzweig: The current design limits the module to 100kw. Each unit takes up 2000square metres, so a 100MW plant would take up 2square km, which is less area than a Brightsource plant, with the same capacity.

The plant can be controlled from a single point, remotely. Theoretically, we could run the Spanish plant from the head office in Israel.

Each unit is small, self-contained, and the mirrors are positioned close to the receiver, so it is very efficient given the high optical efficiency. In traditional tower or trough plants, the mirrors or troughs are located at a greater distance from the central receiver, so they are less efficient.

CSP Today: Given that it is a Brayton cycle, what is the plant’s overall water requirement?

Zev Rosenzweig: It uses a closed circuit cooling system to cool the edge of the receiver. In the receiver there is a quartz window through which the radiation is concentrated.

There is a collar to reflect any stray rays onto the receiver and this steel collar is the only part of the receiver that is cooled. This water is always recirculated. The only water consumed is used to cool the intake air when it is above 35 degrees Celsius.

This requires less than 200 litres of water to cool per MWh of power produced, which is negligible if you compare that with CSP plants using steam turbines, which use 3000 litres/MWh of electricity generated all the time.

CSP Today: What is the timeline leading up to the official launch?

Zev Rosenzweig: The official launch is scheduled for February 07. We finished commissioning mid-January, and have been carrying out trial runs prior to the official launch.

CSP Today: How many units will be installed?

Zev Rosenzweig: Initially, one unit will be installed, in order to provide a demonstration of the technology’s efficiency and viability. We have already been contacted to build small-scale plants as a precursor to larger plants.

In 2012 we expect contracts to build 50 units, in ones and two’s, as a means of demonstrating the technology. These we would expect to be followed up by orders for an additional 60MW.

CSP Today: What kind of typography are these modules suited to?

Zev Rosenzweig: They can be built on sloped land – it is actually preferable, as there is less shade and higher mirror efficiency. So the technology can accommodate slopes and is optimised to take advantage of the existing topography.

CSP Today: Are you marketing the technology for off-grid applications?

Zev Rosenzweig: Because it is designed to run 24-7, it can work off grid, or on local as opposed to centralised grids. We are currently in discussion with towns in Mexico that are poorly served by the grid.

CSP Today: Which key markets are you targeting for centralised-grid applications?

Zev Rosenzweig: Our initial 3-year plan targets Spain, Southern Italy, Mexico and Southwest US. We need to gain experience in producing large volumes before we tackle India.

CSP Today: How does the design lend itself to high volume manufacturing?

Zev Rosenzweig: Very large CSP units achieve economies of scale through their size. We achieve economy of scale through a high volume, repeat manufacturing process.

The tower uses structural steel and is small and easy to fabricate. The heliostat frames also use structural steel, so the key components use basic materials. The mirrors are solar quality mirrors, with 94% reflectivity and aluminium backing.

Aside from the sophisticated receiver, for which the solar window is composed of high purity quartz that is manufactured in Germany, the components are rather simple and low cost to manufacture.

CSP Today: how does the technology compete on price?

Zev Rosenzweig: We are targeting price equality with other CSP plants, but the price varies according to the market and the quantity ordered. As a rough indicator, US$0.5mn is the unit price for a turnkey product. This compares favourably with other CSP plants.

CSP Today: Aesthetically, the towers are very unique, in terms of both colour and design. What is the thinking behind this?

Zev Rosenzweig: The colour was chosen by the architect, who happens to be one of Israel’s leading architect, Haim Dotan.  He selected it on the grounds that it enabled the towers to blend more easily into the surrounding desert environment, as a means of minimising their visual impact.

The technology was designed to have a minimal environmental impact. For example, in order to generate 100MW, you don’t need to have 1000 towers clustered together. Instead, they can be spread in smaller groups across the landscape.

To respond to this article, please write to the Editor:

Rikki Stancich: rstancich@csptoday.com