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Storage in development

TuNur and Solana are two examples of solar projects in development that bring CSP and storage together using salt solutions.

TuNur's solar construction project
The first phase of TuNur’s construction is expected to begin in 2014

TuNur is a 2000MW CSP project under development in Tunisia, North Africa, and is part of the Desertec project. The project aims to use the world’s deserts as sources for largescale CSP plant development.

Using thousands of mirrors to track the Tunisian sun to generate solar power, the TuNur CSP plant will ultimately produce 2GW of electricity, which will be exported over 600km across to Europe. The first phase of construction is expected to begin in 2014.

A key feature of TunNur will be its storage technology. Using heat storage tanks, the CSP project will supply dispatchable electricity day and night, providing stability to grids with fluctuating energy sources to produce electricity on demand.

Alex Phocas Cosmetatos, chief technical Officer of Nur Energie says he is interested in using a molten salt tower design for the project, which will provide the plant with a good energy storage system. It will involve heating salts and transferring this heat to steam, which is in turn fed into a steam turbine. “We are looking to design the project with ample storage,” he says.

“We are focusing on providing a complete solution and thus have opted for the storage solution to increase the capacity factor of the plant and induce dispatchability.”

Cosmetatos says the benefits of this include being able to “extend production by many hours” and as such to increase the “utilisation rate of the plant”.

“We are looking at molten salt towers and other technologies to integrate storage with even higher temperatures and efficiencies,” he says.

TuNur’s CSP and storage technology price tag is expected to come to between EUR 7bn and 9bn. But it is hoped it will prove cost effective, lowering the cost of solar energy, while facilitating grid integration. Developer hope the plant design will be replicated the world over.

Kevin Sara, Nur Energie’s chief executive officer, says: “TuNur is going to be the blueprint for things to come.”

Stateside storage
Under construction in the US, Solana is soon set to be the largest CSP power plant in the world. The 280MW parabolic trough plant is being developed by Spanish firm Abengoa Solar in Phoenix, Arizona. Construction began at the end of 2010 and the plant is expected to begin operation later this year.

Using parabolic trough technology, Solana will have six hours of molten salt thermal energy storage, which will allow energy to be dispatched “as needed during cloudy periods and after sunset to help with peak demand”, says Abengoa Solar.

Solana’s parabolic mirrors focus the sun’s heat on a heat transfer fluid. The fluid can reach a temperature of 735°F. Like TuNur, to produce electricity the hot fluid transfers its heat energy to water, creating steam. The steam is then used to run conventional steam turbines.

Large thermos-like buildings containing the molten salt will be located next to the steam boilers. At select times, instead of immediately creating steam, the heat transfer fluid will heat the molten salt. Then, if electricity is needed when the sun is not shining, the fluid can be heated by running it through the hot salt instead of through the mirrors. Using this process, electricity can be made from heat energy that was created up to six hours earlier. Abengoa Solar says Solana´s production will prevent 475,000 tonnes of CO2 emissions per year.