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Siemens Sweden produces steam turbines for solar thermal power plants
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08:35, July 28, 2009

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Siemens Sweden produces steam turbines for solar thermal power plants which generate power without emission of carbon dioxide. The factory is located in Finspång in Norrköping, an hour by train from Stockholm. The factory began to manufacture steam turbines since 1913.

Now the company can produce turbines to use nearly 100% solar energy to produce electricity.

Lars-Göran Sjöberg, chief of the Steam Turbine's Division of Siemens Turbomachinery told us about the history of solar energy usage.

"The first solar energy collector was developed by a Philadelphia inventor, Frank Shuman and was established in Egypt in 1912. The collectors were installed in a small community 25 kilometer south of Cairo. The 70 meter long sun power collectors were used to produce steam which drove the large water pump. Together they produced an equivalent of 55 horsepower and was capable to deliver 23 cubic meter water per minute for irrigation of the dry land."


Siemens turbine


It is well known that the advantage of solar energy is that the fuel is free, abundant and inexhaustible. In the face of global warming, solar projects are proving increasingly valuable cutting the use of energy and greenhouse gas emission.

Sjöberg said Siemens solar turbines are sold in the US, Spain, Algeria and Egypt and they are keen to open the market to more places that are suitable for solar energy development such as Asia, Africa and Latin America.

Their products include SST-700 DRH, ISCCS or SST-900 and SST-600 steam turbine for solar power plants.

Solar power technologies

One type of solar technique is to use mirror to focus the sunlight on to a tower and the heat will be transferred into a steam cycle or other kind of heat-receiving medium, such as liquid sodium. The linear Fresnel concept uses flat mirrors close to the ground to reflect and concentrate sunlight on water-refilled pipes that hang over the mirrors.

In a parabolic trough plant, sunlight is focused onto a receiver tube filled with thermal oil in the center of the parabolic mirror collectors, the heat being transferred via heat exchangers to the steam turbine, which generates electrical power. In all cycles, surplus heat can be stored in large storage tanks and used to extend the running hours of the steam turbine during times without sun radiation.

Siemens turbine technology can fit all of these concentrated solar power (CSP)concepts.

Efficiency

For a typical Spain solar steam turbine, investment can reach 260 to 300 million Euro. But steam turbine only accounts for 5-8% of total investment. The solar field can be approximately 80 football fields in size. Thermal storage can be up to 6-7 hours of full operation.

In order to justify the high investment cost for a CSP plant, which will not be run 24 hours per day, high demands for efficiency and increasing economic returns are imposed on the steam turbine used in the process. Siemens has cooperated closely with leading solar thermal EPC companies to develop and finetune the SST-700 DRH(dual-casing reheat) steam turbine, now optimized for solar steam cycles and capable of generating up to 175 MW in CSP applications. This highly efficient turbine with its high-speed, high pressure module enables a smaller solar mirror collector field with associated reduction in investment cost for generation of the required electrical power output.

Alternatively, the surplus heat can be put into thermal storage to extend the production time for the plant. The reheat solution improves efficiency and reduces problems with erosion/corrosion and moisture in the LP turbine, according to Mr. Sjöberg.

Excellent daily-cycling capacity

When focusing on annual power production, the short start-up times the turbine can provide are of great benefit to the CSP plant owner. Daily cycling and temperature variations require special attention. The SST-700 DRH, with its low-mass rotors and casings, is ideal for daily cycling and has a low minimum load, enabling maximum running hours per day for plants without heat storage. The cycle has also been optimized for stand-still at night and rapid restart in the mornings. The SST-700 DRH uses high quality materials specially chosen for long and trouble free operation in a solar plant, bearing in mind the potential wear and tear of the special cycle conditions.

In Southern Spain, due largely to government-granted price surplus for solar-produced power from units under 50 MW, the 50-MW size has proved to have the optimal fit and flexibility for single or multiple units.
Advantages of the solution is flexibility, long lifetime, high availability and reliability, short start up time, fast and easy assembly, lower installation cost, high efficiency and savings on the solar field,
Sjöberg claimed that Siemens' solar thermal experience is best in class and the solidity and reach of the Siemens global network is an advantage in terms of security of investment, supply and after-sales service. "Our experience shows that customers still want the best product even if the price is a bit higher," said Sjöberg confidently.

ISCCS-integrated Solar Combined-Cycle System

For excellent performance and attractive emission reduction, parabolic troughs can be effectively integrated with a conventional combined-cycle plant as well as a steam-cycle plant.

The Siemens ISCSS(integrated Solar Combined-Cycle System) is a single-casing high pressure non-reheat unit, suited to demands of the combined cycle. This SST-900 can be used with any gas turbine or in combination with one or more Siemens 47 MW SGT-800 gas turbines, as in a pioneering ISCCS in Morocco.

This configuration is doubly effective. It not only minimizes the investment associated with the solar field by sharing components with the combined cycle, it also reduces the CO2 emissions associated with a conventional plant. The integration maximizes operation efficiency even though solar energy intensity varies according to the weather and time of the day. Peak thermal-to-electric efficiency can exceed 70% for an ISCCS plant compared to 50/55% for a conventional gas-fired combined cycle plant.

Although the SST-700DRH turbine configuration is the most used on the market, all Siemens steam turbines have the potential for solar applications. Demonstration tests are currently underway with leading institutions in Spain and Germany to test both the lower end of the industrial turbine range-around 1.5 MW and also the mid-range around 20 MW-in solar tower applications. One commercial order has been placed for a 19 MW SST-600 steam turbine for the solar tower project Solar Tres in southern Spain.

Sjöberg said market trends indicate that solar power will increase up to 20 fold in the midterm future. The benefits of solar power are compelling: environmental protection, economic growth, job creation, diversity of fuel supply and rapid deployment technology transfer and innovation.
Solar thermal technology undoubtedly has a large global potential. Where there is sun there is heat, where there is heat, there is power-clean and renewable power. And the Siemens industrial turbine ensures that customer confidence is not misplaced, said Sjöberg.

By Xuefei Chen, People's Daily Online, Stockholm.



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