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Concentrated Solar Power with highly efficient Siemens steam turbines

With a daily start-up and shut-down high demands are placed on CSP-plants. Siemens power generation equipment and instrumentations and controls enable plant operators to make highest efficient use of every single sun beam.

Concentrated solar thermal power is worldwide becoming a more and more important source for power generation. The reasons for this are obvious: The sun is an inexhaustible source for power production. And it is not only a free fuel source but also a complete emissions-free source. Steam turbine generator sets convert solar energy into electricity. Instrumentation and controlls help to make optimal use of every single sun beam. Siemens has equipped more than 70 CSP plants all over the world and is as such the market leader in that field.

Since the solar boom of the eighties in USA, solar thermal energy has been a proven technology. The most common type of plant is the parabolic trough collector, but alternative technologies are rapidly coming to the fore, such as Linear Fresnel collector plants with flat mirrors and central tower plants with slightly curved mirrors or heliostats.
The basic principle is the same for all three plant technologies: Mirrors concentrate the incident solar radiation onto a receiver where it is converted into heat that is used to produce steam to drive a steam turbine. Heat storage systems like molten salt tanks provide for power supply even during unfavorable weather conditions or at night. They significantly increase the number of full-load operation hours with optimal steam turbine efficiency.

Turbines for all main CSP technologies

With its broad steam turbine portfolio, Siemens offers a range of turbines for different types of solar plants and all power outputs. The turbine technology fits all three common concentrated solar power concepts. Siemens was the first steam turbine supplier to re-enter the CSP market in the 21st century, pioneering commercial solutions in the US and Spain. Today, Siemens is the world market leader in steam turbines for CSP plants, and has more than 20 years of experience with steam turbines for daily cycling.

Parabolic trough technology

Parabolic systems use trough-shaped mirrors to focus sunlight onto an absorber tube (receiver) placed in the trough’s focal line. The troughs are designed to track the sun along one axis, predominantly north-south. The receivers contain a heat transfer fluid (e.g. synthetic thermal oil, molten salt) which is heated by the focused sunlight. It is circulated in these tubes and pumped through heat exchangers to produce steam.

The parabolic trough technology is currently the best proven and most used technology, even though the live steam parameters are lower than in solar power tower plants.

Solar power tower

A circular array of flat heliostats (suntracking mirrors) concentrates sunlight on to a central receiver at the top of a tower. A heat transfer medium (water/steam, molten salt or air) in the receiver absorbs the thermal energy and transfers it into the steam cycle to generate superheated steam for the turbine.

The advantage over the parabolic trough or Fresnel collector concept is that the sunlight on the central receiver is focused to a smaller area, and the heat transfer medium does not have to be piped around the large solar field. This means that higher working fluid temperatures in the receiver (up to 1000°C) and better steam parameters are feasible, even supercritical steam is expected.

The number of concentrated solar power plants has increased tremendously in the past ten years. Today we see many different regimes of operations, each of which poses a different challenge to power generation equipment. The design of each steam turbine is adapted to these challenges.
Examples for the regimes of operation for a solarthermal power plant, with a power output of 50 MW:

As market leader in industrial steam turbines, Siemens commands a comprehensive product portfolio for solar thermal plants, covering the full range from 1.5 MW to more than 250 MW.

CSP plants require steam turbines which are optimized for their complex and challenging cycle conditions. Bearing in mind that efficiency and total cost of ownership are key to any investment decision, Siemens incorporates its operational experience into extensive R&D and engineering activities to adapt the turbines to the specific requirements of the CSP technology.

Day and night cycle often requires a large number of starts and fast daily startup capabilities from CSP steam turbines. When focusing on annual power production, the short start-up times of the turbines are of great benefit to the CSP plant owner. Daily cycling and temperature variations require special attention.

Reheat solutions improve efficiency and reduce problems with erosion/corrosion and moisture in the LP turbine. Siemens steam turbines meet all customer requirements for economic installation and operation and provide excellent flexibility for all cycling conditions. The turbines are suitable for higher steam parameters and can be operated in non-reheat, single reheat and double reheat cycles.

Siemens steam turbines are tailored to the customer requirements and shipped assembled for easy installation at site. This reduces time and manpower in the installation phase. All steam turbines are available with axial or radial exhaust and suitable for air- and water-cooled plants.

Siemens provides optimal instrumentation and controls (I&C) design for CSP & Hybrid-PV plants for achieving the full dispatchability of solar energy power plants. With start-up and shut-down 365 days a year, high demands are placed on your plant even on the sunniest of days. Thanks to Siemens’ I&C’s integration expertise in steam turbine controls, balance-of-plant, and solar fields the plant’s performance is optimized and long-term reliability is maintained.

Siemens industrial steam turbines for solar solutions are ordered by customers all over the world and provide energy at CSP plants in the US, Spain, Germany, India and Northern Africa.