1/7 Solar Thermal Power Plants Clean power from the sun Siemens test area in the Negev desert Increasing numbers of solar thermal parabolic trough power plants are going online in southern Europe. Mirrors concentrate sunlight, warming a heat transfer fluid inside receiver tubes. In Lebrija, a special oil flows through the tubes. The oil later releases the heat to water, which evaporates. Under high pressure, the steam finally drives a turbine. There are currently projects for solar thermal power plants in many parts of the world in the planning phase. One example is northern Africa, where irradiation data are even better than in southern Europe, enabling a particularly rich energy harvest, even in winter. Solar power plant Lebrija 1 in the building phase greater efficiency through synergies Lebrija 1 is a solar thermal power plant predominantly manufactured with Siemens components: the solar field which captures solar heat and the power plant unit in which this energy is converted into electricity come from Siemens. The technology for the solar field comes from the Israeli company Solel, whose product range includes mirrors and receiver tubes and which has been part of Siemens since 2009. Boosting competitiveness Siemens solar test area in the Negev desert Solar thermal energy is no new discovery experiments with this technology already existed in northern Africa around 100 years ago. Solar thermal power plants have also been supplying the grid in the U.S. state of Arizona with electricity for over 20 years. The need to make increased use of renewable energies also and especially with regard to climate change may now decisively help make solar thermal power accepted. Increases in efficiency through innovative components and better interplay among the individual systems also make the plants increasingly economically competitive. The objective is so-called wholesale parity, i.e. a competitive price at which electricity generated from solar thermal power plants can be fed into the grid.
2/7 Solar Thermal Power Plants Solar power plant Lebrija 1 in the building phase achieving the goal with plug and play Although the individual components are manufactured in high-tech factories, assembly must take place on-site, sometimes in remote regions, as simply as possible. In Lebrija, former cotton pickers fit the modules together to make the power plant. Their operating principle is called plug and play: the primary aim is to avoid complex refinishing of the component parts on site. The modular construction is important for a future time when power plants are constructed with the help of local staff on a large scale, for example in the north African rocky desert. Solar power plant Lebrija 1 in the building phase scalable technology Just under 170,000 individual mirrors were installed on 6,048 parabolic troughs in Lebrija placed next to one another, the troughs would extend 60 km. This power plant generates an output of around 50 megawatts enough for over 50,000 households. Larger power plants could operate even more efficiently, as they can make better use of the power plant unit. Flexible turbine SST-700 Siemens has efficient solutions in its product range not just for the solar fields but also for the power plant unit in solar thermal power plants. The demands on the steam turbine are highly specific: it must be able to start up quickly when the sun rises in the morning and flexibly adapt to the variable thermal input during the day, for example if clouds form. Siemens delivered a steam turbine of type SST-700 with an output of 50 megawatts to the CSP plant Lebrija. Global market leader for turbines in solar thermal parabolic trough power plants At the Solnova solar thermal power plant, the same Siemens SST-700 model is being used as in Lebrija. The turbines global market share in the parabolic trough power plant segment is currently around 80 percent. The market for solar thermal power plants is also experiencing dynamic growth; experts estimate double-digit figures annually by 2020.
3/7 Collector Production Perfect curves The mirrors perfect curvature and special coatings increase the efficiency of a solar power plant, as the mirrors focus the solar energy more accurately on to the receiver tubes while absorbing as little energy as possible themselves. Several layers of corrosion protection help to extend the life of the mirrors which are exposed to the elements for decades. Flawless mirrors Up to 30 percent of the mirrors are subjected to quality control tests. This relatively high number of spot checks is required to detect even the smallest errors. If a mirror is not perfect, its lower efficiency reduces the output of the power plant in the following decades of operation. Individual parts are digitally logged and their position in the power plant documented so that faulty parts can be detected and exchanged, also at a later point in time.
4/7 Receiver Production Greenhouses in tube form the receivers The receivers are technologically highly demanding components in solar thermal power plants and also the ones with the great influence on the overall efficiency. They work on a similar principle to greenhouses, absorbing as much solar energy as possible and releasing as little heat as possible. The external glass casing of the receivers is composed of several pieces which added together make up the full length of a receiver, approximately four meters. Combination of steel and glass A coated steel tube through which special oil will later flow is located within the receiver. Connecting this to the glass casing is no easy task: a type of bellows forms the end fitting and the link between steel and glass. This bellows can flexibly compensate for the varying expansion of the materials which inevitably occurs on heating. In the course of the day, the receivers are always in motion with their dynamic expansion and contraction. The parabolic mirrors are also not static when it is light; powered hydraulically, they constantly track the sun s orientation. Splendid isolation vacuum ensures low irradiation loss The space between the metal tube and the external glass casing is filled with a vacuum. In one of the last stages of operation, air is pumped out. The advantage: the receivers irradiate less heat as a result. The complete receivers are packed in protective covers and shipped currently primarily to Spain, but presumably soon also to a multitude of countries in the so-called sunbelt which are also planning the construction of solar thermal power plants.
5/7 Desertec Desertec a vision becomes reality The visionary Desertec project plans a network of power plants, in particular wind and solar thermal plants in northern Africa and the Middle East. The generated electricity would be of benefit to the countries of production and later, with high-voltage direct current (HVDC) transmission, customers in Europe. It is also a politically pioneering project which may bring growth opportunities and economic stability to regions with considerable potential for development. Green energy from wind Black Law wind farm Wind power is an essential aspect of the plans for Desertec. The wind farm shown, Black Law wind farm has largely become known for its exceptional environmental compatibility. It was constructed in part on the grounds of a former coalmine. This was completely renaturated as wetlands by the operating company within a habitat management plan and also comprises pastureland and commercial timberland. The farm has a combined output of around 125 megawatts. Low-maintenance giants In modern wind turbines, the essential components for the generation of electricity are located in a gondola in the nose, sometimes at a height of over 60 meters. Maintenance work in the nacelle is complex. As a result, particular attention is focused on enabling long maintenance intervals in the design and manufacture of the turbines. Lillgrund offshore wind farm Offshore wind farms play a subordinate role in the Desertec concept. However, their share in Europe s power supply has been increasingly steadily for years. In strong winds, Denmark can now generate more power with its existing wind turbine generators than the country actually consumes. Nevertheless, the plants weather-dependent fluctuations mean that more intelligent networks are required to expand capacity. One day, these might rapidly and automatically switch to other energy generators in calm weather without becoming unstable or temporarily store electricity, for example in the batteries of electric vehicles. At the Lillgrund offshore wind farm in Öresund between Malmö and Copenhagen, shown in the picture, 48 wind turbine generators of type SWT-2.3-93 are installed. Each of them has an output of 2.3 megawatts.
6/7 High-Voltage Direct Current Transmission 800,000 volt transformer for high-voltage direct current (HVDC) transmission Electrical testing at the Siemens factory in Nuremberg High-voltage direct current (HVDC) transmission distributes electrical energy with low loss across large distances possibly one day from desert power plants in northern Africa to Central Europe. Extremely high voltages are required for this. The photo shows the first ready-to-ship 800 kv transformer during electrical testing at the Siemens factory in Nuremberg, Germany. A test voltage of 940 kv is being applied. High output HVDC in China The world s most powerful high-voltage direct current transmission line for output of 5,000 megawatts is currently being built in China. At the receiving station near Guangzhou, visitors are proudly informed of this world record. In late December 2009, Siemens Energy and the power supply company China Southern Power Grid started up the first pole of the plant. The core of the system are ten transformers for voltage of 800 kv. They are each as large as a house and weigh 350 tons. Energy from hydroelectric power plants is transmitted over 1,400 km to supply the densely populated coastal region. Despite this enormous distance, around 95 percent of the energy still arrives at the receiving station. The technology for this extremely low-loss transmission of large amounts of electricity therefore does exist and work and will one day help to realize the vision of Desertec. Power highways HVDC in China The individual components of a high-voltage direct-current transmission system are huge. With the help of high-performance transistors, rectifier modules and smoothing chokes, the transmission voltage reaches 800,000 volts. This extremely high direct current is the reason why 95 percent of fed-in power still arrives at the centers of consumption with the record-breaking HVDC system in China. With alternating current lines, this figure would be only around 87 percent, in this case 400 megawatts less corresponding to the output of a medium-sized power plant or 160 wind turbine generators.
7/7 People René Umlauft CEO of the Siemens Renewable Energy Division. Dr. Bernd Utz Head of the Project Desertec Initative of the Renewable Energy Division.