The required temperatures of about 700 degrees Celsius can be achieved by the concentration of solar radiation with mirrors. This image shows the DLR Jülich experimental solar thermal power plant.
In Almería, Spain, DLR scientists are researching solar power plants. The solar tower power plant is surrounded by mirrors, which reflect the Sun’s radiation onto the radiation receiver. The collected thermal energy drives a turbine that generates electricity.
As a dependable technology, solar thermal power stations can play an important role in transitioning the power grid to renewable energy sources. In contrast to other renewable sources, they supply electricity on demand and can stabilise the grid. This fact was emphasised in the study produced by EASAC (the European Academies Science Advisory Council), a body set up by leading European scientists and lead by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). On 7 November 2011, this study was handed over to the German Federal Minister for Education and Research, Annette Schavan, in Brussels. In solar power stations, mirrors are used to concentrate sunlight and convert it into thermal energy). This process enables temperatures of more than 1000 degrees Celsius to be achieved, which can be used to generate electricity, among other things.
DLR (CC-BY 3.0).
Since the beginning of 2013 at the Plataforma Solar de Almería research site in Spain, DLR researchers have been testing a new system in which steam to drive a turbine is generated directly in the receiver tubes of parabolic troughs.
In the DUKE (Durchlaufkonzept – Entwicklung und Erprobung [Cycle Concept – Development and Testing]) test system, the steam needed to generate electricity is produced directly in the receiver tubes of the parabolic troughs. Intermediate steps employing a heat transfer medium are no longer needed and higher operating temperatures are possible.
In the DUKE (Durchlaufkonzept – Entwicklung und Erprobung; Once-through Concept – Development and Testing) test facility, at the Plataforma Solar in Almería (Spain), the steam that drives the turbine is generated directly in the receiver tube. In today's plants, synthetic thermal oil is used as the heat transfer medium.
Receiver of the solar tower at the Plataforma Solar de Almería test site in southern Spain. Here, DLR tests new developments in solar thermal power plants. Some 35 German companies and research institutions have published a joint position paper on the market opportunities for solar thermal power plants and concentrating solar power. The newly established network with the name ‘Deutsche CSP’ will combine the strengths and interests of German companies and increase their chances in the international market. Through joint research and development, the network aims to increase the efficiency of the technology and reduce the generation cost.
The first solar tower power plant in North Africa will be built in Algeria. The People’s Democratic Republic of Algeria Ministry of Higher Education and Scientific Research and the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministeriums für Umwelt, Naturschutz und Reaktorsicherheit; BMU) have agreed to collaborate on this project. The aim is to build a solar-gas hybrid power plant with an output of up to seven megawatts. Important components of power station technology were, to a great extent, developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) with partners.
In parabolic trough power plants, solar radiation is concentrated on a receiver tube at the focus of the mirror. The thermal energy collected by the pipe is used to produce steam, which is used to drive a turbine as in a conventional power plant.
In parabolic trough solar power plants, sunlight is concentrated onto a receiver tube located at the focus of the parabolic mirrors. The sunlight is then converted into heat. The heated oil heats water, producing steam that drives a turbine to generate electricity.
Fresnel collectors consist of numerous slightly curved mirrors, which focus solar radiation onto a central absorber pipe. In this pipe, water can be evaporated and superheated and the thermal energy is then converted into electricity by a steam turbine. The Puerto Errado Fresnel collector solar thermal power plant is located in Murcia, southern Spain.
In Dish-Stirling systems, a parabolic mirror concentrates solar radiation into a focal point, where the Stirling motor is placed. Heat energy is transformed into mechanical energy by the Stirling motor. As a general rule, a generator then uses the mechanical energy to generate electricity.
With KONTAS (Konzentrator-Teststand Almeria Spanien), energy researchers from the DLR Institute for Solar Research will be able to test parabolic trough collectors up to 20 metres long at any angle to the Sun and measure their efficiency. The new test stand can be used to evaluate complete modules of parabolic trough collectors as well as individual components such as mirrors and absorber pipes. DLR operates the new test stand at the Plataforma Solar de Almería with CIEMAT.
With KONTAS, researchers have expanded the techniques and possibilities for testing solar-thermal power plant components even further.
A researcher from the DLR Institute for Solar Research tests a mirror for a solar-thermal power plant. DLR has developed its own test facilities and methods for verifying quality. In important areas, they have succeeded in developing internationally recognised quality standards.
At the Jülich site, set up on an area covering about eight hectares, are 2153 moving mirrors (heliostats). These mirrors track the path of the sun and concentrate the solar radiation on a receiver, about 22 square metres in size, installed at the top of a 60-metre-tall tower. The receiver is made of porous ceramic elements permeated by ambient air. This heats the air up to about 700 degrees Celsius and then, it releases this heat to the water-steam cycle. The steam generated here drives a turbine, which produces electrical power.
At the Jülich site, set up on an area covering about eight hectares, are 2153 moving mirrors that concentrate the solar radiation onto a receiver atop the 60-metre tower.
The solar tower power plant in Jülich serves as a pilot plant and reference for commercial power plants in Southern Europe and North Africa. A nearly identical power plant is currently at the detailed planning stage in Algeria. Technology developed in Germany is being utilised in regions where solar radiation is highest. Here, solar thermal power plants have the greatest potential to play a major role in the desert electricity project DESERTEC.
Studies have demonstrated the vast potential of solar power; for example, the deserts on Earth receive more solar energy in just six hours than the world's population consumes in an entire year. To enable the cost-efficient conversion of solar power into electricity, solar cells and solar thermal power stations need to operate more efficiently and become much less expensive to build.
At the DLR Institute of Solar Research, scientists develop new components for solar power plants, from first principles through to pilot plants. Here, researchers can test new components for the future under power plant conditions. The solar tower in Jülich will be expanded as a large-scale test facility.
DLR researcher in Almeria checks the reflectance properties of a parabolic mirror. Parabolic troughs are already used in large solar thermal power plants. Researchers are now working on improving efficiency, lowering maintenance requirements and increasing the lifespan of the individual components.
DLR is conducting research into energy for the future in Stuttgart, Cologne and Almeria, southern Spain. With thermal storage, the electricity production of solar-thermal power plants can be decoupled from variations in solar radiation. Solar-thermal power plants could then provide a more uniform flow of power, operating even at night or during heavy cloud cover.