The goal of the HelioMesh project was to evaluate and validate the feasibility of a wireless mesh network as control technology in a field of self-powered heliostats, thus eliminating the need for cabling. A wireless field bus reduces the investment costs to a minimum while ensuring reliable and failsafe communication at the same time. To enhance precision of control, an auto-calibration method was implemented.
The team chosed a combination of a practical approach combined with simulations to ensure scalability for large heliostat field to be build in the future: about 100 small communication devices, so called HelioNodes, were deployed in the DLR Solar Tower Demonstration Plant heliostat field, controlled by a base station located in the tower. The deployment validates the feasibility and the industrial capability of the wireless mesh control system. A good performance of the wireless communication is shown in simulations for huge fields. Additionally, the auto-calibration technology was optimized and successfully tested using self-developed, self-powered 8m² heliostats. These heliostats were tested and optimized with a focus on power management and drive efficiency. Results prove that stepper motors are a good choice in case state-of-the-art electronics are used for control.
The HelioMesh project was successfully completed in 2011 when the meshed network was installed at the German CSP power plant in Jülich. It proved the potential regarding the evaluation of the solar tower technology, with a focus on the introduction of new technologies to reduce cost and time of field construction. Especially the wireless communication proved to be very robust, making it highly competitive in comparison to wired technologies.
A consortium signed responsibility for the project with significant scientific input from the German Aerospace Center. This consortium was comprised of representatives from research institutions, the wider industry, and local energy providers. The power plant was part of DLR’s “Solar Thermal Testing and Demonstration Power Plant“ project. After its successful completion – since July 1, 2011 – Stadtwerke Jülich GmbH, who is the regional energy provider, started operating the sun tower power plant. The federal state of North-Rhine Westphalia funded the project.
To this day, the DLR engages in research and scientific development at the Jülich site. Together with partners from industry and research institutions, the DLR is developing additional equipment and establishing test fields to upgrade the Jülich experimental solar power plant and to turn it into a full-fledged solar research center. A variety of research projects include research and test runs for new components and processes that could help make solar power plants more cost-effective and much more energy-efficient. Other research projects that are well on their way are methods to produce solar fuels, and to use solar thermal installations for industrial processes (such as sea water desalination).
When you look at the site from a bird’s view, an area of about ten hectares, controlled by 2153 mirrors, stretches out before you. The heliostats redirect the incident solar radiation to the top of a 60 meter high solar tower where the focused sunlight is collected via a 22 m² solar receiver and converted into heat. The receiver consists of a porous ceramic material that is constantly permeated by ambient air. In the process, the air reaches a temperature of up to 700 degrees Celsius. It is then used to generate steam that, in turn, powers a turbine generator to produce electricity.
The powerful sun tower has an output of 1.5 MW, which is fed into a medium-voltage public grid. A high-temperature heat storage buffer is put in place. It decouples the energy requirement of the process from any temporary fluctuations of incoming solar radiation and ensures a steadier feed into the grid.
Research is continuing with a clear aim: Establishing a complete solar research center. Primary areas of research are to study newly designed mirror systems for redirecting and concentrating sunlight, solar absorbers, and the practical application of energy storage systems. Further research looks at theoretical and computer-assisted analysis and engineering developments in the field of flow mechanics and heat transfer. For these purposes, the site has been given a number of additional office, workshop and storage facilities in the immediate vicinity of the solar tower.
The HelioMesh project was successfully completed with a live test in Jülich. It’s purpose was hardware and software verification as well as investigation into achievable quality levels of service. Technological improvement continues to spur on all parties involved. During the AutoR project, a testbed will also be set up in Jülich.