Concentrated solar power (CSP) plants, or solar power tower plants, are of immense value as they are expected to secure a sustainable and reliable energy supply in the future. Their value becomes evident when compared against photovoltaic plants, as only CSP enable full-time energy supply.
CSP plants are also known as solar power tower plants due to their setup. A field of computer-controlled mirrors called heliostats reflects the sun on a tall tower as the sun moves across the sky. The solar light is sent to a central absorber and the produced heat is converted to electrical power via heat exchangers and turbines. Thus, they can serve as base load power plants.
Recognizing the need for secure and environmentally friendly energy supply, the German Federal Ministry for Economic Affairs and Energy founded a new research project, which supports the development of renewable solutions.
The AutoR “autonomous rim drive heliostat” project was launched in December 2013 with the purpose of offering innovative technological enhancement to the world of concentrated solar power. The project’s goal is to develop a CSP plant technology that lowers the threshold of implementing the technology. It does so by significantly reducing the cost of heliostat fields, by making the heliostat field system more competitive, and by enhancing its availability to the industry.
In order to cater to the afore mentioned aspects, several approaches that facilitate cost reductions of heliostats have been developed, from the technological level to the manufacturing processes. They are carefully aligned with each other and fitted to form a new compliant heliostat concept with unique features.
The project’s purpose is to both prompt and advance the development of a wide range of autonomous smaller heliostats, which are managed wirelessly.
One major advantage of the concept of the rim drive heliostat is the fact that all components of the drive train have a high efficiency, compared to solutions based on slew drives or lead screw linear actuators.
The electrical system architecture is divided in three parts:
PV/Wireless for communication and energy sourcing.
Stepper motor drives for the rim drives control. The drive control is optimized for low cost as well as for optimum efficiency of the motors, employing a smart sensor system. This closed loop system allows for flexible response concerning wind gusts, as the system’s behavior can be programmed.
Battery management for energy harvesting.
The HelioDRIVE™ is an innovated drive solution that is mounted on a heliostat. Each axis of the heliostat requires one HelioDRIVE™. it is the efficient mechatronic solution for concentrated solar power and sun tracking applications.
All components – motor, gearbox, linear actuator for braking, sensor, encoder, electronics – are integrated in one single housing. The result is a very compact, plug and play solution, completely preinstalled and easy to mount. Its unique characteristics also include complete software with sun position algorithm and kinematic transformation.
One of the AutoR design’s unique features is its energy and battery management unit.
Small PV cells are used to power the heliostat. Batteries or supercaps are locally installed to buffer the energy for emergency moves to stow position, or for moves at night, e.g. to move the mirror into a cleaning position.
The PV panel is dimensioned for sufficient power for tracking in sunny conditions, and to keep the energy buffer device charged, which is dimensioned to support a certain number of full moves.
The energy harvesting is performed by a photovoltaic panel in combination with a battery, using a voltage conversion unit.
The PV cells are operated at maximum power point. The provided energy management ensures maximum lifetime of the battery, in dependence on the chosen battery technology.
The energy storage and management unit is realized as smart building block with extensive diagnostic features.
Wireless mesh networks are an upcoming technology for different industrial and scientific applications. In this type of network the devices must not only transmit their own data but also serve as a relay for adjacent nodes.
HelioNode™ is a hardware platform and includes dedicated protocols for wireless monitoring and control of solar power plants.
Sep. 2014, SolarPACES 2014, Beijing.
The AutoR-project takes a holistic approach to reduce the cost of heliostat fields: Wireless control and energy supply enables to use smaller heliostats which need less steel per mirror area (but usually have high wiring cost). A low cost but high efficient drive system is chosen which reduces energy consumption to a minimum amount and leads to low cost for PV cell and energy storage. The usual boundary layer wind tunnels tests for heliostats are proven regarding energy spectra to avoid oversizing of steel structure and drives or failures because of underestimations of the loads. The concepts for wireless control and energy supply, the wind tunnel investigations and the first rim drive heliostat prototype are presented.
Sept. 2012, SolarPACES 2012, Marakesch.
To achieve the current challenging cost objectives, several approaches for cost reduction, which fit well to each other, are combined: The wind loads are reduced by appropriate manipulators which reduces weight and cost of the heliostat structure and the ground anchor foundation. Laminated mirror facets are of high reflectivity and shape accuracy and of low weight. The low weight is advantageous for the dimensioning of the bearings and regarding energy consumption. Energy consumption is further reduced by a highly efficient drive train. Thus small capacity of the wireless energy supply of the autonomous heliostat is sufficient which reduces significantly its cost. By the combination of horizontal primary axis with rims and winch wheels a cheap and precise solution for the drives was found. Ray tracing calculations show that the losses due to the reduced angle range are negligible. With the new heliostat concept the current cost goals seem to be achievable.
Sep. 2011, SolarPACES 2011 Granada.
The HELIOMESH project pursues the goal 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. To enhance precision of control, an auto-calibration method was implemented. The team chose a combination of a practical approach combined with simulations to ensure scalability for large heliostats field to be build in the future: About 100 small communication devices, so called HelioNodes, are 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. In simulations, the good performance of the wireless communication is shown 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.