By Roland Wenzel
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Reacts in Real Time: Optoelectronic Control
 Like a sunflower, the tracking system constantly aligns itself with the sun. The drive motor hums almost inaudibly while the system readjusts itself. Shortly afterwards, the sun disappears behind gathering clouds. ¡°Now the tracking system continues to work, as it aligns itself with the brightest, most energy-rich point in the sky, even when the sun is not visible,¡± says Michael Prei¥âel, explaining the functionality of the optoelectronically controlled tracking system called Skytrap. The single-axis tracking system reacts in real time to changes in the sun¡¯s position. It achieves the highest possible irradiation yields with a precise sensor which guarantees a maximum deviation of less than two degrees relative to the sun. Skytrap is particularly suitable for regions which are often partly cloudy, as for instance Central and Northern Europe as well as parts of Asia and Central and North America.
Highly Sensitive Sensor Technology, Robust Construction
The highly sensitive sensor cells react even at low global irradiation, increasing yields by up to 30% in comparison with static systems. The sensor works with great efficiency, drawing only 0.1 VA during operation. Prei¥âel explains the challenges during the development of the tracker, ¡°As early as the design phase, we had to make sure that the systems would operate affordably over many years. Important aspects such as simple replacement of modules, maintenance-free bearings, and robust linear drives must be considered during the design stage of a system.¡±
Efficient Energy Production Which Pays Off
Integrated control electronics driven by a microprocessor ensure such things as the automatic orientation of the module mount in the transition from night to day. With rapid amortisation of the investment costs, the system quickly pays for itself. Skytrap is suitable for all module types and offers a module surface area of up to 18 square meters on a galvanised steel platform. With its small size, it can be flexibly mounted on either a concrete base or ground screw foundations. It can even be firmly secured in sandy soils. The basis of the systems module mounting elements is the proven and DEKRA certified aluminium and stainless steel profiles from the in-house Quick-Line assembly system.
Defying the Elements
The module mount surface can be pivoted up to 90 degrees on a swivel axis. Maintenance-free polymer bearings enable stable and smooth rotational movement. In designing the linear drive with direct control, mp-tec particularly focussed on the stability of the system under wind and snow loads. As an example, hurricane Kyrill generated wind speeds in many parts of Europe of up to 225 kilometers an hour in January 2007. The hurricane not only devastated buildings, it also rendered entire solar farms inoperative. To be able to remain viable, tracking systems must, therefore, withstand storms, snow loads, and temperature fluctuations. For this reason, the system features a powerful linear drive with integrated overload protection. Skytrap is suitable for fully functional use in winds up to force twelve on the Beaufort scale and, with its premium materials, can expect a long service life even in extreme climates, promises managing director Prei¥âel.
Tested under Extreme Conditions
Before the system entered mass production in 2009, it was tested for several months under extreme conditions. mp-tec installed a range of Skytrap versions in a testing area to measure energy yields over a longer period in order to ensure that the system can withstand exceptional stresses. Since then, this system has repeatedly proven itself in real-world scenarios. For example, several Skytrap trackers can be found in Denmark¡¯s first solar farm in Nordborg. The solar farm is currently under construction and due to open in early 2011. The client is Linak GmbH, a leading supplier of linear drive technology, which is also used in Skytrap. Together with mp-tec, a development team worked on an efficient, long-life drive which was also to be maintenance-free to avoid any subsequent costs. Linak is so impressed with the result that the company is now using the system itself. Linak¡¯s nearby production facility will be supplied with the electricity generated by the solar farm. Once the installation works are completed, 500 square meters of solar modules are expected to generate 90,000 kWh of power annually. By using renewable energies, the company plans to reduce its CO2 emissions by 10% within one year. In addition to photovoltaic, Linak will, in future, also focus on wind energy, biogas and the use of electric vehicles.
Similar Advantages with Astronomical Control
With their temperature-resistant components, tracking systems should be fit for use in a wide range of geographical conditions. The Skytrap was developed for operation in temperatures from minus 25 to plus 70¡ÆC. For use in solar farms, the systems can be interconnected or remain in single-user mode. In this way, each system can work independently and generate the maximum energy yield for its location. In virtually cloudless regions such as the Middle East, deserts, and near the Equator, tracking systems should preferably use astronomical control, as the amount of irradiation is constantly very high in almost cloudless hemispheres. This is also the case in countries such as Spain, Greece and Southern Italy. For astronomical tracking, the drive software stores the rise and setting times of the sun as well as its angle of incidence at one location for the whole year, using this information to calculate the system tracking.
¡°To ensure the efficient global deployment of our tracking systems, we have now also developed a tracker with astronomical control in addition to the one with an optoelectronic drive,¡± adds Prei¥âel, who was involved in the development of both systems. In addition, the astronomically controlled version of Skytrap also features a backtracking function. This enables shading-free operation of the tracking systems with a minimum footprint to reduce energy losses.
Effective and Economic Systems
Like its optoelectronic brother, the astronomical control enables increased yields of up to 30% in comparison with static, fixed systems. The portfolio of trackers allows mp-tec to equip its products with the most effective and economic control system. Not only is the accuracy of the tracking system important for the calculation of a year¡¯s solar output, but the longevity of the linear drives and the materials used.
As a manufacturer, supplier and project developer in the field of solar technology, mp-tec is a partner for distributors, craftspeople, planners and investors European wide. Founded in 2002 the German company is a specialist for photovoltaics, solar thermal and mounting systems. Another area of operations is the realization of turn-key solar power plants. Being well-connected to about 4,000 nationwide craft partners, mp-tec is the largest solar system company in the new-formed German states, employing 70 people.
Roland Wenzel has been CTO of mp-tec GmbH & Co. KG (http://www.mp-tec.de/) for several years and has over 30 years of professional experience in the field of electronic drive control and automatic control technique in process and production engineering. The 57-year-old engineer is responsible for research and development, as well as design, production, and logistics at mp-tec. At the present time, Roland Wenzel is working with his developer team on new, even more affordable tracking systems with even higher energy yields.
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