Solar tracking systems and sensors

Over the last few years there has been a lot of discussion on how we will meet the global energy demand in the future. And what will be the technologies to generate it? In the end it all comes down to the levelized cost of electricity (LCOE), which is the sum of all costs of a power plant divided by the total electricity that is generated over the plant’s lifetime. All companies in the renewable energy industry focus on reaching lower LCOE compared to conventional power generation (especially gas). Their biggest advantage is that there are no costs for fuel (sun light, wind, water).

solarpanelsLet’s take solar power as an example. Principally there are two ways to use the sun light: First it can be converted directly to electricity (photovoltaics). Second, it can be used indirectly by generating thermal energy (concentrated solar power). In order to reach higher efficiency solar trackers are used to orient photovoltaic panels, reflectors, or mirror towards the sun. On the other hand they add costs to the system. Therefore it must be carefully calculated whether a tracker (single or dual axis) is required or not (fixed installation).

solarpanels2Single axis trackers are used to position photovoltaic panels, parabolic troughs or linear Fresnel collectors from east to west on a north to south orientation. Depending on the required tracking accuracy different sensors are used for this task. As most of the photovoltaic trackers use electric linear actuators, very often inductive sensors are installed on the actuator for position feedback. They are cost optimized and are a standard feature in the actuators. Another option is to use inclination sensors that are directly mounted on the rotating shaft to provide angle feedback (e.g. in linear Fresnel plants). As inclinometers are mounted on the moving part, there is cable wear that could lead to failure over time. For high end tracking, as is required in parabolic trough plants, magnetic tape systems are used as rotary encoders. A magnetic tape is mounted around the shaft and a sensor head is installed on the frame of the tracker. The sensor counts the pulses accurately and provides continuous position feedback without any wear.

solarpanels3Dual axis trackers are used to position concentrated photovoltaic (CPV) panels, parabolic reflectors (dish) or mirrors (heliostats). Especially in central receiver plants high accuracy is required. They need high temperatures and therefore have to focus lots of light on a central receiver on top of a tower in the middle of the heliostat field. As there is an azimuth and an elevation axis, two position feedback systems are required. The elevation angle could be solved with an inclinometer, but this does not work for the azimuth position.  Again, the position could be measured with embedded rotary encoders directly on the drive. But there is again backlash, and accuracy is of highest importance as heliostats could be one mile away from the central receiver. Magnetically coded position and angle measurement systems can be mounted on both axis (azimuth and elevation) and provide direct position feedback with highest accuracy.

More information can be found in this brochure about power generation. http://asset.balluff.com/std.lang.all/pdf/binary/861522_162563_1305_en-US.pdf

Special thank you to Bernd Schneider, Industry Manger – Balluff GmbH for contributing to this post.

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