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Solar Positioning Function Block

Solar Positioning Function Block

WAGO Corporation's free solar positioning function block (SPFB) enables concentrated solar applications to dynamically position solar mirrors and precisely track the sun's arc within +0.02degrees.

Solar Positioning Function Block
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Precise east-to-west tracking relies on multiple variables and inputs including atmospheric pressure, site elevation, azimuth, latitude, longitude, date and local time. Calculations in the function block are paired with the internal clock in a WAGO programmable fieldbus controller to optimize mirror position. Data is then communicated to a dc motor control module and encoder, or a variable frequency drive, for accurate alignment.

"The process of precisely tracking the sun across the sky boosts energy production significantly," says Charlie Norz, Product Manager for the WAGO-I/O-SYSTEM. "In many applications, a single board computer controls tracking but typically they are not networked together. We have looked at ways to be more efficient in medium to larger size applications where one PLC can perform the solar tracking calculations, and remote I/O at each array can control the position of the panels."

WAGO has developed two function blocks including a lower accuracy version (plus/minus 1 degree) that works well in photovoltaic applications and the newer version targets concentrated solar applications.

"Customers working on concentrated solar applications, typically a parabolic mirror that uses one axis to focus the sun's rays on a particular pipe or Sterling engine, need a much more accurate calculation than one degree," says Norz. "The high accuracy function block incorporates more input variables to increase the performance. Photovoltaic systems only move the panels a dozen times a day, so one degree up or down is not a major issue. But with concentrated solar applications, much more accuracy is required."

Unlike many traditional sensor-driven systems, the function block also provides remote access and manual control by linking to a central PC using a fieldbus. System status/alarms are available via e-mail and a "stow" feature positions panels horizontally (wind) or vertically (snow) to reduce stress during inclement weather.

WAGO's standard I/O modules are used to control variable frequency drives or a dc motor with an encoder. For larger
Solar Positioning Function Block
applications, Norz says engineers tend to use variable frequency drives which require a 4-20 mA signal to set the drive speed and positioning feedback. The I/O node can be easily configured to match the needs of the mechanical equipment used in the application.

One central controller managing the process from a single location, versus a controller at each array, reduces costs. Support for SNTP (simple network time protocol) simplifies development because time and day information is very critical. Systems can connect to a GPS system to get time and day but that approach tends to be more expensive. SNTP is available at no charge by connecting to various time servers, and enables the controller's clock to be easily updated twice a day via the Internet.

WAGO developed the function block using data from both the U.S. National Resource Energy Laboratory and the 2011 Astronomical Almanac produced by the U.S. Naval Observatory and H.M. Nautical Almanac Office.
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