WAGOCorporation's free solar positioningfunction block (SPFB) enables concentrated solar applications to dynamicallyposition solar mirrors and precisely track the sun's arc within +0.02degrees.

Precise east-to-west tracking relies onmultiple variables and inputs including atmospheric pressure, site elevation,azimuth, latitude, longitude, date and local time. Calculations in the functionblock are paired with the internal clock in a WAGO programmable fieldbus controllerto optimize mirror position. Data is then communicated to a dc motor control moduleand encoder, or a variable frequency drive, for accurate alignment.

"The process of precisely tracking the sunacross the sky boosts energy production significantly," says Charlie Norz, ProductManager for the WAGO-I/O-SYSTEM. "In many applications, a single board computercontrols tracking but typically they are not networked together. We have lookedat ways to be more efficient in medium to larger size applications where onePLC can perform the solar tracking calculations, and remote I/O at each arraycan control the position of the panels."

WAGO has developed two functionblocks including a lower accuracy version (plus/minus 1 degree) that works wellin photovoltaic applications and the newer version targets concentrated solarapplications.

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

Unlike many traditional sensor-drivensystems, the function block also provides remote access and manual control bylinking to a central PC using a fieldbus. System status/alarms are availablevia e-mail and a "stow" feature positions panels horizontally (wind) orvertically (snow) to reduce stress during inclement weather.

WAGO's standard I/O modules are usedto control variable frequency drives or a dc motor with an encoder. For larger

applications, Norz says engineers tend to use variable frequency drives whichrequire a 4-20 mA signal to set the drive speed and positioning feedback. TheI/O node can be easily configured to match the needs of the mechanicalequipment used in the application.

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

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