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.
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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
"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
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