Heliostat Calibration for Concentrating
Solar Power Plants using Machine Vision
A wider exploitation of renewable energy
sources is a key priority for the western
countries. This interest has allowed big
investments in order to develop new type of
solar plants based on Concentring Solar Power
(CSP) systems. In such plants the incoming
solar radiation is concentrated by a heliostats
field on the receiver situated at the top of a
tower. These big mirrors follow the sun
movement using a two-axes tracking system to
maximize the luminous flux reflected on each
mirror. At any time, each heliostat has to correct
their elevation and azimuth angles to track the
sun movement across the sky. Therefore, the
calibrating system is a key piece in order to
assure these corrections.
Our company has developed an automatic
calibration system for PS-10 (it generates 11
Mw) and PS-20 tower based concentrating solar
power plants. The built system calibrates 624
heliostats in the case of PS-10 and 1.255 for PS20 using machine vision. Each heliostat has a
reflecting surface of 120 m2. These plants have
been built by Abengoa Solar and its sister
company Abener, in Sanlúcar la Mayor (located
very close of Seville – Spain).
Particularly, the PS10 installation has
been the first commercial solar tower in
the world to generate electricity and
deliver it reliably to the grid (23 GWh
annually) and it works since March 2007.
It was very useful experience during more
than 25 years from PSA (Plataforma Solar
de Almería) owned by CIEMAT (a
Spanish R&D agency).
BCB has developed and customized a
very innovating application based on
Machine Vision for the capture, analysis
and image treatment of the solar disc
projection of the heliostats on the target
situated under the receiver at the top of
the tower of 165 m, in the case of PS-20.
Basically,
the
system
adjusts
automatically the offset of a heliostat
movement axis regarding the another,
marked by an end of running (each
heliostat has two engines, for azimuth and
elevation) We have to take in
consideration that for the heliostats
located far away (more than 1.000 meters)
from the central tower site, an error of
mili-radians gives a big error to
concentrate its power on the receiver, and
so a reduction in the generated power. The
developed system is able to calibrate the
heliostat field automatically or manually.
According to an automatic and periodical
planning, the mirrors are calibrated one by one
distributed in groups (i.e. the calibrating
frequency for central is lower than for external
mirrors).
In order to supervise the heliostat command,
two IP cameras are used over GigaEthernet (in
order to guarantee the required bandwidth) in
the middle of mirror field.
The IP camera is a B/W high resolution one,
GigaEthernet and it aims on the receiver located
more than 500 meters away of the tower. Its
wide dynamic range of 120 dB easy provides
the image capture and analysis of the projection
of the solar disc for every heliostat.
BCB Informática y Control
Pl. Emilio Jiménez Millas 2
28008 Madrid (Spain)
A third (colour) camera is located at the
top of the tower and it’s used for
supervision purposes. It is automatically
tele-commanded (zoom, pan and tilt) and
its main goal is the preventive maintenance of the heliostat field.
Normally, illumination in machine vision
systems is controlled in order to guarantee
an optimum performance. In this case,
due to the same system definition (i.e. the
solar illumination), it is not possible to
“control” illumination, because of
working in open air basis with sun and in
real atmosphere conditions. These items
have added more challenges to be worked
out
during
system
design
and
commissioning.
The construction of the PS10 plant was a
complete success. Currently, a second
generation tower, the PS20, is under
construction at Sanlúcar. Operation of the
plant will be similar to the PS10, but the
PS20 will have twice the capacity of the
PS10 and will therefore supply 50,6
GWh/year with an area of 85 Ha.
Tlf: (+34) 91 758 00 50 (*)
Fax: (+34) 91 541 84 17
Web: www.bcb.es,, www.bcbshape.com
EN-BCB125-1-0810.doc