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energy
required by the heliostat to be optimally
positioned at all times. The heliostat design
specifi es low-cost components and simple
systems.
To capitalise on existing knowledge,
the German Aerospace Centre, DLR,
was called upon to design the layout
of the heliostat fi eld. This requires the
optimisation of the tower height and the
individual positions of the many heliostats
in the fi eld to minimise mutual shading
and blocking, maximising heat collected
throughout the year and minimising the
combined heliostat and tower infrastructure
costs. Shading of a heliostat occurs when
another heliostat, moving to track the sun,
obstructs incoming sunlight at some time
of the day; by contrast blocking occurs
when sunlight refl ected by the heliostat
is obstructed from reaching the target.
The site’s contours add another level of
complexity. Furthermore, the design must
guarantee enough power during sunshine
hours to simultaneously drive the gas
turbine and to build suffi cient heat reserve
in the storage system.
Outputs
While the research is ongoing and the
facility is in the design phase, good
progress has been made in building
expertise required for solar power
research, with researchers undergoing
training in gas turbine combustion
and modelling different solar power
technologies. In turn the CSIR shared the
knowledge it has generated to date at
the SolarPaces 2010 conference, by
presenting two papers. Four mechanical
engineering Master’s students – studying
the country’s only postgraduate course in
Concentrating Solar Power at the University
of Stellenbosch – spent time working at the
CSIR on CSP topics, gaining experience
and helping the CSIR achieve research
deliverables.
Funding
All work undertaken to date has been
funded through the CSIR’s parliamentary
grant.
Getting to grips
Heliostat: (from helios, the Greek word for sun, and stat, as in stationary) is a device that
includes a mirror, which turns so as to keep refl ecting sunlight toward a predetermined
target, compensating for the sun’s apparent motions in the sky.
A gas turbine capable of running on
natural gas (which is used commercially
in other parts of the world) was
commissioned. Rated at 100kW, the
turbine is large enough to behave in a
manner representative of much larger gas
turbine plants and so prove the concept,
yet small enough to greatly reduce the
capital outlay for the plant. While the
turbine can run on solar and diesel in a
hybrid model, CSIR researchers hope to
operate the system on solar and biogas
from sewage, replacing the diesel. The
design of the tower, which houses the
thermal storage system and the receiver,
is in progress. This design has to heed
aspects such as the weight of storage to
enable running for several hours when the
sun is not shining.
A mini-heliostat was installed to check the tracking and control system. Pointing to
where the focal beam that is refl ected from this single heliostat is concentrated, is
Thomas Roos with students from the universities of Stellenbosch and Johannesburg.
29 PROJECT HIGHLIGHTS