1. Low-cost and high performance heliostats
The TITAN TRACKER concept
Abstract:
Heliostats are the component with the greatest impact on the cost in solar tower CSP
installations, assuming 50% of the total investment1. In the last years, there have been
serious attempts to reduce cost by relaxing some features. The TITAN TRACKER concept
achieves the goal of reducing cost offering higher performance than the rest of heliostats.
Introduction
The main conclusion of the comprehensive report2 of Sandia National Laboratories
“Heliostat Cost Reduction Study” published in June 2007 is that the feasibility of the
solar tower thermoelectric power plant goes through get reliable and efficient heliostats
at a cost much lower than the different known solutions.
The working group which took part this study, about 30 international experts, pointed
out 100 $/m2 rate (base 2006) as target cost for heliostats at a long term defining a
series of R&D projects to achieve it, among others, increasing the size, mega heliostats,
reducing the cost of the drive or apply carousel designs.
Later, TITAN TRACKER presented its innovative technology, which allows the
complete fulfillment of all these targets for the heliostats, both economical and
technical, to facilitate commercial deployment of the CSP central receiver technology.
Heliostat field in PSA www.psa.es
1
Sargent & Lundy, Assesment of Parabolic Trough and Power Tower Solar Technology Cost and
Performance Forecast, SL-5641, May 2003
http://www.nrel.gov/docs/fy04osti/34440.pdf
2
Heliostat Cost Reduction Study Gregory J. Kolb, Scott A. Jones, Matthew W. Donnelly, David Gorman,
Robert Thomas, Roger Davenport, and Ron Lumia
http://prod.sandia.gov/techlib/access-control.cgi/2007/073293.pdf
2. History and state-of-the art
As we deal with heliostats for CSP tower plants, we are talking about two-axis solar
tracking systems and obviously the tracking accuracy. The solutions better known up-
to-date are many and varied types, which demonstrates that determining the right
solution is not a trivial matter.
The largest group among the heliostats is characterized by "a single central support",
with single pole (pole mounted) and also without pole.
Pole mounted type heliostat. Courtesy of PSA
Another important family is the “carousel” type heliostats characterized in that the
azimuth rotation is achieved by rolling on a track, usually made of concrete and, in
some cases, of metal grid. In this family of carousel trackers, it should be distinguished
a subtype as "rotating table or lentil”; this subtype is characterized in that the mirrors
are arranged in different parallel planes.
Carousel type heliostat
3. Out of these families, there are other different solutions, but sorting these solutions is
really difficult because the characteristics of each are both unique and common to other
solutions, this makes their classification not easy and not provide significant
advantages.
Other heliostat solutions
Technical evaluation
Consequence of the first concept, each of the types of heliostats meets technical
specifications that facilitate or hinder the implementation of the functional
requirements, and consequently, the target costs.
“SINGLE CENTRAL SUPPORT” HELIOSTATS:
• Since these heliostats have a single central support, are more sensitive to wind
loads (less rigid) and their deformations are really high, losing the functionality
because high deformations even under low winds, inducing less energy yield.
• The junction between the wing and the ground always passes through the drive.
Drive is subjected to high and pulsating loads that determine its durability by
making it work as a structural component. In many cases, it is very difficult to
repair or replace.
• Low accuracy because of their driving from the center and, consequently, suffer
the following problems:
Reduced lever action ⇒ discontinuous movement ⇒ Slacks ⇒ Hysteresis
• They suffer high stress because large number of start-stop cycles (more
numerous for greater accuracy desired)
4. • Drive with nonstandard “ad hoc” design components, which affects high price
(one of the elements identified in the study as a precursor of the high price of the
heliostats of one central support)
“CAROUSEL” HELIOSTATS:
The carousel concept avoids most of the drawbacks of the previous family of "one
central support"
• They have several points of support, therefore, are more stable and rigid.
• The driving system is not a part of the structure.
• The lever arm is longer because movement is not done from the center it may be
more accurate and can track continuous without stops, less stress, etc ...
• The motor gears may be standard components.
In the type of "rotating table or lentil" the biggest drawback is that it also carries the
shadow area and, therefore, is carrying a useless area or zone with a corresponding
impact on cost, hampering competition in costs with other carousel solutions.
The implementation of the track, in some cases may involve a high cost, especially in
those types that require high quality grading for the proper functioning of the heliostat.
Other heliostats types:
Outside these two main families we do not know any system or relevant concept that
deserves to be analyzed in detail.
5. TITAN TRACKER heliostat concept
The Titan Tracker heliostat is an enhanced carousel type by having part of the support
structure located in front of the mirrors or panels; this structure is its "nose" feature.
The geometry of the tracker allows the establishment of the "nose" without shadow.
It is a proven technology that confirms in use their theoretical advantages. Since its
launching in the market, this concept has been used in flat PV, having hundreds of
Titan Trackers running some years ago without any problem. Therefore, Titan Tracker
is not only an idea but a real proven technology working which demonstrates all its
advantages.
TITAN TRACKER geometry
The benefits derived of this new geometry are, among others:
• Support: There are five supports: a central support and four rolling outside. The
five supports and their location give a great stability.
• Structure: Its geometry allows manufacture by 3D beams, which provides great
rigidity compatible with a great economy of steel.
6. These two features imply that deformations are low even under high winds,
maintaining the functionality with medium and high winds, and allowing their
calculation and design for wind loads much higher than usually considered.
• Foundation: It takes only 65% of concrete and 20% of steel necessary in a
mounted pole with similar mirror surface. The track does not require high quality
grading, admitting irregularities of ± 10 mm. in the 220 m2 models This provides an
extremely economic foundation.
• Drive: The drive and structure are completely independent. The azimuth drive is
located in the outer sides, allowing the tracking of the sun with a continuous
movement of very high precision (without frequent starts and stops). Their
geometry can work with one drive in azimuth about 50 times greater than a central
support tracker of the same size (equivalent to 50 times more accurate and 50 times
less power need for the same motor)
The drive components are standard (low price).
• Accuracy: The intrinsic accuracy "closed-loop control-drive-structure" obtained is
very high, about 0.01° and, therefore, an order of magnitude 10 times better than
the one central support trackers known.
Note that if the pointing accuracy is increased about 10 times, receiving surface can
be reduced about 100 times.
Please fin below a track record of the extreme accuracy of the model 125-219
PRECISION model first prototype for CPV installed in the ISFOC facilities dated
August 1st 2009.
Pointing accuracy with TITAN TRACKER
7. • Energy yield: The accuracy of this technology is a synonymous of higher
performance and, therefore, more profitabiliy.
TITAN trackers for flat PV.
Comparative analysis: performance
The technical requirements in the previously referenced study carried out by SANDIA labs
for the second generation heliostats are detailed in the table below; also are attached the
features that TITAN TRACKER offer.
Request Current heliostats TITAN TRACKER
Modes Track, standby, wirewalk, Idem
stow
Operational winds Track up to 35 Mph Track up to 50 Mph
Slew up to 50 Mph Slew up to 78 Mph
Tracking singularity Resolve in 15 minutes Idem
Quick off-tracking 3 minutes Idem
Targeting precision 1,5 mrad rms 0,17 mrad3
Ray quality According to reflector4 According to reflector4
Wind deformations 3,6 mrad rms max < 1 mrad a 27 Mph
Foundation deformations 0,45 mrad rms max after 0 mrad
survival loads; 1,5 mrad
max tilt in 27 Mph
Survival winds 50 Mph in any orientation 78 Mph in any orientation
90 Mph in stow position
Operation life 30 years, minimum cost 35 years, minimum cost
O&M O&M
Performance comparative
3
Accuracy of the “closed-loop control-drive-structure”
4
A sufficient ray quality is considered below 1 mrad, according to some experts
8. We understand that these benefits objective established for current heliostats can be treated
very undemanding. We imagine that the problem is that if demand increases, also increases
the index "cost/m2" of the heliostat, and therefore there would be a disservice to the target
cost rather than economic approach. In fact, one of the proposals of SANDIA report was to
reduce further the performance to lower the drive in mounted pole design.
We analyze the two most important technical requirements in the heliostats: design loads
and pointing accuracy.
• Design loads. The requirements for survival of 50 Mph in any direction and 90
Mph in stow position (horizontal) are much lower than those that should be
established as safe or minimum for a long life outdoors. In the case of TITAN
TRACKER is designed to withstand wind load of 78 Mph (125 km/h) in working
positions with 100% imbalance. The dynamic pressure of a wind of 78 Mph is 2.43
times higher than the proposed 50 mph wind.
• Pointing accuracy. The accumulated limit error for the pointing5 accuracy set is
clearly improved (set as 3,93 mrad or sqrt ∑ ε2 ). In the case of TITAN TRACKER
this accumulated error in the pointing accuracy under wind conditions of 27 Mph is
1,01 mrad, and hence four times better than the 3,93 mrad target.
Regardless of any economic assessment, to consider equipment as valid, the first thing is to
meet the needs of functionality to the desired working life. We understand that the
technical requirements set by the current standard are little demanding.
Despite the above, TITAN TRACKER offers much better benefits than those set as a goal.
5
(Control = 1,5 mrad / Beam = 1,4 mrad / wind = 3,6 mrad. Foundation: 1,5 and hence the accumulated
pointing error = 3,93 mrad)
9. Comparative analysis: cost
SANDIA report makes the study of the cost in the heliostats, and the estimation of their
evolution based on the effect of economies of scale (manufacturing large volumes) and the
learning effect for two different designs: glass-metal (ATS) and stretched membrane (SM)
both models of the family of "one central support" In the comparative analysis we have
focused on the first (ATS), being the most common in the industry.
Components / Designs6 Helio ATS TITAN Savings
(USD 2010) (USD 2010) $/m2
Mirrors 23,0 23,0
Support structure 36,5 35,8 0,7
Azimuthal drive 33,4 4,57 28,9
Elevation drive 8,7 5,9 2,8
Electronics and control 4,2 (*)8
Total direct costs 105,8 75,8
Profit (20%) 21,2 15,2
Field wiring 7,1 (*)8
Foundation 2,2 4,2 -2,5
Assembly and commissioning 6,1 (*)8
Total installed cost 142,4 106,6 35,8
Cost comparison9. Production 50.000 unit/year
Considering a low level of performance we have discussed and the manufacturing of the
amount about 7.5 million m2 (50,000 pcs. Heliostats of 150 m2) in 2006 and in dollars of
that year, the report estimates that the cost would be at about 126 $/m2 (equivalent to 142.4
$/m2 of 2010) also believes that maintaining this rate of production of 7.5 million m2 per
year, the effects of learning and volume manufacturing that lead to achieving the target of
100 $/m2 (112 $/m2 of 2010) in 2015.
In the case of TITAN TRACKER we currently have for those 7.5 million m2 (3,400 units
of the standard model 125-211 PRECISION) a manufacturing price of 106 $/m2 which
represents a radical improvement on the 142.4 $/m2 (2010) given by SANDIA, as well as
achieving and even exceeding the target of 112.4 $/m2 (2010) given. TITAN TRACKER
also improves performance, and if we choose to reduce benefits with the SANDIA
standard analyzed would be added an improvement, further reducing the cost index.
Also is remarkable the influence due to the current euro-dollar exchange at 1.3652
USD/EUR (in 2006 the rate was 1.2 USD/EUR and the strong euro hurts TITAN
TRACKER in the comparative for being a European company and all its current data to be
in euros)
The table above highlights that some components such as azimuth drive reduces its cost in
TITAN TRACKER in an order of magnitude of about 8 times (33.4 $/m2 to 4.5 $/m2 )
6
Considered designs: ATS: 150 m2 one central support heliostat; TITAN TRACKER: TITAN TRACKER
125-211 PRECISION de 220 m2 heliostat.
7
Including drive and wheels
8
(*) Not relevant for the analysis.
9
Average annual change IPI 3% ; Exchange rate euro-dollar 1,3652 €/$
10. Regarding the structure shows a similar cost, but we should mention the influence of the
wind load design (50 Mph <<78 Mph) in the calculations. TITAN TRACKER uses simple
components that enable large scale manufacture as recommended by the SANDIA report.
The geometry of TITAN TRACKER can be easily increased in size (megaheliostats) due
to the intrinsic characteristics that have been mentioned above. Furthermore, this effect
size has additional benefits in cabling costs, as well as maintenance. The increased size is
not possible as a cost reduction strategy in the heliostats of one central support.
In the case of TITAN TRACKER cost of the foundation is only about 5% of the total due
to a patented mechanism that resolves this difficulty in some carousel designs. We consider
little realistic the reported ratio of 2,2 $/m2 in case of the mounted pole heliostat.
160
Cost Reduction
140
Target cost:
120
112 $/m2
100
Costs $/m2
80
60
40
20
0
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
TITAN TRACKER 50000 uds. Heliostato ATS 50000 uds.
Conclusions
We understand that it should not be trusted any cost reductions to the economies of scale,
requirement for minimum benefits or learning effect. It is necessary to take all
commercially available technologies that help reduce time-to-market for the commercial
deployment of central tower type power plants.
The study published in 2007 by the SANDIA Labs pointed out as a possible solution to
reduce cost the development of large carousel heliostat, and in them, seek to reduce the
cost of the foundation.
This is what TITAN TRACKER patented in late 2006 and working so far, demonstrating
its advantages, managing to get a drastic reduction in costs with significantly improved the
technical performance of the heliostats.
11. References
Heliostat Cost Reduction Study Gregory J. Kolb, Scott A. Jones, Matthew W. Donnelly, David Gorman,
Robert Thomas, Roger Davenport, and Ron Lumia
http://prod.sandia.gov/techlib/access-control.cgi/2007/073293.pdf
Sargent & Lundy, Assesment of Parabolic Trough and Power Tower Solar Technology Cost and
Performance Forecast, SL-5641, May 2003
http://www.nrel.gov/docs/fy04osti/34440.pdf
About the authors
Juan Pablo Cabanillas is founder and Managing Director of TITAN
TRACKER, a Spanish firm specialized in dual‐axis solar trackers for flat‐
plate and concentrating photovoltaics (CPV) recently developing
prototypes for CSP tower and Stirling dish. He has consolidated a solid
background in mechanical engineering during the last 30 years. He has
also held several positions in Gibs&Hill and Empresarios Agrupados. He
was graduated with a degree in Mechanical Engineering ICAI from
University of Comillas, Spain.
Carlos García is Manager of Sales & Marketing of TITAN TRACKER since
the year 2008. He has also consolidated a solid background in his previous
stage in an international consulting firm specialized in business strategy
and product innovation during almost 10 years. He was graduated with a
degree in Electronic Engineering ICAI from University of Comillas and
Executive MBA by the IE Business School in Madrid, Spain.
