Presentation about the current status of Tonatiuh, an open source program for the optical analysis of solar concentrating systems.

2. Index
• Program background
• Design goals
• Implementation approach
• Current status
• Comparison with SolTrace
• Experimental validation
• Usage example
• Conclusion
• Acknowledgments

3. Tonatiuh, in Mesoamerican religion, Nahua sun deity of the fifth and final
era (the Fifth Sun). In most myths of the Mesoamerican Nahua peoples,
including those of the Aztecs, four eras preceded the era of Tonatiuh, each
ended by cataclysmic destruction. (Ref.: Encyclopædia Britannica)

4. Program background

5. Design Goal
Simulate the optical behavior
of solar concentrating
systems, providing detailed
information regarding the flux
distributions incident upon its
surfaces.

6. Design Goal
• Simulate most concentrating
systems of interest.
• Be easy to learn, use, and
maintain.
• Be easy to improve, and extent.

7. Design Goal

8. Design Goal
Tonatiuh

9. Implementation approach
• Full-fledge public Open Source
project
• C++ (object-oriented)
• Leveraging on well established
open source libraries and tools

10. Implementation approach

11. Implementation approach

12. Implementation approach
video channel
developers blog
users group
main web site

13. Current status
• Ray tracing and plug-in architecture
fully implemented and operational.
• Program able to model a large
variety of reflective concentrating
systems.
• Users around the world are using it,
reporting bugs, and providing
valuable feed back.

14. Current status
• Ray tracing and plug-in architecture
fully implemented and operational.
• Parallel computation capabilities
fully implemented and operational.
• Scripting, dynamic help, and self-
updating capabilities in well-
advanced development stages.
• Continuous extreme programming
development with monthly release
cycles consolidated.

15. Current status
• Able to model a large variety of
reflective and refractive solar
concentrating systems.
• Successful comparison with
SolTrace to the point that Soltrace
is evolving to adopt Tonatiuh
characteristics (e.g. it is being
rewritten in C++, its user interface
is being modernize, etc.)

16. Current status
Since the opening of the
Tonatiuh website in June
2008, it has received 23,496
visits, which came from 147
countries / territories.

17. Comparison with
SolTrace
SOLTRACE
• C++ (former Borland
Delphi) Monte Carlo
Ray Tracer
• Windows-based
• Simple GUI
• Commercial use,
closed development

18. Comparison with
SolTrace
TONATIUH
• C++ object oriented
Monte Carlo Ray
Tracer
• Plug-in architecture.
• Operating system
independent
• State-of-the-art GUI
• Open source

19. Comparison with
SolTrace
Parabolic Dish Parabolic Trough Solar Furnace

20. Parabolic dish
Power at the target
Difference from Tonatiuh’s estimate (%)
Tonatiuh
SolTrace

21. Parabolic dish
Frequency distribution of photons
Tonatiuh
SolTrace

22. Parabolic dish
Maximum flux density
Difference from Tonatiuh’s estimate (%)
Tonatiuh
SolTrace

23. Parabolic trough
Power at the target
Difference from Tonatiuh’s estimate (%)
Tonatiuh
SolTrace

24. Parabolic trough
Frequency distribution of photons
Tonatiuh
SolTrace

25. Parabolic trough
Maximum Fluxdensity
Maximum flux Density
Difference from Tonatiuh’s estimate (%)
Difference form Tonatiuh reference value
Tonatiuh
100
SolTrace
50
0
10 20 50 100 200 500 1000
Thousand rays

26. NREL solar furnace
Power at the target
Difference from Tonatiuh’s estimate (%)
Tonatiuh
SolTrace

27. NREL solar furnace
Frequency distribution of photons
Tonatiuh
SolTrace
Frequency
Radius (m)

28. NREL solar furnace
Maximum flux density
Difference from Tonatiuh’s estimate (%)
Tonatiuh
SolTrace

29. SolTrace comparison
conclusions
• Tonatiuh and SolTrace generate
similar estimates
– In the comparison differences never
exceeded 2.4%, and were negligible in
most cases.
• Both trace similar number of
photons to converge in their
estimates
– Between 1 to 2 millions, depending on
the value being estimated.

30. Experimental validation
The general goals of the
experimantal validation exercise
were:
• To test Tonatiuh’s flexibility to be
adapted to simulate real
experiments performed on a
relatively complex system.
• To test the usefulness of
Tonatiuh as a design and
analysis tool.

31. Goals of the experimental
validation
• To adapt and use Tonatiuh to
simulate several experiments
that were carried out at the
Plataforma Solar de Almería
(PSA) during the testing of a
secondary concentrator, and
compare Tonatiuh’s solar flux
estimates with experimental
results.

32. Boundary conditions
Use as input values to Tonatiuh:
• The appropriate measured values
if available.
• Reasonable “a priori” estimates
determined without using any
experimental results from the
secondary concentrator tests to
simulate.

33. Execution steps
• Develop a new sunshape plug-in
based on a more realistic
sunshape model than the pill-box.
• Develop a new shape plug-in to
facilitate the simulation of the
hexagonal CPC secondary
concentrator.
• Define an “a priori” set of input
values for each of the test to
simulate.

34. Execution steps
New, more realistic, sun shape plug-in.
Sunshape: Distribution of
radiance (W/m2 sr) as a
function of the angular
distance from the centre
of the solar disc.
CSR = 30%

35. Execution steps
New, more realistic, sun shape plug-in.
Buie’s sunshape
model
L=f(DNI,CSR)
CSR = 50%
CSR = 30%
Equivalent probability
density function

36. Execution steps
New, more realistic, sun shape plug-in.
Relative error
standard deviation (%)
Million of rays

37. Execution steps
New shape plug-in to
facilitate the simulation of
the hexagonal CPC
secondary concentrator.

38. Execution steps

39. Execution steps

40. Execution steps

41. Execution steps
Test # 01
Configuration
Test # 02
Configuration

42. Execution steps
TEST 01 TEST 02
Date 10-15-1990 10-30-1990
Solar time (hh:mm:ss) 12:18:00 13:15:00
Direct Normal Irradiance (W/m2) 932 975
Sunshape type Buie sunshape Buie sunshape
Circumsolar ratio (%) 0,9 0,9
Transmissivity (%) 100 100
Number of heliostats 2 14
Heliostats reflectivity (%) 87 86
Heliostats optical quality (mrad) 1,55 1,55
Reconcentrator reflectivity (%) 77 77
Reconcentrator optical quality (mrad) 1,55 1,55

43. Test results
TEST 01
Total Power Average Flux Maximum
(kW) (kW/m2) Flux (kW/m2)
Measured 31,04 38,32 241,37
Tonatiuh 29,92 36,94 230,80
Relative error (%) -3,59 -3,59 -4,38
TEST 02
Total Power Average Flux Maximum
(kW) (kW/m2) Flux (kW/m2)
Measured 164,76 203,40 1.050,99
Tonatiuh 174,98 216,02 1.181,39
Relative error (%) 6,20 6,20 12,41

44. Results: Test # 01
Measured
Tonatiuh

45. Results: Test # 02
Measured
Tonatiuh

46. Experimental validation
conclusions
• Tonatiuh has been able to predict
the total energy, the average and
peak fluxes, and the overall shape
of the flux distributions at the exit of
the secondary concentrator, using
only “a priori” and measured input
values.

47. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 5º

48. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 10º

49. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 20º

50. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 30º

51. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 40º

52. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 50º

53. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 60º

54. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 70º

55. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 80º

56. Usage example:
Parabolic Trough Incident Angle Modifier
Sun Elevation: 90º

57. Conclusion
• Tonatiuh is a flexible an
accurate tool for the analysis
and design of complex solar
concentrating systems
operating under real working
conditions.

58. Acknowledgments
• Since 2004, Tonatiuh’s development is being
supported at the University of Texas at
Brownsville by DOE and NREL under Minority
Research Associate (MURA) Program
Subcontract ACQ-4-33623-06.
• Since 2006, it is being also supported by the
National Renewable Energy Centre of Spain
(CENER), which is contributing the core
development team, and providing overall
project coordination.