FAQ and tips
- Can I run concurrent simulations?
- What units should I use for absorption coefficient data?
- (pvtrace v1.4 only) What is the data format for input data such as absorption coefficient?
- (pvtrace v1.4 only) What does the data mean in the output file?
Not at the moment, but there is an issue to resolve this and it will be added to the project.
pvtrace uses the natural logarithm formulation of the Lambert-Beer Law. That means, that the absorption spectra used must be represented as logarithms of the absorption with basis e=2.71... . If you are provided with absorption spectra represented as decadic logarithms of the absorption (basis 10) you will have to convert your log10(abs) to base e,
The units of absorption coefficient are expected to be per meter. For spectral data the x-axis is expected to be in units of nanometers.
For example, to make a material using the bundled absorption coefficient data file fluro-red.abs.txt,
file = os.path.join(PVTDATA, 'dyes', 'fluro-red.abs.txt')
abs = load_spectrum(file)
fluro_red = Material(absorption_data=abs, emission_data=ems, quantum_efficiency=0.95, refractive_index=1.5)
The spectrum fluro-red.abs.txt is a text-file with two values per line, which are separated by a tab-stop or space. The first value is the wavelength (in nanometers) the second is the absorption coefficient (in inverse meters). When using your own data with pvtrace please convert you absorption coefficient files to base e and place them in the work folder as such work_folder/pvtrace/data/dyes/.
If you run one of the example scripts for a basic luminescence concentrator the output will summarise where all of the input photons ended up. Let's look at the output file lines:
Run Time: 1692.63570747
Simply the tun time in seconds.
Technical details:
Generated 1000
Killed 49
Thrown 951
Generated is the number of rays that you specified to use for the simulation. However, ray tracing is not perfect and sometime if an error occurs or a ray is trapped in an infinite loop there needs to be a termination criteria. For these reasons sometimes rays are terminated and their presence is erased from history. Killed tells you the number of rays that were terminated, Thrown simply tells you Generated - Killed. That is, Thrown is the actual number of rays that entered the scene and died of natural causes.
Summary:
Optical efficiency 26.3932702419 %
Photon efficiency 92.7444794953 %
By default the Optical efficiency is defined as the fraction of entering rays which exit from the edge surfaces. This follows the classical luminescence concentration configuration in which solar cells are attached to the edges. The Photon efficiency is the ratio of all entering photons to all exiting photons; it gives you a feel for the non-radiative losses in the system.
The next two blocks summarise the end point location of the photons. For connivence we distinguish between 'luminescence photons' (those emitted by a material) and 'solar photons' (those which are unabsorbed).
Luminescent photons:
left 5.67823343849 %
near 8.20189274448 %
far 6.8349106204 %
right 5.67823343849 %
top 8.72765509989 %
bottom 8.30704521556 %
lost 7.25552050473 %
Solar photons (transmitted/reflected):
left 0.0 %
near 0.0 %
far 0.0 %
right 0.0 %
top 4.52155625657 %
bottom 44.7949526814 %
Note that,
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For luminescence photons 'left 5.7%' means that 54 (i.e. 951 * 5.7%) of the rays exited the left surfaces.
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Similarly for solar photons 'left 0.0%', 'top 4.5%' and 'bottom 44.8%' mean that no rays from the light source exited from the left surface, and 4.5% of the incident rays exited the scene by reflecting from the top and 44% of the incident rays where transmitted through without being absorbed.
In summary the output files provides a nice overview for the fate of entering rays for a very simply bare plastic sheet containing dyes. For more details simulation it would be better to includes solar cells layers where you wish to collect photons and simply count the rays which hit those layers to determine the optical efficiency for you specific configuration.