COMPARISON OF ATACAMA DESERT SOLAR SPECTRUM vs. ASTM G17303 REFERENCE SPECTRA FOR SOLAR ENERGY APPLICATIONS
Summary
The knowledge on the solar spectrum is essential for the design and study of numerous technologies based
on use of the solar resource. In spite of the fact that the Atacama Desert is in the spotlight of solar industry,
there is not information about the spectral irradiance present on it. This fact and the special atmospheric
conditions of Atacama cause an increasing interest of solar industry to know the spectral differences with
other places of the world. In this paper, the information derived from the first spectral measurement
campaign in Chile, carried on 2015, is processed and compared with the standard ASTM G173-03 Reference
Spectra with the aim of obtain useful information for solar energy applications.
1. Introduction
The Atacama Desert is rising like one of the places with the greatest potential in the world for installing solar
power plants, which has attracted the positive attention of solar energy industry from Europe. Solar spectral
irradiance measurements are required in a lot of studies on solar energy technologies, e.g. water treatment,
aging, corrosion, PV cell design, photochemical, etc. In particular, in 1993 Nann and Bakenfelder described
12 possible uses of spectral solar radiation for solar energy systems and building construction applications
(Nann and Bakenfelder, 1993).
The ASTM G173-03 Reference Spectra was created by the North American PV industry in conjunction with
the American Society for Testing and Materials (ASTM) and the research and development laboratories of
the US government. It is extensively used worldwide by solar research centres and solar industry, which
attests to the recognition of its usefulness. Even though, it was calculated in relation to the atmospheric and
geographic conditions of USA (National Renewable Energy Laboratory (NREL), 2015).
The lack of information about the solar spectrum in the Atacama Desert has involved a first measurement
campaign. It was developed between February 8th and March 9th of 2015 in Antofagasta Region, Chile. The
spectral irradiance was measured using a spectroradiometer system based on a double monochromator
Bentham DTMS300 (Cordero et al., 2016). This paper recollect the information derived from the spectral
measurements. This information is used to estimate a mean tilted global and direct solar spectral irradiance
by using a radiative transfer code. The results are compared with the Reference Spectra in order to obtain
useful information for the solar energy industry.
2. Procedure and results
The atmospheric radiative transfer code can compute clear sky spectral irradiances for specific atmospheric
conditions that users can define by inputs. Aerosol Optical Depth, Precipitable Water, Ozone Column and
Single Scattering Albedo are derived from the spectral measurements. This atmospheric information is
averaged for the area of interest for the construction of solar power plants. The mean values are used for the
calculations. Complementary information, as the air mass at noon (eq. 1) or the surface tilt, is derived from
equations. In the case of missing information, the input is left equal to the ASTM spectral reference if the
code cannot calculate it by default.
(eq. 1)
Where Mnoon is the air mass at noon,
for the latitudes of the area of interest.
is the local latitude, and
is the declination. The Mnoon is averaged
The results of the inter-comparison with the ASTM G173-03 Reference Spectra are shown below.
Direct Normal Irradiance [W m-2]
ASTM
ATACAMA
0.55
1.79
UV-B
45.86
58.02
UV-A
521.37
559.32
VIS
391.05
379.41
NIR_1
32.48
32.84
NIR_2
7.79
7.71
MIR
999.1
1039.09
TOTAL
Global Tilted Irradiance [W m-2]
ASTM
ATACAMA
0.3
0.74
UV-B
29.65
37.09
UV-A
458.35
492.26
VIS
369.87
362.73
NIR_1
32.04
32.16
NIR_2
7.85
7.66
MIR
898.06
932.64
TOTAL
Fig. 1 Direct Normal Irradiance and Global Tilted Irradiance results are shown on the top and bottom row, respectively. First
column corresponds to the solar spectra, the black line is the extraterrestrial spectrum, blue line is the spectrum for Atacama,
and the red line is the ASTM reference spectrum. The spectral differences between the reference and the estimated Atacama
spectrum are shown in the second column in [W m-2 nm-1]. In the third column the table with the integral values are presented.
The considereted spectral rage are: UV-B [290, 315] nm, UV-A [315, 400] nm, VIS [400, 780] nm, NIR_ 1 [780, 1800] nm, NIR_
2 [1800, 2500] nm, MIR [2500, 4000] nm.
As seen in Fig.1, the shorter the wavelength is, the higher are the differences between the estimated Atacama
spectral irradiance with the reference. This fact is mainly due to the low levels of AOD, 0.08 at 550nm,
derived from the spectral measurements that was in agreement with the ground-based measurements. The
highest differences are found in the UVB and UVA spectral ranges in comparison with the ASTM G173-03
Reference Spectra. Relevant differences are not found in the infrared spectral range. The total irradiance is a
4% higher than the reference.
3. Conclusions
On one hand, the high irradiance present in the UVB and UVA spectral ranges implies that special care must
to be taken with the design of multi-junction photocells and with the degradation and ageing of materials,
such as the used in encapsulates or solar receivers. These conclusion have to take into account in the plant
design and the economic feasibility study of the projects. On the other hand, this solar spectrum shape can be
used to encourage the processes of water treatment and detoxification.
4. References
Cordero, R.R., Damiani, A., Seckmeyer, G., Jorquera, J., Caballero, M., Rowe, P., Ferrer, J., Mubarak, R.,
Carrasco, J., Rondanelli, R., Matus, M., Laroze, D., 2016. The Solar Spectrum in the Atacama Desert.
Scientific Reports 6, 22457.
Nann, S., Bakenfelder, A., 1993. Narrow-band Spectral Radiation Data Acquisition, Analysis and Modeling.
IEA-SHC P-17 C-1.
National Renewable Energy Laboratory (NREL), 2015. Reference Solar Spectral Irradiance: Air Mass 1.5.
2015.