Experts from the International Solar Energy Society explains how regional spectral shifts of the standard spectral distribution of sunlight bring new insights into the implementation of bifacial perovskiet-silicon tandem solar cells.
The ASTM G173 Standard spectral distribution of sunlight Represents a standard, reference solar spectrum that is used for testing and calibration purposes of solar photovoltaic tests. It was defined in the seventies and is derived from measurements at a location with clear atmospheric conditions and an air mass of 1.5 (AM 1.5), which is typical of sunlight on middle-widths (such as the Midwest USA) when the sun is at a moderate corner. The spectral content of sunlight in Sunbelt countries, where more than 60% of the worldwide population lives and where the recording of PV is growing at a rapid pace, is very different from the standard spectrum, and these differences influence the output of emerging PV technologies such as Tandem Perovskite-Si.
The well-proven and more than 70-year-old Crystalline Silicon PV technology represents 98% the photovoltaic market for solar energy, and while it is closer to Maximum theoretical efficiencyemerging technologies such as Tandem Perovskite-Si has already achieved almost 35% conversion efficiencyand are expected Get the market share in the coming decade. Solar cell -Conversion -Efficiency are measured at Standard test conditions (STC), including the standard spectrum, but never occur in the field simultaneously. Despite attempts to introduce the concept of Realistic reporting conditions In the early nineties, STC remains the preferred and handy series of power assessment conditions for the solar industry. However, what the consumer buys when purchasing a solar -PV module with a certain power (WP) at STC is the corresponding energy output (kWh/year), which will depend on where he works. This energy output will mainly depend on the operating temperature of the PV cell (very rarely the standard 25 ° C, especially under high irradiations in warm climates), the irradiation integrated into the year and the spectral distribution of this irradiation (very rarely the standard Am 1.5).
Spectral shifts of the ASTM G-173 standard distribution of sunlight, which was defined for the 1976 USA standard atmosphere With a rural aerosol load, under am 1.5 conditions, which represent a specific solar -so -called angle of approximately 48.2 degrees, are common. The most important atmospheric parameters For this standard spectrum include a total column water vapor of 1.42 cm, a total column Ozone of 0.34 ATM-CM, a CO2 concentration of 370 ppmv (Current CO2 Levels at the time of writing are 426 ppmv), and a Aerosol optical depth (AOD) from 0.084. Variations in these atmospheric parameters lead to spectra that are poorly rich and red light, as shown in the figure below, for four different locations in Brazil.
Image: Ises
These spectral variations have different consequences in the output performance of PV devices, depending on their spectral response. Show the figures below Simulations performed in Brazil For the spectral factors (SF) of these shifts in the spectral content of sunlight on the performance of silicon HBC (heterojunction back contact), CDTE (Cadmium Telluride) and Perovskiet Dunne Film, as well as Tandem Perovskiet-Solarcel devices. In Brazil, thin film technologies have shown important performance extensions (up to 4%) caused by the characteristic spectral distribution of light. For silicon devices with one junction, the effects of spectral distribution are negligible (less than 0.5%), because of their wide spectral response. For Tandem Perovskiet-Silicon, significant spectral losses (up to 6%) are expected due to the current mismatch between the upper perovskite and the lower silicon cell. This happens because the upper and soil cells in a series must have in a tandem of 2 terminal and the same current. The bottom of the silicon, however, only absorbs the red side of the spectrum and the local spectrum is very Blauwrijk, making it possible that the upper perovskiet cell can have a much higher current, but is limited by the lower silicon cell.
These losses can be compensated in bifacial tandem perovskiet-silicon over high-albedo ground coverings. When a tandem cell is made bifacial, the soil cell stream is stimulated with lighting from the rear, which reduces the current mismatch, so that the full potential of the upper perovskiet cell is unlocked, which benefits from the local blue-shifting spectral distribution. An Albedo value of 50% is needed to compensate for the upper/lower cell steamism match under Brazilian atmospheric conditions. These results show the importance of ground coverings with high reflections in unleashing the full potential of perovskiet/silicon PV devices.
Image: Ises
Image: Ises
Image: Ises
Authors: Prof. dr. Ricardo Rüther (UFSC), Prof. Andrew Blakers /Anu
Andre.blakers@anu.edu.au
ruther@gmail.com
Isesthe International Solar Energy Society a non-accredited membership NGO was founded in 1954 working on a world with 100% renewable energy for everyone, used efficiently and wisely.
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