The metallic top contacts are necessary to collect the current generated by a solar cell. Those are busbars and finges. Fingers are linear areas of metallization that collect current to deliver it to busbars and those are connected directly to the external leads.
Busbars: ideal number
What number of busbars is ideal for photovoltaic cell? In solar industry its always about efficiency vs. price but in this case it is also about shaded area vs. efficiency.
The most common solution is 2 or 3 bus bars and they are usually made from silver paste. What’s interesting is that around 70s, photovoltaic cells had only 1 busbar.
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Around 2002 three busbars were introduced, mainly by Kyocera and Mitsubishi. The latter one decided to introduce 4 busbars few years later and was followed by Canadian Solar.
Later there was Meyer Burger that commercialized the Smart Wire technology. NPC and Meyer Burger have in their offer 4 and 5 wire solution.
The surface of a string ribbon soldered to a busbar usually exhibits a highly specular reflective surface. There are technologies that allow an increase of light-trapping like interconnect wire with grooved surface from 1366 technologies, Schlenk or Ulbrich Solar. This can result even 6 extra Watts per 300 W module, GreenTechMedia comments. It is also possible to paint the wires in white like researchers from the University of Stuttgard did. It is also worth mentioning that 3M offers special photovoltaic cells with light-trapping films.
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Another technology solution is using round wires instead of flat ones, that help to reduce shading. Naturally, higher number of busbars introduces some rate of shading, nevertheless it also reduces breakage rates (by around 0,2% using 5 busbars) and solar cells can reach higher module efficiencies.
The GTM report showed that increasing the number of wires in a solar cell has a strong correlation with a reduction of finger paste being used which is good news. Additionally, companies have been trying to find efficient replacement for silver in solar cell production. Studies show that tin, copper or nickel could be possible replacements. For instance, Roth and Rau introduced a new concept, creating nickel busbars and introducing this way savings of silver of up to 70%.
It is good to follow GTM or Fraunhofer studies as well as other tech reports to find our the best solution for ourselves.EasySolar app contains full and always updated components base. Moreover, the app will generate the most attractive offers for you supporting your solar sales. Find out more!
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