Truths and Myths of PV Modules
By: Tala Ramadan
Tags: Solar Panel Installation, Solar Panels, Pv Modules, Solar Power, Solar Energy

Here are some of them:

1. Efficiency ≠ Quality

By definition, efficiency is output over input. In solar terms, a PV module’s efficiency is its output (in Wp or watt-peaks, measured at STC) over the input, which is assumed to be the solar irradiance at sea level multiplied by area. Looking closely, and given a certain area, we see that efficiency is only a function of the output power. Efficiency (in solar terms) is only a measure of how much energy we can get out from a certain area and is therefore not a quality issue.

2. Multi busbars (MBBs)

Busbars are small conductors that transfer current. Previously, 2 busbars were the norm, and the number kept on increasing to 5~6. Some sophisticated manufacturers take it all the way up to 12 or more. However, beyond 4 busbars, the increased reliability and power gain becomes so insignificant. Therefore, as a rule of thumb, 4 busbars is enough to have a very powerful module.

Left to Right: Fig. 1. Busbar number trend, Fig.2. Effect of busbar number on power loss (courtesy of Jinko Solar)

3. Half-cut vs. Full-cell

A recent trend in the PV industry is half-cut cells. The trend is catching up fast enough that several notable manufacturers are completely phasing out from full-cell to half-cut production (no more full cell modules!). With a simple manufacturing tweak (cutting the cells into 2), resistive losses are reduced, and hence the power output is increased.

4. PERC vs. BSF vs. the rest

Not all photovoltaic cells are the same. In fact, there exist more than 4 subgroups as of today. Each subgroup has many different cell types and architectures. The crystalline silicon cells subgroup has been the most economical so far, whereas others have advantages but haven’t been as economical. For manufacturing crystalline silicon cells, the conventional cell architecture was BSF (back surface field), as shown below. Today, increasingly, PERC (passive emitter rear contact) cells are replacing BSF as PERC enables light capture on the cell’s rear surface, enabling further efficiency improvements. Without digging too deep into technicalities (a separate article on that later), it’s a great idea to look for PERC modules.

BSF vs. PERC

5. Double-glass vs. Aluminum Frame

Standard PV modules used to have an aluminum frame. Today, many come frameless, especially when the back layer is glass instead of a polymer sheet. Frameless, double-glass modules are thinner (8mm thin vs. 35~40mm for framed), can survive harsher conditions (thus have longer power output warranties), but might pose some quality issues. These range from ribbon corrosion all the way to localized crack in the rear glass. It pays to wait and see how double-glass will do, especially that it’s still in the early deployment phase. As a take-out, be aware when the manufacturer pitches that the warranty is 30 years (which subconsciously makes you assume that it’s better).

6. Made in Germany = Better

Whereas in the not-too-distant past, Germany was the powerhouse of PV production, this is all too different today. China is the powerhouse of PV as of 2018 (even slightly before that). PV production in Europe is so marginal that even PV projects in Europe use Made-in-China modules, which the layman should understand. And whereas made in Germany is better might be the case for other products, this is certainly no longer the case for PV modules.

7. Bigger = Better

Bigger can be better but not necessarily so. Some Chinese manufacturers are selling 500 Wp modules to realize that the modules are way larger than the conventional 2m-square configuration. What EPCs ought to look for is efficiency and not power output (or nominal power rating) in relation to size. Another point is Fit-for-purpose.

We hope to update this article regularly to help our customers and partners discern facts from marketing pitches. Please share your ideas below on what else might be misunderstood on the module’s end.