l'Actualité du Solaire

Half cell technology is emerging as a relevant concept. Several major panel producers have adopted it. Advantages of using half-cut cells :

It is the increase in power. Using 330 W cells, a panel using half cells will achieve a power of 325.2 W, while a panel using full cells will have a power of 316.7 W. The only difference in the panels is a 1.8% larger size in the half cut because there is more space between the cells. The increase in the conversion rate is moderate, from 18.84% to 19.12%.

In the graph above, the losses when switching from cell to panel occur mainly at the cell connection: the loss of 6.05 W in a full cell panel falls to 1.56 W using half cells. Cutting the cells in half also reduces the volume of electric current, which means that the resistive losses decrease. In panels using half-cells, losses due to the area lost between cells are increased. In panels using half cells, there are half as many spaces as in full cells. These losses are partially recovered by the multiple reflection of light. This recovery is higher in cut half-cells than in full panels because the losses are higher. "When light falls into the intercellular space, it is partially reflected and in turn partially reflected back to the cell at the front glass-to-air interface",

The round wire for cell interconnection can also increase recovery through increased reflection compared to ribbon,

When using a panel with 144 half cells which is delivered with a power of 395 W, the first big advantage is the higher power, about 3%, because of the half cell itself, the different interconnection, and because the resistive losses are reduced in the panel.

Another advantage of the half-cells is increased mechanical stability, because they are smaller and more difficult to break, which has reduced the annual degradation from 0.6% to 0.54%,

Using round wire instead of ribbon increases the power by about 2%: a round wire provides more reflection of incoming light. Light hitting the round wire is reflected back to the glass panel and from the glass to the active surface of the cell, although it provides less area of adhesion and is more difficult to align because the contact area is smaller.

The use of six bars further reduces the resistive losses in the panel as it reduces the distance that the electrons have to travel once captured. However, its advantages are limited. The biggest gains have come from moving from three to four bars. It has been reduced from four to five, and even more so from five to six. The addition of a sixth busbar limits the power increase to 0.5%.

After monosilicon represented an advance over polycrystalline, many manufacturers are now returning to polycrystalline.

In addition to light-induced degradation (LID), temperature-induced degradation (TID) also has the potential to negate the increased efficiency of PERC technology and even lower it compared to that of a standard panel. Tools have been developed to minimise these degradation mechanisms in the production of mono-PERC. These are under development for polycrystalline cells.

PV Magazine of^1st December

https://www.pv-magazine.com/2017/12/01/the-weekend-read-every-last-watt/