Dutch consortium paves the way to affordable solar electricity

Petten - Within the scope of the Dutch Sunovation II project, the consortium TTA/Eurotron, Solland Solar, TNO and ECN have developed pilot-line equipment and corresponding low-stress interconnection technology to produce solar modules with extremely thin rear-contact solar cells. This pilot line shows the feasibility of producing solar modules with a throughput rate of one solar cell per second, which is six to eight times better in comparison to any existing technology. This paves the way to low-cost, high performance silicon solar modules and hence, to price-competitive solar electricity.

Need for cost reduction
An important goal of the current development of solar modules is to enable solar electricity production at costs that are competitive with retail prices, thus achieving so-called “grid parity”. For this, modules need to be produced at costs around 1 € per watt peak power.

Silicon solar modules are composed of wafer-like solar cells, which are series connected and encapsulated to form the module. Since the silicon used to make cells represents a substantial part of the total module manufacturing costs it is important to reduce the amount of silicon needed per unit of cell and module power. This reduction results in the use of very thin cells with a thickness of eventually only 0.1 mm. Thin cells, however, are fragile and easily broken during module manufacture. Especially the stresses induced by the hot soldering process used to interconnect the cells can be so high that they cause damage to the cell. This results in reduced module performance or even complete failure during operation. In addition, the soldering process limits the throughput of commercial equipment to 1 cell per 6-8 seconds, which cannot be accelerated. Furthermore, the soldering process involves a number of handling steps which regularly results in broken cells.

New module concept
The Energy Research Centre of the Netherlands (ECN) has developed a module concept, the “Pin-Up Module” (PUM), which offers a solution to these problems. In the PUM cell, the electrical connections at the cell’s front-side are routed to its rear through holes in the cell. This results in an improved performance of the solar module. The benefit is that more of the available solar energy can be captured because of a reduction of shadow losses. The electrical interconnections are made from the cell’s rear side towards a patterned conductive backsheet foil. The Sunovation II consortium has developed the manufacturing processes and equipment to lay-up very thin rear-contact solar cells. This is done at a rate of 1 cell per second, which is six to eight times faster than any existing technology.

Conductive adhesives
The key technology to this new module manufacturing process is a low-stress interconnection technology using conductive adhesives. Conductive adhesives need curing at an elevated temperature which is carried out in combination with the encapsulation process. This reduces the handling of solar cells to a simple pick-and-place action, which is extremely important for very large-scale manufacturing at high yield.

Since the quality of the interconnections and the encapsulation is decisive for the lifetime and reliability of solar modules (which often come with a 20-25 years performance warranty!), very thorough testing is required. The tests showed that the modules made in the Sunovation II project perform just as well as modules made with conventional soldering technology.

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Editorial Note

Illustrations
Illustrations can be found below.  An impression of the pilot line is can be found on the TTA/Eurotron website at www.eurotron.nl.

For more information please contact:
Dr. ir. P.C. de Jong, phone: +31 224 56 4731, email: p.dejong@remove-this-part-ecn.nl
Press officer Florentine de Maar, phone: +31 224 56 4050, email: demaar@remove-this-part-ecn.nl

Solar module with PUM back-contacted cells.

Equipment for automated module manufacturing with back-contacted cells.

ECN’s module concept with Back-contacted PUM (MWT) solar cells and a patterned conductive backsheet foil.

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