Dutch consortium paves the way to affordable solar panels

Within the scope of the Dutch Sunovation II project, the consortium TTA/Eurotron, Solland, TNO and ECN have developed pilot-line equipment and corresponding low-stress interconnection technology to produce solar modules with very thin rear-contact solar cells. This pilot line shows the feasibility of producing solar modules with a throughput rate, 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.

The new pilot production line at TTA/Eurotron.

Silicon solar modules are composed of solar cells, made of silicium wafers, 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. 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
ECN, the Energy research Centre of the Netherlands, 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.

Ready for the future
Paul de Jong, group manager PV-module technology, explains the benefits for the consumers. “We are ready for the future with this technology. It will enable us to produce the next generation solar panels. Such production plants are targeting at an annual output of approximately 100 megawatt per production line. This is a substantial improvement in comparison to the current annual output of 15 megawatt per line. Currently, only with the help of subsidies solar energy can compete with energy made with the use of fossil sources. We have high hopes that this will no longer be necessary in 2015. Solar energy will then be an interesting alternative for everyone.

Solar cells attractiveness is another aspect, they are striking to see. Several architects have stated that they appreciate the esthetic appearance of the solar cells. However, the most important aspect is of course the environmental impact of solar energy.”

The first assembly line is produced by TTA/Eurotron. CEO Simon den Hartigh is delighted about the machine. “The assembly line is already up and running at the ECN research site, this only two and a half years after our first contact with ECN. A first in solar technology and the beginning of worldwide sales in double digit numbers! We expect demands to multiply in accordance to the worldwide increased interest in alternative energy sources. In particular the practical use of solar cell technology will rise. TTA/Eurotron wants to be involved in this great opportunity; and will do this by supplying high standard technology solutions.”

Ilustrations
An impression of the pilot line can be seen at the TTA/Eurotron website at www.eurotron.nl.

Contact:
Paul de Jong
ECN Solar Energy
Tel. (+31) 224 - 56 4731
p.dejong@remove-this-part-ecn.nl