PV Module Technology
Photovoltaic (PV) modules convert solar radiation into electricity. The continuous drive to reduce the cost level of PV modules leads to larger and thinner solar cells. It is a challenge to interconnect and encapsulate such fragile solar cells while realising high efficiencies and lifetimes in excess of 25 years. At ECN Solar Energy, an enthusiastic and skilled team of scientists and technicians works on new generations of photovoltaic modules in national and international projects.
Need for new module manufacturing concepts
The module manufacturing process is responsible for roughly one-third of the total module cost price. This is caused by expensive materials and labour-intensive manufacturing processes because they are difficult to fully automate. For example, the front side of a conventional “H-pattern” solar cell has to be electrically interconnected to the rear of the next cell, which is an awkward and slow process. In addition, the encapsulation of cell strings into a module between two sheets of EVA encapsulant material requires an elongated period of time at 150ºC in vacuum. In order to reduce the cost level of PV modules, larger and thinner solar cells are necessary because such cells can produce more electrical power at comparable costs.
Electrical series connection of conventional 'H-pattern' cells into a cell string
This leads to a need for thick interconnection material to conduct the large currents and to reduce shadowing losses due to the strips at the front side. The drawback of thick ribbon is that it is difficult to solder without introducing large stresses into the solar cell which lead to cell warping and possible breakage. The problem becomes even worse when the cell thickness decreases, and when PV industry has to comply with lead-free legislation.
With competences in materials science, mechanical, electrical and chemical engineering, the Module Technology Group works on new module technology developments that cope with these challenges. 
Encapsulation of a cell string into a module. From top to bottom: tempered glass sheet, EVA encapsulant, solar cells, EVA encapsulant and tedlar back-sheet foil
Stress-free interconnections
The mechanical stress problem introduced with soldering processes can be avoided with the use
of conductive adhesives because they can be cured at temperatures well below their maximum operational temperature. Wide experience with alternative stress-free interconnection methods is
available such as spot soldering, ultrasonic bonding, mechanical interconnection with magnets.
Module technologies for back-contacted cells
In the avant-garde looking “back-contacted” solar cell, the front side electrical connections are routed through holes in the cell to the back side. Since there are no more tabs on the front side, more of the available solar radiation can be captured, improving the performance of the cell. A back-contacted solar cell is also easier to assemble into modules, since the electrical connection only needs to be made on one side. Improved performance and easier assembly will result in lower costs.
The ECN back-contacted cell is not only better performing and easier to assemble compared to conventional cells - it is also better looking. The design of the front-side metallization pattern is much more uniform and visually appealing than the conventional "H-pattern" solar cells.
Avant-garde looking 'back-contacted' solar cell
Glued interconnection after destructive peel testing
Semi-automated equipment for module manufacturing with back-contacted cells
PV module with back-contacted cells
More information: Innovative interconnection and lamination.
Contact person: Dr.ir. P.C. de Jong
Tel.no. +31 224 56 4731
p.dejong@ecn.nl
