Project 024 – Realising a concept

Design of an MWT Solar Cell

I drew this pattern for a research institute for renewable energies. It is based on the simulation of the electrical current distribution made by one of their researchers. The challenge was to meet all requirements for efficiency and production. For example, these patterns are applied to the solar cell by using silk screen printing which forces restrictions on the minimum line width. I also calculated and drew the rear side pattern, which has to match the back-sheet interconnection foil.

This solar cell was designed within a project that aimed to half the cost price of PV solar panels.

In this solar panel concept, the electrical series connection of the solar cells is all done behind the solar cells. Traditionally, copper strips run from the front side of one solar cell to the back side of the next solar cell to make the series connection.

By laser-drilling small holes in the solar cell, the electrical current from the front side of the solar cell is now routed to the back of the solar cell to several contact pads. By using a patterned conductive metal foil (similar to a printed circuit board) the solar cells are connected in series.

This concept has several advantages:

  • the solar cells can be made larger because there is no more mechanical stress from the thick copper ribbons
  • there is less metal on the front side of the solar cell, so there is more active area which increases the overall efficiency
  • because there is less metal (silver) on the front side, the material costs go down
  • the metal conductor for the series connection is now behind the solar cells so it doesn't block the sunlight and can thus be wider and more conductive which increases the efficiency of the solar panel
  • automating the solar panel production is now simpler since a pick-and-place machine can be used, there is no need for a so-called stringing machines that solder copper strips to the solar cells
  • it is now easier to use electrically conductive adhesives instead of lead-free solders, this further reduces mechanical stress resulting in more robust solar panels that can withstand extreme climates

To be able to measure this new MWT type solar cell it was necessary to develop special tooling, so I designed and built that too. To be able to measure the performance of these solar cells under a sun simulator, it was necessary to build a water cooled vacuum plate with spring probes to make contact with the contact pads at the back of the solar cell.

This solar cell design inspired many people and companies. However, recent developments in MWT solar cell technology show a preference for standard H-pattern look-alike metallisation patterns. Therefore it is not likely this pattern will still be produced in the future.

For more information see also Project 025 and Project 026.