Variances in Solar Cells

							Variances in Solar Cells

       Shortcourse
     David W. Parent


                           1
                    TOPICS
• Why we care about solar cell variances.
• What can vary in a solar cell.
  –   Base starting materials
  –   Process parameters
  –   Circuit parameters
  –   Test Bench
• Steps to reduce variance

                                            2
 Why we care (Company level)
• The solar cell is designed to meet a specified operating
  voltage and current under a range of conditions.
• Devices that depend of solar cells for power are designed
  to operate at the specification.
• If the cells do not perform to specification, the devices that
  depend on them will not work.
• If the cells give power but not the correct amount, it can
  not be sold.
• All the resources used to make that cell are wasted, and
  this reduces your profit margin.
• Solar cells are expensive enough with out “rejects”.
                                                               3
    Why we care (System level)
• Solar cells are used in arrays.
• The arrays consist of parallel and series
  connections of solar cells.
• The cell with the lowest operating voltage and
  current will dominate the performance of the
  entire array!




                                                   4
   Why we care (System level)
• Cells connected in parallel
  – Current of each cell is added together
  – Smallest voltage determines output voltage of
    the entire array.
• Cells connected in series
  – Voltage of each cell is added together
  – Smallest current determine output current of the
    entire array.
                                                    5