Single Crystal Cell P.V.

1. Single Crystal Cell P.V. By Ari lejfer & Luke Brown

2. In the beginning • French physicist Antoine-Cesar Becquerel found that certain metals and solutions produce small amounts of electric current when exposed to light. • The oldest and most efficient type of photovoltaic cell is made from single-crystalline Silicon.  It is called single-crystalline because the atoms form a nearly perfect, regular lattice. • In these cells, electrons released during the photovoltaic effect have clear, unobstructed paths on which to travel.

3. From where has thou come • Most silicon comes from ordinary sand and several steps are required to turn it into a crystalline solar cell.  The silicon must first be separated from the oxygen with which it is chemically bound.  Then it must be purified to a point where the material includes less than one non-silicon atom per billion.  The resulting semiconductor grade silicon is one of the world’s purest commercial materials and has a price tag of $40 to $50 per kilogram.

4. The Process • The process of growing crystalline silicon begins with a vat of extremely hot, liquid silicon.  A “seed” of single-crystal silicon on a long wire is placed inside the vat.  Then, over the course of many hours, the liquid silicon is cooled while the seed is slowly rotated and withdrawn.  As they cool, silicon atoms inside the vat bond with silicon atoms of the seed.  The slower and smoother the process, the more likely the atoms are to bond in the perfect lattice structure.

5. The final process • When the wire in fully removed, it holds a crystal about 8 inches in diameter and 3 feet long – the size of long salami.  It is cut into wafers, 8/1000 to 10/1000 of an inch thick with a diamond-edge blade and much of the silicon crystal, now worth hundreds of dollars per kilogram, is turned into dust in the process.  The wafers are polished, processed into cells, and mounted in modules.

6. Efficency and Degradation • Degradation is very slow with this technology, typically 0.25% to 0.5% or less degradation per year. Silicon crystals are characteristically blue, and single crystalline cells look like deep blue glass. • Complete modules have sunlight to wire output efficiency averages of about 10% to 12%. Efficiencies up to 20% have been achieved in the lab, but these are single cells using highly exotic components, like unobtainium, that couldn't economically be used in commercial production.

7. Cost • 1 panel: 36-series connected single crystal silicon solar cells. • 6.5 amps of charging current • $514-$798