Complex sentence: Solar cells were bought in batches of 10 or 20 from Radio Shack and tested for efficiency by group members (A. Sergio Torloni then a senior in high school) the most efficient cells were kept for the project, the rest were returned to RadioShack.
Split into simpler sentences: Solar cells were bought in batches of 10 or 20 from Radio Shack and tested for efficiency by group members. The most efficient cells were kept for the project, the rest were returned to RadioShack.