30% vs 12% in the original arrays when they were new. That's why the new ones are so much smaller.

The Space Shuttle ran off fuel cells, which meant a limited time on orbit. They had a goal of 30 day science missions, so a project was started for a "Power Extension Package" that had fold-out solar arrays.

That never flew on the Shuttle, but when the Space Station project started in the 1980's, it was adapted for the Station's main solar arrays. State of the art at the time was 12% efficient silicon cells.

Current state of the art are Gallium Arsenide + two other layers to capture more of the solar spectrum. So new satellite arrays get ~30% efficiency. Multi-layer cells are mostly too expensive for ground use, but silicon has been constantly improving, to where panels on Earth can convert up to 20-22% of incoming sunlight today.