This was a significant improvement over the selenium solar cell, which had been the most common type before the introduction of the silicon solar cell.
The efficiency rating for selenium solar cells was only about 0.5%.
Solar cell research since that time has made a priority of both improving efficiency and bringing down manufacturing costs. So far, researchers have managed to create cells with up to 40% efficiency, using exotic materials. These materials add substantially to the manufacturing cost of cells as well, though; these high-performance cells can cost over 100 times more than ordinary 8% efficient cells to produce.

Reducing production cost may be even more important than improving efficiency when it comes to encouraging more homeowners to switch to solar power.
The sun delivers about 1,000 watts of power per square meter under ideal conditions. These are the conditions that are assumed when a particular solar cell