Busbars conduct the power generated by solar cells when they are hit by photons. 5BB means there are five busbars in each solar cell. 10BB mean there are 10 busbars in each solar cell. Back in the day, solar panels used to have only 2 busbars, but as technology evolves, the solar industry has been increasing the number of busbars in solar panels, to reduce internal resistance losses and increase cell efficiency.