From what I've seen, the solar beam now has strength levels (depicted by the 3 orbs by the fire button).
Using a solar beam once you have 100%, but less than 200% will use the standard beam and lower the gauge by 100%.
Once you have over 200%, but less than 300% you use the stronger version and it drains 200% of the gauge, and so on.
I haven't searched for an option to fire a specific beam level yet.