voltage is not your problem, especially on high powered leds, bonus for arrays
as they heat up your current draw will continue to rise, great set them for a voltage, its going to be the wrong current 10 min later, its going to be way off an hour later, you going to sit there fiddling with a knob adjusting hundreds of milivolts as currents continue to increase?
my advice, a constant current driver
what current are you trying to keep the panel at?