[OffGridKindaGuy]

Producing heat from any power source is dependant on the amount of constant current available. The amount of current used is calulated by the resistance of the heating device. Pulsing it only reduces the duty cycle, which would reduce the constant current input to the heating device to around half, regardless of frequency.

Lowering the resistance of the heating device will allow the array to achieve a higher operating voltage but you are still restricted to the amount of current that your array can provide. If you reconfigured your array to a lower operating voltage to produce more current, you may have better results. Raw current produces heat, not voltage.