Complex sentence: This may be a method of thermoregulation, because if "N. atramentosa" is on a horizontal surface, it would absorb the maximum solar radiation, whereas on sloped or vertical surfaces it absorbs less energy (and thus heat).
Split into simpler sentences: This may be a method of thermoregulation, as if "N. atramentosa" is on a horizontal surface, it will absorb the maximum solar radiation. By contrast, if it is on a greater angle to the sun, it absorbs less energy (and thus heat).